Hey all,

I have a 1990 Miata with a turbo and COP setup. When I purchased the car, everything was fine but randomly started acting up.

Exactly at 3k RPM, the injectors lose pulse (I verified this by hooking up an oscilloscope to the PCM). I checked every single input related to the fuel injectors and none of them seemed to lose signal when the injectors did. I also wired a separate ground from the battery to the ground bus, and the injectors still went flat. I purchased a used PCM off of ebay and it had the same problem. The resistance of the injectors is also within spec.

I'm at a loss here and would really appreciate some input.

 

Id be more inclined to think it was your CAS. Especially considering it's like the only thing your ODB-I reports back AND you're throwing a CEL.

 

I thought the same thing, but the CAS does not lose pulse when hooked up to the oscilloscope. The spark plugs are also firing when they need to...

 

make sense since the tach isn't going crazy either. but i can hear/see that your fueling goes to complete ****.

is it all injectors or just one pairing?

 

All the injectors are causing the problem. I unplugged each one to verify as well and it does the same thing.

 

Are they hi-z or lo-z injectors?

Many years ago i had issues with flyback voltage spikes from lo-z injectors causing issues with my megasquirt. Swapped in hi-z injectors and never had a problem again.

 

I am not exactly sure, but I believe the injectors are stock.