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I have a 1979 Porsche 924 with an electric fuel pump. It…

I have a 1979 Porsche...
I have a 1979 Porsche 924 with an electric fuel pump. It hadn't been run for a long time when I bought it. I had to have the gas tank opened up, cleaned, and sealed. I put on a new fuel pump at that time. Since then, I have only run the car in my driveway, never any longer than about 15 minutes, a total of 10 hours at the max. The most recent time I tried it would not start. I realized after several attempts that the fuel filter was clogged. Junk from the sealent, probably. I replaced the filter and it still will not start. There is no gas flow from the tank to the filter. I made sure the line is open. There is electricity to the fuel pump, and I can hear it running. Would the fuel pump have gone bad by running (trying to start that is) against a clogged filter? Even though it is almost brand new? Thanks Ron
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Answered in 11 days by:
3/23/2011
Matt
Matt, Engineer - BEng Hons
Category: Porsche
Satisfied Customers: 22,639
Experience: Mechanical Engineer with 20 years experience in the auto industry, 8 yrs in formula 1 engine testing
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Hello Ron

Providing the pump had fuel inside it when it was running then it should be OK as the fuel keeps it cool and lubricates the moving parts.

If you want to check this I'd suggest measuring the fuel pressure at the fuel distributor l to confirm its OK

also if the connections to the pump are corroded or damaged then the pump could stop at any time or could not be running at full speed. Check that its relay switches in and out and the relay contacts are clean and bright – replace the relay if in any doubt and do the same for the fuse,


If this is OK then remove the rubber intake boot from the fuel distributor and unscrew the central nut , pipe feed into the fuel distributor and push down on the aluminum plate under the rubber boot you should see the main fuel metering pin / needle rise up smoothly as you push down the plate its sticky or dirty then its possible this is getting stuck.

If this is OK then remove all the injectors but leave them connected to their fuel lines and put all into a clear container then turn the ignition on and (having replaced the central feed pipe nut) push down on the aluminum plate all the injectors should spray at once and look for ones that aren't spraying as much as the others - and replace or ultrasonically clean as required.

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Customer reply replied 6 years ago

I'm not clear on whether fuel should be coming out of the pump at all. It's not. There is only one line from the fuel pump to the fuel filter. It is not clogged. But there is no fuel coming out of that line that goes into the filter. This indicates no fuel is coming out of the fuel pump, right? If there is no fuel coming out of the pump, how can it be expected to build up any pressure furthur down the line, like at the fuel distributor? Am I missing something?

tank --- fuel pump ---- fuel line (disconnected here, no fuel) fuel filter ----- fuel distributor

And the pump does seem to be working. At least there is power going to it and I can hear it run. If the relay is bad, would the pump be running, but not providing enough pressure to even go through an emply line? It that's the case, does it mean the fuel pump has to be replaced?

Hello

You're correct if the pump is running - you should be getting fuel out of the other end of the pipe

If you're getting 12V at the pump and still no fuel then yes its possible the pump is faulty
- however there is another possiblity to a faulty pump

This is that the pickup inside the tank is blocked - I'd suggest removing the feed pipe from the tank to the pump ( do this over a container to catch any fuel) and see if fuel freely flows out - it should come out at a fair rate - definitely not a trickle

let me know what you find
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Customer reply replied 6 years ago

Thanks Matt,

I had already checked to make sure fuel comes freely from the tank when that line is removed.

I wanted to check with somebody before I spent a couple hundred dollars on a new fuel pump.

I'll just repeat the one question before I accept the answer. Do you know if turning over the engine against a clogged fuel filter while trying to start if would make the pump go bad?

Ron

Hello Ron

To be honest I'd be surprised if this was enough to hurt the pump as they're pretty tough - you can confirm if its OK by measuring the pressure against a load - if it can't make the 5 to 5.8 bar then it needs replacing
Matt
Matt, Engineer - BEng Hons
Category: Porsche
Satisfied Customers: 22,639
Experience: Mechanical Engineer with 20 years experience in the auto industry, 8 yrs in formula 1 engine testing
Verified
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