iloveporsches

*See update below
*Final update for anyone doing a search


Had I fun time trying to get back down to school this morning.

It seems like the fuel on my car is cutting out. It'll stumble when I give it gas, lurch hard, or just completely lose power. It started intermittedly, and I pulled off the highway for a few minutes at a gas station. I fired it back up and everything seemed to be ok.

About 30 miles later, same thing happened, so I pulled off, got some gas, and continued on my way. Again, everything seemed fine.

Then, about 10 miles from school, it started getting really bad. I had to pull over on the side of the highway and limp down the shoulder because it would barely move or just die when I gave it gas.

Limped it off the highway and it wasn't any better on surface streets. It would barely go off the line from a stop light, and then "catch" and accelerate normally for a little bit until stumbling again.

Any ideas on what this could be? DME relay? Fuel pump?

krahmlow

If it's intermittent, I think it's unlikely to be either of those possibilities, but you never really know. Unfortunately, it could be any number of things, including the ignition system; the only way to figure it out is to start eliminating possibilities. I'd check all the wiring. If you can get it to idle, wiggle everything you can find to see if that causes a change. Check the connections to sensors. It sounds like you're having the problem when the engine heats up, no? Test plug wires, coil, check if you've got a cracked dist. cap. If you can get test lights, put a light on the wires and on the injectors to see if the signal is intermittent. Test fuel pressure and flow volume and check for fuel leaks. If you don't have a fuel pressure guage, you can at least check the volume easily enough. Clark's has a good write-up on that.

StoogeMoe

When's the last time you changed your fuel filter?
____________________________________
1986 944 NA - Guards Red - 91k miles - minty
1983 944 NA - Platinum metallic - 6000 mi beginning a new life
1985.1 944 NA - Guards Red - donor car
1984 911 Carrera Coupe - Guards Red (gone, but not forgotten)
"If you're not living on the edge, you're not living"

iloveporsches

I've never changed the fuel filter in the roughly 15000 miles I've driven the car. That was on my list for things "to do" over winter break.

I'll do what I can to test the rest of those things. Unfortunately, I don't really have much of a space to work on it down here at school.

jgleano

this is a very interesting post. I had the same problem with my car last night as I was driving home from a study group......its so strange....i was accelerating to get on the freeway...when the car lost power and acted as if it was in neutral....i checked the car for leaks or anything, but nothing.

ill have to check for those things listed.

TheRealLefty

Interesting my dear Watson. The fact that you can induce the stumble mode with the throttle is key to the diagnosis, IMO. I would swap out the fuel filter first before looking at other options, just in case it's that simple. Would a malfunctioning TPS induce this mode?

iloveporsches

Perhaps, though it "clicks" normally like it should when I checked it earlier. No strange noises underhood.

I fired it up and blipped the throttle a few times. Everything sounded ok, but I didn't actually drive it and put any load on the engine. I won't get a chance to until later tonight.

I should note that, at its worst, I had my foot to the floor and the car was decelerating. Probably as much as it would if you were in 5th on the highway and just took your foot off of the gas.

Red1

I took the car out of the garage this afternoon for the first time in a couple weeks, and it was doing something like this too!

Idled fine. Would rev in neutral fine. Give it gas in gear and it wanted to wheeze out. Drove three blocks and was about to turn around and suddenly all is well and runs like a champ. So weird.

yellowline

See if something is stuck in your AFM? Maybe you're not getting proper airflow. You'd probably notice an odor if your car was running rich, though.

iloveporsches

Minor update: I just had to move my car from a 2-hour parking spot to my normal spot, and there was a tiny bit of stumbling. I drove fine except maybe 10 ft. But, this means that it will do it while cold.

Weston

I'm experiencing a similar problem with my '83 944. Does your tachometer drop rapidly when the engine cuts out (ie the tach loses it's signal completely)? Mine does, so the engine speed / reference sensors seem to be the prime suspects, as I'm not aware of much else that would kill the tach signal like that. I'm not sure what those sensors would have to do with me giving it throttle though, as my problem seems to be somewhat throttle related. It also seems to happen only after the car had been sitting outside in below-freezing temperatures for several hours. I'm going to try to find time to put it in the garage and check the connectors tonight...

iloveporsches

You know, I didn't notice. But I'll check on that next time I drive it. Will probably be tomorrow after I get some new parts (distributor, spark plugs, coil) installed.

skene

Don't you love 23 year old electrics? My bet is there's a loose connection or shorting wire somewhere in your wiring harness for the injectors and/or reference sensors. A short in either of those will cut fuel to the engine and cause rough running. A bad TPS can do something similar, but you'll probably be running rich if it's not giving out a signal.

I finally fixed my car from randomly cutting out and not starting by replacing the whole set of ignition wires and both ref. sensor wire harnesses all the way to the DME. It's the nuclear option, but my car's been running perfectly since then.

iloveporsches

I replaced the coil, distributor, and rotor over the weekend. Checked the plug wires and various other connections.

I drove around for about 15 miles today without incident. I'm still going to replace the fuel filter before I go home on Friday or Saturday. We'll see, I'm going to be keeping my fingers crossed and following my roommate.

Edit: For some closure on this in case anyone ever digs this up with a search:

It ran fine for about 45 minutes on Friday and ~150 miles yesterday without incident. My guess is that it was the rotor as it looked a little worn, but I'm not 100% sure because I replaced several things at once.

iloveporsches

Well, it happened again on Monday morning. I was driving back down to school and about 40 miles into the trip the car bucked a little. Telling myself it was all in my mind, I continued on. It just got worse and worse, however. Several times I had to pull off the road and wait for the car to decide it would like to move again.

At first, it would just stumble or miss a little. Maybe 5 seconds at most. It slowly got worse. Sometimes my foot would be on the floor and I'd still be slowing down -- another time it wouldn't go above 3000 RPM. It eventually got to the point where opening the throttle at all would kill the motor. After sitting on the side of the road for a few minutes (swearing profusely as it's -11 outside and I'm stranded in central Illinois), I tried to get it to move again and it stumbled on its way. Once I got back on the highway, it seemed to be okay when I was doing over 70. I had to limp down side streets at idle back in town though, because any gas just killed it.

The entire time it would have no problem just idling, though. I was idling slightly high, at about 1200 RPM (usually my car idles 900-1000), but I don't know if the engine was really spinning that fast or if it was some electrical problem.

Does anyone have any more ideas on what it could be or what I could check? I think at this point I'm going to try and find a cheap, used fuel pump and replace both that and the fuel filter. Could it be some sort of electrical problem, though?