no fuel pulse 88 carrera

[viperstang]

hi i have a 88 carerra. while driving home the car just died. I tried checking all the basic stuff to see why it would not start(dme, spark, fuel pump,ect) it seem that the injectors are not pulsing. what would cause the injectors not to open. I was thinking bad ecu, is there anything else it could be?

[hcoles]

dme relay? get one, it is good to have anyway

[viperstang]

tried that still the same results

[ischmitz]

Your post doesn't say whether you had spark. If you have spark but no fuel chances are the DME is bad. The injectors receive permanent +12V from the igntion switch (in RUN or START) and pulsed GND from the DME.

With the igntion in RUN but the engine not running check that the connector to the injector has +12V on one of the two pins. If that is the case you pretty much have narrowed it down to the DME not delivering the GND pulse.

If you do have sparks but no fuel pulses then the DME is most likely bad. If you don't have spark and no fuel pulses it could be the sensors (speed, reference) or still the DME.

Ingo

[NY91184]

Reference sensor is my guess. Located on the bellhousing. Easy test to see if its working: crank the car, if the tach needle does not bounce, it is not working.

[papajetta]

Assuming that its similar to motronic 1.x like bmws, make sure both batches are not firing, dme should be pulsing injectors 1,2,3 at once, and 4,5,6 afterwards. If u have a batch not pulsing then u might have a open from the ecm wire

[ischmitz]

Wrong. All injectors pulse at the same time. There are two wires, one to each bank but they are internally connected in the DME.

[viperstang]

ok guys love the ideas.. i did have spark. I also had voltage at the injectors... so it could be a bad dme. I will get another DMe and try to see if that fixes the problem. i will keep you posted as to what happens.

[ischmitz]

Good idea on testing with the second DME. This will be conclusive proof that the fault lies within your DME.

The fact that you have spark strongly points towards the DME and away from the sensors. If the sensors are at fault both fuel and spark would be absent or at least spark would be wrongly timed.

Let us know your findings.
Ingo

[viperstang]

ok I am back with no luck...tried a new DME relay no luck. there is voltage going to the injector but there is no pulse. I also saw the rpm gauge needle move while cranking the car. I put some gas into the intake and the car momentaraly started up. so could the no injector pulse be a bad computer? any other ideas as what it could be?

[ischmitz]

I missunderstood. I thought you were trying another DME.

However, the fact that the car started when you put fuel into the intake leaves only two possibilities. No fuel pressure or bad DME.

Ingo

[kidrock]

take off your front cover plate and inspect your fuel pump....make sure it's pumping fuel. Be safe.

[viperstang]

i dont have a spare computer. i tried a new dme relay...fuel pump powers up and is working fine.... the injectors are not pulsing so i am leaning torward a bad computer.

[Joe Bob]

Is the relay clicking when you turn the ignition on? If not you may lack switched power to the DME.

I would test the DME harness for constant 12v and switched 12v. The PET will give you the pins to check. Porsche Classic Original Parts Catalogue - Classic Genuine Parts & Literature - Porsche Classic - Dr. Ing. h.c. F. Porsche AG

[viperstang]

ok i am going to send my DME to be check out. fuel pump is working fine. thanks for your help

[Joe Bob]

I sent mine out...it was fine. Check your DME voltage first.

[viperstang]

any steps as how i should go about doing that?

[Joe Bob]

There are a few DME testing threads you can look at and you can download the PET that I mentioned earlier....but with mine, which is a 3.6..... Search under my screen name and/or "ischmitz".

I pulled the harness off the side of the DME, took a test lamp and stuck it in pin 19. Count from the left with the thick wire on the left. Count all holes. Pin 19 should have constant 12v power.

Then turn on the ignition, pin 37 should have 12v, ONLY when the ignition is ON.

12v should remain when cranking the ignition, you must have the DME click when the ignition goes from off to on. While cranking the DME relay should NOT click intermittently.

Mine did and I traced it to the fuse box where I had a short.

As I mentioned, I have a 3.6 and it's a conversion in an 83 SC. There was also a 6 pin connector under the seat where the DME and the relay live.

After I confirmed both constant and switched 12v power, I put the DME harness back together. I tested Pin#3 with the test light, Pin #3 was flickering when cranking the engine.

With the test light firmly in Pin #3, I started wiggling wires on the fuse block with the ignition ON. When I saw the light flicker, I found my problem. My test light was a little short in length to be able to see it while under the hood. Either get a friend or do what I did, alligator clip to the end of the test light probe, decent sized gauge wire to another clip that sits in Pin #3. Ground the test lisght to complete the circuit.

Again, I had issues due to this being a conversion and not being aware what fuse my DME power was being fed from.

Your mileage may vary since your dealing with a 3.2. The pin count may be different, that's what the PET is for, finding the proper pins to test.

I sent you a PM if you want to discuss further on the phone or SKYPE if you have it.

[ischmitz]

I think he already is way past what you suggest. He has power and spark. His DME is damaged (no fuel pulses).

[viperstang]

does anyone have a place they could recomend for the rebuild?