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Chaos · Joined: 07 Nov 2005 Posts: 289 Location: Newark, DE, US

ok.. so i've been noticing a bit of RPM droppage and general nastyness while driving my 931 around lately. It originally was happening very infrequently and would be so sudden, it would feel like the car just got hit with something heavy.. just a very sudden jolt in which the power decreases, and then goes back to how it was. In some cases, it would flutter. That was really weird, and quite jarring. Those behaviours were so infrequent and didn't seem to relate to anything in particular, so i was confused and had no idea what might cause it... so decided to leave it be until i had time to look into it. At the time, my only suspicion was that it occurred during warm-up. Now, I'm not so sure about that. It appers to be more frequent, and the halts seem to be a fuel starvation issue.. it's more obvious now based on the behaviour i'm seeing. It basically now behaves as if I've run out of fuel for a few moments at a time. It happened at a particularly uncomfortable time today, just as i was pulling up to a stop light in front of my work parking lot. The car actually stalled on me and shut off as i was sitting there.. and what's worse, it took me several attempts to get it restarted.. it seemed (once again) as if it were out of fuel. Of course, I know that's not the case.. i've got a half tank, and just ran some techron through the system twice within the last two weeks. I'm figuring i must have some kind of leakage somewhere, and i'm also wondering if maybe it's due to the recent barrage of cold weather. I THINK (but i'm not sure) that it seems to perform worse when it's cold than when it's hot.. but again, it's very hard to tell. Now, I'm really just looking for advice on what to look at first.

useful info:
-in the last four months the wheel-well fuel pump has been replaced.
-last week the fuel filter has been replaced (and yes, it's pointing the right way)
-the fuel filter i recieved was NOT the same number as the one i took out. it was a Mahle KL21 instead of a KL8. I changed one fitting on it and everything seemed fine.. furthermore, it seemed better than it was before.. i had figured that maybe my problem was solved. guess i was wrong.
-after the stall today, i believe i smelled some fuel in/around the car. I don't usually smell that. (there are other smells, but not that one)

any suggestions or insight would be greatly appreciated. bear in mind, i'm not at all familiar with this CIS thing as of yet.. only having this car for a couple months and the closest work to the fuel system i've done is fixing the gauge sender unit.

thanks guys. you really are my heroes

oh yeah.. how much trouble/time/money would it require to change to a better/different fuel system? would it be worth the effort as compared to fixing this one?
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'81 US 931 "Rochelle"

Smoothie · Posted: Wed Feb 15, 2006 4:19 am Post subject:

One thing that can cause a sudden fuel shutoff is when the overboost cutoff switch is tripped. -But you also have the problem at idle, so that makes it unlikely to be the cause - except if the connection to that switch is flakey, then you could have it cut off at any time. -So check the connection to the switch. It's on the front of the charge tube.

The other, more likely cause is a missing or disconnected braket at the front of the block. There should be a small 3-bolt bracket that holds the lower charge tube to the front of the engine block. If that's missing, you'll have a large air leak usually when you hit a certain boost level, but it's concievable that it could occur while idling. If this is the problem, the leak occurs at the lower-pressure-pipe-to-turbo-outlet joint. Another quick-easy check (other than seeing the bracket's disconnected) is to push down on the charge tube - if the bracket's loose, the tube will be loose. When the bracket's tight, the tube feels solidly connected to the engine.
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"..it's made in Germany. You know the Germans always make good stuff."

'82 924T, US version, dark green metallic, 5 speed Audi 016G gearbox

Chaos · Joined: 07 Nov 2005 Posts: 289 Location: Newark, DE, US

wow.. if it's either of those, i'll be pretty stoked cause they sound like fairly easy fixes. I'll check em both asap.
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'81 US 931 "Rochelle"

Ozzie · Posted: Wed Feb 15, 2006 7:57 am Post subject:

Have you checked the in tank fuel pump?

