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Posted by: Philip W. Dec 15 2014, 12:39 PM

OK. car has been in shop for the past week, and today Bob spent several hours on it but what he found was when the MPS is disconnected from the vac hose it will idle and run, but when it gets connected it goes immediately lean and dies, and will not run with that hose on there- the MPS holds Vac no loss of pressure, but that doesnt mean that its not bad.
1- i thought that if an MPS went bad it defaulted rich? but when this is getting vac it goes lean right away and dies. but it will run and idle with out the vac , the AF meter then shows 9.8-10.2 or so which is of course rich but not flooding out.

so the question is why is it going lean when hooked up? when this issue started about 2 weeks ago, it had been running just fine and all of a sudden it quit running.

2. could there be another issue we dont see that would be making it way to lean other than the MPS?

might need to test another MPS, my 2nd one i just bought from someone here and it has never been opened but will not hold vac (slowly looses vac pressure) so it probably need to be opened and re-sealed. not a good candidate to trouble shoot with. ------

FYI- 1975 d-jet 2.0. newer wiring harness , CHT is newish(replaced 2 months before this issue started and was running perfect at that time)

Posted by: SLITS Dec 15 2014, 12:44 PM

http://members.rennlist.com/pbanders/DJetParts.htm

On the MPS check the ohms between:

Terminal 7 & 15 = 90 ohms
Termianl 8 & 10 = 350 ohms

Check each terminal to the MPS case for ground short.

Posted by: Jeff Bowlsby Dec 15 2014, 01:22 PM

There might be a couple things going on here. If everything is correct the engine should not operate without the MPS. Something else could be fooling it to provide fuel to make it run. MPS do fail rich. Can you pull a vacuum with a vacuum pump on the MPS or not? Sucking on it with your mouth is no where near sufficient to test its ability to maintain a vacuum.

You said its new but just to be sure check the function (continuity and resistance of the TS2, if its out of spec, it could be dumping fuel that the MPS normally provides, enough to allow it to run.

Also, have you checked the injectors including the CSV? Leaking?

Posted by: Philip W. Dec 15 2014, 03:16 PM

The mps holds vac no loss or drop seen on vac pump gauge. The wires are connected to mps , it will not run when the vac is applied. .
I'm going to suggest to him that he recheck the cht again and check those values on the mps that slits suggested.

Posted by: 76-914 Dec 15 2014, 05:06 PM

That ain't right. I've got a working MPS I'll loan you for the cost of postage. PM me if you need Phil.

Posted by: r_towle Dec 15 2014, 05:07 PM

Flip the plug over on the MPS

Posted by: Dave_Darling Dec 15 2014, 05:59 PM

The MPS plug is bi-directional; flipping it should have no effect.

Something is making the mixture very lean. Unplugging the MPS hose is making the mixture rich enough for the motor to run.

Last time I heard of something like this, the fuel pump had failed or very nearly so. There was just enough fuel making it through that the absurdly-large injector pulses from having the MPS unplugged allowed the car to idle, but only just.

How's the fuel pressure?

--DD

Posted by: Philip W. Dec 15 2014, 08:10 PM

Dave, my fuel pressue is right at 30. I dont think its the fuel pump, but before I verified that I ordered a could a new one. Would a bad cht cause that super lean condition? It was cutting in and out before going completely bad. Has not come but I already towed the car to my mechanic.

Posted by: SLITS Dec 15 2014, 09:02 PM

A bad CHT can cause bad problems as in the car not starting.

I bought one they couldn't get running. Upon examination, the CHT was not hooked up. Installed and connected one and the car fired right up.

Posted by: 914bub Dec 15 2014, 09:13 PM

Not trying to Hi-jack here, but one of the hoses to the MPS on my car is plugged off
. I heard that when the MPS diaphramn is bad, some people do that to "override" the problem?

Isn't there someone here that sells kits to rebuild an MPS's?

Posted by: BeatNavy Dec 15 2014, 09:23 PM

Tangerine. Check with Racer Chris or go their website: http://www.tangerineracing.com/whats_new.htm.

