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914World.com _ 914World Garage _ Fuel pump intermittent

Posted by: porschefool Aug 24 2004, 06:46 AM

Hey guys, (and gals)
Tracking down my intermittent fuel pump cutout prob. Got it traced all the way (using the flow charts on PP tech site) to either the fuse block (tight and clean) or the ignition switch. Here's what happens: relay 74 only gets that 1.5 second "blast" current intermittently. Does the ignition switch actually carry the current for the fuel pump? I can hear the relay click fairly reliably, but the pump doesn't run. I just got done cleaning/resoldering the relay board-which I thought solved it. (silly me)
Before I replace YET ANOTHER unnecessary part (electrical portion of ignition switch) I'd like to know if it really does carry the current for the pump.
Thanks...

Eric
'72 1.7 D-Jet

Posted by: DNHunt Aug 24 2004, 07:38 AM

Eric

The ignition switch just powers the coil side of the relay. I suppose you did all this already but, i would check the gound for the pump, and clean the spade connectors on the fuel pump itself. It's a pretty dirty environment down there if it's in the stock spot. Then I'd swap relays to check the one you have in there and clean the contacts. Also clean up the fuses on the relay board and their connectors. I just relace my ignition switch, but for a start problem, not too hard and pretty cheap.

Dave

Posted by: porschefool Aug 24 2004, 10:02 AM

Relay board is spotless, as is the fuse block.
I haven't touched the pump connections yet, because I saw that the 1.5 sec. relay "burst" wasn't consistent. Does this come form the ECU?
Thanks!

Posted by: DNHunt Aug 24 2004, 11:51 AM

Try the relay. The coil in it could be failing. As a test take the headlight relay and swap it.

dave

Posted by: porschefool Aug 24 2004, 11:57 AM

I don't think it's the relay, I tried others plus the contact socket for that relay isn't showing voltage. BTW, where are the headlight relays? I can't find them...
The problem is the control signal that gives the relay that 1.5 sec burst.
Can anyone help with the path of that signal?

Posted by: SirAndy Aug 24 2004, 11:57 AM

the fuel pump relay is triggered by the *BRAIN* ...

you can test the circuit (and the brain for that matter) by disconnecting the 4-prong connector to the brain and shorting out PIN 3 to ground. this will bypass the brain and make the pump run all the time. if that works, your brain is faulty (haha) ...

i'm sure you switched relays around as well, just to be sure. they do brake.
also make sure the relay fits in there snug, bend the pins a bit if you think it's to loose.

Andy

Posted by: porschefool Aug 24 2004, 01:17 PM

Shorting things out to make gas squirt!!
YES!
I can't wait to get home...

I've got another brain, too..
Abby- something......
Normal, yes..that's it.

Thanks, all.