Meine44

I am looking for suggestions of things to check to find the root cause if this problem. Stumbling seems to become a problem with our cars as they get on in years, and there are a wide range of failing parts that could cause this issue. Because of this, I am hoping to compile much of the information to diagnose this problem into one thread.

Below I will list all information I believe to be relevant about my 951. I will also list things that have been done, things that I have yet to check, and any helpful tech articles I have come across that will help with the diagnosis.


If anyone has other suggestions, or more links to tech articles, it would be appreciated to have them added to this thread. I am sure more people than me are looking for all of this information to be in one place.

Symptoms:

The car will run fine at idle, but it is very rich. It also has a popping sound from the exhaust (this could be due to bad AOS seals or bad intake gaskets, so I'm told)

It will drive fine, and build boost normally, as long as the engine is cold.

Once the car warms up, it will hesitate/stumble. This occurs both at WOT and at cruising speeds. Feathering the gas pedal will stop the stumbling.

Once the car stumbles, it will catch itself if I either let off the gas or floor it. If I do nothing, the car will go into emergency shut-down and lose all power. Starts back up right away [in neutral, still rolling. Wonder how I haven't had a crash yet].

Car has been drained of fuel, and filled with fresh gasoline [93 Octane].

Info:

Car is 1988 944 Turbo, k26-6
+ Autothority MAF/Chips
+ Lindsey Racing boost enhancer
+ 3" exhaust, no catalytic converter
+ Throttle body bored 8mm over stock
+ 3.0bar FPR
+ Lindsey Racing wastegate

Items fixed so far:
Cleaned MAF ==> It was covered in oil. After cleaning with MAF
.............................cleaner/electrical parts cleaner, problem went away
.............................but has returned. [AOS seals ==> see below]

Injectors ==> Cleaned; O-rings replaced. One injector replaced entirely.

New FPR ==> Did not see any fuel in the vacuum line

Tune-Up ==> Cap, rotor, plugs, wires [Beru]

Ignition Coil ==> MSD Blaster 2 [Lindsey Racing]

Alternator ==> Stator was junk, serviced locally by (reputable) rebuilder

Wastegate ==> CLUBGATE [Lindsey Racing]; currently single-port

Fuel Filter ==> Replaced 3yrs/7,500mi ago. It was leaking badly


Items not yet addressed:

TPS ==> Shop inspected, claimed good. I have my doubts
.................. http://www.clarks-garage.com/pdf-manual/fuel-06.pdf

Injector Harness ==> Look good on inspection, have not tested electrically

DME Relay ==> Jumper can be used to test
.................. http://www.clarks-garage.com/shop-manual/fuel-05.htm

Speed/Ref ==> Sensors need to be checked
.................. http://www.clarks-garage.com/shop-manual/ign-02.htm

Vacuum Lines ==> Supposedly re-done 40,000mi ago

KLR ==> High-tech blinky light not yet fabricated
.................. http://www.lindseyracing.com/LR/Parts/BLINKCODE.html

DME ==> No good check for this, except replacement.
.................. If anyone has a DME they are willing to part with at a reasonable
...................price (read: CHEAP), I would be willing to free up that shelf space
...................in your garage for you. Please send me a PM.

Temp Sensor ==> From what I've read, causes poor idle [not my symptoms]
.................. http://www.clarks-garage.com/shop-manual/elect-19.htm

Idle Stabilizer ==> Again, causes poor idle [not my symptoms]
.................. http://www.clarks-garage.com/shop-ma...htm#idle-surge

Cracks ==> Any cracks in the fuel rail/ IC pipes would expand when hot


AOS SEALS ==> Should solve oil presence in IC pipes; keep MAF clean
+Oil Catch Can


Again, if anyone has anymore information about diagnostic procedures or things to check that I have not listed, please add them to the thread. Links to tech articles and/or other threads with diagnostic information would be helpful.

If there is one particular fix (unlikely, hence this posting) that seems to be a common cure for these hiccups, I'm all ears.

**Disclaimer**
I have done my research, and searched the forums on this topic. There are plenty of threads that have great information, but few of them post final solutions. I am simply attempting to consolidate much of that information into one thread.

fast951

It appears that you may have multiple issues. More than likely, they are related.

1) The rich running condition can be caused by multiple things:
- Eng Temp sensor (affects all running conditions, Idle, PT, WOT).
- O2 sensor (affects Idle, PT).
- High Fuel Pressure (Idle, PT, WOT).
- Faulty or dirty/oily MAF sensor (Idle, PT, WOT).
- faulty or badly adjusted TPS.
.....

2) Rich under boost.
- Pressure leak after the turbo will allow the metered air to exit the system instead of getting into the combustion chamber. This could cause hesitation under load, but will not go away
A pressure test is recommended.

You state that you are using a 3bar FPR. Are you sure your MAF + Software call for a 3bar FPR instead of the 2.5bar FPR?

Have you adjusted the FQS on the side of the DME to make sure you are not adding fuel?

I'm sure there are many more causes.. I would start with the simple things, and eliminate possibilities as you go.

Meine44

It was also brought to my attention that I would want to check the condition of the grounds in the engine compartment.

The Autothority MAF does use a 3.0bar FPR. It is what was in the car when I purchased it in perfect working order, so I replaced it with the same.

The plan of attack is to attack each possible issue in order of difficulty.

I am not familiar with the FQS, and would love more information.

I am specifically looking for problems that would lead to it running poorly mostly at operating temperature, but obviously I can't ignore the poor idle condition.