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Strange 944 Running/ No Start Issues....

 
Old 01-07-2019, 05:06 PM
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Dan youíre a legend. I think I owe you something like 2 cases of beer by now 😂
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Old 01-07-2019, 07:04 PM
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Keep up the good work!
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Old 01-20-2019, 02:55 AM
  #18  
Jacob AbuKhader
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Well i ordered the speed/ ref sensor harness from Lindsey and a fresh sensor and did my best to solder everything up and shield the wiring. Finally got the bracket as well and used the .8 mm washer gap trick... however when I tried starting the car I got no tach bounce (which I had before) and no MPG gauge swing (which I had before). Not going to lie I mangled the DME pins trying to open up that plug so Iím very confident the issue lies there but the MPG gauge thing has me a little worried that I didnít install the new harness correctly or that I didnít pin the DME plug connector correctly when reassembling everything. I do realize the gap could also be incorrect on the sensors but I want to narrow everything down one at a time. I just put everything back I donít want to take the intake off unless I have to.

I used pinouts i found for the 35 pin DME.

When installing the reference sensor harness I soldered the brown wire from pin 5 to the ďdrainĒ ground, did I misfollow the instructions? I didnít connect the ground from the o2 to anything to pin 26. Not sure if thatís where my mistake lies. Everything else seems to me working great and the car cranked healthy so I didnít do anything super stupid.
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Old 01-20-2019, 10:19 AM
  #19  
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Originally Posted by Jacob AbuKhader View Post
Well i ordered the speed/ ref sensor harness from Lindsey and a fresh sensor and did my best to solder everything up and shield the wiring. Finally got the bracket as well and used the .8 mm washer gap trick... however when I tried starting the car I got no tach bounce (which I had before) and no MPG gauge swing (which I had before). Not going to lie I mangled the DME pins trying to open up that plug so Iím very confident the issue lies there but the MPG gauge thing has me a little worried that I didnít install the new harness correctly or that I didnít pin the DME plug connector correctly when reassembling everything. I do realize the gap could also be incorrect on the sensors but I want to narrow everything down one at a time. I just put everything back I donít want to take the intake off unless I have to.

I used pinouts i found for the 35 pin DME.

When installing the reference sensor harness I soldered the brown wire from pin 5 to the ďdrainĒ ground, did I misfollow the instructions? I didnít connect the ground from the o2 to anything to pin 26. Not sure if thatís where my mistake lies. Everything else seems to me working great and the car cranked healthy so I didnít do anything super stupid.
First step would to test reference and speed sensor per Clark Garage procedure at the DME plug. Are the reference and speed sensors connections reversed?
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Old 01-20-2019, 04:57 PM
  #20  
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Originally Posted by T&T Racing View Post
First step would to test reference and speed sensor per Clark Garage procedure at the DME plug. Are the reference and speed sensors connections reversed?
One sensor is brand new and the other one is a few years old but it was working before I removed it. I triple checked when making sure the sensors werenít reversed but I did switch them around once as a hail marry when starting.
But I am 100% sure the sensors them selves are not the issue.
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Old 02-01-2019, 09:38 AM
  #21  
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my first thought was that you're FPR fuel pressure relief valve is letting by ,...allowing small amounts of fuel to enter the vacuum system and ending up in the inlet making your idle mixture too rich.
next time you get the engine running remove the vacuum hose off the FPR and check if there is any fuel in the vacuum hose or you can smell fuel . if the FPR is letting by you'll see gas weeping out the FPR vacuum hose spigot.
With the vacuum hose disconnected if the engine runs better then I would replace the FPR .
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Old 02-01-2019, 09:52 AM
  #22  
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Originally Posted by peanut View Post
my first thought was that you're FPR fuel pressure relief valve is letting by ,...allowing small amounts of fuel to enter the vacuum system and ending up in the inlet making your idle mixture too rich.
next time you get the engine running remove the vacuum hose off the FPR and check if there is any fuel in the vacuum hose or you can smell fuel . if the FPR is letting by you'll see gas weeping out the FPR vacuum hose spigot.
With the vacuum hose disconnected if the engine runs better then I would replace the FPR .
Initially I had the same idea Iíve already replaced the FPR. Something else is causing a mixture issue causing the car to run rich/ flood. However it is unrelated to pressure as my fuel pressure readings are correct. Every component in the fuel system is new except for the tank strainer.


I ran into some issues installing a new crank sensor so now Iím currently waiting on a new wiring harness. When I installed the old harness back into the car I had zero tach bounce, no mpg gauge reading, and no oil pressure reading and rather than throw more money into the old harness I decided to replace it. Iím also going to have that bracket readjusted to make sure the gap is set correctly. The DME is brand new as well so really there shouldnít be any reason this car doesnít run properly once those last gremlins are sorted. I hope Iím right!
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Old 02-01-2019, 10:29 AM
  #23  
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if the engine is over fueling at idle and fouling the plugs then there has to still be an issue somewhere with the fuel delivery system.
I know you have replaced the FPR but it is still worth pulling off the vacuum hose and checking that there is no fuel or smell of gas from the vacuum hose and nothing weeping from the FPR it only takes a tiny minute amount of excess gas at idle to flood the engine , foul the plugs and cause plumes of black and white smoke from the exhaust.

