944 won't start (seems like that's normal here)

[Thorton0]

I just purchased a 87 Porsche 944.
The car will start while spraying starting fluid into the intake. But only until you stop spraying. So I believe I have a fuel issue. I tested my dme relay, and it is bad. I will be buying a new one.
I used the jumper wire to try to run the car without the relay. No luck. The fuel pump is still not turning on. I disconnected it and ran power directly to the pump and it does work. Any ideas why it isn't turning on with the car?
Also I read that I should be able to test power at the fuel injectors. Just using a test light I cannot get power there. I tested while trying to start the car too. Is this issue related?
Sort of on a side note, there should be a double sized relay in the fuse box, above the dme relay. Auxiliary fan I believe. I do not have this relay. Did a previous owner remove it? What's it do and do I need it?
Thanks for any help. Lots of good info here.

[mattdavis11]

It might be that you have a bad ignition switch.

[sausagehacker]

If it runs on starting fluid you have spark, so the ignition switch is fine (coils gets switched 12v right from it). The dme is also getting power. It sounds like the problem has to be between the DME and the fuel pump.

When the dme senses that the RPM is over 200 (using the speed sensor over the bellhousing) it will provide a ground to the second stage of the dme relay. This in turn allows 12v go to the fuel pump.

So here are the first things I would try:
1) install the new relay, maybe your jumper wasn't set up right
2) speed sensor not giving a real reading
3) DME could have a cracked solder joint
4) wiring could be bad.

Ordered from most to least likely, IMO

[944 Ecology]

Look for a bad connection between the fuse block and the fuel pump.

[mytrplseven]

From experience I ask the question: What brand of DME relay are you using? I have two brand new Uro relays and both are defective. They could be the answer to starting problems and then masking the solution by being bad as well. I'd recommend finding some other manufacturer, such as Stribel, and check again. Buy two.

There's a big double relay box that is silver colored and it's relays run the fans when the A/C is on and when there's an over-temp condition. I can't imagine why the PO removed it but it's possible there was a over-heat condition that may have been caused by the Temp sensor in the radiator. Read up on this matter at Clarks Garage to get a better handle on this.

[Thorton0]

Thanks alot. That gives me some things to check. Definitely starting with the new dme relay.

[Thorton0]

so I replaced the dme relay. I checked the resistance on the position sensors, they seem fine. I am leaning towards the ecu. is there any way to test it before paying for a new one?

[jeffrsmith]

About the only way to check is if you can find someone with a known good spare and swap them out. You can send yours to ECU Doctors and they will test for a fee ($75) before they refurbish. Check them out Dead or Faulty ECU? Here are a few ideas and solutions - Specialized ECU Repair

[dcarlson]

BTW, 944's not starting is not normal here or anywhere actually. Check all fuses if you have not yet done that.

[Thorton0]

Well the car does not turn on the fuel pump. I know there is power at the fuel pump fuse. While trying to start the car I do not get power at the fuel injectors. I also can not hear them clicking.
I can run 12 volts to the fuel pump and it will work. But the car will still not fire. I assume because the fuel injectors are not working.
I will double check all of my fuses. I opened the ECU and do not see any obvious damage. I believe I've checked everything and therefore I am thinking its the ECU.
But I'm no expert, and I hate to spend money on something that I can't prove is broken.

[devin3200]

Thorton, I was experienced a similar condition with mine. I found a great tread that helped me with my DME. I had to crack open the computer. and on the back right side where you see a silver button shape circuit (looks like a riser between the top and bottom boards). There are 3 soldered contracts that where cracked ( fuel control). I re soldered and test. worked great. if I can find the pic. I will forward. Something to look into. Also in the past I've had to unplug the crank and speed sensors and clean the dirt off the bottom to get a better signal. which worked and easy enough to do. ( note) put something over the bell housing hold to keep from dropping the screw down it. That will ruin your day.. Good luck

[devin3200]

Thorton, I find the link right here on Pelican. it shows for bmw has well. but when you crack the case you'll see this contacts. Pelican Technical Article: BMW DME Motronic ECU Swap / Repair

[johnnyxs]

The ECU does not control the fuel pump and has no direct connection with it. Fuel delivery is controlled by the ECU (DME) indirectly, by pulsing the injectors .