Posted by: r_towle Dec 15 2014, 09:35 PM

Given what is happening, a two minute test might help here.

Flip the plug, see if the condition changes.
If it does, you need to troubleshoot your wiring harness.

Posted by: Philip W. Dec 15 2014, 09:42 PM

Ive seen that too.
When I bought the car it would not run. Pulled the mps and it was full of water . Got a rebuilt unit from automotion. Plugged it in and ran great for about a year. Then it gave out snd I sent it back for a refund. Found a working unit here and had been using it for past 3 or so years. Seems now it has tanked as well. But I want to get the car back , I dont think the shop really wants to try to figure it out . Once I have a good working mps should be able to figure out what else is going on.

Posted by: r_towle Dec 15 2014, 10:55 PM

Get the car home.
you can do all the testing with an ohm meter, well most of it.

Rich

Posted by: Philip W. Dec 16 2014, 07:17 AM

Rich,

that is probably what i need to do. I was just at my wits end and really thought it was something non-djet related at the point where i gave up. i really did not suspect the MPS, but then i only tested the vac and that was perfect. I'd been thru everything else and was mad enough if someone had offered me $$ for what i have in it for parts(which is a lot) i would have just walked away. especially since i really needed to be driving the car this past 2 weeks. Ive been down a vehicl since i sold the boxster and regretted that, and this week an opportunity arose to get a high milage 2002 911 cabriolet for under 10K - needs a bit of work but could be a daily driver and that has taken my mind off the 914 for now- i've recommitted to getting back on the road just because im so stubburn and i cant sell it like this.....

btw another member here says that (scott NH) if the vac holds the diaphragm is fine, but that its the inner electronics that have failed . if that is the case then it might fail lean when hooked up to the vac hose, and when disconnected go rich.

Someone is sending me their MPS thats good to test on it.

Posted by: r_towle Dec 16 2014, 09:18 AM

Get the car home.
I can send you down the official Bosch DJet tester ( to borrow)
Put that inline in between the plug and the ECu and run it through some tests.

But in the end, it can all be done with a multi meter.

First thing I would suggest is you do a simple ohm test on the whole fuel injection wiring harness.
When things get weird, that can be the culprit.
40 year old wires shorting out makes diagnosis a nightmare.
Then you can test out everything else.

You really need two things to make the car run.
The MPS and the cht.
So test those circuits, and unplug all others.

Rich

Posted by: Dave_Darling Dec 16 2014, 10:48 AM

The MPS should only have one hose going to it. If the component in question has more than one, it isn't an MPS. Maybe the decel valve?

--DD

Posted by: r_towle Dec 16 2014, 11:08 AM

Oh, an interesting test.
Have your mechanic unplug ALL other vacuum lines and plug them at the plenum.
The. Plug in the one line to the MPS, it's the only one required to run.

If your DECEL valve is stuck, added vacuum may make it change the timing.
If your AAR is stuck open, added vacuum may make it run lean.

When I diagnose these, I do unplug all other vacuum lines from the plenum.
I use rubber covers or electrical tape and close off all ports on the plenum.
You can then use just the MPS to have the car run fine.

If that works, you will then add ONLY one vacuum line at a time back into the system to see which one it doing it.

Rich

Posted by: Bleyseng Dec 16 2014, 08:13 PM

Posted by: brant Dec 16 2014, 10:00 PM

I've seen this once before. Ron's 74 LE did this. He bought an true NOS mps that was still in a bow he box brand new

Car would not run with the vacuum attached but ran well with the hose disconnected.

Posted by: Philip W. Dec 17 2014, 01:00 PM

i went over and tested the MPS at lunch time- holds vac, and T7-15 was 92ohms, and T 8-10 was 340. so that means its good, right?

i also have 2 other s and one does not hold vac perfectly but the values were the same on it, 92 and 335.

i think from here i can still test a known working MPS but i need to go thru the harness like Rich suggested since it seems like it may be something else making it super lean and taking the hose off the mps makes it default rich so it will run -? i kind of suspect either the new CHT went bad or that circuit did, either way this is what thact could cause. hm....

