GlenL

Update!

Put in the new fuel pressure regulator (FPR) and the first trial run shows a huge improvement. A bit of wavering on throttle application when cold, but no bogging or cloud of rich smoke. Didn't smell any rich stink on the on-ramp runs.

Still too early to pronounce a winner, but looks very promising.

For anyone who hasn't done an FPR, it is very easy and cheap. At least on my model ('87 N/A). Maybe not "cheap" at about $60 for a small vacuum can deal, but I've become numb to "Porsche Pricing."

Let it sit overnight. A couple of 10mm bolts and a small screwdriver are needed. Might have a check-valve issue as no fuel sprayed out. About 3 minutes to replace.

GlenL

Update again...

After further review, the new FPR has made a significant improvement in cold running behavior although the problems of a bogging and blowing rich exhasut have not been fully solved.

Next up: Full swap of vacuum lines and, if the ones off the old 928 fit, plugs wires. The wires look really crappy and were re-routed along the top of the fuel rail.

RJB

Glen,

Thanks for the updates. Please continue to post them so we can see what finally resolved your problms. I am still searching for the fix.

GlenL

Spent some time fixing the engine and still no complete resolution.

Added new vacuum hoses as needed. Glued around the top to the thermo switch on the water outlet as that was a vacuum leak. Replaced O-rings on oil separator and at throttle-to-manifold connection.

I think the intake is tight now. Still runs rich on acceleration. Thinking to toss a new block temp sensor at it. Only ~$15 to lose.

One other thought cam to me on the problem of belching rich smoke. This seems to happen after a 3-4 hour sit but not longer or shorter. Maybe the charcoal canister is not venting right or doing it all at once.

GlenL

And another try:

Pulled out the DME unit to check the "Fuel Quality" setting. Thinking that maybe some genius had set it rich for that wuick power boost. Nope. Set to full CCW position 0. Cap looked to be virgin.

Being a genius myself, I set it to position 6 which is -3% gas and -4.77 degress advance. Worked fairly well with it stinking less and a bit more performance on the buttometer. (Or maybe not!) In any case, didn't solve the problem.

surfun

Hey, I was just curious if you ever made good on fixing your issue? My car has a similar issue, a hesitation between say 2200 and 3500 RPMS. Mine does it at all times but slightly less when warm, and there is no smoke or anything of that nature, just a stumble until you push past 3500.

thanks in advance, surfun!

GlenL

Progress but no complete fix yet.

Driving it more, I notice that it drives the worst after a 4 hour cool down. Starting up in the morning is not as bad as going to lunch. (Anyone?)

surfun

Well, good news here. Today I was just randomly looking around the engine compartment, and I noticed a loose clamp on one of the small the hoses that goes into the intake stream. After tightening it up, the hesitation was nearly gone. It is still there ever so slightly, but now the range of it is maybe 400 rpms wide, and as I said, just barely there, and may actually just be a factor of the car sitting alot lately. For that matter I remember RX7's I owned in the past had the exact same thing, and it was actually the "6 ports" not opening and closing perfectly due to carbon buildup, so I am sure the 944 has some similar butterfly technique built into the intake that may be causing this too (most performance cars do). Either way, it is so slight that it is totally liveable, plus I am sure it wouldn't hurt to go through all of my hoses and clamps, and possibly then it would be irradicated.
Hopefully this will help you out too, but I doubt it will be that simple for you since you have already been through your car pretty thoroughly, but good luck and let me know when you get success!

GlenL

Congrats on that Surfun.

I'm getting desperate...and it's getting cold here. Thinking to (pause) take it to a shop. Needs an alignment anyways.

surfun

Getting cold in MN? LOL.
Anyway, yes, it is rather irritating, but do you really think a shop will be able to find it? My experience with shops is that they like to "throw parts at it" to see what fixes the problem at the customer's expense. I guess if you have a true specialist in Porsche, other than the dealer, it would be OK. Either way, let us know if you get it fixed one way or another.

GlenL

Finally some progress on this!

Picked up a rebuilt air flow meter. (Cheap at $40!) Put it in today and gave it a run. Car seemed to have a bit more power but was certainly idling more smoothly and didn't hesitate on acceleration. Car had been idling a bit roughly and high (1200rpm). Engine mounts are new. With new AFM it's idling smoothly at 1000rpm.

Comparing the units, the door on the old one seemed more lightly sprung. If it was opening more for a given flow the ECU would dump in more fuel.