spark cutting out

[zguy360]

So it is a bum day for my megasquirt. I've been chasing low volage problems for two weeks and I finally sorted them all out. The car ran great for two days, now back to running like garbage.

280zx turbo, optical dizzy, HEI coil
MSII, V3 board, v2.3 firmware

I have been using the MS to directly drive the hei coil, but seem to be having problems now. When everything gets good and warmed up, the car won't drive above 3000rpm. When trying to rev above that, ignition cuts out, the tach jumps around like it is on crack, and massive backfires. The tach on megatune seems to be reading pretty accurate and stays steady and smooth. The tach in the car drops to zero for a second, bounces up to 4000 and back to zero. When the engine drops below 3000 again, things resume to working normally. I've tried reflashing the ecu and had the same luck.

Question 1) if the tach in megatune is reading normally and smooth, does this mean that the distibutor is not causing this problem?

Question 2) Does this sound like a problem in the megasquirt itself, or in the car?

thanks for all of your help. this forum is great.
-jeremy-

[zguy360]

Anyone?

[Bernard Fife]

if the tach in megatune is reading normally and smooth, does this mean that the distibutor is not causing this problem?

zguy360,

It likely means the distributor isn't a problem for MegaSquirt.

Does this sound like a problem in the megasquirt itself, or in the car?

Hard to say. It could be the harness, it could be something to do with the coil, or it could be something to do with the VB921 itself. If you haven't already, I'd wash the PCB in acetone or 99% isopropyl alcohol, I'd inspect the VB921 for any signs of damage, and I'd look very carefully at the DB37 connector on both MegaSquirt and the harness.

Lance.

[woh]

Not sure what it is, but it sounds like a bad coil. Assuming it worked initially.

Feel the coil and see if it is very hot? (almost too hot to touch) Or try another coil.

Do you have access to a scope?