Thread: Trying to find a miss in 96 Discovery 3.9

Can you trace which cylinder the misfire is in by removing HT leads ?
Make sure you earth the disconnected lead, the electrics dont like open circuits too much.
If you can trace it to one cylinder, carry out a compression test. If the pressures are OK & you have plenty of spark at that cylinder, then start looking at the injector.

How many Km on the engine ?
Worn camshafts are common but generally don't knock one cylinder out completely.

Not too sure on the buzz. You have to listen where it's coming from. Engine bay, underdash.......more info req on that one.

Originally Posted by Scouse

Can you trace which cylinder the misfire is in by removing HT leads ?
Make sure you earth the disconnected lead, the electrics dont like open circuits too much.

As an aside, I think that unplugging the HT lead is not recommended for the P38A and the D2 V8 owing to the possibility of damaging the electronics. Dunno if it is OK to earth it or not. An interesting point. I think they recommend unplugging an injector connector.

Ron

Woops, I did the unplugging leads thing before I replaced them and could not make out any difference. The Buzzing is from under the bonet, posabably to the paseenger side. maybe I hurt it unplugging leads.
The engine has 195 000 km on it. Never blew any smoke other then fuel smoke, seems to be running rich but still getting same km out of tank, if not more, then they have been reportd too. Compression test might be next on the cards.

Depends on the miss of course ie. when, but have you checked & thoroughly cleaned & lightly lubed the Idle Air Control Valve?

Originally Posted by SpeedWayRover

Woops, I did the unplugging leads thing before I replaced them and could not make out any difference. The Buzzing is from under the bonet, posabably to the paseenger side. maybe I hurt it unplugging leads.
The engine has 195 000 km on it. Never blew any smoke other then fuel smoke, seems to be running rich but still getting same km out of tank, if not more, then they have been reportd too. Compression test might be next on the cards.

I had symptoms like this. For me it turned out to be the Injector O-Rings. If this is the reason for the miss, it will be sucking an audible amount of air. You can check each injector easily, by getting a small diameter piece of hose, stick one end in your ear, and move the other end around the base of each injector where it plugs into the manifold. You can easily hear the difference between one that is sealing properly, and one that is sucking air.

Cheers
Andre

the buzzing noise could be coming from the ABS pump. i had a problem with mine last year, i had to unplug it when i turned the ignition off and reconnect it when i was going for a drive. i did this for about a week and the problem fixed its self, no problem since.

I had the same problem once in the rangie, turned out to be a broke piece of plastic on the electrical coupling to an injector, it essentially made worthless the steel retaining clip so Idling it would be fine and reving whilst stationary was good but road movement was enough to break contact and cause a miss.
I tracked down the offender by looking for the rich cylinder and concentrating on that till I found it.

Thanks for all the the tips. I will be going through everything till I find the problem this weekend. Hopefully I will be able to let you know what it was by Monday.