Posted by: SLITS Dec 17 2014, 02:19 PM

The only thing you didn't state was whether you tested each of the terminals to the MPS case (short to ground). The ohms are in specification so the coils inside are good.

Posted by: Philip W. Dec 17 2014, 02:22 PM

i did but did not know what i should be reading on this. i tested all 4 and the meter stayed at 1, ( sorry for my ignorance, i forget which is good - but it showed 1)

Posted by: SLITS Dec 17 2014, 02:57 PM

If you have a digital multimeter and it read "1", you have no continuity hence no short to ground.

Sound like the MPS is good, unless someone putzed with the adjustment screws. If the epoxy is still covering the screw then I have no more ideas.

Posted by: Java2570 Dec 17 2014, 03:45 PM

Phil, you've got a bizarre one going there! I found this thread on PP....relates to some of what you're seeing. Don't know if it'll help but who knows....
http://forums.pelicanparts.com/porsche-914-914-6-technical-forum/318720-mps-issue-car-only-runs-hose-disconnected.html

Posted by: Java2570 Dec 17 2014, 03:49 PM

Did you ever try out that spare ECU I sent down? I don't know if it could be related but try it for the hell of it if you haven't already. Jon

Posted by: Spoke Dec 17 2014, 04:00 PM

I think what you've determined is there is no open in the electrical circuitry.

The real key is the electrical inductance of the 2 sections.

The purpose of the MPS is to sense the pressure and change the inductance accordingly. The inductances are used by the ECU in a monostable multivibrator to control the width of the injector pulses.

Thus if the inductance is off, the engine will run lean or rich.

When I got my 1.8L running with DJET the MPS was way off in its setting for the ECU as the engine was super lean. It wouldn't idle and ran like shit. I had to dig out the epoxy on the MPS and adjust it to richen up the mixture.

By the engine running when the MPS disconnected from the intake vacuum, this is telling the MPS to apply maximum pulse width. So it sounds like your engine like mine is running really lean with the MPS.

Initially I fooled the ECU by adding resistance in series with the CHT sender. This fooled the ECU into thinking the engine was cold and the ECU needed to widen the injector pulses making the engine run a bit richer. I solved this issue by adjusting the MPS.

BTW, what resistance is the CHT sender reading when the engine is cold and hot? If the CHT is shorted or very low resistance, this could also cause the engine to run really lean.

Posted by: Philip W. Dec 17 2014, 07:54 PM

Usually a really lean condition will still run but have really high idle and hunt like a vac leak. In that case I did adjust the mps until it brought it back into the 12 range on the AF meter. Right now I have not gone back to test the cht but I am suspecting the cht or cht circuit. I just think that unplugging the mps making it go rich is a compensation for the lean r inning due to cht not being right somehow. I Called AND Left Him A Message To Try To Go Over This With him but he did not return my call. so I will try again tomorrow.

Posted by: r_towle Dec 17 2014, 08:41 PM

Oh, you have already adjusted the MPS from the stock setup?

Posted by: Philip W. Dec 18 2014, 09:29 AM

I got one ive been using that was already adjusted. the i had set to factory specs by Scott in NH but it was way too lean. so i tuned it with a/f meter, about 2 years ago, but since this new issue began i had not messed with it.

Posted by: 76-914 Dec 18 2014, 09:33 AM

I sent him a variable resistor so he could check that side of the puzzle, also.

Posted by: Philip W. Dec 18 2014, 09:38 AM

going to re-test that CHT, and see wheere the values are before i us the variable resistor, then use that to see what's required to bring it into spec if its out- but on the advice of another member i went ahead and orederd another new CHT as well because i figured it could not hurt to have an extra one on hand

Posted by: Philip W. Dec 18 2014, 10:41 AM

alright a bit of an update: just spoke with Bob Woodman, my mechanic. I pulled the ECU and went thru the harness and tested all circuits - no issue there. Pulled the Cht, tested hot and cold, all good right on spec as well. Next went back to the MPS. with car on and running but that vac hose off it starts and runs, although very rich at @8-9. next he hooked up the vac meter to test it and once he had it ot just 5mmhg it killed the car- and the AF went crazy lean! - at this point we both think that its that stupid MPS so we should have a good test mule coming from kent iin a couple days, and see if that is it for sure. Now i also have a spare ECU that was sent to me to test and that really is the only other thing it could be, and i just dont think it is the ECU.

