Fishey

So, My 924S is injecting far far to much fuel from the injectors!

What I have tested

No vac leaks

Fuel Pressure is correct

Injectors test good (Resistance) also injecting cleanly (Just to much)

AFM and the wiring both test good (replaced AFM with another from a working car as a further test)

Fuel injector wiring test correct

Temp sensors test correct and pulled some from running car to test

Speed/Ref sensors testing correctly as well as wiring

I have 3 ECU's work fine in other cars and changing them has no effect

DME relay checked and fine (Dont ask shouldnt effect it)

Throttle Position sensor is working correctly and wiring tests good.

All grounds test good and most have been checked physically at there termination points.


The car will run cold (VERY POORLY and will not restart once hot and will not run hot at all) Serious amounts of fuel is being sprayed and cannot think of anything else that would effect the amount being sprayed so maybe some help?

I think I am down to replacing all fuel injectors basically...

Hollywood D

Would the FPR or damper affect the amount of fuel being supplied by the injectors?

M758

Not really.

Fuel is controlled by 3 things.

1) Fuel Pressure (Fuel Pressure regulator)
2) Flow through the injector (can be checked by testing)
3) Pulse time (Controlled by DME programing)


You have swapped DMEs, AFM, How did you check fuel pressure? How did you clean the injectors? Is it one cylinder with too much fuel or all?
The car should run without the O2 sensor so you can unplug it and that will cause it to run in open loop mode.

Fishey

The problem is pulse width. It runs 6ms first two rotations then jumps around from 6 to 30ms on time on all injectors. The wiring harness has no provision for 02 sensor but that did give me an idea. So I'm going to check and see if the 02 pin is getting some crazy reading.

Fishey

So, after looking at it 02 sensor wiring is entirely removed from car at pin going to new relay and at pin 24 of the DME. The only thing I can find is the speed sensor signal isn't the cleanest when compared to our 944 race car. So I reset the air gap with no change. Then I changed sensors and still it looks a bit fuzzy but not overwhelmingly so.

M758

Sounds like an electrical issue.. if you have known good parts swap all the injecotr control elements. One by one and test. Make sure you change DME harness as well DME, AFM, and sensors.

Fishey

I have replaced DME with 2 other units same with AFR and all wiring test good for connectivity to DME with no shorts. All grounds test good as well as all power wires. The throttle position sensor test good and unplugging it does not improve the the problem. The temp sensor test good and I even tried another. So far the only thing I have found is this slightly funny reading on speed sensor. So, I am going to test that some more and if I need to I will pull the flywheel out since its not a big job and if I don't see anything with the flywheel I will replace harness. If still nothing I'm just going to torch the car.

F18Rep

Did you test the Temp II sensor from the DME, I ask bc I had one do this, intermittent short to ground caused super rich condition. And then much later read the 951 DME test plan an sure enough it says something like will cause rich enough situation to make the engine die.

Interesting that you have the pulse timing, we usually don't get that good info...Bruce

Fishey

is that the blue sensor on the side of the head? That you are referencing?

F18Rep

Yep, well the connector for it is blue.

The other temp sensor, that is 2 inches further back is just of for the gage....Bruce

f1rocks

Just something else to take a look at,

Are you mis-matching any late/early DME's and AFM's? I'm assuming it's either an 87 or 88 so early injectors are also not a good match as well.

whalebird

924S uses late AFM and DME. I have seen a temp sensor do exactly what F18 describes as well.
DME test plan performed at the control unit plug would probably find your problem. Maybe somebody here has a link to the procedure, sorry I do not.

whalebird

go here. Engine volume 1, group 28 DEE diagnosis
http://www.mikepellegrini.com/porsche_manual.php

lee101315

You should have 6-8ms of injection at a cold start, and then it should slowly dwindle down to about 2.5-3.3ms after 4-5 min or so

30ms indicates a part load enrichment, and the only signal the dme can read to identify that is the AFM.

The TPS is more like an off/on switch, unlike the turbo. Youd have a crappy idle if you disconnect it, but it would never flood the engine

Same with the O2 sensor. Disconnect it during testing if you have any doubts.

Here's a quick list of places the insulation in the harness breaks and gives heartache:
Under the intake manifold, around the coolant neck. ( DME water temp sensor is in that harness, you should have 330 OHMs when the coolant is at operating temp at the DME connector)
Right behind the TPS connector
Right behind the AFM connector
Injector harness.
Slice the harnesses open at those points as far as reasonable to eliminate the possibility of short circuits

Assuming all grounds are ok, and the wires attached to the + terminal on the battery are clean, you should find your problem there.

And always, when in doubt, change the reference sensors and harness to ECU. These cause more headaches than you can imagine.