Talk Morgan Forums Morgan Sports Cars Classic Morgans (pre-CX) Severe misfiring on 3.7 V6 Roadster

On a GEG holiday three weeks ago whilst leading our group a strange misfire occurred. The engine idled and accelerated normally but dribbling along or blipping the engine in neutral with very light (FBW) throttle openings a severe misfire resulted actually sounding like a V twin at some points and making progress through villages a misery with violent snatching on transmission. As a consequence we reached our destination some 15 miles away quickly . After letting car cool down we checked all visible connectors and then wiggled (technical term) all fuses and relays in electrics box.

Engine started and then ran fine for rest of holiday but fault occured again last week some 1000 miles later during very light throttle openings in a village. Again no management lights showing. This time I was able to pull over immediately and went through the same routine although with a hot engine. Given I was on another holiday and 200 miles from home I didn't want to investigate further once I found the wiggling of components and restart again cured the issue, with no further problems on return home yesterday.

I'm now going to be looking deeper though, as a start replacing the ECU/PCM relay, re-seating all fuses etc. Will also check FBW throttle connector if I can access. I'm almost certain this is an electrical/electronic issue although not involving fuel system or its relay since anything above light throttle has the engine pulling smoothly including full throttle. It may be the temporary cure is simply the restart (PCM reboot) itself but clearly something is triggering this very intermittent behaviour.

I would appreciate comments from any other 3.7 Roadster owner especially if they have had similar.

Could it be a temporary sticking idle control valve. Shut at idle, wife open when accelerating hard, but when lighter rev, doesn't move? Not even sure this even cause the symptoms, just a bit of musing.

Did water play a role, Richard? E.g. A car wash shortly before?
I had these symptoms after washing the car, the OBD showed the injectors not making contact because the plugs were wet. In the meantime, I have had a cover for the injectors for a few months and everything was fine. But just today I had the same symptoms as you after a car wash. The difference is that this time the injectors were not displayed in the OBD. But the air temperature sensor in the MAF sensor was indicated as faulty, it is also an area that gets wet when washing the car. I disconnected the plug from the MAF sensor and blew it dry. The car drives normally again and no error was displayed in the OBD, I read and delete morer times. I think that after nine years the rubber gaskets in the connectors don't seal as well and the material is not as soft. I don't have a 3.7, but a 2014 4/4, the causes of the engine misfires could be similar. But...it could be anything as a reason, from the accelerator pedal via the electric throttle to the coil pack....I would start with the MAF sensor or its plug.

Thanks for suggestion Leroy but the Cyclone engine in my car has an electronically operated (FBW) throttle so no need for an IACV. Idle never fluctuated from 750 rpm norm once warm anyway.

As an aside I have swapped ECU relay for a spare and checked and reseated all engine fuses. I also put in my Bluetooth OBD2 adapter and used the Torque app on my phone to check for stored fault codes - none found. I did notice whilst ignition on but not engine that the throttle position display was set at approx 17%. I'm guessing this is a cold start position. Pushing pedal moved it through the range on dial display and you could hear the actual stepper motor operating which seems normal.

Frustrating thing is I now need to drive for maybe a couple of thousand miles to prove I've fixed issue (or it's fixed itself )

Thanks for your suggestion too Heinz but engine and general conditions were dry. On each occasion it happened car had run fine for 20 miles or more. Have checked MAF sensor plug and have cleaned it in the past but it was spotless.

I've tried the wife open when accelerating mode but find I tire easily

Hi Richard, just as an aside, if it turns out it is related in any way to the coil packs. I have two brand new Hella coil packs you can have, they are a left over from my touring spares for our ex 2016 3.7 Roadster.
Dave

PM sent Dave.

How are your plug leads? I had a misfire in an Escort XR3i that was solved by new leads. Engine started ok and ran up to 2000rpm. Any more and it misfired badly. The new set of standard leads worked immediately. The suspect ones looked ok but clearly failing in use. Can you try a swop with another set? The misfire started intermittently but progressed to all the time.

Richard, may be a long shot but may be worth cleaning your MAF sensor as you run one of those fancy 'oily' air filters don't you ?