Also check that your air idle valve is working and not sticking. test the engine temperature sender at the front of the engine which the ECU uses to open the AIV to allow more air to mix with the extra fuel at cold start . if the AIV is stuck or non functioning or the engine temperature sensor is faulty then your idle and cold start mix will be incorrect

I know I'm probably teaching my Gmother to suck eggs but you do start the car with zero throttle don't you ? many owners do not ............ touching the throttle during startup completely defeats the cold start fuel and air enrichment parameters

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Old 02-01-2019, 10:51 AM
  #24  
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Originally Posted by peanut View Post
if the engine is over fueling at idle and fouling the plugs then there has to still be an issue somewhere with the fuel delivery system.
I know you have replaced the FPR but it is still worth pulling off the vacuum hose and checking that there is no fuel or smell of gas from the vacuum hose and nothing weeping from the FPR it only takes a tiny minute amount of excess gas at idle to flood the engine , foul the plugs and cause plumes of black and white smoke from the exhaust.

Also check that your air idle valve is working and not sticking. test the engine temperature sender at the front of the engine which the ECU uses to open the AIV to allow more air to mix with the extra fuel at cold start . if the AIV is stuck or non functioning or the engine temperature sensor is faulty then your idle and cold start mix will be incorrect

I know I'm probably teaching my Gmother to suck eggs but you do start the car with zero throttle don't you ? many owners do not ............ touching the throttle during startup completely defeats the cold start fuel and air enrichment parameters
Hahahahaha no I do not start the car applying any throttle input. The service tech at my dealer told me about that making sure I wasnít causing the car to flood. I have done it once or twice just to get the car running but when the car runs normally I donít apply any throttle.

I should have been more specific when I said I replaced the FPR. I did run the car with the vacuum lines off both the FPR and the damper separately to see if fuel spilled out of the lines. I ran the car for over 10 minutes with each line disconnected and no fuel ever spilled out. When I had the injectors tested 2 werenít spraying enough, one was dumping fuel, and the other was functioning normally. Those were all replaced with freshly rebuilt factory originals which were also tested before going in the car.

The coolant temperature sensor for the DME is one of the first items I replaced that didnít help either.

I have not tested the AIV yet but after reading a few other posts that was kind of the direction I was going to head if the crank position sensors didnít solve the issue.

Its worth noting that I have checked timing and itís dead on.

In that picture I posted of that service receipt from 2014, a PO took the car in to a shop for the same exact symptoms Iím experiencing and it ended up being one of those sensors. However instead of replacing both they only replaced one so my thinking is the other one finally went bad. When I pulled it out it was all black and dirty and the wiring from both the harness itself was totally frayed and corroded which is why I decided to replace it.

For future reference, how should I go about testing that air idle valve? Itís basically a spring that opens and closes in relation to temperature right? Or am I thinking of the auxiliary air valve under the intake?
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Old 02-01-2019, 11:28 AM
  #25  
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sorry I wasn't paying attention and failed to notice that you have an early pre 86 2.5 944 so the cold start mechanism is different on your car it has an IAC beneath the inlet which operates in the same way the later IAC valve does on the late models ......however that doesn't alter the fact that the crank speed and position sensors have nothing whatsoever to do with over-rich starting or running. !

you say that you replaced the engine temperature sensor but did you test what temperature either switch operated at by attaching it to a multimeter and dunking it in a glass of hot water with a thermometer and noting the temperature the switch operated ? or did you just assume that as a new sensor it should work ok ?
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Old 02-01-2019, 11:43 AM
  #26  
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Originally Posted by peanut View Post
sorry I wasn't paying attention and failed to notice that you have an early pre 86 2.5 944 so the cold start mechanism is different on your car it has an IAC beneath the inlet which operates in the same way the later IAC valve does on the late models ......however that doesn't alter the fact that the crank speed and position sensors have nothing whatsoever to do with over-rich starting or running. !

you say that you replaced the engine temperature sensor but did you test what temperature either switch operated at by attaching it to a multimeter and dunking it in a glass of hot water with a thermometer and noting the temperature the switch operated ? or did you just assume that as a new sensor it should work ok ?

I assumed it was a new sensor and it should work okay out of the box but I can still remove it and test it. Everything Iíve replaced so far hasnít had any effect on how the car runs.


Theres no cold start injector on the early cars. The DME just pulses the injectors longer and that air valve I described is fully open when the engine is cold and slowly closes as the engine reaches temp. Again the issue isnít really temperature related in any case. I could be driving for a half hour and then in the middle of the road the engine will die and not restart.