Ign switch?
Distributor sensor?
Ign coil?
EIS?
DITC?
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Porsche 924 1984 (UK import) NA
Its AUTO and its BLACK
Montego Black on black/red
Engineer of Electro/Mechanical Systems Maintenance

Chaos · Joined: 07 Nov 2005 Posts: 289 Location: Newark, DE, US

the ignition switch is brand new, and the DITC is at the top of my list of things to go look at when i leave work tonight. otherwise, no. do you happen to have a good way to check the in-tank pump? if any of that is in the haynes, just let me know, i've got that out in the car, too.. and just haven't gotten to look through it yet today.
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'81 US 931 "Rochelle"

Chaos · Joined: 07 Nov 2005 Posts: 289 Location: Newark, DE, US

also real handy info: there's a guy i work with who's got a 944 and a shed full of 924 parts with no 924 to put them in.. i can get all sorts of stuff from him real cheap cause he's looking to get rid of it.
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'81 US 931 "Rochelle"

Chaos · Joined: 07 Nov 2005 Posts: 289 Location: Newark, DE, US

ok.. i've pretty much confirmed that the temperature outside the car plays a large factor. This morning, when i had lots of problems, it was about 25-27F outside. This evening, driving home, it was about 40F, and I had no problem at all, aside from a slightly rough idle during warm-up. Based on my best memories, it seems to have the most problems when it's coldest.

I'd love to hear that that means something to someone.

it indicates a few possibilities to me, but only general possibilities.. not component-specific. and general possibilities don't do me any good here, unfortunately.
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'81 US 931 "Rochelle"

Ozzie · Posted: Wed Feb 15, 2006 10:39 am Post subject:

If you disconnect the external pump and then bypass the relay the internal pump only will run.
If you disconnect a fuel line and put the line in a container you'll be able to tell if its pumping.
Connect the external pump.
With both connected and relay bypassed you should collect (IIRC) 1 liter / minute. Use a measuring container. Old drink jug etc.
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Porsche 924 1984 (UK import) NA
Its AUTO and its BLACK
Montego Black on black/red
Engineer of Electro/Mechanical Systems Maintenance

tj924 · Posted: Wed Feb 15, 2006 11:10 am Post subject:

D Hook · Joined: 02 Nov 2002 Posts: 3158 Location: Omaha, NE

One of the guys (Jazzerpet) here in Omaha was having trouble with an intermittent fuel pump relay, signs it was starting to go out. He jumped the relay and the problem would go away, put the relay back in and it came back. First noticed it, IIRC, when the car was under load, going up a hill. Eventually it started doing it all the time 'till it finally quit altogether.

My fuel pump relay did the same thing, would make the engine stutter, until the relay finally quit for good one night. Popped in a new one and it was fine.

Might try jumpering the relay slot as described in the Haynes, just to rule it out. Won't cost you anything....unless you do it wrong and burn up the car. But hey, what's the chances of THAT happening?

Maybe Jim (Jazzerpet) will jump on here and fill in the blanks.
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'80 924 n/a SOLD

Chaos · Joined: 07 Nov 2005 Posts: 289 Location: Newark, DE, US

haha. that's interesting, too. i not entirely sure, but i THINK that it seems worse going up hills, etc. i should try that. maybe start looking for relays. *shrug* there's also the chance that i could fix the relay i have if the problem isn't too major (ie: a cold solder joint or something)
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'81 US 931 "Rochelle"

Ozzie · Posted: Wed Feb 15, 2006 3:19 pm Post subject:

tj924 · Posted: Wed Feb 15, 2006 4:22 pm Post subject:

Ozzie · Posted: Wed Feb 15, 2006 4:59 pm Post subject:

Why not? the only restriction would be the filter and other pump, maybe the accumulator.
It wouldn't be high pressure like with 2 running.
Another option would be to fit a longer hose to the intank pump and hold it above the tank and into a container.
_________________
Porsche 924 1984 (UK import) NA
Its AUTO and its BLACK
Montego Black on black/red
Engineer of Electro/Mechanical Systems Maintenance

Smoothie · Posted: Thu Feb 16, 2006 4:19 am Post subject:

A leak at the rubber boot that connects the air meter/fuel distributor to the turbo can also cause your symptoms. To check it, it would have to be removed and given a thorough look-over inside and out.
_________________
"..it's made in Germany. You know the Germans always make good stuff."

'82 924T, US version, dark green metallic, 5 speed Audi 016G gearbox