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Fuel pump troubleshooting help...

 
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Svobodin  



Joined: 08 Oct 2013
Posts: 65
Location: Colorado

PostPosted: Wed Feb 26, 2014 9:02 am    Post subject: Fuel pump troubleshooting help... Reply with quote

1979 924 N/A

My fuel pump has not been working, it does not turn on when I turn the key anymore. I've checked the fuses and swapped out the relay for another used one I had. The old relay did not appear damaged so I might put it back as there is no guarantee that my spare one is functioning...

I have been toying with the idea of running the fuel pump directly from the battery, partially to check if the fuel pump is still working, partially to get the engine running since it has been about 5 months now that the car has been sitting since the HG blew and was replaced.

Any advice on either troubleshooting the fuel pump, or wiring directly would be appreciated.
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Svobodin  



Joined: 08 Oct 2013
Posts: 65
Location: Colorado

PostPosted: Wed Feb 26, 2014 9:04 am    Post subject: Reply with quote

to clarify, I have a switch to shut off the fuel pump when wired directly so that it is not running constantly, and a fuse to protect the pump from excessive amperage.
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ThomasJoseph315  
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PostPosted: Wed Feb 26, 2014 9:14 am    Post subject: Reply with quote

Check for voltage at the pump with the key on with a volt/multi-meter. If none check the relay. The fuse for the fuel pump is right on the relay.
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Svobodin  



Joined: 08 Oct 2013
Posts: 65
Location: Colorado

PostPosted: Wed Feb 26, 2014 9:20 am    Post subject: Reply with quote

no voltage at the pump, going to check the relay now
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larchie  



Joined: 19 Jun 2003
Posts: 297

PostPosted: Wed Feb 26, 2014 9:45 am    Post subject: Reply with quote

Here's a thorough and helpful PDF troubleshooting procedure for a relay which also applies to the 924 fuel pump relay and incorporating specific electrical checks: Troubleshooting a Nonfunctional Fuel Pump.

Also see the very helpful thread on trouble shooting here: Post subject: Fuel Relay fuse keeps blowing (even though you're not having fuse problems).
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Svobodin  



Joined: 08 Oct 2013
Posts: 65
Location: Colorado

PostPosted: Wed Feb 26, 2014 10:04 am    Post subject: Reply with quote

checked the relay, no voltage. Put back old relay, no voltage. Checked the fuel pump, no voltage both internal and external. reading the pdf now.
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Svobodin  



Joined: 08 Oct 2013
Posts: 65
Location: Colorado

PostPosted: Wed Feb 26, 2014 10:48 am    Post subject: Reply with quote

also checked fuse #2 in the auxiliary fuse box, no current there.

And I had stumbled upon your second link Larchie when I did a forum search prior to posting

And btw, how do I "check for 12v on both sides of the fuse"? step #3 in the first link?

I have been putting the pos prob on one end and the neg on the other to check voltage across the fuse. Is this incorrect?
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Svobodin  



Joined: 08 Oct 2013
Posts: 65
Location: Colorado

PostPosted: Wed Feb 26, 2014 11:10 am    Post subject: Reply with quote

ok, well apparently I was doing it wrong... live and learn.

SO now that I can test the fuses properly, the current at the relay is 13.6v or so at both sides, but the current at fuse #2 in the auxiliary fuse box and at both pumps is 0v, I guess that means the relay is working.
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ThomasJoseph315  
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PostPosted: Wed Feb 26, 2014 11:48 am    Post subject: Reply with quote

does the relay have a diagram on it. Just because your getting voltage through the fuse doesn't mean the relay is working properly. If your relay has a diagram and you know how to SAFELY check the relay on a bench see if your getting voltage.
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Svobodin  



Joined: 08 Oct 2013
Posts: 65
Location: Colorado

PostPosted: Wed Feb 26, 2014 12:19 pm    Post subject: Reply with quote

I don't know how to test on a bench, nor do I think I have the proper equipment to do so. I did go ahead and test the relay in the harness as described in link 1 by larchie. The relay does not give power at 87 when I turn the ignition. 31 does give a reading of 12v however. I cant remember if 15 reads anything when the ignition it turned atm. I can retest it.
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Svobodin  



Joined: 08 Oct 2013
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Location: Colorado

PostPosted: Wed Feb 26, 2014 12:21 pm    Post subject: Reply with quote

I'm also not much of an electrician, what does correct mean when used in 4 b and c of that link? and how would I go about correcting those connections if I had to?
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Svobodin  



Joined: 08 Oct 2013
Posts: 65
Location: Colorado

PostPosted: Wed Feb 26, 2014 1:44 pm    Post subject: Reply with quote

Pulled the relay and opened it up. Its nasty inside. guess I'll need a new one. I'm gonna see if I can just jumper the fuel pump to check whether it has crapped out or whether there are more problems before I go about ordering up some parts.. thanks for the help guys!
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larchie  



Joined: 19 Jun 2003
Posts: 297

PostPosted: Wed Feb 26, 2014 5:10 pm    Post subject: Reply with quote

The wiring diagram for the fuel pump relay (courtesy jwillman Rennlist):



Terminal 1 (L-12) is Ignition Coil
Terminal 30 (L-13) is Battery
Terminal 87 (L-14) is Fuel Pump
Terminal 31 (L-15) is Ground
Terminal 15 (L-16) is Ignition Switch



Some quick tests on my spare relay PN 433 906 059 for the '79 924
(Hopefully not both of your relays are bad) show the following:
Measure continuity between ...
30 Battery and 31 Ground -- infinite
31 Ground and 87 Pump -- infinite
31 Ground and 15 Ignition Switch -- ~15 KOhm
15 Ignition Switch and 1 Ignition Coil -- ~35 KOhm
15 Ignition Switch and 87 Pump -- infinite
87 Pump and 30 Battery -- infinite
87 Pump and 1 Ignition Coil --infinite
1 Ignition Coil and 30 Battery -- ~20 KOhm

Quick Troubleshooting:
1. Check the 16 amp fuse 2 on Additional Fuse Board.
2. Remove relay from relay board.
3. Check voltage on relay board terminals between L-13 30 Battery and L-15 31 Ground with ignition switch on --> 12 V Note especially The Hanes Manual covering the '79 924 states "Before we begin, a word of warning. Using the electrical system with the ignition switched on but the engine not running can lead to burning out of the alternator diodes. To avoid this possibility slip the plug out of the alternator. "
4. Connect 1.5 mm wire with 8 Amp bottle-fuse jumper between 30 Battery and 87 Pump -- if pump does not run i.e., fails to run, connection between relay and pump is bad.
5. With relay still out, check voltage between 15 Ignition and 31 Ground --> 12 V.
6. Check continuity between 1 Ignition coil and 31 Ground --> continuity
---
Edit: Fuel pump fuse 2 on additional fuse board is 25 Amps not 16 Amps
The ground for the fuel pump relay terminal 31 is under dash near fuse relay board, and the ground for (both) fuel pumps is in the luggage compartment near the left rear light.
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