If the pump works when you apply 12v+ and the fuse is ok , then there has to be a break in the supply wire between the pump fuse and the pump live terminal. (assuming that you have verified that the pump is permanently grounded as it should be)


The only other possible explanation is if someone has fitted an isolating switch or Immobiliser between the fuse and the pump.

Connect a bypass cable between the pump fuse and the pump live terminal , This should get your pump working continuously when the 3x wire DME relay bypass is fitted..... or as normal on the ignition switch if you fit a DME relay instead.

Everything else is clearly working to some degree otherwise it would not start and run on ether.

Try starting and running the car on normal gas with ether assistance if needed. Don't touch the throttle until it starts or you'll defeat the cold start and risk flooding it.


If it still doesn't run without ether then your FPR valve could be faulty. you should probably check the fuel pressure and flow rate anyway .
If it hasn't run much for a long period the injector solenoids will probably be sticky or gummed up with gas additive residue . There is an easy DIY method of operating your injectors and cleaning them without removing them which I'll explain if the car still doesn't run

[sausagehacker]

Originally Posted by johnnyxs

The ECU does not control the fuel pump and has no direct connection with it. Fuel delivery is controlled by the ECU (DME) indirectly, by pulsing the injectors

Actually it does - the DME relay is 2 stages. The first stage provides power to the DME itself, along with the fuel rail and the auxiliary air valve. It is activated when you hit the ignition switch.

Then there's a second stage, which controls the fuel pump. The DME is in charge of activating this stage, which is important to know. It will activate when two conditions are met: 1) the DME has to be on, obviously. and 2) the DME has to see that the engine is spinning > 200 RPM.

So if there is no +12v at the fuel rail, start by looking at the relay or the wiring. Remember, you want to look for 12v between a GROUND and one of the pins on each injector connector, not 12v between the 2 pins. If you DO have voltage between the pins and chassis ground, the DME relay first stage is good.

The +12v to the injectors is actually constant, believe it or not. The DME controls the injectors by pulsing a ground to each channel. That's why you won't see voltage BETWEEN the two injector pins unless they're supposed to be firing, and you should use a chassis ground.

Going back to the part about sensing the engine speed, check out the sensors over the bellhousing and their connectors. That's what reports the engine speed and position to the DME and if it's not working, the DME won't activate the fuel pump.

[johnnyxs]

sausagehacker you are using the wrong terminology here which is confusing the issue.

The engine management unit is called an ECU not a DME .If you insist on referring to the ECU as a DME then use the term DME Control Unit so that everybody knows that you are referring to the ECU not the DME relay with the word relay left off.

The DME relay is called a DME relay. if lazy people leave the word 'relay' off then its impossible to tell if the person is reffing to the ECU or the DME relay

By using the same term DME for both the ECU and the DME relay you are perpetuating this silly incorrect and ambiguous terminology. If you use the correct terms eveyone will know exactly to which component you are referring.There can be no ambiguity or misunderstanding

You do not need to demonstrate your understanding of the Boche fuel injection and ignition system to me , I can see that you have a reasonable grasp of the principles involved although you clearly do not have a complete and thorough understanding as I do

[DannoXYZ]

Originally Posted by johnnyxs

... clearly do not have a complete and thorough understanding as I do

John, please answer these:

1. What does DME stand for in "DME relay"?

2. Why is this relay called "DME relay"? HINT: why is a relay called "horn relay"?

3. Have you seen the schematic for the internal wiring of the "DME relay"? From Clark's Garage - fuel 05.

4. What do we get for doing a Google image search for "Bosch DME"?

5. What does this Bosch box say on it?
http://www.tav-autoverwertung.de/shop/bilder/produkte/gross/3006_1.jpg

[johnnyxs]

Originally Posted by sausagehacker

Actually it does - the DME relay is 2 stages. The first stage provides power to the DME itself, along with the fuel rail and the auxiliary air valve. It is activated when you hit the ignition switch.

The ECU also has an additional constant power supply otherwise you'd lose your stored data like error codes etc

Then there's a second stage, which controls the fuel pump. The DME is in charge of activating this stage, which is important to know.