Posted by: worn Dec 18 2014, 01:21 PM

Rich,
Why flip the plug? The inner prongs go to one coil and outer to the other, so either way you will get the same inductance signal. Which may not be correct as we have heard. Just my $.02

Posted by: Philip W. Dec 18 2014, 11:21 PM

Picked up the car tonight and drove it home.
A/F meter reading high I think. Idle at warm is 13, under part load is between 14.5- 15; or so. That seems too lean but it did go well . Now.it will be interesting to see how the other one that is being sent to me reads.

Posted by: Dave_Darling Dec 19 2014, 01:39 AM

So what did you do in order to drive the car home? Sounds like you either fixed the problem or at least got it partly solved.

--DD

Posted by: Philip W. Dec 19 2014, 05:32 AM

Switched out the mps with another unit that I had. It's been nested with and has a ver slight leak down on the vac but good enough to start and rum with out killing dying or stalling. Just have to source a good mps for keeps. Going to be able to test one that Kent is sending over. But it seems like the at was the major issue.

Posted by: Racer Chris Dec 19 2014, 07:13 AM

Under light load you should be leaner than that, but when you tip into the throttle it should go rich - 13.2 to 12.5.

Posted by: brant Dec 19 2014, 08:40 AM

Was that mps a brand new one?
Sounds jet exactly like the scenario I've seen previously
Put Kent's mps in and verify your numbers get better

Chris is right that your afr is still wrong. I'm betting you have adjusted the one in the car? Way off.

If Kent's mps truly proves to the you good numbers.
Then take the diaphragm from your good mps and rebuild your old one.
I think there a something wrong with your new mps. I've seen this only once before. Carefully compare the two diaphragms and use nothing else.
Maybe have Geoff calibrate it if you want it perfect

Posted by: Philip W. Dec 19 2014, 02:22 PM

That's where I was before it went bad. I'm going to try to get this one adjusted to a better mix . I have 2 of the rebuild kits from the group buy so I'm going to go ahead and find out if I can make one of the other ones work. I will do some comparison with the one from kent, Nad another one that I will be testing and purchase it it tests out good - that one is an unmolested one so I what to see where the numbers on these are.

Phil

Posted by: Philip W. Dec 19 2014, 02:25 PM

The one that got me home was one i picked up a few years ago that was opened up and revealed by someone else at some point. It holds vac good. Epoxy plug was taken out so at some pint I had it sent to Scott to set to factory settings. Had not use it until now and it appears that the factory settings are lean on my car. Scott used a LCR set it up.

Posted by: Jeff Bowlsby Dec 19 2014, 03:05 PM

The only published MPS calibrations are on Brad Anders page, which are a collection of measured calibrations of existing known good and NOS MPS. I have found that they are also lean for unknown reasons. The Wavetek meter (I have one) can be useful to get the calibration close and that is all. The only way to get the A:F ratio exact is to use an exhaust gas analyzer or WB O2 to calibrate the MPS. Each engine will be different based on its condition, wear, differential flow rates of injectors, fuel pump settings and performance, sensor variations, etc and the EGA/WBO2 is the only way to get it optimized.

Convincing evidence that the factory fine tuned each car individually is indicated by the mark on the ECU idle knob ring.

Posted by: brant Dec 19 2014, 03:51 PM

I agree
the factory setting are far from ideal
remember how different gasoline formula's were back then!

todays gas is a lot different
perhaps the factory settings were better? for gasoline of the day
or perhaps the factory settings were too lean even back then for fuel mileage and simplistic testing equiptment.


as you rebuild one of your cores, make sure that its a 2.0 housing...
the 1.7 housing have a WOT stop in the casting that you would need to grind out if you are using one of them on a bigger motor.

I still can't wait to hear what happens when you plug a different, known good MPS into the car. I think that your entire problem was caused by this MPS. Hell if I know why, but i've seen it once before.

you never replied.... was this MPS a NOS one?

