944 Running Rich all the time - Tearing my hair out! - PROBLEM SOLVED 10/2/2017!!

[peanut]

No 5th Injector system on 944's

R

then presumably the ECU increases the injector pulsing as the aux air flow valve increases the air flow during cold starting like the later cars.

its still worth checking for a faulty leaking injector by removing the wire retaining clips and pulling off each of the injector connectors in turn with the engine running. No change in the idle would indicate a faulty injector.

 

[George_Mayson]

just thinking out loud and I am not familiar with the early models but don't the early N/A 944 have a 5th cold start injector ? If it does....... it might be worth testing with the cold start disconnected

A good test for fuel over-pressure is simply pull off the connector for one of the injectors and see if the idle improves and the mixture weakens. That would indicate one of the injectors was faulty.

To test the injectors you could remove the retainer clips and with the engine running pull off each of the injector connectors in turn. If there is no change in the engine note then that injector is faulty.

Have you checked the spark plugs to see if the rich mixture is effecting all cylinders or just one ?

All spark plugs are equally black, and under normal driving conditions the engine is smooth and powerful but still awfully rich, can smell it and after a good drive the plugs come out black.

Will be checking this test though, cheers!

 

[924Srr27l]

just thinking out loud and I am not familiar with the early models but don't the early N/A 944 have a 5th cold start injector ? If it does....... it might be worth testing with the cold start disconnected

A good test for fuel over-pressure is simply pull off the connector for one of the injectors and see if the idle improves and the mixture weakens. That would indicate one of the injectors was faulty.

To test the injectors you could remove the retainer clips and with the engine running pull off each of the injector connectors in turn. If there is no change in the engine note then that injector is faulty.

Have you checked the spark plugs to see if the rich mixture is effecting all cylinders or just one ?

All spark plugs are equally black, and under normal driving conditions the engine is smooth and powerful but still awfully rich, can smell it and after a good drive the plugs come out black.

Will be checking this test though, cheers!

It's gonna be something simply and silly ! What Plugs out of interest ? and have you checked the Coil?

Does it smoke from the exhaust ?

R

 

[peanut]

All spark plugs are equally black, and under normal driving conditions the engine is smooth and powerful but still awfully rich, can smell it and after a good drive the plugs come out black.

Will be checking this test though, cheers!

well thats good in a way because that information confirms that it is not a single injector leaking.

Its likely now that it will be one of the sensors or the ECU.

Its cold and damp so it would be worth checking that there is no moisure /condensation or water ingress to the ECU or the ECU connector first. Unplug and replug the ECU connector which will clean the contact terminals and possibly disclose a bad connection.

Over-rich running is usually down to high fuel pressure or inconsistant pressure. or a faulty sensor making the ECU pulse the injectors too much

 

[George_Mayson]

I've been through the MAF, Inlet air temp, DME coolant temp, Speed Sensor/Reference Sensor (Although not with an occiloscope), all reading perfectly.

Fuel Pressure was also reading perfectly, including bleed down.

DME connector has been on/off a few times with no effect.

Totally confused but agree it'll be something stupid!

Again thanks for all the help, it's been brilliant!

 

[peanut]

sounds like you have been very thorough in testing all the various sensors and fuel pressure components

however the sensors may well test ok but without testing that the sensor data is actually reaching the ECU the sensors might just as well be faulty or missing.

If everything tests out ok as you say it does then you may need to carry out some continuity testing of the sensor wiring .

I would start with the engine temperature sensor and test the wiring from sensor to ECU plug. Don't whatever you do put the multimeter leads on the ECU terminals as you might damage the ECU circuitry.

Incidentally I find it less confusing if the term DME is reserved for the relay and ECU used to refer to the engine control unit as per the Bosch fuel injection & engine management service manual otherwise its necessary to state clearly whether one is referring to the DME (relay) or the DME ( engine control unit) to avoid unnecessary confusion and misunderstanding when using the same term for both components

 

[George_Mayson]

FIXED!

