sometimes 928 won't start - please help

Ebs · 10-15-2004, 05:21 AM

Hi, this is the first time I have had a Porsche that won't start.

My car is an '84 928s, is a 4 speed auto, with a US spec engine, but with no cat etc.

Basically when I turn the key it has traditionally fired up quite easily, even if it has not been driven for a week or so. Yesterday after standing for a week, when I turned the key, the starter motor started running normally, but the engine would not turn over (kind of like in an old carby car where you'd turn the key and unless you had your foot on the gas pedal it would not actualy start). I tried holding down the gas pedal and then pumping it, and still nothing. I tried again later the same day and it fired up easily.

The strange thing is that sometimes it starts, other times it doesn't. It seems 2/3 of the time it starts, 1/3 it will take many tries, and sometimes I just give up and try it a few hours later when it will start. I will also point out that whether the car has just been driven or not seems to make no difference.

The care has fuel in it, I think the battery is fine, and the fuel pump was chaned 2,500 miles ago (in March of this year). I checked the plug leads etc and they are all on and look fine I also checked all the relays are in position/plugged in properly. I don't think car has an MAF.

Any ideas what this could be or where I should start looking? (my mechanical knowledge is fairly limited).

Please help.

928ram · 10-15-2004, 05:26 AM

Check your fuel pump fuse, it my have a little corosion on the tabs that hold it in. It could also be the pump relay is going south, try swapping it for identical from another system; I think the w/s wiper and a couple other systems use the same relay.

Ebs · 10-15-2004, 06:13 PM

Thanks for your reply.

I spoke to my mechanic, who suggested we remove and clean the fuel injectors. I also see some of the fuel hoses look a bit old and cracked, so it may be a good time to replace them.

What do you think - could this cause the problem?

928ram · 10-16-2004, 06:22 AM

I'd definatly replace the fuel hose if the are cracked but I seriously doubt the injectors are causing the problem as dirty injectors would cause poor running consistantly, not intermitent.
This sounds more like electrical, once you've checked the fuse and relay to be OK I'd look toward other elec. faults; cap and rotor, poor connections under hood, body grounds. Other common fail points would be the ignition elec. switch, the "green wire" that sends signal from the distributor to the ignition control box(underhood), fuel pump check-valve (this would normally cause hard starting or delayed starting rather than no-start), bad ballast resistors.
Intermittant electrical can be hard to diagnose, sometimes having "known good" parts handy to swap can save hours of head scratching.

armandodiaz · armandodiaz's Garage

I would say to double check your battery's charge. I remember in the later 928s if the voltage was too low, the engine would turn but fuel pump would not run. Not sure about your year. This was to prevent the engine from flooding. Being that your car was sitting it sounds like a logical answer to your problem.

hackerpat · 10-21-2004, 07:42 PM

I don't know where they are but I know a mechanic fixed a similar problem for me. Loosen, clean, then tighten every wire ground strap to the engine block. Motor is al and the connectors are cu. I was plaged for years with this problem. The car would crank for ever - other times it would start. When it would start, it would run as if nothing was ever a problem. Hope your problem is this simple. I replaced a lot of good items looking for this bug.

Ebs · 10-28-2004, 05:18 AM

Thanks for your replies. Still working on a solution

THE BIG DOG · 10-30-2004, 03:04 PM

HAVING SAME PROBLEM I AM GUESSING ITS IN THE ALARM IS THERE ANYBODY WHO KNOWS HOW TO DISABLE THE INTIRE ALARM SYSTEM

whiteSC59 · 05-08-2008, 07:23 AM

I know this an old thread but my car shocked me when it started and ran last night and sounded great. I shut it off and then would restart immediately afterwards. I came out this morning fired right up with same result. it ran for 10 mins at idle and then wouldnt restart.

Ive been having issues with NO START at all, and now after sitting for a few hours with fully charged battery (new) it jumps to life but wont restart after shutting off and immediately trying to restart. it tries to rumble and then just turns...Im gonna check all the relays today and start on ground wires. Wheres the green wire on a euro (2 distributer) engine run??

wag928s · wag928s's Garage

Check ground at battery to frame, make sure that 12mm nut is in good shape. I had this similar issue with my 85s and after months of aggravation. The nut corrodes and does not make a connection from the computer from what I understand. A more complete turn of events is on the porsche 928 club site.

Walt
85 s

Alan in AZ · 05-27-2008, 07:19 AM

928's vary substantially by year in equipment & wiring. It is possible to disable any 928 alarm - but the procedure is year specific. Send me a PM with your cars model/year and I will tell you how. (its also good to have your car details in your signature for this...)

First though are you sure you have an alarm? does it seem to work normally? for me If it were my alarm disabling the car I would know about it... horn, lights, blinking door posts etc...

Alan

Danglerb · 05-27-2008, 08:40 AM

All three of my 928's have had "some" of the old alarm present. I paid a bundle to a local stereo shop, chosen because they had experience installing the ancient alarm in my 83, and they removed the easy stuff like the keypad wiring and left the basic alarm unit buried in the wiring, which occasionally would activate when the battery was reconnected. Greg removed the rest at his usual low rate. ;(

The 83 would honk horns and blink lights, the other two just didn't start.