Ed Hughes

Getting ready for the trip to Monterey Car Week in a couple of weeks. I drove the car to OC yesterday for a meeting, and on the way home, she stumbled several times for a couple of seconds, mostly on acceleration. It did drop power twice for a second or so under constant power at cruising speed in 6th gear-high 2K's. I'm pretty sure it's fuel, as when I let off the gas, the engine recovers, and seemed related to throttle position when it happened under accel. I'd also think that if I had fuel, and lost ignition, it would result in some kind of combustion event when the accumulated fuel lit off. It also seems to be at lower R's, accelerating at about 2.5K. It is intermittent and hard to repeat. It is not an injector of two or three cutting out, it loses all power momentarily.

So, I'd already planned on installing the new fuel filter sitting on my bench in conjunction with an oil change this weekend. I've got a new DME relay as well, which will go in. Stopped off today at the auto parts store for a can of MAF cleaner, and I'll have a new O2 sensor tomorrow for install this weekend.

It seems to me, with the above, that I'll address the likely culprits with the exception of a new fuel pump. Any other thoughts?

MarkD

I think you are on the right track with the fuel filter, Ed
DME relay was my 2nd thought, intermittent connection perhaps

NC TRACKRAT

My first reaction is that the fuel filter would be high on my list as it is on yours. I'd get a cutter and inspect the innerds of the old one. Then I'd start thinking about where I last got gas and if there was water in the gas. A can of "Dry Gas" in the tank might be advisable to absorb any that might be present. If you find a significant amount of sediment in the filter, there might be enough "trash" in the tank to foul the strainer in the fuel pick-up.

Ed Hughes

Thanks guys. Maybe having the filter on my list this weekend was a premonition. I can't find when the fuel filter was specifically replaced in the records....I'm at 66K now. Glad I took it on the 160 mile roundtrip yesterday and having this rear its head now.

I was 200 miles into a tank of Chevron from where I normally fill up, but you never know...

1pcarnut

Same thoughts here, fuel contamination or DME. Have you checked the dist. belt recently?

Ed Hughes

Yes, but as noted, I find it hard to believe this has anything to do with spark. It has fuel starvation written all over it in my mind.

Terry Adams

Happened to me decades ago in my '59 MGA. Turned out to be water in the gas tank.

Pure speculation here. Water has a specific gravity of 1000, gasoline 737. So they mix a little, but the water is mostly on the bottom. When you accelerate, the water sloshes back to the fuel intake line.

Tomorrow I will give you my take on the stock market.

C4SJOHN

Ed, Was your 30K and 60K major service ever done on your 993 Porsche? If not could be spark plugs, distributor rotors and caps may be shot

race911

I can't say I've seen worse caps and rotors than what I pulled off of my 4S a few weeks ago. Neglected to do them last service, so they'd been on for 50K. Never a stumble, hesitation, anything.

Anyone pulled apart a fuel filter on one of these? I haven't. At least not for the EFI cars since I had my shop, and that would have been on a 3.2L car. They have to be the same internally, don't they? If so, incredibly robust.

Again, no expert on 3.6s specifically since I've been out of the game only slightly after the 964 was a new car. But when I hear problems like these, on the 3.2L cars it led back to the air flow sensor (not applicable on a 993 with MAF), head temp sensor, or the other two flywheel sensors.

In any case, tough to diagnose.

IXLR8

If it were a fuel fump issue and the power drop only lasts a second, wouldn't there be enough pressure in the line to compensate...sort of like an accumulator. Now it could be that the fault initialed a few seconds earlier and it took that long for the pressure to drop to the point you are having the power drop.

The only time my 993 stumbled was during initial start this summer after winter storage, and only because it took a few seconds for the new fuel filter to fill.

I'd pull the DME, pop off the cover and have a look at the solder joints and circuit board. Putting a new one in might not explain the issue since you say it is intermittent...looking at the old one might. Measure the contact resistances.

Look at the easy-to-check stuff first.

Ed Hughes

Yes, that was all done. Again, loud pedal down when it occurs-loss of power; back off pedal-power starts to come back.

I've got all of the goodies to address the low-hanging fruit, so that is where I'll start. She's only going on the lift once, so I'm not going to do them one at a time, but I will attempt to do an autopsy on replaced components.

Quadcammer

don't forget the fuel pressure regulator. If the diaphram is torn, fuel pressure may be dropping when you want the exact opposite.

Easiest way to check is just pull the vac line off and see if fuel runs out.

IXLR8

Throttle position sensor?

ironimages

At 66K miles I'd be doing the distributor belt, that's the one thing that could cost you some serious cash if your not ahead of the game. Not saying that is your problem here but that would scare me....

C4SJOHN

Ed, good luck this weekend on your 993 repairs. Let us know when you are done and if this problem is fixed......