bad miss as car (or MS unit) warms up

Jamesl · Post by **Jamesl** » Fri Mar 24, 2006 7:18 pm

I'm having issues with my year-old MSnS-Extra install (v2.2 board with an ancient version of megatune).

The car seems to run fine for the first few minutes, say 3 or 4, but then starts to miss, with the miss getting worse the warmer the car gets.

It's an apparently random miss on all four cylinders. Watching the AFR, you can see it jumping lean -- I'm assuming that's actually the result of unburned gasoline passing thru.

I have replaced the injectors and I have listened to each one with a stethoscope and can hear them clicking away just fine.

Putting a timing light on the individual plug wires, you can see the steady blink, pause, steady blink, pause, etc, on all the plugs as the individual cylinders fail to fire.

I've replaced the plugs, distributor cap and rotor. The plug wires all check out within spec. I swapped in a spare coil and ignitor, but that didn't change anything. I haven't replaced the distributor itself, but can't see how it's the problem.

At this point I'm pretty sure it must be a problem with the MegaSquirt unit. Perhaps I've got some sort of bad connection either inside the case or in the leads running to the unit.

Any clue what might cause this behaviour, and what circuits to troubleshoot within MS?

Jamesl · Post by **Jamesl** » Sat Mar 25, 2006 11:28 am

Lance:
Thanks for the tips. I haven't checked MS on the stim in awhile, so will do that. I've done some datalogs and it's not resetting.

How do you log for power? I don't see that as an option.

Jamesl · Post by **Jamesl** » Sat Mar 25, 2006 3:36 pm

Thanks for the info. That worked. I found the appropriate line in the msns-e ini file and the datalog now displays voltage.

Car's apart right now, but once I get it running again I will monitor voltage to see if there's any variation.

Jamesl · Post by **Jamesl** » Sat Mar 25, 2006 6:10 pm

I think I've discovered the problem. I went thru my harness connector wiggling wires, and four came off in my hand -- including the main lead that carries the ignition signal from MS to the car.

I went back thru and desoldered then resoldered all the harness connector leads, and now the car seems to be running fine...

The harness connector is over a year old and I guess that year in the trunk of my car had taken its toll.

By the way, I took a datalogging run and battery voltage averaged around 13.5 -- and ranged from 12.8 to 14.2