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

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.

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.

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

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

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

Valve adjustment cold
Dwell
Timing
Vacuum leaks

Rich

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

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.

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 Anders' page, and to me the FI is well worth it. Keep researching and trying!

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

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

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

--DD

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 ?

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.

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.

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

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.

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?

Nope, not I.

--DD

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.

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

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

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.

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

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 .

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.

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.!!!

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.

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 --

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!!