924Board.org

[Mars478]

Since the forum server transfer ate my thread about this, I am going to repost it and try my best to recreate the post I had made before.

This past sunday I was on the Merritt Parkway following two of my friends, and gradually the car started sputtering and not making it up the hills of the highway even when I downshifted. It was making no power and sputtering like hell. I pulled off to the side of the highway where my friends were waiting for me and the car was running like sh*t. Sounded like it was running on 2 cylinders or 1 at most. What was interesting is that it would turn on and idle properly for like half a second then run poorly, and sometimes it would have some moments of idling properly, but if you gave it any gas it would die.

My roadside tests pretty much confirmed it was a fuel delivery issue, but I could be wrong. Can anyone explain to me how the fuel system works BEFORE the CIS? I know there is a fuel pump, accumulator, and filter. I know my accumulator is leaking but that's not really an issue. Previously before this happened, the car's fuel pump locked up and I got it working again by banging on it with a hard object. Car had at the very least half a tank of gas in it when this happened.

Anyone have any suggestions for me? Also looking for some sources for the CIS hose because my friend stupidly put some pliers onto them to see if they could remove it and it sprung a leak. It's the hose from the filter to the fuel distributor.

Thanks guys, for helping get another '24 on the road.
_________________
924, 82, 5 speed, dark red, 500 dollar special.

Daily: 99 ML320, 210k and still trucking.

[fiat22turbo]

Buy and read the book on the Bosch CIS system to get an understanding.
_________________
Stefan
1979 924 Carrera GTS (clone-ish)
1988 944 Turbo S (Silver Rose)

[ideola]

I would start with the basics: spark, air, fuel. In that order. While it may ultimately be a fuel problem, the first two are typically easier to diagnose and cheaper to repair. And frankly, on a 30+ year old car, it's quite likely that there are multiple faults causing your problem.

I would start with spark. Pull the fuel pump relay so you don't wash fuel down the cylinders while doing the tests. Get a spark tester and check for good clean spark at the main lead between the coil and distributor cap. Then check each spark plug lead one at a time.

If the car lost power and wasn't running on all four cylinders, it could easily just be a problem with a failed coil, distributor cap, failed rotor, plug wires, and the plugs themselves.

It also would be a good idea to pull the plugs and see what they tell you. Haynes has a nice diagram that shows different conditions and what they mean. If the plugs are wet with unburnt fuel, it's more likely you have a spark issue than a fuel issue (although it could be over-fueling that's dousing the spark).

If spark checks out, then move on and check the entire air tract for any obvious signs of leaks. It will be hard to diagnose if the car isn't running, but you can at least look for obvious things like cracked or broken vac lines, and cracks or holes in the main air plenum pieces from the AFM to the throttle body.

After that, then dive into CIS. Here is a tutorial.
http://www.924board.org/viewtopic.php?t=35734
_________________
erstwhile owner of just about every 924 variant ever made

[Peter_in_AU]

while you're at it replace all those 30 year old cloth-covered rubber vaccuum hoses in the engine bay with good quality hi-temp BLACK silicone hoses. It probably won't fix your problem but it's the best $20 you could spend on ebay on a 924.
_________________
1979 924 (Gone to a better place)
1974 Lotus 7 S4 "Big Valve" Twin-cam (waiting)
1982 924 (As featured on Wikipedia)

Learn to love your multimeter and may the search be with you

[ThomasJoseph315]

The fact you had to bang on the fuel pump before to get if functioning recently suggest that maybe your problem. If there was something logged in the pump, like debris, and you banged on it to get it working, where ever that pump stopped before could have overloaded the motor in that one spot, it's possible that bad spot spread or even damaged the rest of the pump it's self. Certainly try what Dan and turbo said, but if it ran fine before, then just started happening instantly, I wouldn't think it would be CIS (injectors or fuel distributor), or Air related. Could be spark related, but a very quick test would be pull the intake tube off and try ether, if it fires right up for a second, you know it's not spark or air.

As far as how the fuel system works it varies on year, but only little. It starts in the tank some cars have a prepump, then goes out to the elbo filter, Then to the main pump, then to the accumulators, then to the fuel filter.

You can use a standard fuel pressure tester just before the fuel filter to see what fuel pressure your getting upstream, make sure you use a "T" fitting is all.