A quick reminder, my 944 was running permanently rich, with hideous fuel economy, popping from the exhaust and black plugs.

Fuel Pressure was OK, including bleed-down

Throttle position sensor (TPS) working perfectly

Coolant Temp Sensor OK

Air Inlet Temp Sensor OK

MAF Supply Voltage OK

MAF Potentiometer track good, no dead spots

Speed Sensor OK

Reference Sensor OK

ECU Connector terminals all clean.

ALL sensor readings were taken both at the Sensor and at the ECU Plug, and all readings were identical between sensor/plug

The Fix - Opened up the MAF Unit to get to the potentiometer and the carbon tracks inside. I then looked at the position of the spring on the cogwheel and decided that the car was evidently reading too much air coming in and thus giving too much fuel. I therefore moved the position of the spring on the cogwheel to increase the tension against the "barn door" metering flap to restore the correct metering of air and thus the ECU brought down the fuel supply of it's own accord.

Could the spring have weakened due to fatigue over 33 years of cycling? Maybe, but either way problem solved and mixture stable now.

Interestingly this also affected the idle, so the MAF unit evidently is NOT ignored at idle when the TPS shows closed.

The cogwheel teeth were marked "0.1" which means that for every tooth moved it reduces the CO emissions by 0.1%. Clever Porsche/Bosch.

Car still needs finer tuning on a gas analyser but passed it's MOT and is no longer guzzling fuel so badly.

Thanks for all the help guys, much appreciated!

George

 

[924Srr27l]

FIXED!

Thanks for all the help guys, much appreciated!

George

Excellent News,

R

 

[Eldavo]

#helpfulmodeon

You dont have to quote every post to comment you know. It makes reading any thread that you've posted in (which seems to be most of them) a very laborious task.

#normalserviceresumes-holdon!

***edit***

Well edited Rog, trying to make me look like the bad one

 

[vitesse]

I can't see that Spring weakening -it's a fairly stout item -our Stone Grey 924S has had the spring setting altered in conjunction with mixture/idle speed adjustment - this improves initial pick up in conjunction with a throttle cam & is also what I did to my Rover SD1 Vitesse many years ago once I fitted the fast road/rally cam & Jaguar air intake/filter -adjusted idle speed/timing as the engine progressively responded to the changes by speeding up-car still did 32-36 mpg on fast trips to South of France.

This tuning tweak is little taked about but with a Gunson gas tester you can probably get a significant improvement with the NA 2.5l Porsche engine with little expense

 

[peanut]

great to hear that you found a fix George albeit a little unconventional ..ahem.. Thanks for posting back with your fix

Coincidentally since I responded to your thread I had pretty much the same problem with my 944S2 this past week or two.

My car suddenly became really hard to start overnight. Normally it starts instantly with zero throttle.

It failed the MOT .....as like yours, the HC and CO were way too high.

it will only start on full throttle and lots of pumping and then coughs and splutters for a minute before settling down to a near perfect idle and brilliant all round performance. That has to be a diagnostic symptom but I cannot find the source for the life of me

When I find the source of the problem I'll post back here to add some further info to your thread for future viewers.

By the way I take it that you adjusted your spring tighter by 4x teeth yes ?[] I was considering adjusting the idle mixture on the AFM as a temporary solution to get the MOT then I can fix it at my leisure.

 

[Sy924]

Sounds a little like ECU temp sensor symptoms

 

[peanut]

I managed to start the car by disconnecting the coil and cranking the engine 5-6 times to pressurize the fuel system prior to starting. This tells me that part of the hard starting problem is that the system is not getting pressurized before firing.

This could be due to the ECU not triggering the fuel pump briefly on initial ignition on .

I also suspect that the in tank strainer /filter is partially blocked which would confirm why the car has been hard to start in the past when the fuel is low in the tank as the lower half of the strainer might be blocked .

I have ordered a tank filter and a inline filter and will clean out the fuel pump and tank before chasing the rich idle problem.

Thanks for your suggestion .....I did replace the engine temp sensor last week without any improvement unfortunately but I haven't tested the ECU yet