Missfire on low revs

[Paul (93 Chim)]

I have developed a missfire that disappears at around 3000rpm in all gears.I have conected a fault code reader which dosen't pick-up any faults
I have changed the plugs, leads, coil, extenders, dizzy cap, rotor arm and air filter.
I also have a new fuel filter to fit over the next few days.

Any thoughts/help would be most helpful.

Thanks

Paul.

[chassis 33]

It disappearing at around 3000rpm suggests it could be a lambda sensor down, however the fault reader should of picked up on that.

There have been a couple of topics on similar misfires in the past, I'll try and dig out some links.

Regards
Iain

[paul (93 chim)]

Cheers for that, can I check out the Lambda with a multi meter?

[dadamsv8]

check you have the correct extenders i recently fitted the wrong extenders with built in resistors that caused miss-fire.

[prtvr]

How about an air leak on on the induction system after the AFM, this would lead to lean mixture
at low revs but would not be as noticeable at a higher flow rate.
IIRC you can spray carb cleaner to check for leaks but only spray it after the air flow meter
and around the stepper motor(avoiding the exhaust and anything that sparks) and check for the revs increasing.

Phil
but first might be a good idea, just to check all the hoses are tight and no splits.

[chassis 33]

yes you can, you can download the whole hotwire checking sheets from www.rangie.com/articles_topic.php?id=167&cat=7&subCat=51 as jpegs

The lambda test is number 27, although it may be worth working through everything, you need to take the back off the ECU plug which is done by removing the plug, prising out the seal and undoing the two screws, the backing then pulls back.

Regards
Iain

[Paul (93 Chim)]

Cheers Iain,

I'll have a play at the weekend and let you know how I get on.

Paul.

[Paul (93 Chim)]

Thanks for your input it's been very helpful, especially chassis33. I've been away working and have only just had a chance to have a good look at the problem.
I've had an intermittent misfire for a while but it turned into a constant misfire on one cylinder (NO. 7).
The code reader couldn't pick up any faults, anyway I set-to and followed a basic fault finding system, eventually a problem became apparent with the left bank of fuel injectors.
I measured the resistance for each injector (Approx 16.9 ohms) and found one to not give a reading, I replaced the injector and she is back to normal.
It's interesting that the code reader didn't pick any faults up.

Regards,

Paul