I know but that hose attaches to the top of the AOS, no? What hose were you suggesting I disconnect. Yes I would not doubt at all that valve guide seals could be failed. I'll take steps to diagnose it. I could be mixing gas and fuel exhaust smell. With that said, couldn't that dark oil on the plugs be from oil I put on the threads to lubricate them?

 

Yes on the oil on the plugs. But the center and left spark plug deposits at electrode are not normal, indicating something is not functioning properly

 

The hose is #19 to detach and plug from AOS #15

 

Thanks for your clarity, T&T Racing. Got it. I'll prepare to do a leak down test. I'll also investigate fuel contamination, DME temp sensor signal issues, the aos, and maybe even get a boroscope / cylinder cam.

Please keep the analysis coming. One thousand thanks for the help so far. I have some work ahead of me and hope this leads to a solution.

 

A leaking fuel injector could cause a stumble on start up, the smoke and the smell of fuel you are experiencing. I know you said you tested the fuel pressure, was that a snapshot or long term pressure test?

 

It was both. Got readings with engine off and fuel pump engaged, at idle, and at 20+ minute leak down. I've thoroughly inspected the injector issue and even put in some refurbished factory ones.

 

My S2 had a hard to start issue that once started would run rough then smooth out. Turned out to be a bad fuel dampener dumping raw fuel into the intake. I assume the turbo has a similar set up. Easy check. Pull vacuum and check for a fuel leak.

 

This test with the leaking fuel injector provides significant data, too much fuel yields misfiring.

My hypothesis to the chronic issue is poor atomization of fuel on startup.

On a cold engine start, the fuel injectors are pulsed the DME at a higher rate (like a choke in a carburetor restricting airflow to increase the fuel/air ratio) to increase the fuel/air ratio to improve ignition.

But if one or more fuel injectors are not fully atomizing the fuel (having fuel droplets enter the intake), then there is insufficient atomized fuel for combustion and the spark plug electrode could get wet impeding full spark). After the 30-40 seconds, the combustion chamber is warm enough to atomized enough of the droplets so the F/A ratio is not too rich.

The left and center spark plugs indicate abnormal fuel/air ratios, probably rich, while the right one indicates a proper fuel/air ratio.

My suggestion is to contact SouthBay Fuel Injector Service for consultation (Google for contact phone number). I believe the issue is a couple of fuel injectors are not in spec but can the cleaned and rebuilt. Obviously all 4 would be cleaned, rebuilt if necessary and flow tested.

If the answer is new injectors, contact Five0motorsports.com for new injectors

 

Thanks for the continued help, team T&T. Just the other week, I installed newly refurbished injectors because I really thought this was the problem after all that evidence. But they have not fixed the problem. LIke I said, I tested these ones and they stayed bone dry over time.

 

Then, I believe the visual appearance of the spark plugs are your focus. #1(not shown) and #2 are normal; #3 and #4 are abnormal indicating an issue with #3/4 proper combustion, with #4 not as good as #3.
Has the intake manifold been removed prior to the issue?
One person who knows 951 is Karl Poetl, owner of Racers Edge Porsche Racing and Dave Lindsey at Lindsey Racing

 

Use a Mityvac and check the leakdown (if any) on the fuel dampner diaphragm..That would be an explanation of extra fuel getting into the engine..since you've done the injector thing..If water was getting into a cylinder or more, the plug insulators on those cylinders would be bright white and appear to be steam cleaned...not all gunked up like the one cylinder you showed there..Is the spark coming to the plugs nice fat and blue if you bench test them? You may be experiencing a combination of factors here. just spitballing ..hope you get it worked out soon.

 

White smoke is generally coolant or condensation. Oil can be white-ish too, but is pretty distinctive so you'd probably know if it was oil smoke. Excess fuel (gas) tends to show as black sooty exhaust, not white. Is it possible you have a cold-start issue and normal condensation? Or a cold-issue and an unrelated smoke issue?

I'd repeat my comment in post 9 about the DME temp sensor connector and suggest you check the signal on the 35-pin DME connector to make sure it is surviving the journey from the sensor to the DME.

I'd also suggest putting the coolant overflow tube in a plastic soda bottle and take the car out for a good long hard drive with lots of boosting to see if it spits up at all. If your car is a daily driver, I agree you'd probably notice a coolant loss by now, but if it's just a weekend car, etc., I'd say it's possible you have been displacing coolant with air and just haven't noticed it yet. Water in the tank would also probably burn off after 6 months of daily driving, but if you don't drive much, maybe not. Does the car gurgle when you turn on the heater; or does the temp drop fast after sitting at a light and taking off? Both would be signs of air in the system, which would bump the head gasket back to the leader board...

 

Just a quick update. I confirmed the DME temp sensor is working. When I unplugged it before cold starting, it was really chugging. It actually seemed like the same symptoms I have but 10 times worse. I plugged it in and back to normal. The exhaust cloud was much bigger, even without revving, and had all the same characteristics ... super stinky and and pretty thick in the air. But it's not black. It's not a clean white, steamy, or sweet type of exhaust, either. It's like a grey (blue is a stretch for any exhaust, no?).

I am going to certainly pursue a leak down test to assess the valve guides. But is there anything that would cause the system to want dump a rich mixture into the cylinders in a cold engine other than the DME temp sensor?

My 944 is a daily driver at the moment. Plenty of miles to track coolant loss and there isn't any. Since this problem has began, black soot does build up around the tailpipe area.

I'm not sure what the timing is like, but I might have. I didn't notice this new problem being caused by something like that. What's the significance? I put in new gaskets last time I had the manifold off, and was careful to orient them right with the injector openings.

 

Has the distributor rotor been checked for a loose screw which affects timing?

 

That description sounds more and more like oil smoke. Maybe take a video of it happening? Assuming it's oil smoke, and on cold start up only, I think you're wise to be looking at the valve guides/seals. The right ratio of air and gas is probably going in, but then the oily plugs can't get the mixture to burn cleanly, creating exhaust that includes partially burned fuel and even some raw fuel if it's bad enough. So it's not so much that the motor is actually running rich, but rather it's not fully burning the gas it has, which means the exhaust comes out with lots of unburned fuel, as though the motor were rich.