Posted by: Philip W. Dec 19 2014, 09:23 PM

No, as stated in my previous post, it was rebuilt at some point but too lean. I spent a hour on it tonight adjusting slowly the mps trying to bring the mix closer to 12.7 that anders says is the target for part load mix. It's still hitting about 14 on acceleration up a slight grade. That was after adjusting the center screw about 3/4 turn. At.least it starts and runs. Tomorrow I'll work a bit more on it but will take it a quarter turn at a time , test drive, and I will keep working it down closer to the 12-13 under part to full load. I've been going back over all of anders data etc. For some.reason the idle is a bit high but that could be the lean setting as well. I have to recheck the tps setting. It seems like it is not set exactly where I set it after it was in the shop. I think there a are is fine. It was fully closed tonight after the engine warned up.

Posted by: 76-914 Dec 19 2014, 09:44 PM

FWIW Phil, that one is for a 75-76 so may run a bit lean. But it will sure as Hell work for your needs.

Posted by: 76-914 Dec 21 2014, 09:26 AM

Any news?

Posted by: Philip W. Dec 21 2014, 12:12 PM

Spent part of one day messing with it , reading up on the mps tuning, it did start right up Friday night, and took it for a drive but have not done anything with it the past 2 days. Yesterday I spent the day inspecting and test driving the Audi tt, - bought it and brought it home. Big reason was really all day rain yesterday and today.

Posted by: Philip W. Dec 27 2014, 10:57 PM

So I have not been able to try out the mps that you sent to test until today.

The car started but was a bit rough at first. I let it warm up and see where the idle would settle to and see what the A.F. meter was reading then took it for a drive around the neighborhood.
Upon starting the a.f. reading was 10, after warming up went to 12-12.5 during drive on acceleration it was reading about 15-16 ,y cruise was about 13.5-14. . This is a never opened or adjusted one from Kevin (rhoadguy)
Buy I think I can say that this thing is still not running right. There is something else causing problems. It just does not run smooth, feels like it misses here and there. Yes my other MPS was a major cause of it not starting but there is something else going on here too that I have not figured out yet. It will be running fairly well and idling and suddenly the idle drops l I me it's going to die. Also feels like it's misses or skips here a ND there. Almost like a short.

Now that I have an mps that is known good, I may have to go back thru and try a couple things like plug wires, points etc.
I should get a chance to test a few things tomorrow, might even hook up the spare ecu. I might even try some other plug wires

Posted by: Jeff Bowlsby Dec 27 2014, 11:13 PM

I wonder if this is related to the advance weights binding in the dizzy? Have you lubed it in the last year? 1 drop of 30 weight in the center of the dizzy shaft, annually per the manual, to lube the advance weights. It may cause the hiccups you describe.

Posted by: Philip W. Dec 28 2014, 12:13 AM

No I've not done that.

Posted by: Philip W. Dec 28 2014, 01:54 PM

Is it possible for this one part, the temp sensor to cause the issues if ev described?


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Posted by: Philip W. Dec 29 2014, 08:20 AM

so yesterday i decided to try and figure out where my other issues were coming from and then tune the MPS a bit more;
- ended up recheck ing the TPS setting because it was off after being at the mechanic and reset that, and i had to pull that temp sensor to make it easier to get the cover on and off the TPS, not sure why but in my box of parts i ran across a brand new one i had inmy stash so i put that new one in there because i noticed that if that temp sensor is disconnected the car will not run, same as a CHT or MPS AND it is the one part i had not tested or tried a replacement of. IT is possible there is another short somewhere in the system and i had a few ideas from reading other similar theads. so i went back thru the grounds- all good. one post mentioned the 3 red wires that attach to the positive terminal of the battery. No corosion there but that whole connector could be re-done so i might do that.
-anyway yesterday i could not get the car to idle , or stay running , but after replacing that sensor, car ran perfect with no sputtering or cutting out at all, perfect idle with out surge or variation. Yes we had a bad MPS but car ran when the vac hose was off due to it being super lean other wise and i now think it was this sensor causing that lean running condition.

