Choina

Hi all.
I'm new to the forum, and to Porsche as a brand. I got an '87 944 that been stored for last few years. I have done quite a lot of work to recommission the car, but still have rich mixture and low power.
Car starts without issue, runs smooth but acceleration is slow, and struggles above 60mph.
The compression is good and even on all cylinders. Brand new ignition system, plugs, wires, distributor.
Fuel pressure tested on the rail with correct reading both engine on and off.
MAF tested at the DME with correct voltages across all range.
TDC and speed reference sensors tested on DME with oscilloscope showing correct readings.
Brand new coolant temperature sensor.
ALL plugs are equally black, exhaust is covered in soot, I can smell rich mixture.
Is there anything else I could be missing before replacing injectors and DME? I assume that chances for all inectors to be faulty are slim, and therefore suspect the DME, but I could be missing something.
Is there anyone in Scotland who would test the DME for me before I spash £500 out for reconditioning? I'm in central belt and can come to you when suits.
Thanks
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Gage

Is the DME temperature sensor a Bosch?

Choina

DME temp sensor, as the coolant temperature sensor? Yes, it's Bosch.

Gage

Has the air temperature output from the AFM (no MAF on these cars) been tested?
Verify that the DME, AFM, and injectors are all late model and compatible.

Gage

Also check for fuel bypassing the FPR and damper diaphragms via vacuum connections.

Choina

Yes, I have tested air temperature sensor from AFM, on the DME ports. Reading within the specs in clarks-garage manual (2.6k ohms at 20°C). I have never replaced the AFM, DME or the injectors. I will double check if the are late model, I assume I should be able to check that by part numbers?

Choina

Vacuum connections are dry inside.

Jfrahm

I wonder if anyone has measured injector duty cycle at various RPMs for comparison? Assuming your fuel pressure is correct that should tell you if your DME is deliberately over-fueling, if you have numbers from a good-running engine to compare to.
Duty cycle is a feature on many inexpensive digital multimeters these days. I do not have a 944 to measure.

Do you have an O2 sensor?
What about the FQS? Shouldn't cause this big a problem.

Choina

The car is UK spec, so no O2 sensor. I haven't tried adjusting FQS, I don't think it would have such an impact on performance. Unfortunately, I don't know anyone with the same car to measure and compare duty cycle. If there is anyone in Scotland, I would be greatful for swapping and testing my DME, that would tell me a lot.

Gage

Yes, part numbers for the DME, AFM and injectors can allow a compatibility confirmation. I can check them against US specs but ROW may be different. It is my experience that the DME is not on the "normal" failure list so best to test everything else first. So getting farther from that "normal" failure list you might verify that camshaft timing is correct and the cam sprocket aligns with the mark at crankshaft tdc ignition #1. Also check the function of the three TPS modes (idle, off idle, WOT). How are the ignition components? Plugs are new? Bosch wr7? Good strong spark? Grounds are good on the engine? There are two critical ground points at the rear of the block / bellhousing, the smaller is the injection harness ground. Injector harness visually okay? Under the boots?

T&T Racing

Take the simple approach.
1. Verify the DME temp sensor is functioning with in spec's, if no, replace, then step #2
,2. If yes, verify fuel pressure is with in spec's at the rail. If no, replace FPR. Then go to step #3.
3. If yes, flow test and clean fuel injectors.
Follow Clark's Garage test procedures for steps #1 and #2.

Choina

Fuel pressure was just right, and I have done flow test. It's around 1050 ml in 30 second. That's a bit more than Clarks Garage specify (850ml). How do you suggest cleaning injectors? Using additives to fuel or cleaning these manually?

Gage

Nice touch! Posting at 9:44
With a rich condition observed, seems unlikely the injectors need cleaning unless the discharge is a stream and not atomized. The typical cleaning process is removal and third party cleaning and testing. Several good sources for that in the US, must be some in the UK. Home remedies can work, back when I had time, I had set up a rig that back flushed to give the inlet screen a fresh start. It worked okay but at $20 each with new screen and o-rings, the outside service is a great value.
As a test, try introducing some false air (maybe at the J tube) to see if performance increases. This would verify over fueling.
Are there any coding plugs on the DME for O2 or non O2 applications?

Choina

Numbers for the DME and AFM match my model. I checked TPS as well and I get correct signals on closed and WOT. All ignition components are new apart from coil, but the spark is strong, do I don't suspect that. I will clean all the grounds, as I haven't done that, but the car is nice and rust free, these all look good, no oxidation. I will have a look at the injector harness as well. Cheers

T&T Racing

Nice work on diagnostics.
1. I would pull one of the injectors to get the p/n. Download
http://www.users.interport.net/s/r/srweiss/tableifc.htm to compare the expected flow rate and to Clark's Garage expected flow rate for the 944.
2. Then post and decide next step
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