D_jet trouble shooting question - car is home, journey continues, June, update- no more problem-- the fix was simple.... Options

[DRPHIL914]

D-Jet Trouble Shooting

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.

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

Rich

i went over and tested the MPS at lunch time- holds vac, and T7-15 was 92ohms, and T 8-10 was 340. (IMG:style_emoticons/default/confused24.gif) 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....

[SLITS]

i went over and tested the MPS at lunch time- holds vac, and T7-15 was 92ohms, and T 8-10 was 340. (IMG:style_emoticons/default/confused24.gif) so that means its good, right?

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.

[DRPHIL914]

i went over and tested the MPS at lunch time- holds vac, and T7-15 was 92ohms, and T 8-10 was 340. (IMG:style_emoticons/default/confused24.gif) so that means its good, right?

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.

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)

[SLITS]

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.

[Java2570]

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...sconnected.html

[Java2570]

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

[Spoke]

i went over and tested the MPS at lunch time- holds vac, and T7-15 was 92ohms, and T 8-10 was 340. (IMG:style_emoticons/default/confused24.gif) so that means its good, right?

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.

[DRPHIL914]

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. (IMG:style_emoticons/default/dry.gif) so I will try again tomorrow.

[r_towle]

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

[DRPHIL914]

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

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.

[76-914]

i went over and tested the MPS at lunch time- holds vac, and T7-15 was 92ohms, and T 8-10 was 340. (IMG:style_emoticons/default/confused24.gif) so that means its good, right?

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.

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

[DRPHIL914]

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

i went over and tested the MPS at lunch time- holds vac, and T7-15 was 92ohms, and T 8-10 was 340. (IMG:style_emoticons/default/confused24.gif) so that means its good, right?

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.

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

[DRPHIL914]

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.

[worn]

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

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.

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

[DRPHIL914]

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.

[Dave_Darling]

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

[DRPHIL914]

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

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.

[ChrisFoley]

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.

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.

[brant]

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

[DRPHIL914]

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.

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.

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