Misfire

[GM Rules]

I have a 2001 GMC Jimmy with 144k on it. I have a small amount of misfire on all cyls, but a high amount on number 4; only on power not at idle. Here is what I have done: Compression is good, new cap,rotor, plugs, wires, all GM parts. New fuel pump, filter, and new CPI. On the scanner, the crank and cam signals look good and the cam is + or - 1, right in GM spects. I am now at a loss. I think I got a bad CPI; fuel press drops fast after the engine is shut off.
HELP

Thank you

 

[Molson02536]

I have a 2001 GMC Jimmy with 144k on it. I have a small amount of misfire on all cyls, but a high amount on number 4; only on power not at idle. Here is what I have done: Compression is good, new cap,rotor, plugs, wires, all GM parts. New fuel pump, filter, and new CPI. On the scanner, the crank and cam signals look good and the cam is + or - 1, right in GM spects. I am now at a loss. I think I got a bad CPI; fuel press drops fast after the engine is shut off.
HELP

Thank you

Fuel pressure drop fast when ignition drops and miss fire throughout all cylinders. Good chance that your fuel pressure regulator is leaking fuel in to your upper intake platinum. Replace your fuel pressure regulator which is a serviceable part from your CPI in the upper intake platinum. The other thing also that comes to mind is that the distributor gear are known to wear and can cause the timing to be off when the RPM's rises.

Start with the fuel issues first and post back.

 

[GM Rules]

fixed

The new CPI was bad, it was leaking down so fast the engine was not getting fuel it had to have. New CPI and misfire gone!