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Strange fault, cutting out, DME?

H

homesea

New member
I have had a strange fault over the past 2-3 weeks, it's only happened twice but I would like to get it sorted. It first happened nearly 3 weeks ago the car started from cold, drove about 100m down the road and cut out, it would not start straight away but after about 5 mins started up and drove fine. Then on Saturday I had used the car and parked it up for about 15mins came back to it and it started, drove about ¼ mile and it cut out and would not start again for about 40mins. I could smell petrol and tested the spark with a spare plug (it looked a little weak). The car has now run fine for 4 days. I did some reading and it sounded like a DME relay fault, I didn't have a spare to check but last time it didn't start I could hear and feel the relay click. I then read about dry joints on track 1 in the ECU, I took this off last night and let an electrical engineer have a look at it but I was assured it all looked ok but it wasn't tested. Am I missing anything obvious? The odd thing is the car has always idled a little high at about 1100 rpm but now the ECU is back in it idles fine at about 850-900RPM, would this be because the ECU would have reset itself by being disconnected for about 2hrs? Any help would be much appreciated. P.S. the car is an 88 Lux 2.5.
 
Have a wiggle of your speed and reference sensors. It probaly isnt these as the symptoms are slightly different than you describe but it's worth a check just in case. When I was having starting problems I found that these were loose and once I tightened them up everytings been fine since. They are mounted on the top of your bell housing at roughly the 12 o'clock position behind your main engine block. There are two of them (one is the speed sensor the other the reference sensor) and there is a black lead coming our of them that leads into a plug that is mounted through a metal bracket. Like I say it's a long shot but worth a look just in case.
 
I had very similar symptoms on my Mk3 golf gti a while ago... diagnostic showed no fault codes, it turned out that the fuel tank breather was blocked...cleared it out and the problem dissappeared......

migh be worth a go.....
 
Sounds exactly the same as a recent case, traced to a faulty fuel pressure regulator.

I'm not the Club Technical Advisor.....[:)] but this was the same symptoms.
 
I have tried wiggling the speed and reference sensors but cant get it to cut out again. Dont the fuel pressure regulator fail closed so leave high fuel pressure, so would this make it cut out? Also tried wiggling the maf wire. Its runing fine at the moment, if I could just make it cut out I could fix it. I hate problems like this. Might just sell it and buy a turbo.
 
..........it's a bit of a coincidence but my 944 was a bugger to start this morning, it turned over fine but just wouldn't fire. After trying for a few minutes it eventually started up. I've still got to go round and check all contacts/plugs etc. to rule out a more simpler explanation but I wonder if I too could be having DME relay troubles ? I've not had my car cut out while driving though.

Being new to Porsche ownership are things like relays easy to get hold of, say from Halfrauds or a highstreet uni-parts shop ? or do I need to go to a Porsche or VW dealership ? Do any internet shops do things like relays ?
 
Hi , Sounds like a DME Relay issue to me , I have a 87 944S for the past year and twice I have had to replace the DME Relay , once because the car failed to start and the AA diagnosed it and the second time was when the car just cut out whilst I was doing 70mph +++ in the outside lane of the M4 !!!! I got them of ebay for £20 , I always carry a spare now !!!.
 
Don't know if it's the source of my particuler problem at the moment but I thought I'd better get one anyway just in case from what everyone's said ............. after a search on the net I got one off ebay @ £21.94 all in. At least when fitted its one thing less to cause trouble.
 
My 944 turbo did this when I first got it, my alarm kept beeping as well as the car cutting out. Found out it was a faulty crank sensor.
 
my 86 lux did this occasionally. It only ever happened after it had driven a couple of miles and warmed up and I switched it off. Then it wouldn't restart no matter what until I had left it at least 15 minutes . After that it never gave any problems on that day at all !?

It must have been heat related or it would have effected starting drom cold also. I had my air flow sensor and throttle position sensor sensor checked and contacts etc cleaned and never had the problem again ?

I think it was due to the rapid increase in heat after switching off
 
Hi Paul, The pressure regulator symptoms were full-time , rather than intermittent like this. My money`s on the relay in this case.Maybe the fuel pump fuse is worn?
Incidentaly GMF motor factors got me a Bosch pressure regulator for £50 inc VAT (£84+VAT, OPC listed price), in 72 hours .Here`s their web address.
www.gmfmotorfactors.co.uk ( Thanks Ian ).
regards,
jr.
 
More I read it sounds like the DME relay or the DME. I hate spending money swopping pars until I know whats wrong. Think I will give the testing the relay and making an emergeny jumper wire a try first. Thanks for all the help will keep this updated as I try to track down the problem so it might help another person.
 
I own 3 older Porsches and each one has a DME/ECU relay in the glove compartment.
I would rather start a journey without a spare wheel than without a relay.
 
homesea, I've previously had had very similar - well, virtually identical - symptoms as yourself (on an S2) which proved to be due to a faulty temperature sender. Twice. Sorry to muddy the waters............
 
ORIGINAL: homesea

More I read it sounds like the DME relay or the DME. I hate spending money swopping pars until I know whats wrong. Think I will give the testing the relay and making an emergeny jumper wire a try first. Thanks for all the help will keep this updated as I try to track down the problem so it might help another person.
Click to expand...

Bear in mind it is worth having a spare DME relay kicking about so if you do replace it and it turns out not to be the DME then you can always keep your old one in your glove box in case the next time it goes you are on the side of the road. I got my DME from Promax for £19 odd.
 
Used the car all day today and no cutting out but its back to its high idle of just over 1000rpm, how odd. Looking to get a new relay this weekend , just in case.
 
Sorry to hijack this, but I've just got back from Tescos, but it was touch and go...
The 944 started ok outside tescos, but when i stopped to get fuel, it wouldn't start again- wiggled the DME but nothing....bugger!
Anyway, it started after 5 mins, but was idling really slowly, although it ran fine when revved, and by the time i got home it was fine again
Does this sound like the same issue as the one being discussed? can we get any group buys on DME relays ?[:D]

PS mine also idles at just over 1000rpm usually
 
I been messing about with the car all evening and I think I am going back to a fuel issue. The car smells a bit strong of petrol a bit like cold start. Could also explain the high idle and when it went for the MOT it was 2.9%. Could this be down to a temp switch? If anyone knows a good inde in Sheffield let me know.

 
my 86 Lux used to do this ,idle over 1000 fluctuate up and down and cut out intermittanly and I'm sure it was because of the throttle sensor . Might be worth checking out rennlist and pelical/parragon etc see if the subject has been raised over the pond
 
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