924 Fuel Pump Relay Problem

free82924 · 08-21-2010, 07:17 PM

I've been looking through the fuel pump threads, but can't find anything that fits my problem. Car is a '82 924 (not turbo) and was running fine. Stalled on the hwy doing about 50 MPH under a light load. Issue seems to be no fuel pressure (pump not running). Followed the trouble shooting procedures in my Haynes manual and the results point to the relay. Pump, hose and pipe all check good when I jump number 30 and 87 in the relay socket. Number 31 is a good ground and number 1 and 15 have 12V. However, the relay will not energize the pump when the key is on and the starter turning. I tired a new relay with the same results. Would sure appreciate any ideas on what the problem is!!

Grandad#3 · 08-21-2010, 08:04 PM

Hello, I'm not that familiar with the 924, but if a new relay failed to start the fuel pump it sounds as if the ignition switch is at fault. The switch is forward of where you put the key, under the dash. The plastic housing will crack and lose contact inside. It will still let you turn the engine over until the battery dies without starting. Sorry I can't be of more help.

Cheers,
Larry

Rasta Monsta · Rasta Monsta's Garage

Does the car start and drive with the relay jumpered.

drew1 · 08-22-2010, 04:31 AM

Had a similiar problem years back with an 82 924t. The relay grounded through (terminal 31) the boost safety switch. Switch went bad.

Don't know if there is something similiar on 924 na or not. A jumper from 31 to ground while cranking could pin point.

Does your car have an alarm? I know crazy things can happen in early 944 with alarm circuit.

924RACR · 08-22-2010, 05:00 AM

No boost safety switch or similar on the NA, but IIRC it does also require a tach signal to trigger the relay. Other than the ignition switch failing, this is about the only failure that should likely fit your description (good work on the diagnostics, BTW).

So first I'd try hotwiring it at the ignition switch, see if that'll get the pump to run.

I forget which wire is the tach lead, but that'd be the next thing, to verify that it's got continuity to the coil/tach. I assume the tach jumps when you crank? I don't know for certain, but I don't think the NA has the same problematic DITC ignition that the 81-82 turbo does?

free82924 · 08-23-2010, 07:02 PM

I just got back in town and the first thing I did was to check this site -- wow, thanks for all the suggestions! One of the things that caught my eye was the post about the tach being a problem. Now that I think about it, the tach does not even twitch when I crank the engine. I can't check it until tomorrow evening, but will sure give it a try and let you know what happens. Thanks again to everyone!

free82924 · 08-24-2010, 07:49 PM

Ok, here we go.... I tried hot wiring the car and it still won't fire the fuel pump. The ignition comes on and the engine turns over, but no pump action. I tested the wires at the ignition switch connector and all have the proper continuity and voltage. The tach connector on the wiring harness side has five contacts, but only three are used (#4 which is a ground, # 5 is 12V and #6 has continuity with the green wire on the coil). All these check good. Does this mean the circuitry in the tach is bad? Is there a way to test the tach? Is there some other part I've missed? I have some electronic test equipment and basic circuitry knowledge, but can't go too deep. Sorry guys, but I'm just an old shade-tree mechanic with no Porsche experience.

Paul Stewart · 08-25-2010, 08:28 PM

The car will run without the tach, but the fuel pump relay will not close if there is no signal (tach signal) coming from the coil. We ask the tach bouncing question since if it is bouncing the signal is present and thus the ignition switch and wiring is probably OK.

924RACR · 08-26-2010, 10:30 AM

The green wire/#6 wire at the tach would be the one that ought to also have continuity with the relevant contact in the pump relay... just a question of which one that is (can't remember offhand, but should more or less be indicated by the wiring diagram printed on the side of the relay).

free82924 · 08-26-2010, 01:58 PM

There is continuity on the green wire from the tach connector to the coil. However, there must be some type of pulsed signal the coil sends out for the tach to convert to rpm. Other than looking for the needle bounce, is there a way to see if the correct signal is present from the coil? I'm beginning to think I may have an ignition problem. I'm going to jumper the 30/87 contacts on the pump relay tonight and see if the car will run like that. If so, then I guess it's a bad tach. If not then maybe it's a coil/distributor problem? Does that sound right??

free82924 · 08-26-2010, 06:55 PM

Well, I did a little more testing and now have more head-scratching to do. The engine will not start (but a cylinder will fire a time or two) when the fuel relay is jumped and it's hot-wired. To me that means it's probably not the tach, but something else in the ignition system which is causing it to be "intermittent". I've tied resetting all the connections I can find (including the grounds), but no luck. I guess I go to the ignition troubleshoot section of the Haynes manual now!

Paul Stewart · 03:00 PM

The car will run without the tach unless it is shorting the coil. Unplug the tach and see if the car starts. Also it's time to check the fuel pressure and the flow through the injectors. Haynes has a good test procedure. Haynes also a procedure for checking the coil and the connections to it and the other components in the ignition system.

free82924 · 08-27-2010, 05:33 PM

Thanks Paul. The last test done above, when I hot wired the ignition, was with the tach out of the circuit. I think the fuel pressure is OK, because the pump provided the correct volume in the 30 second test period outlined in the Haynes manual, but I'll try a pressure test also. I had previously done a coil check and it was good. I'll jump back in the manual for the remainder of the ignition checks. Thanks for the suggestions.

Paul Stewart · 08-27-2010, 08:49 PM

Just for fun check the valve timing, the ignition timing, and do a compression check.

free82924 · 09-21-2010, 09:59 AM

I can close this thread out finally -- the root cause of the problem turned out to be a bad ignition distributor. Pulled the cap and dust cover off the distributor and found the magnet and plastic holder had self-destructed. Got an electronic rebuild kit and rebuilt that part of the distributor and everything is operational again. Just need to tweak the timing and it's on the road again! Thanks to everyone for the suggestions and help.