Sudden "missing"

[billus99]

took my 944 S2 cab for run last weekend, suddenly had bad case of "missing" on the A34 dual carriageway at speed. Solved itself after about 20 secs, but came back about half an hour later, again for only 15-20 secs whilst trying to turn round, at slow speed. Fine after that, got me home the 30 odd miles with no issues at all.
Felt like "loose wire syndrome", or even immediate fuel starvation, but what could it be?
Any ideas?
Andy

 

[Frenchy]

DME Relay on the way out would cause the symptoms you describe, keep us posted.
Cheers Jim.

 

[pauljmcnulty]

Or fuel pressure regulator? Getting more common that DME relay now, as most relays are replaced with new.

 

[scam75]

AFM or connections to the AFM could do it. Mine done this a while back, eventually started dying on throttle but would idle if you lifted off. It would then clear itself magically and be alright for miles and miles!

It was a bad connection to the AFM causing it.

Stuart

 

[billus99]

thanks guys. its due for service shortly, so might get mr promax to have a look... bl00dy cold out there! lol

 

[Vic Rattlehead]

My frst S had a sill replace on the nearside years ago. After that it would intermittently miss and kangeroo violently. Couldn't figure out what was causing it until one day I was having a root around under the floor board where the DME is located. Turns out it wasn't attached to it's metal frame, which in turn wasn't attached to the car.

Less obvious then all the other solutions, but if all those fail it might be worth a look.

 

[Fat Albert]

Mine misses on full throttle/under load when it is damp or has been left a few days in damp conditions, clears up once it is warm, I am assuming that this is just old ignition leads rather than anything more sinister?

 

[billus99]

Problem has reappeared only two times in last 2 months, however this morning it left me "abandoned" on hard shoulder of A5 for a few minutes, in the fog - started fine afterwards though.
So, have ordered DME as first pass, to see if that solves it. Trouble is, its so intermittent I might have to wait another 500 miles!

 

[George Elliott]

Andy,
i have nothing to add as the comments above are good ones, I have seen all except the fuel pressure suggestion, (which will develop next week now i have said that [8|]) and I have found Promax helpful in the past.

What I would add ref the AFM is that for a car which see's occasional use, you can "exercise" the voltage wiper in the AFM and perhaps overcome any minutely corroded surfaces which can confuse the voltage signal coming back to the ECU.

What I have done in the past is run the car in second gear on a quiet road and operate the engine so that the air flow into the AFM/engine varies from nothing (tickover) up to high flow (say 5000 revs) and back down again. You may think this could be done parked in the carpark, but it cant. The reason is to do with engine load as I am sure you will appreciate.

Hope this helps
Good luck
George

If the problem occurs at 9000rpm dont worry they all do that, its the rev limiter[]

 

[billus99]

thanks all again - new DME fitted now, so need to wait and see....

 

[billus99]

hmmm...
new DME in yesterday - was one incident during the day that it didn't seem to want to start, but then all was fine.
However, this morning, wouldn't start at all, put old one back in and was fine - guess I've got a dodgy "new" DME, too...

 

[billus99]

bought a new DME Relay from OPC Silverstone, the "993" part no - latest updates etc. so far so good...
need more miles on tomorrow!