Or the car could be sitting for weeks and still not start. It would run perfectly and then suddenly develop a misfire that would correct itself.
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Old 02-01-2019, 01:08 PM
  #27  
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ok thats a good description of an intermittent fault . It could still be temperature related though . Don't dismiss anything out of hand jacob . you have spent a lot of money replacing many things at random without achieving a solution so it would be fair to say that you do not have any idea what is causing this issue.

ideally we should all concentrate on the fault on our cars and diagnose the issue by methodical sequential testing but like most owners that do not have a good understanding of how the Bosch fuel injection and ignition system functions we randomly replace components which is what a lot of garages do too.

Clearly the engine has compression a spark and fuel and air and the timing is fine or it would not run as well as it does some of the time.
it could be a component breaking down with temperature change ...it could be a poor electrical connection which also could be aggravated by temperature change as the engine warms up. it could be poor solder connections or tracks on the ECU boards which break down when the car is jolted or due to temperature ....

One simple way that you can eliminate the DME relay being part of this intermittent issue is to fit a 3x wire bypass in place of the DME relay. (see Clarkes garage tech section ) This serves several purposes and is a useful diagnostic.
With a 3x wire bypass in place it provides a consistant electrical supply to the fuel pump, injectors and the ECU and all the various sensors.

The bypass will power up the fuel pump continuously without the ignition being on so you will need to remove it once testing is finished but it is quite safe to run the car with it fitted. I have fitted a switch to my 3x wire bypass and fitted it into a empty relay can.

the next thing I would check would be the important ground connections for the ECU which are bolted under the dash near the Fuse relay box . it would be worth checking connections at the fuel pump and fuel pump fuse and even wiggling the ignition key next time it dies . Bad ignitions switch contacts will effect the 12v+ supply to the base of the DME relay terminal 30 so next time it cuts out check that you have 12v+ at terminal 30 of the DME relay.
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Old 02-01-2019, 07:41 PM
  #28  
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Have the spark plugs been replaced with new ones?
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Old 02-01-2019, 08:04 PM
  #29  
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went through six sets of spark plugs in 9 months. New ones have only been in the car running maybe twice which was about 2 months ago.


Ive been systemically troubleshooting both the fuel and electrical ignition system thatís what the replacement of those parts was all about. If need be I can post a link to the previous thread I started that goes over all of that. I started this one because that one was getting ridiculously long lol.

I just to make it clear that that I havenít randomly thrown parts at the car. I began trouble shooting the overfueling issue as a fuel issue. Iíve jumpered the pump and measured pressure, Iíve measured voltage at the pump while cranking I tested every single sensor three times with a multi meter per Clarkís garage, I tested every sensor plug on the harness multiple times. I couldnít find a fault with anything. I removed and inspected the fuse block looking for burnt wires or shorts. Found none of that. Inspected and cleaned the grounds.

Everything mechanically works, I have spark I have fuel I have compression and I have mechanical timing.

I measured voltages, resistances, continuity across everything you can think of. Nothing was showing fault. The only physical thing left that could cause overfueling was the injectors themselves. Either by being stuck open or worn out. Pulling the fuel pump fuse keeps all of those components functioning, AFM TPS DME injectors coil and plugs. It only eliminates the pump from the system. As the car cranks and pressure drops it only would start after the pressure completely dropped. It still did this even with a fresh set of injectors. Yet somehow my plugs were still fouling and getting soaked causing incomplete combustion or lack of ignition altogether. And thatís not the plugs fault because again like I said I tested them. I have spark. So my coil and my cap and rotor are working.Which made me think ďokay well if everything else is doing what itís supposed to be doing then the pulse length is the issue and the plugs must be getting doused.Ē The main thing that controls the injector pulse length is the DME unit. And it does that by using signals from the Speed and reference sensors in conjunction with the AFM and TPS and coolant temp sensors

i havent had the chance to start the car with the new DME so I canít eliminate the old one as being the problem yet. Every component I replaced I did it one at a time tracing down the steps as to what could be the issue. Lengthy post but in order for you guys to help me you need as much detailed info as possible. Thatís whats so aggravating about this issue. Iím looking everywhere and testing everything and replacing everything under the sun that would even cause any uncertainty or doubt to eliminate it as being a possible issue and thereís still do difinitive answer. Some things were done as preventative too I got a good deal on the coil the pump and the filter so I replaced them. Again one at a time as part of troubleshooting. I donít want to give off the impression that I threw parts at the car.
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Old 02-01-2019, 08:09 PM
  #30  
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https://rennlist.com/forums/924-931-...ery-issue.html

here is the link to the old thread. You can get a better idea of what I tested and how I tested it. Let me know if any mistakes jump out or if any tests were done incorrectly and I will do my best to retest and post results. Feel free to ask any questions too. I do appreciate everyone taking time to help me out.
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