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Early 944-DME relay fault?

jwindwood

jwindwood

New member
Guys

1985 square dash 944. One day last week, it wouldn't start-no fuel pump noise so I immediately suspected DME relay. Took it out, put in my (Untested) spare-still nothing.

Made up jumper wire, fuel pump ran fine, started normally. Resoldered both relays with no improvement. Bought a new relay (Genuine)-still no fuel pump.

Looked closer at the relay board with a view to wiring tests and realised that the earth terminal was missing from the relay holder (Terminal 86, IIRC). Took the fuse panel out and the connector had pushed through the back. Refitted it, fitted relay and the car started fine. Tested the other two relays and again, all started fine but now a new problem....

Car starts and idles fine, but as soon as I give it throttle it becomes lumpy and almost backfires. It is drivable, but not easily-coughing and spluttering at times.

Question-could this be caused by a poor earth to the DME relay? I noticed whilst I was refitting the connector that the wire has been cut and respliced poorly in the past and the terminals are looking past their best. I'm going to replace it anyway, but I'm interested to know if my car is displaying typical symptoms of this problem, or whether it's likely to be something else?

It seems a major coincidence that I have never had any running problems before this occurred.

Thanks for any advice!
 
Ive only skimmed but I suspect two separate problems. As it is now, will the engine run properly on three cylinders if you remove the control wire for one injector?
 
http://www.clarks-garage.com/pdf-manual/fuel-07.pdf

Thats a printable version as the site uses frames making direct linking impossible. Go to www.clarks-garage.com and select the 'Garage Shop Manual' link on the left.
 
I appreciate what you're saying, and I have heard of FPR problems before, but I feel it's too much of a coincidence that this has occurred IMMEDIATELY after DME relay issues. I'm going to remake the earth first and check the rest of the wiring before exploring further.
 
My first thought from your description of the fault you have would have been air leak on the inlet manifold side of the barn-door, but agree if you have just fiddled with something, it would be more likely to be related. Before remaking it, to prove the point, I would but a "jumper earth" across it to prove the point. I must admit... on the early dash cars, I always loath going into the fusebox... 9 times out of 10 my experience is you fix the problem you had, but something else will stop working as a result, but you might not notice it for a while. In other words, it could well be another ignition related connector on the fusebox which has now been disturbed.
 
Thanks guys. I think I've eliminated the DME relay as the cause-with the relay bypassed, the car is still running just as badly. I don't have the facilities to pressure test the FPR and I can't take it anywhere because (typically) the MOT expires on Friday!
Any other ideas as to how I can narrow the fault down other than throwing new parts at it? (Can't afford to do that at the moment.)
Thanks for your advice.
 

ORIGINAL: jwindwood

Guys

1985 square dash 944. One day last week, it wouldn't start-no fuel pump noise so I immediately suspected DME relay. Took it out, put in my (Untested) spare-still nothing.

Made up jumper wire, fuel pump ran fine, started normally. Resoldered both relays with no improvement. Bought a new relay (Genuine)-still no fuel pump.

Looked closer at the relay board with a view to wiring tests and realised that the earth terminal was missing from the relay holder (Terminal 86, IIRC). Took the fuse panel out and the connector had pushed through the back. Refitted it, fitted relay and the car started fine. Tested the other two relays and again, all started fine but now a new problem....

Car starts and idles fine, but as soon as I give it throttle it becomes lumpy and almost backfires. It is drivable, but not easily-coughing and spluttering at times.

Question-could this be caused by a poor earth to the DME relay? I noticed whilst I was refitting the connector that the wire has been cut and respliced poorly in the past and the terminals are looking past their best. I'm going to replace it anyway, but I'm interested to know if my car is displaying typical symptoms of this problem, or whether it's likely to be something else?

It seems a major coincidence that I have never had any running problems before this occurred.

Thanks for any advice!
Click to expand...


I'm with you on this I think if you go back to the fuse box you will find that you have disturbed something that is causing the problem. When you say the earth terminal was missing and you pushed it back, did you mean the copper/brass terminal in the fuse box. If so have you checked that you have'nt cracked it causing it to give a higher resistance and therefore not letting the system run at full efficiency.
 
No-I have actually removed the damaged wire and terminal and completely replaced it, with new connectors at both ends. I'm sure it's not that. Besides which, bypassing the DME removes the need for the earth, so it would run normally with the bypass if that was the issue.
 
And it's solved! [:)]

A guy on the Tipec forum asked how old the plugs, cap and rotor were. Cap and rotor about 2 years, plugs 8 months. BUT I had a spare set of NGK plugs sitting on the shelf so thought I had nothing to lose by swapping them-problem solved!!
These were quality Bosch plugs, nothing visually wrong with them, but clearly faulty.

Seriously happy ! [:D]
 
PLUGS!!!!!! Doh !!!!!!![:(][:(][:(][:(][:(]

Sometimes it's the simple things that do the damage.

Glad you've got it going and sorry we couldn't help more.
 
Electronic ignition systems give huge voltages because of their efficiency, and it is not uncommon for the plug gap, which it is universally agreed, to erode at the rate of 0.001" per thousand miles, and the ignition system can cope with gaps of over 0.040" which is 0.012 over spec, then suddenly the spark will not jump the gap consistantly or indeed at regular intervals, and now that you mention it I had it on my golf gti. Got it in one morning, " cough bang splutter when trying to start, and then evntually effecting the running as well so just out of interest check the gaps on those plugs I think and hope you wil find they have a gap of over a millimeter (0.040") which will help explain why the plugs failed.
 
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