Cylinders 1 and 2 missfiring

[Daniel Purcell]

I have a motor out of a 96 chevy 3/4 ton. 5.7 vortec. Everything is stock except I put in a 99 Tahoe computer. Cylinders 1 and 2 are missfiring. Have spark, fuel pressure is fine, and holds after turning key off. All plug wires are in correct locations. All other cylinders seem to be doing what they are supposed to. While running, I pull 1 and 2 off the distributor and no change in how it runs. Also engine ran perfect before we pulled it.

Thanks
Daniel

 

[Daniel Purcell]

So now it looks like those 2 cylinders aren't getting fuel. Would there be any wiring issues for the injectors with putting a 99 computer into a 96 wiring harness? If not then I guess next step is to pull the spider injection.

 

[df2x4]

I've never compared wiring diagrams between '96-'97 and '98+ PCMs but there are definitely differences. The '96-'97 models have five connectors while the '98+ only has four.

 

[Daniel Purcell]

I did notice that. The 5th plug is for knock sensor. Everything else is running fine. Just not getting fuel to 1 and 2 cylinders.

 

[df2x4]

The '98+ PCMs also have PassLock/VATS, so honestly I'm surprised it's running at all at this point unless you've had the PCM tuned and disabled PassLock.

I'm not sure exactly why you're trying to mix and match PCMs/wiring harnesses, but it seems to be like it would be much easier and less headache inducing to just have the '96 PCM that matches your wiring harness tuned for whatever you're trying to accomplish.

 

[Daniel Purcell]

So what happened, this is all in an 87 s10. I bought a stand alone harness from Howell efi for a 96 half ton. Motor is out of a 98 3/4 ton. Computer has been tuned, but my tuner said he needed a 98+ computer to work with his hp tuner. So I found a 99 computer. Everything works except 1 and 2 cylinders not getting fuel.

 

[Daniel Purcell]

Ok so I've got it figured out. And I misspoke. 1 and 8 were misfiring. 96 and 97 vs 98+ the number 1 and 8 injector wire pin locations are different at the computer pins. The manufacturer of my wiring harness was awesome and sent me file for both so I could look for diffenances. Thanks