The op has fitted a 3x wire bypass in place of the DME relay so the ECU control of the DME relay to supply the fuel pump is irrelevant in this respect as there is already 12v+ on the fuel pump fuse.

So if there is no +12v at the fuel rail, start by looking at the relay or the wiring. Remember, you want to look for 12v between a GROUND and one of the pins on each injector connector, not 12v between the 2 pins. If you DO have voltage between the pins and chassis ground, the DME relay first stage is good.

The +12v to the injectors is actually constant, believe it or not. The DME controls the injectors by pulsing a ground to each channel. That's why you won't see voltage BETWEEN the two injector pins unless they're supposed to be firing, and you should use a chassis ground.

Going back to the part about sensing the engine speed, check out the sensors over the bellhousing and their connectors.

There is only one sensor on the bellhousing of a late car its the CPS( crank position sensor ).
That's what reports the engine speed and position to the DME and if it's not working, the DME won't activate the fuel pump.

The fuel pump is being continously supplied by the 3x wire bypass remember ?

[johnnyxs]

Danno

I think you have misunderstood my intention. I was referring to the ECU not the DME relay .

If you refer to the BOSCH Technical Manual and Technical Supplements you'll see that Bosch refer to the Engine Management system as an ECU Electronic Control Unit not a DME.
These are Bosch own tecnical manuals writted and produced by Robert Bosch GmbH .
Nowhere do Bosch refer to the ECU as a DME anywhere in their literature or training courses .

DME is a term that has been used for many years and perhaps originated at BMW where the early Bosch ECU were first used.
My conviction is that the term DME often leads to confusion as many owners are not clear what is being referred to and put DME when referring to the ECU and leave off the word relay when referring to the DME relay.
By using ECU and DME relay there can be no ambiguity.

[sausagehacker]

Johnny, I was not intending that post as a d*** measuring contest aimed at you - I was posting it because it's at the heart of Thorton0's issue. So I apologize if that seemed demeaning but I just want to be clear, it is technical information derived directly from the factory wiring diagram.

1. we use the term "DME" because that's what that part is. It IS the ECU, but it's just known as the DME because that's what Bosch called it, not my idea. Porsche also calls it the DME in the PET manual for the 1987 944: http://www.porsche.com/all/media/pdf/originalparts/usa/944_2_USA_85_88_KATALOG.pdf page 308

The bottom line is that it's the same part, if you look through any other thread on here (or anywhere) where the ECU/DME is mentioned, you will see how often it's called the DME. Sorry to the OP my post was unclear, but this part IS different from the DME relay. Let's not make a big deal over something stupid like what we call the part, anyone who is troubleshooting these cars needs to understand what "DME" refers to.

2.

The ECU also has an additional constant power supply otherwise you'd lose your stored data like error codes etc

Not true. The +12v going to the ECU/DME is from the DME relay. Check the wiring diagram and you will see. When the ignition is off, the DME has no power.

3.

There is only one sensor on the bellhousing of a late car its the CPS( crank position sensor ).

Also not true. 8v cars (OP has an 1987 944... not 944S) have two sensors. 16v cars have one reading the reluctor ring in the bellhousing and one hall effect sensor in the cam gear area. You're probably thinking of the latter.

4.

The fuel pump is being continously supplied by the 3x wire bypass remember ?

Ok, this is valid. To the OP: what that jumper does it allow voltage to the fuel pump and the DME directly from the battery. Is there 12v between pin #30's spot in the relay board and a chassis ground? If so, check for 12v between pin 18 on the DME/ECU harness and a chassis ground. Do the same test for pin 35 on that harness. Those are the 2 pins that deliver power from the DME relay to the DME/ECU.

[DannoXYZ]

Originally Posted by johnnyxs

The ECU also has an additional constant power supply otherwise you'd lose your stored data like error codes etc

- have you looked at the wiring diagram for this '87 944?
- which wire on the harness-connector provides constant power supply?
- which chip on circuit-board stores error codes?

Originally Posted by johnnyxs

There is only one sensor on the bellhousing of a late car its the CPS( crank position sensor ).

- which year did the 944 go to single crank sensor?
- which year 944 does the OP have?