How common is it for that plenum temp sensor to go bad? i am going to spend some time over the next week driving the car and seeing if i can get it dialed in. Because i have spent weeks chasing my tail on this car and have had it running only to find another part that was part of this problem coming and going, i am optimistic but cautious. i feel like i could get in the car 2 days from now and find it not running again. I hope this is it, time will tell.

Posted by: Jeff Bowlsby Dec 29 2014, 08:27 AM

Interesting. Never heard of a D-Jet 914 that did not run because of that sensor (TS1). Its a temp sensor that sends a signal to the ECU to correct the A:F mixture for air temperature variation. Many simply unplug the harness from it, which has the effect of richening the mixture about about 10%. The car should easily run without it, some would say better without out it than with it, but I run my 2.0L with it connected and no issues.

Posted by: r_towle Dec 29 2014, 08:29 AM

its the ambient air temp, and I have never had one fail, but this stuff is 40 years old now.

In the end, you had a bad MPS sensor.

maybe with all the moving of the wiring harness you may have loosened the connection to the ambient air temp sensor, which may have done something.

I cannot recall what the conditions are for that to work/not work.

rich

Posted by: Philip W. Dec 29 2014, 09:49 AM

well that is certainly a possibility. we do know for sure that MPS was bad, and putting a different one, ones in made it run, but i was still having an issue. i know the harness is good but that doesnt mean there wasnt a bad connection either there or somewhere else. I thought it might even be the CHT connection. the CHT tested good but if that connection is not right that would cause issues. . it seems odd that sensor would go bad, but i do know that right now its running pretty good. I will have to wait and see if that lasts.

Phil

Posted by: r_towle Dec 29 2014, 10:59 AM

if you still have an issue, I would go back to the basics.

Valve adjustment cold
Dwell
Timing
Vacuum leaks

Rich

Posted by: Dave_Darling Dec 29 2014, 03:26 PM

The intake air temp sensor doesn't contribute a whole lot to the mixture--it should not be enough to make a massively lean condition on its own. It is more of a fine-tuning adjustment.

Not sure what could be going on with your mixture. Could it have anything to do with the TPS that you adjusted?

--DD

Posted by: Larmo63 Dec 29 2014, 05:37 PM

After reading this thread and screwing around with my own '73 1.7 FI, I think carbs are a better solution. I know just stating this may start a whole sh*tstorm, but my new engine will have carbs.

With all these acronym parts, hoses, wires, vacuum, testing, the whole mess has me worn out.

Posted by: BeatNavy Dec 29 2014, 05:44 PM

Don't do it, Clint! I've probably replaced every sensor and component on my DJet, and I enjoy the challenge. I spend a lot of time on http://members.rennlist.com/pbanders/djetparts.htm, and to me the FI is well worth it. Keep researching and trying!

Posted by: r_towle Dec 29 2014, 06:35 PM

Not going to argue you out of it, but I would suggest you research what you want to do so you can achieve the goals you want.

With carbs you can use a more aggressive camshaft which could deliver more power.
With carbs you will have constant maintenance of the jets to keep it clean.
You will need new fuel lines for today's fuel.

Overall, if you approach it the right way, both carbs and FI can be fun and simple.

Rich

Posted by: Larmo63 Dec 29 2014, 10:41 PM

Yes, engine is already built with Webers in mind. Proper lift cam has been fitted.

Posted by: Dave_Darling Dec 29 2014, 10:49 PM

Should be fun! And if you already know Webers and don't know D-jet, the decision sounds pretty simple...

--DD

Posted by: Philip W. Jan 3 2015, 05:10 PM

Well back to the matter at hand..
Went to go drive the car today--- would not start! Finally did but missing really bad WTF! Drove it just a few days ago and ran fine???? This is NOT and MPS or air temp sensor issue but what the hell is it??? I mean why the hell can I not park this car for more than 2 days and come back to drive it? Really. What would cause it ?

