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Starts with fuel pump relay jumpered, but not with brand new

 
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andreasledet  



Joined: 14 Mar 2018
Posts: 1
Location: Denmark

PostPosted: Wed Mar 14, 2018 9:09 am    Post subject: Starts with fuel pump relay jumpered, but not with brand new Reply with quote

Hi everyone

My 1980 N/A 924 died on me a couple of weeks ago - it simply wouldn't start, even though I had driven it 200 miles the day before.
I could tell the fuel pump wasn't running, so I turned my attention to the dreaded fuel pump relay. And sure enough - with a jumper between the 30 and 87 ports, the fuel pump came on and the car fired up just fine.
So I assumed I just needed a new relay, and went and ordered a new one just like the one that was in the car before - the 3.300.300 type.

But after receiving the new relay and installing it in the car, it still wouldn't start. Put the jumper back in, and it started.
So I guess the relay is not at fault after all? What else could be causing a problem like this?

Bonus info: Before I had this problem, the fuel pump always came on when the ignition was on. Meaning not only when the engine was turning. I believe this is not the way it was meant to work in its stock form. But that shouldn't have anything to do with it, right?
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agfisher  



Joined: 09 May 2007
Posts: 451
Location: West Hartford, CT

PostPosted: Wed Mar 14, 2018 11:36 am    Post subject: Reply with quote

Did you verify that the relay is identical to the one you replaced?
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1977 924 N/A Martini Edition
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Eric P  



Joined: 21 Jun 2017
Posts: 175
Location: NY, USA

PostPosted: Wed Mar 14, 2018 12:31 pm    Post subject: Reply with quote

I had a similar issue. In my case it ended up being a bad ground to the relay. If you have a multimeter, check for the following:

Pin 15 switched 12v (with key on)
Pin 31 ground
Pin 31b coil (pulse)
30 positive 12v
87 positive side of fuel pump

I would start by checking pin 31 for ground. This ground goes to the crown under the dash and commonly suffers from corrosion issues. This was the issue on my car. Or at least one of them. I had a lot of wiring Gremlins at first.

You know pin 30 and 87 are fine if jumpering it works. That leaves 3 more pins to check. If everything checks out, you may have gotten a bad or incorrect relay. If you suspect the relay may have burnt out, pull the cover off and take a look. You can usually see a burned circuit trace if the relay is fried.
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1980 924 NA, US model
1987 924S, US model
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snakoil  



Joined: 09 Feb 2010
Posts: 362
Location: Montreal, Canada

PostPosted: Wed Mar 14, 2018 11:38 pm    Post subject: Reply with quote

I had the exact same issue, turns out the brand new relay I got from VW was DOA.
I bought a second one and it fired right up
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1979 924 NA
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