Porsche Enthusiasts Club Forum

Hi All,

I bought a 1980 928S Manual in the summer and really love it already. I've put about 1000 miles on it (53K in total).

Recently it has developed a fault where it will only run when cold. As soon as it gets any heat at all (2 - 5 minutes running) it cuts out and will not restart until stone cold again.

In the last 48 hours I have replaced coil, dizzie cap, rotor arm, leads and plugs, but the problem persists.

Are there any other parts that people would recommend I swap out or check/clean? (easy-medium skill highly-amateur level !)

I live in rural Argyll so getting the car to a specialist is non-trivial and I should really exhaust any and all easy fixes before doing that.

I look forward to contributing and not just "using" in future.

Smells to me of a temp sensor or crank sensor starting to die when it heats up.

Hope you get it sorted Ecurie, let us know update!

I don't think your L-jet car has crank sensor?

Anyway start with simple things first. Huge proportion of 928 problems are just down to old relays, and contact problems as they warm up. Number one suspect is fuel pump relay, so change that first (standard type 53 spst relay).

If that doesn't fix it replace the other "running" relays. Not sure which you have on a 928S, but the running relays are fuel pump, injection ECU, ignition ECU. Replace whichever of these the 928S has, using relay list stored on central electric cover in passenger side footwell.

Update I've just read thread you started on Rennlist on this issue. There's nothing those guys don't know about 928s!

Was worried by your comment on clicking relay, then saw last post about your 80S having special fuel pump relay, not standard relay same as horn (as in later cars like mine).

Sure enough when I check relay chart for your MY the pump relay is different from horn.

It was indeed the fuel pump relay.

On the 928S it is a bigger and badder beast than the Horn relay, but the Horn relay suffices as a test/bridge to rule out the fuel relay.

Part is 928 615 113 01. Roughly £115 wherever you look.

Very pleased with PorscheShop.co.uk shipping one to me in the middle of Argyll to arrive on a Saturday morning having been ordered on a Friday lunchtime.

I eventually got out for a test drive and the car is revving really nicely so I guess the "throw some parts at it" replacement of leads, plugs, cap, coil etc wasn't such a bad thing.

Clearly the initial symptoms where I thought it related to time or temp were wrong and it was just the relay gradually and erratically giving up.

Thanks for all the suggestions and tips.

That's great news John, and ignition components always good to replace unless you know when last changed anyway.

In general it's a good rule of thumb with 928 problems to suspect relay first! The fuel pump carries heaviest current of all the running relays, so is the most likely to fail.

So, I can get a shot next weekend when I'm staying at your house?

The one shot round the car park at Euro Central wasn't enough to satisfy my 928 craving......

Unbelievable.
I started the car this morning. I was about to step out to go open the gate, when it cut out.

To cut to the chase....... Relay and fuse all fine. Jumpered/tested to prove all that. You can hear the relay clicking off after the initial 2 seconds.

So I took the rear panel off and got the wife to crank it while I held a meter on the pump. Voltage is reaching the pump but its not pumping!!! Dead pump!

Being cautious, I only got her to bump it, not continually crank it, so the meter only got as far as showing 8V but I presume that's evidence enough.

So it looks like my 5 year old, 1500 mile fuel pump has just given up in coincidence or sympathy with the earlier relay issues.

I was so happy after the first fix and a nice wee smooth running drive. I'm not a happy bunny now. New pump and filter I guess.

Now you're just teasing me......

If you get the parts on time we can fit them next weekend.

Make sure you use flare nut spanners to remove the faulty pump (or risk distorting metal pipes), and use new copper crush washers at banjo bolt or it will probably leak!