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madhatter · Posted: Tue Nov 09, 2004 3:30 am Post subject: Fuel pump relay going beserk...

While vacuuming out the car today, I had the vacuum plugged into the cars cigarette lighter for power and the car running. Suddenly the car started sputtering and caughing and then died. Restarted the car and the symptoms continued, but I noticed that the fuel pump relay was making a chattering noise like it was going on and off rapidly. Thinking the relay was going bad, I removed it and jumpered the pump to see if there was any change. There was no change as the car still barely ran, and now I am thinking that that the pump might be on its way out and it causing the relay to chatter on and off. The archives seem to also suggest that maybe the wires and grounds behind the fusebox could cause this problem. If so, is the relay board easy to remove? Thanks,

Steve

CMXXXI · Joined: 05 Nov 2002 Posts: 1939 Location: Vicksburg, MS

I'm not an electrical guru, but I don't think if the pump were <going> bad, it would cause the relay to click. After jumpering the relay you got the same poor running makes me think that it's an electrical issue with power getting to the relay block.

Removing the fuse panel/relay block is actually quite simple, but the trick is to not mess up any of the wiring while you are at it. To remove, you have to unplug the 5-6 color "cannon plugs" and some other spade connector from the thing. The relay seats sort of slide/clip on to the top of the fuse panel and can be pretty tough to get off. You'll be spending a pretty good deal of time on your back with your head up by the pedals. Not the most fun job, but not technically taxing.

Disconnect the battery before you start, and label any wires you disconnect.
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'79 Eurospec 931

madhatter · Posted: Tue Nov 09, 2004 6:14 am Post subject:

Great, that sounds like my first plan of attack on the problem. I was thinking that maybe the pump was shorting or going on and off about to die and causing a rapid drawing on and off of power through the relay. Are there any grounds wires behind the board that I should also look at as possible causes? Thanks.

Steve

Smoothie · Posted: Tue Nov 09, 2004 6:25 am Post subject:

To simplify reinstallation later - before you pull the connectors off the back of the relay board, letter them A-F from left to right as viewed facing forward in the car (-or if on your back looking up, letter A-F from right to left). That way you'll know which goes where and which side of each faces down. -Also, that lettering matches the sequence they used in the owners, factory and Haynes manuals - for instance "A15" in the wiring diagrams refers to pin #15 of the first connector on the left side..

Look closely at both the relay board and connectors for burnt pins and/or bad wires once you have it apart.
"C10", "C15" and "H" are the relay board connections that pertain to the fuel pump/s and relay for a '78 (Haynes pg.252). ("H", I believe should be one of the male spade connectors on back of the relay board and they're basically a connection to the battery 12V+.)
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"..it's made in Germany. You know the Germans always make good stuff."

'82 924T, US version, dark green metallic, 5 speed Audi 016G gearbox

CMXXXI · Joined: 05 Nov 2002 Posts: 1939 Location: Vicksburg, MS

All the grounds back behind the dashboard go to the grounding "crowns" up on the "roof" above the fuse panel. These crowns need to be filed, sanded or otherwise 'ground' off (no pun intended, of course) to ensure that a good electrical connection is made. It's a mean job that you won't want to tackle again any time soon, so when you do it, do it good or you'll always have a doubt in your mind of whether this ground point is the cause of future problems you may encounter. I hit mine with a Dremmel tool using a small stone, worked great.

Click photo for a larger image of the grounding crowns
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'79 Eurospec 931

madhatter · Posted: Tue Nov 09, 2004 9:46 am Post subject:

More good information, thanks guys. Once I get the panel off I should get a good idea what's going on in there.....actually I'm really hoping to find a burnt or bad connection somewhere. If it all checks out, then I have to start looking for the problem somewhere else, and I would rather find the answer sooner rather than later...I'll keep you posted on what I find in there.

Steve

924RACR · Posted: Tue Nov 09, 2004 11:01 pm Post subject:

Absolutely expect some burnt and/or corroded wires; I cut off the connectors and crimped new brass terminals on (where the relays plug in), because they were so bad. Given the mention of rapid on/off of the relay, I'd be a bit suspicious (other than the relay board contacts, which need to be checked anyway, no question) of the ground for the relay (assuming it's like the later US turbos, it's grounding by the boost limiting switch on the intake charge tube, could have a poor connection there or a bad switch, try grounding the lead to it) or poor connection to the tach/coil pickup (required to operate the relay, for crash safety).

HTH...
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Vaughan Scott
Webmeister
'79 924 #77 SCCA H Prod racecar
'82 931 Plat. Silver
#25 Hidari Firefly P2 sports prototype

madhatter · Posted: Thu Nov 11, 2004 7:25 am Post subject:

Well, I pulled the relay board today and am happy to report that there were a couple of burnt connectors which I cleaned up and replaced and the problem is now fixed for a change! Actually, one of the connectors was barely connected with the board and I am not sure if that was the bigger problem or the burnt connectors, but whatever one it was is fixed now. Not as bad as I thought it was going to be, but a little hard on the back!

Steve