944 non-turbo turns ON and dies immediately

Santos · 07:12 PM

I have a non-turbo '83 944 Porsche that turns ON but dies immediately. I had some good mechanics look at the car and now I have it at an electrical shop. I would really appreciate input and suggestions from this forum.

Here is what happens:

1. I turn the key and the car turns ON while the Starter is engaged, but as soon as I have the key move to the ON position the car dies immediately. If I keep the key in position such that the Starter is engaged, the engine stays ON and as expected extra noisy. I thought the issue could be the ignition electrical switch and I installed a new one but the issue was not resolved.

2. If I disconnect the air hose at the throttle body input and I pour in starter fluid (I used gasoline from my gas tank to check the fuel quality), the car stays ON without having the Starter engaged continously. I can move the key to the ON position and accelerate the car to a few thousand RPMS (~4000, maybe a little more) as long as I have starter fluid or gasoline flowing into the throttle body input. This tells me that the spark plugs and distributor are doing their job. And, I suspect that the fuel injectors are shutting down completely or getting a weak signal to the fuel injectors when I move the key to the ON position.

3. I took the car to an electric shop. And the technician told me that the fuel injectors were getting a weak electrical signal (barely spraying any fuel). The technician manually grounded the injectors and we were able to maintain the engine running smoothly while the key was in the ON position. So, we know that the issue of the engining dying is due to lack of fuel. Fuel pressure is good. Fuel injectors are opening and firing nice amount of fuel when technian manually turned the fuel injectors ON. Why do the fuel injectors get enough power to turn ON the engine when I have the starter engaged, but then signal is too weak when keys are turned to ON position? Does the fuel pump turn ON at some specific engine RPM?

4. When we disconnect the DME temperature sensor, we were able to turn ON the car and keep the engine running while the key was in the ON position. The engine was difficult to turn ON with the DME temperature sensor disconnected and we are NOT able to accelerate the engine smoothly. If I depress the accelerator quickly, the engine will die out. So, we thought we needed a new DME temperature sensor. I installed a new DME temperature sensor and I still have the same problem. I turn ON the engine with starter engaged and the engine dies out immediately when I turn the key to ON position.

The technician thinks the Mass Air flow sensor might be the issue. But, I am not convinced and I want to avoid spending money on items that will not fix the issue. At first, the technician thought that the mass air flow sensor was good based on voltages he checked. The voltage output on the mass air flow sensor increases as the flap angle opens toward the OPEN position. I recently gave the technician a printout of an article on Clarck's Garage which has details on checking the 944 mass air flow sensor. I hope he can pinpoint the issue with the mass air flow sensor.

Per the technician, all the ground signals from the DME control unit look good. He also checked the fuse BOX and relay BOX and said that all voltages and grounds look good.

Could the issue be related to the TPS sensor? Could the temperature sensor inside the mass air flow sensor cause the issue I am seeing?

Obviously, the fuel injectors are getting a strong enough signal to turn ON the engine when I have the starter engaged. But, then the signal is too weak to feed enough fuel to the engine when I put the key to the ON position.

Any suggestions from the Forum appreciated. I'll check or have the techie check stuff that this forum suggests.

Thanks in advance,
Santos

taki951 · 01-24-2010, 07:17 PM

Sounds like there is a short in the ON position check the current draw on the injectors harness when in the ON position and the ground wire from the ECM to the injectors. Also quick question check and see if there is any moisture on or in your ECM that would cause your problem also.

ddbach · ddbach's Garage

Granddad#3 has a great no start check list in this thread: at wits end...
John_AZ has great advice regarding this subject too.
Searching no start or ignition and their names should help you find some of their other posting on this

Santos · 01-25-2010, 01:22 PM

ddbach: I read the articles and did not find help with my specific issue. I have already pinpointed the problem with weak signal from DME control unit to the fuel injectors when the key is turned to ON position. When I have the key turned such that the starter is engaged, the fuel injectors get good signal from DME and the car starts up.

taki915: The car engine stays on when I disconnect the DME temperature sensor and move the key to ON position. I'll still check for the current draw. I did have a lot of rain lately and the car had a leak on passenger side. The car was sitting outside in high humidity for a month.

~Santos

HondaDustR · 01-25-2010, 03:01 PM

Ok, something crazy that just came to mind... Wire a switch between the starter solenoid wire and the solenoid itself (remote starter switch would be easy). Then you can troubleshoot when holding the key in the start position without actually engaging the starter. Naturally you could do that by just disconnecting it, but the switch would allow you to start the car as well. Have someone hold the key in the start position and use the switch to energize the solenoid to start the motor, release the switch to deactivate the starter, and be able to see just how well the motor runs in the longer term with the key held in the start position without grinding stuff up.

