4.0l Misfire

[chassis 33]

Hi, my Chim is missing quite badly, and idles roughly.

I changed the plugs last week, the ones that came out were more sooty than i would normally expect, the problem went but has come back again now, i've checked the air lines and they all seem to be ok (ie not split).

Any thought as to what to check next? I presume renew the HT components?

BTW, its a '95 with a serp. engine.

Regards
Iain

[Aaron C. Reskew]

Best thing to do is change the distributor cap and rotor if it has not been done in the past couple of years.
Magnecor's are well worth the expense too.
Have you access to a CO meter as it sounds like the engine is running rich.
Other things to look at are a restricted air filter,faulty coolant temp sensor,faulty AFM, faulty lambda sensors.
Clean the throttle pot for good measure.

>> Edited by Aaron C. Reskew on Tuesday 19th July 18:29

[chassis 33]

Cheers will have a tinker at the weekend.

[GreenV8S]

Various faults can make the engine run rich. It could be as simple as a coolant temp sender reading low, or an air leak in the exhaust. On the other hand it could be a more severe fault prompting the ECU to go into 'limp' mode. If there's nothing obviously wrong, you can either ask the ECU what it thinks is wrong, or go round all the sensors and wiring looking for faults on the fuel sie, and round the ignition looking for anything that would cause a weak spark.

[chassis 33]

GreenV8S said:

Various faults can make the engine run rich. It could be as simple ... an air leak in the exhaust.

Hmmm, thats interesting at the same time I changed the pugs, i took apoart and re-sealed the exhaust joint between the manifold and the main cat section on the drivers side, because it was blowing. It wasnt the best job because the pipes were about 3-4mm apart before the connector was tightened up, (i did use firegum on it), maybe that seal hasn't lasted?

From memory thats just before the lamda sensor, so if my logic serves, air is leaking into the exhaust system there the ECU is beig told the engine is running lean, hence over fueling...
Any tips on making sure that joint stays sealed?

Regards
Iain

[GreenV8S]

The lambda sensors are upstream of that joint, although it's quite possible for air to be drawn upstream far enough to reach the sensor by the exhaust pulses.

[chassis 33]

Ah ok, only had the car a fortnight and going from memory!

[chassis 33]

I've just read a few bits in the FAQ's, changed hte coolant sensor for one I had in a spare Discovery V8 manifold, also cleaned up the stepper motor (32mm socket incase anyone doesnt want to use an adjustable or a mole wrench). I'll go and get a new coolant sensor in the next few days

Initial indications (round the yard) suggest things have improved, it will now pull away in 3rd with no throttle, previously it stuggled to do the same in 1st. (Obvioulsly in real life starting in 3rd isnt a common occurance i know).

Thanks for the help,
Regards
Iain