Posted by: Philip W. Jan 3 2015, 05:19 PM

Put about 60 miles on it just 2 days ago. Was running and idling perfectly when I pulled into the garage. Must have been just a coincidence that I replaced that temp sensor and the car ran after that. Must be a short in the harness connection somewhere and upon moving the wires it worked? And I have no idea where to start looking again. Grounds are tight. But that's what it acts like, a bad ground or something.

Posted by: Philip W. Jan 3 2015, 05:19 PM

Put about 60 miles on it just 2 days ago. Was running and idling perfectly when I pulled into the garage. Must have been just a coincidence that I replaced that temp sensor and the car ran after that. Must be a short in the harness connection somewhere and upon moving the wires it worked? And I have no idea where to start looking again. Grounds are tight. But that's what it acts like, a bad ground or something.

Posted by: r_towle Jan 3 2015, 06:43 PM

Injector grounds?
Distributor advance plate ground?
Coil bouncing around?
Wiring near the coil, near the sensor you touched?

Posted by: Philip W. Jan 3 2015, 10:36 PM

1. Double checked them. They are connected
2. Coil is fairly new, was having this problem before replacing coil, appears not to have mattered. I did recheck all of the connectors.
3. Not sure what you mean. It's mounted tightly. Voltage is not bouncing.
4. Rechecked wires and connections.

Remember, car was running fine and was parked, nothing touched, sat for 2 days. Last time it sat for 4-5 days and started right off no issue.
It's not cold.out, it's about 70 degrees, very humid though.

Posted by: rhodyguy Jan 4 2015, 09:27 AM

Remembered from long ago....I think Dave darling had a problem similar issue. Itwas traced down by brad r and the issue was the routing of the wiring for the mps. Interference from a different signal source? See if Dave remembers this. Are you currently using the mps I sent you?

Posted by: Dave_Darling Jan 4 2015, 11:40 AM

Nope, not I.

--DD

Posted by: Philip W. Jan 4 2015, 05:58 PM

No . I have 2 that I wanted to test I was going to do that yesterday. But since car won't start I cant do much. Tomorrow I'm going to go back thru checking the electrical end starting with spark/coil/plug wires etc. I've already gone thru the f.i. harness. I did make sure the mps wire is not next to the spark plug wire and interfering.

Posted by: Philip W. Jan 24 2015, 12:53 PM

Last week end I went to try get workingrightthe car, before doing anything I decided to see if it would start at all - started and ran like there was never an issue. So Monday it ran fine and so I finally did the deep tuna can sump and new billet taco plate and sensors replacement with full oil change etc. Drove it the next day ran perfect.
Now those days it was @65-70 degrees.
NOW- fast forward to today. I come out this morning , it's 40 degrees out, it barely starts, very rough won't stay running or idle with out feathering the pedal . If I reved it it almost ran smooth and idle for 10 to 15 second then die.. trying to restart it it was like it was flooded - no go. Cranked but no fire.
SO I leave to run and the honey do list and garbage run etc. Come back just a few minutes ago. Now its 60 degrees out. --- a friend stops over and I tell him about what's going on with it. So I get in the car to show him how bad it is to get it to start and What the heck? /$^!^#&#
It fires right up! Like perfect no skip miss or other issue at all!!!!!

I HAVE A CRAZY PSYCHO SPLIT PERSONALITY CAR!!!

what are my options here?
Won't do any good to test anything else now it's idling perfect as I speak. A/F meter reads 11.5 fuel pressure 29,
Either I have a bad cold star valve that floods it out when cold, or ther is a short somewhere that is intermittant.

I am befuddled

Posted by: mepstein Jan 24 2015, 02:04 PM

It's a snowbird car. Send it to FL for the winter.

Posted by: 76-914 Jan 24 2015, 04:37 PM

Is the plug on the backside of the dizzy clicked into place. The rubber boot can impede with that snapping into place. Also, check the center pin (coil) on the inside of your dist cap to see how much wear it has. It wears down and makes intermittent contact. BTW, just because it moves in & out when pressed doesn't mean it is making contact.

Posted by: Jeff Bowlsby Jan 24 2015, 08:15 PM

Could it be an electrical connection? Harness issue? Corroded wire terminals or cracked/broken wires?