Outback Porsche · 01-26-2010, 12:53 AM

The car is being starved of fuel. The DME relay also runs the fuel pump - get a new relay. Notorious failure!

Lapponia · 01-26-2010, 02:15 AM

+100 HondaDustR! When checking the electronic circuits in DME I came to the same conclusion that this should work to keep engine running. While cranking the engine the nbr 4 pin in DME gets 12 volt from the solenoid circuit and thereby grounding pin nbr 20 in DME (through electronics in there). Second half of DME relay gets grounded at pin 8or 85b. Relay pulls and will supply 12 Volt to the fuel pump. Enginge will now run(as long as ign key is kept to Start position. Well, this is a good start for a failure search.
But something tells me that a signal within DME is missing, a signal that should take over the 12 Volt to pin nbr 4 in DME making pin 20 grounded when ign key is in ON position. Of course (Jeff) changing the DME relay should be the first step to go considering car is 20++++ years old.
My own idea is that referece or speed transmitters is bad (not both as engine will run erratically). What do you guys think?

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Lapponia 1984 944 NA

Outback Porsche · 04:06 PM

Quote:

Originally Posted by Santos

2. If I disconnect the air hose at the throttle body input and I pour in starter fluid (I used gasoline from my gas tank to check the fuel quality), the car stays ON without having the Starter engaged continously. I can move the key to the ON position and accelerate the car to a few thousand RPMS (~4000, maybe a little more) as long as I have starter fluid or gasoline flowing into the throttle body input. This tells me that the spark plugs and distributor are doing their job. And, I suspect that the fuel injectors are shutting down completely or getting a weak signal to the fuel injectors when I move the key to the ON position.

This tells me the ref/speed sensors and dme injector/coil signals are okay. Fuel is the missing component under normal ops. Go to Troubleshooting Fuel Supply Problems and bypass the dme relay - see if it runs.

Cheers

Lapponia · 01-27-2010, 06:08 AM

Santos. If your fuel pump is not changed since 1983 it may look the same as my did last summer after 215.000 km. Do take a look at the picture of fuel pump internal filter wich you can not reach without breaking it up. I changed the pump and BANG the car fired up like new. Good luck with yours.

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Lapponia 1984 944 NA

Lapponia · 01-27-2010, 06:23 AM

Jeff. Absolutely fuel starvation when I think of it deeper. After a coffe break last summer car sput-tered a few times when engaging the starter. I guess it tried to fire up on the pressure in fule lines and when that pressure became zero a few seconds later I had no fire at all in any cylinder. Tried the bypass wire in the first place but did not get any fuel out of fuel rail (big nut with ball removed).
So FP was sheared and didnt turn. Flatbed home, FP changed and this fixed it. Cheers!
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Lapponia 1984 944 NA

drew1 · 01-27-2010, 07:45 AM

Santos,

several things could cause your problem.

Your mechanic is right about MAF or what you have if it hasn't changed, VAF.
Speedracer & Laponia are right, too in DME relay, different contacts in start & run, & clogged up strainer in fuel tank.

As old as your car is I would like to add air leaks. The bad thing is you have a bunch of hoses under the intake maanifold. This might be an inexpensive fix unless it's that molded T hose.

dagger dog · 01-27-2010, 08:06 AM

santos,

Before diving into the deep end, try"hot wiring" the ignition system, I have had to replace many ignition switches on '44's for the problem you describe.

You can only use this as a test and run it for a few minutes, run a hot wire from the positive battery terminal to the positive side of the ignition coil, the side marked +, then crank the car and see if it stays running, if so the most likley cause is a bad contact inside the very small ignition switch.

I say again you can only run this test long enough to see if it will stay running.

Didn't ask but does it have an alarm?

Santos · 01-27-2010, 10:59 AM

I did try "run a hot wire from the positive battery terminal to the positive side of the ignition coil, the side marked +, then crank the car and see if it stays running". The car had the same problem. I changed the the electrical ignition switch anyways and the problem didn't go away.

I have good fuel pressure. I also bypassed the car's fuel pump and installed my own external fuel pump at the input of the fuel dampener. I had a gasoline container feeding my external fuel pump. I cranked the engine, the engine starts up and dies quickly as soon as I move the key to ON position.

The car is starved of fuel is true, but starved at what point? My fuel pressure is good. I mentioned that the electrician manually grounded the fuel injectors and he can maintain the car engine ON while the key is in ON position. If I had a fuel problem before my injectors, the electrician would not be able to keep the car engine running.