It's common to bang on starters and fuel tanks to get motors working again. Typically if you do get them working again by banging on them, you are on borrowed time at that point. I think a banging on a starter you get like a few weeks before it finally craps out depending on the manufacture. Fuel pumps, if it's like a dodge you would get only 1 or 2 starts before they would go bad. People used to run them dry all the time in the 90's because Dodge relied on at least a 1/4 tank of gas to cool the pumps, a lot of people ran the tanks dry.

Get a Delphi pump, they last forever, good luck!

[Mars478]

Thanks for the information guys. I am reluctant to delve into the CIS system unless I absolutely have to. I pulled some of the spark plugs and they looked as good as the ones on my 1999 ML320 (which runs perfectly), so I do not believe that was the issue. I am also reluctant to believe the ignition system is messed up because it would run properly for half a second and then when the engine wanted more load it would die. However, as a precaution I will check and inspect the spark system.

The recommendations on the vacuum line, thanks, I will look into replacing those.

Judging by the fact that the fuel pump was giving me issues and the fact that when I put my ear up to it it sounded like it was pumping gravel instead of fuel, I'm going to start by replacing that along with the filter after I verify the integrity of my spark and air systems.
_________________
924, 82, 5 speed, dark red, 500 dollar special.

Daily: 99 ML320, 210k and still trucking.

[jason c]

Clean the tank out then change the fuel pump and filter. The relay getting hot (as you stated in the 1st post) is a result of the fuel pump pulling too many amps.

[larchie]

It makes sense to solve the problem at issue before doing a complete overhaul of possible further problems with spark, fuel, air, and lubrication.

Since your in-line exterior fuel pump is failing and so contaminated fuel is entering the pump intake, the contaminated fuel must be egressing from the in-tank pump which in turn implies the in-tank pump is allowing sediment through from the tank.

(1) pull the in-tank pump and inspect it and the condition of the tank.
(2) cut open the engine bay's inline fuel filter at both ends and inspect to see if contamination is likely to have reached the fuel distributor.
(3) flush out fuel lines from the fuel distributor back to the tank.

If steps 1-3 have never been done before on your car, then, in addition to replacing the in-line fuel filter and in-line exterior fuel pump, you might be looking at cleaning the tank and intake fuel lines. The in-tank fuel pump almost always fails at the fuel-resistant hose connector between the pump unit and the out-take port to the fuel line so you'll probably be replacing that also (but be aware most auto-part stores have the in-line exterior fuel pump listed when accessing the in-tank pump part number):


Porsche 924 In-Tank Pump Fail Point

This point of failure is most likely the source of allowing the contaminated fuel to reach the in-line exterior pump. This particular "fuel-resistant" hose doesn't stand up to today's ethanol-laced fuel. See also these posts...

924 In-Tank Fuel Pump
Replacing the 924 Fuel Pumps with 1 External Fuel Pump
Cleaning the fuel system

At this point, if the car is not running well ...

(1) and if you have not already done so follow fiat22turbo's advice and get a Porsche 924 Haynes Repair Manual for 1976 thru 1982 and as parts are needed look them up online in the Porsche AG Genuine Parts Catalogue for your model and year (both are absolutely essential),

(2) and if the there are further problems, follow ideola's advice as you systematically go through check the online tech information troubleshooting outline: BOSCH-K-Jetronic: Troubleshooting Symptoms.

If you cannot get an in-tank fuel pump to fit (as the OEM Bosch in-tank pumps have changed their factory of manufacture and the diameter is somewhat larger), you might have to resort to an in-tank filter as used in some 944s. This being the case, you might have to avoid the OEM Bosch external in-line pump in favor of a 044 pump to maintain performance.

[Mars478]

Guys, I appreciate the wealth of information. I will do some more research on fuel pump setups and drain the tank. I assume since my car is an 82, that I have the dual pump setup. I'm guessing that my in tank pump had long since failed, considering my car had been sitting for years before I got it up and running, leaving only the external pump working, and my hard driving killed the external pump + the debris killed it. Every day I learn more about this car and it is tons of fun to see how they did things in the 80's. Thanks guys.
_________________
924, 82, 5 speed, dark red, 500 dollar special.

Daily: 99 ML320, 210k and still trucking.

[jason c]

[Mars478]

[jason c]

I agree with all of the above except driving hard made it worse. You would have the same problem even if you drove like an old lady. The pump is going to run & build pressure regardless of how hard you drive. Its drive is not attached to engine rpm like a mechanical pump. If it were an engine, oil pump & low oil issue, hard driving would make it worse.

I've had the same issues with my 944s' too.

[Mars478]

[jason c]

[Mars478]