Talk Morgan Forums Morgan Sports Cars Morgan Three Wheeler & Super 3 M3W intermittent misfire

Hello everybody - here's a puzzle for those of you with ECU experience. I have a 2012 car which when ticking over or driving at low revs misses a single beat now and then - every 30 seconds or so. The car performs perfectly well in every other way. I do not think this is an ignition hardware problem. It sounds as though the engine is about to go in to skip fire mode but just for one beat and then everything returns to normal - all very irritating and elusive! All suggestions gratefully received.

Phil

Phil, this is similar but not identical to what I experienced when my Crank Position Sensor went bad. It started as a "misfire" as you indicate, but mine was not consistent. It occurred within the first several minutes then ran fine. It then became difficult to start at times, and when it completely failed it shutoff while running and impossible to start. The sensor should output 1 volt when cranking, so you can do a quick check and see if that may be the issue. Good luck. Bob

I doubt it is an ECU problem Phil, it is usually all or nothing with that, or running very bad. You are back to checking the usual things, plugs, leads, screw plug caps are tight, fuel pressure and ProTune 2 for fault codes and Lambda sensor operation. Not experienced a CPS fault but I would expect more problems than an occasional misfire. A bottle of injector cleaner through the fuel system never hurts. If you have another M3W available you could transpose the ECU just to eliminate or confirm your suspicions? Is the misfire always on one sides cylinder? The RH cylinders often seem to run a bit "fluffy" at idle compared to the LH if you feel the exhaust.

Thanks guys, I have tried a few things such as adopting a dubious pose behind the vehicle with a hand behind each exhaust but needless to say it won't do it then! Plugs leads coil etc seem OK - maybe the injector cleaning stuff will help but this isn't typical from my experience. It has occurred in similar fashion for about 450 miles - I would expect some further deterioration. The ECU switch with the other car is next on the list. The right hand pot on car No.1 has always had the sound of an exhaust valve leaking but it never gets worse so I agree with the fluffy running on that side but this is not the same on the problem car. I'll persevere and keep you up to date.
Phil

Hi Phil
I had a momentary miss at random times.
Eventually tracked to a short in wire from rectifier. Aggravated by rectifier becoming looser with time.

Perhaps could check that system

In the early days of my 2012 I had an problem at idle speeds where the ECU was delivering two doses of petrol instead of one at low revs. Above 2000 it ran perfectly. Fault found by hooking up an oscilloscope thingy at auto electricians
ECU replaced, all was fine!

Good hunting. Lol

Hello Phil, I had something similar on a different vehicle, the loss of firing was particularly noticeable when accellerating. We discovered that the insulation on the ignition leads as broken internally when my mate got a zap from the lead while fiddling around with the throttle. New leads and all fixed. But the old leads looked ok on inspection. Just a thought....good luck! Oh, and while I am at it, do you know if anyone in Australia has had your Centa upgrade?

Had this glitch in the beginning. Found the fault in the way the spark leads were attached to the plugs. The crimps were loose just enough to cause it to misfire sporadically. I crimped the removable nipples down on the spark plugs and tweaked the leads for a firmer contact and now no problem.

Crank sensor may be

Just wondering if you got to the bottom of this misfire Phil?