Misfire problem
Turbo Mini Forums

The mini has developed a (seemingly) erratic misfire.

I'm running a 998 engine, T2 turbo
I have megasquirt 1 extra controlling a ford fiesta coil pack directly (EDIS without the module)
Using a 36-1 wheel which is created by machining cut outs in the damper part of the belt pulley.

See build thread below for any more details on engine...

The car had a very mild and infrequent misfire at motorway cruise for a while but since it caused me no problems and I haven't had time to investigate i've left it.

Last week the car died whilst i was driving. The 2A fuse to megasquirt and the rev counter output circuit (relay and FET) blew.

I put in a 7.5A (only one I had in my car at the time) and carried on home no troubles.

Now this week the misfire has gotten much worse. It occurs all over the rev range. Sometimes I get a bang out the exhaust and a cloud of smoke. I'm guessing this is the unburned fuel/ air igniting when it touches the hot turbo?

I bought new spark plugs on the way back today, which haven't helped. I've looked over my loom to see if a wire is shorting but haven't found any problems. The HT leads all have similar resistance as do each side of the coil.

Any suggestions?

1275 N/A Sprite, 998 T2 Turbo Mayfair
1275 EFi Turbo

check all the wires first and the connections, then replace the coil pack
all the leads.

if its still there the problem may well lie with the mixture too lead under boost. check with lambda AEM GAUGE ........ i hope you have one fitted ?

Coils/coilpacks can read fine for resistance and continuity with a DVM but fail under the stress of high voltage so, as Steve says, try another one first as a simple test.

But first, have you connected the laptop and looked at anything ???

I would start with the tooth logger to check you have a good clean signal off the VR pickup (VR pots may need adjusting) and then log the actual ignition timing output when driving.

For the MegaSquirt itself, it should not have blown a 2A fuse, there are internal polyswitches (self-resetting fuses) rated lower than this. So unless it was a random failure, or a fault inside the box, my long shot would be a problem with the external sensor wiring (which is all 5V) which overloaded the internal 5V regulator and blew the 12V external fuse before the polyswitches tripped.

Logging all the relevant inputs and the ignition output timing should tell you.

Schrödinger's cat - so which one am I ???

Thank for replies chaps,
Sorry been busy so haven't had chance to reply.

I ran a log on the way to work. At misfire there would be an rpm spike up to 14700 rpm.

Teeth logged fine at standstill, just seemed to be under load it went wrong.

I moved the sensor closer but that seemed to make it worse. Pulled it away and played with the pots and all seems good now.

Thanks

1275 N/A Sprite, 998 T2 Turbo Mayfair
1275 EFi Turbo