Random Misfire w/ MS1 Extra and Wasted Spark M20 engine

[Chuckcruzin1986]

Going crazy troubleshooing my E30 m20 since installing MS.

One coil pack does not fire so the engine runs on 4 cylinders at times.

The problem doesn't appear specific to an engine speed, temperature or load. AFR's are fine (13-14) . Will misfire at idle, part throttle and full throttle.

1. The pack that stops firing is always the same one AND we replaced it and the same problem and location continues to missfire at times. I can pull the plug wires and touch the output terminal and it is dead.

2. To fix the problem, I remove a plug wire from the "good" pack and when it shorts to it's main housing, the bad coil starts firing and the engine will run perfectly (something for 5 minutes, sometimes for an hour).

3. If it is idling without miss and I burn the changes to MS, all cylinders will stop firing for a split second then it will sometimes resume firing normally and sometimes continue firing but with a miss on one or more cylinders.
Doing #2 will ALWAYS fix the miss.


Details on my MS:

V3.0 board, MS1 chip running MS1 extra code, using DIY's 55 pin adapter and a Glen's garage accessory board w/ 3 vb921's running spark to the 3 GM coils from at 3.8 V6.

Any suggestions on what to check would be appreciated.

Thanks!
Chuck

PS Nobody believes me when I tell them the symptoms (I have explained the best that I can)

[nando]

try replacing the VB921s with BIP373s. most likely the VB921 that's running your "bad" coil is dying.

[Chuckcruzin1986]

try replacing the VB921s with BIP373s. most likely the VB921 that's running your "bad" coil is dying.

My friend who has been working on this problem said this:

Per the advice here and other places, we replaced the VB921s with BIP373s.

The engine will run, but the misfire is now almost constant and one of the LEDs (the middle one - D15) is not behaving like the other two. The D14 and D16 are off when the car is keyed on but not running and flicker on briefly when the car is running. D15 is on when the car is keyed on and seems to glow brighter when the car is running and flicker off intermittently. It almost seemed like D15 is somehow acting as if I didn't have spark set to "Inverted". So I tried setting spark inverted to "NO" briefly. All LEDs stayed on when car was keyed on, but not running. Next I set spark inverted back to "YES" and reduced the running dwell from 3.0ms to 1.5ms. That seemed to help a little with how it runs but didn't change the fact that the D15 LED behaves differently. The BIP373s got very hot during all of this, with the one connected to R27 being the hottest and I assume heating the others up (they share a heat sink).

I pulled everything out of the car and looked for any short in the D15/R27/Coil 3 circuit I could find, but didn't find anything obvious.

So, what would cause one of the LEDs to stay on all of the time, while the other two seem to behave properly?

Thanks in advance!

Josh

Any ideas our there?

Thanks,
Chuck

[nando]

I can't remember exactly but I think BIP373s require the insulator peice under the transistor between the heatsink. did you have those? that would essentially cause a short. BIP373s are self protecting so you shouldn't be overheating, but the output will shut down if it trips the internal protection.

[whodwho]

Inspect the transistor near the LED with a jewelers loop/magnifying glass, I find those to be solder bridged often.

[Chuckcruzin1986]

Will this cause a miss fire?

Inspect the transistor near the LED with a jewelers loop/magnifying glass, I find those to be solder bridged often.

If a bad joint, would this cause a miss fire?

Thanks,
Chuck

[whodwho]

I have seen it keep the LED on and that circuit is what your triggering the WS drivers off of.

[Chuckcruzin1986]

Problem Solved!

Josh resoldered all of the connections and now the car runs perfect.

Thanks for everyone's help

Chuck