The '83 944 comes with a stock MAF. I will try the relay hotwiring of pins 87, 87b, and 30 for the fuel/dme relay. I think the relay is good based on the fact that the engine will stay ON even with the key in the ON position when I disconnect the DME temperature sensor.

I think we can rule out air leaks if the car engine stays ON as long as fuel is fed in.

The specific problem is weak signal to fuel injectors when key is turned to ON position.
How should the injectors work when starting up the engine?
Do the injectors spray any fuel when the key is initially turned to ON position?
I think the fuel injectors start spraying when the key is turned to 'start' position and starter is engaged. When the key is turned to ON position, the ECU should recognize that the engine is ON through sensors and continue pulsating the fuel injectors. Maybe some sensor is telling my ECU that the car engine is not on, or the ECU is acting funny. I'll comment once I have the problem resolved.

The car does not have an alarm.

thanks,
Santos

Lapponia · 01-27-2010, 12:05 PM

Oh blasted......I wrote for at least 30 minutes and didn´t realise I was logged out. Lost it all, sorry!
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Lapponia 1984 944 NA

Outback Porsche · 01-27-2010, 02:53 PM

Quote:

Originally Posted by Santos

I think the relay is good based on the fact that the engine will stay ON even with the key in the ON position when I disconnect the DME temperature sensor.

Yes, agree. Sorry, I missed this in your first post. This changes everything. Start-up gets a fuel enrichment (injectors open for longer) that doesn't exist during idle. I suspect it dies in this test when you open the throttle because the injectors aren't opening sufficiently.

All injectors fire at the same time, ie there is only one output from the DME (the injectors are on two pins of the DME plug, but inside the DME they originate from the same circuit). If one or more of the injectors are bad they will load the output circuit in the DME incorrectly - possibly the cause of the 'weak' injector signal.

Check impedance of each injector - should be 2-3 ohms.

Check the wiring continuity from the injectors to the DME connector.

You may need to get another DME to try, or send yours away to be tested (944Online test for free).

Cheers,

Outback Porsche · 01-27-2010, 03:03 PM

Oh yeah, it probably runs with the DME temp sensor out because the DME thinks it's in 'start-up' mode all the time.

Lapponia · 01-28-2010, 03:28 AM

Well, that´s just GREAT Jeff. But I wonder what a weak signal is here. One should always get a +12 Volt voltage at all four injectors when ign key is ON and a pulsating ground at pin 14 & 15 on DME when cranking or engine running. So can it be possible that this pulsating ground is not very good e.g. power transistors/solder in DME are bad? I second all your thoughts and about checking DME at 944.online.

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Lapponia 1984 944 NA

Outback Porsche · 01-28-2010, 04:04 AM

Yeah, you could be right about a bad solder joint. It's a little more complicated than just a transistor. If I remember rightly, the signal come from a multi-vibrator circuit. If your game enough to open the DME, you'll have to trace back the circuit from pins 14 & 15. The only schematics floating around the web are from later DME's - they can be used as a guide only for this model.

The shop manual doesn't give any info about signal levels, only pulse durations. I'm guessing the auto elec that told Santos it's a weak signal is looking at a noid light and has determined it's different to what he expects.

One day I'll stick an o'scope on an injector and have a look (means I'll have to borrow one from work - not always that easy) at the signal level. If anyone has done this already please impart with your knowledge.

Anyway Santos, it looks like you've got something to work with for a while. Do the easy things like measurements first.

Cheers,

Lapponia · 01-28-2010, 08:23 AM

When I bougth this 944 of mine I could never believe that I should need an o´scope for fault finding. I´m 69 and retired and cleaned some closets from old instruments. My double channel o´scope found its way to the scrap yard, too bad!
However, I found a cirquit drawing on internet and added some small information. It was said the DME was very much like the ones in our 944´s. Hopefully it could be used for tracking down your fuel injector issues S

antos. Good luck!

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Lapponia 1984 944 NA

taki951 · 01-28-2010, 03:55 PM

Quote:

Originally Posted by Santos

ddbach: I read the articles and did not find help with my specific issue. I have already pinpointed the problem with weak signal from DME control unit to the fuel injectors when the key is turned to ON position. When I have the key turned such that the starter is engaged, the fuel injectors get good signal from DME and the car starts up.

taki915: The car engine stays on when I disconnect the DME temperature sensor and move the key to ON position. I'll still check for the current draw. I did have a lot of rain lately and the car had a leak on passenger side. The car was sitting outside in high humidity for a month.

~Santos

If the pass side got wet the DME has moisture in it had it happen to my 88 N/A and my 87 M6 take out the DME open it and dry it out then let it sit for a few hours got both of mine to work perfect again Pete