1987Porsche944WithRealLongName

When my car is warmed up (but not hot) it idles perfectly at 14.7 give or take a point or two and drives good at partial throttle. However if I drive hard or take a couple of runs up to 4000 it will begin to stumble at partial throttle and idle rich. I pull 15 hg of vacuum cold and 18 or so hot, and I've yet to find any vacuum leaks by poking around the engine. I tested a couple of things like the tps and afm for fun but they're fine. I've also got a fuel pressure gauge on the rail and I've noticed the needle shakes a lot at idle and when I rev, although it stays in the 40psi range.

Has anyone experienced similar symptoms before? I'm using the a-tune

Rogue_Ant

Check your coolant temp sensor & wiring. That can add a lot of extra fuel if it isn't working correctly.
Additionally, have you checked fuel pressure?
What FQS position are you on?

1987Porsche944WithRealLongName

Coolant sensor wiring looks good visually. When I first start up it's rich as usual and then it gradually leans out to high 14s as the coolant warms up.

I can only check the fuel pressure with the hood up, it remains at 40psi throughout revving and stuff.

FQS is on 0

Rogue_Ant

40psi with the vacuum line on? If so, what is it with the vacuum line off?
Also, what is the condition of your AFM?

1987Porsche944WithRealLongName

Yeah, 40psi with vacuum. 50 or so without.
It's a bosch 3 bar

AFM is pretty good, I tested it today and even moved the arm over to see if any good would come of it.

JFreeman

Could be the fuel pressure dampener? Sounds like the symptoms a friend's car was having.

Rogue_Ant

Your fuel pressure is too high... I've seen this quite a bit, not sure whats up with the quality control of the 3bar FPRs, but they should be 43.5psi with the vacuum off.
At 50psi, your system is running about 7% richer than expected (at least). So, first thing, is to take out some of that excess fuel via the FQS switch - go to position #2.

1987Porsche944WithRealLongName

Thanks, I'll give it a shot tomorrow

1987Porsche944WithRealLongName

The problem persists. My wideband sensor died so I had to buy a new one before I could try out playing with the DME.

The thing is my first run through the gears is great. Then if I try another spurt immediately after that I'll get the stumbles. My idle will be rich immediately afterwards too but eventually if I drive normally long enough it'll settle back up to 14.7.

I pulled the plugs and they all looked normal, is it possible that a failing fpr could do something with fuel that's too fast for the wideband to catch? Is it possible to have a vacuum leak screwing with things that leaks just enough to cause problems but not make things look bad? (I get 18in. warm)

1987Porsche944WithRealLongName

Got bored and pressure tested the intake and found some leaks, one of which being from the KLR vacuum port on the intake, it started to rotate as I was taking it off.

Do these things just slide out or is there more to it?

1987Porsche944WithRealLongName

Well I tied up a couple of leaks and gained another inch on vacuum (one of the intake manifold gaskets was leaking as well). Problem still persists.

Wouldn't clicking down fuel on the FQS cut fuel by 3% everywhere? When the car is warm and I haven't been running boost the fuel is fine, even the first run into it is good. I don't want to make the car lean everywhere to try and save a post-boost richness. I don't even think the stumbling is coming from this as the wideband usually reads where it should.

1987Porsche944WithRealLongName

Bought a new fpr, sits at 46psi when I jump the pump, figures my replacement would be off too. I clicked down to -3% fuel on the DME as well.

Nothing has changed. Stumble still apparent after I make a run up to boost. Could my really laggy turbo have anything to do with it? Everyone seems to say 1 bar by 4200rpm on a 60-1 isn't right.

Tom M'Guinn

Did it ever run properly it this configuration or did the problem start when you changed something? If two fpr's read rich, your gauge could be reading high. How is the injector harness? Can you change the AFR by wiggling the injector harness? Any chance an injector is sticking open after warming up? Do you know how to spot cracked solder joints and have you checked the solder joints on the DME and KLR where the main harness header attaches to the mother board? How is your ignition (caps, rotor, plugs, wires, coil)? When it's rich, does it remain rich at both full throttle and part throttle, or only on part throttle when in closed loop? If only in closed loop, does the problem persist with the factory 02 disconnected? Do you have any way to log the AFM and TPS signals to see if either is going haywire? 4200 for full boost is quite late, though I can't comment on what's normal for that turbo.

shortyboy

43.5 psi, my gauge is showing close to 60psi with a 3bar fpr.. need to install my CEP fuel rail asap

1987Porsche944WithRealLongName

Problem sort of crept up on its own. The thing is my rich idle calms down after sitting still for a good 10 seconds or so. DME looks fine, just replaced the rotor and plugs are new and gapped to .025" and I have magnecore wires. The richness does not occur outside of idle, that's when the stumbling that occurs after high boost is. As I mentioned the first run up to full boost is great and there is no hesitation. I have no way to log things but the afm and tps test out fine (tps is new), I even cracked open the afm to realign the contact just in case.