Posted by: Philip W. Jan 24 2015, 08:56 PM

Jeff,
To me it acts like a short or bad connection, like the f.i. Grounds are not tight I once had one come off and thats what it felt like. But it's not that. And the harness I got new from you 2 years ago and my mechanic when thru each circuit last month and double tested every one of them and I'd course at that time we found the bad mps which we swapped out and it ran fine. It didn't do its little trick until I got it home. Did that before I took it over and after I got home a week later.
new optima battery no corrosion. I have not found any cracked or broken wires.
After this started I replaced the circuit board and rear relay board. I guess it was not those as I did not get rid of the issue.
I was thinking it could be a plug wire or the cap. I've heard ts of that happening so I might swap those out and see.
right now I am sitting in it in the driveway. Perfect idle at about 1000, no hesitation at all. It's about 45 out . Will be interesting to see if it fires up in the morning. But while it's running I'm going for a short drive now .

Posted by: Philip W. Jan 26 2015, 01:40 PM

started this morning- so i drove it to work!(25 miles each way), as long as the rain stays away im going to driv it to work aleast 3x a week until it decides not to start or gives me fits. going to keep fiddling around until i figure out what the issue is.
so far since installing the tuna can and the nwe oil temp sensor and taco plate no leaks - but the VDO sender and the nitrous gauge seem to work fine together,- temp gauge reads almost exactly waht the dips stick thermometer reads.
seems like this car still runs a bit hot. The air guides for under the car are not there. timing and advance are right on, not running lean. Does not go into dangerous levels but seems like at 50 degrees it would not go over 210 and after running for 30 minutes , under more load that temp will go up to the 230 - 235 range.

Posted by: Philip W. Feb 11 2015, 07:57 AM

over the last few weeks ive been driving the car a good bit. really running fine, but i either have to disconnect the battery or hook up the maintainer because if i go over a week with out running it it really gets run down so not sure whats up with that. - but back to the temp issue. ive bee rechecking this and it appears that the gauge reads about 230 or so when really warmed up , but the dipstick gauge actually reads closer to 180-190 which means that i probably need to get a VDO gauge to hook up that would read correctly from this VDO sender i installed, and 2. that it is cooling a bit better now with the deep sump installed as well.

So now hopefully it will run good the next few weeks as there are several carsncoffee deals coming up in this area and as much fun as the TT has been to drive, its not the same as taking the 914.!!!

Posted by: cary Feb 11 2015, 08:23 AM

Did a quick read.

I'd disconnect the cold start injector, both fuel and electrical. I haven't run one in years, even in Montana.

If it hasn't been suggested or done. I'd also suggest getting new harnesses in the engine compartment. Forty years is a lot of heat cycles. Especially on an air cooled car.

Posted by: Philip W. Feb 11 2015, 12:40 PM

thanks for the comments- i agree about the cold start injector- it really acted like it was flooded out those couple times it wouldnt start, so i might do that.
The FI harness was replaced a couple years ago, new from Jeff Bowlsby. and just to make sure my mechanic went thru every circuit on it to double check that there were no shorts and each one check out correctly according to anders and what the ohm readings should be etc. i think that cold start injector is the only thing i have not touched since this started- and to complicate issues, at some point the MSP was going as well but that has been sorted and the one i have in there now is right on where i want it. Supposed to be really chilly saturday morning ( @40 degrees) but i'm still planning on going to the cars n coffee --

Posted by: Philip W. Jun 24 2015, 01:26 PM

this goes back a few months and i never posted after resolving the issue, but after having the cold start injector disconnected, having the injectors tested, i almost gave up.
- long story short- the whole issue of sometimes starting sometimes not was caused by a bad contact in the distributor cap. - I replaced the cap and rotor and have not had an issue since!! - the center contact with a spring in it was not making solid contact all the time . so both during the cooler weather in march/april and the heat of this summer ive had not one issue with the car not starting right up. Back in december we did have the MPS die and that was replaced . just strange tha this happened so soon after that problem was diagnosed and fixed...
sometimes the solution can be so simple!!