About two years ago i started having a Misfire code, P0304 - Cylinder 4 Misfire, under heavy acceleration. The problem occured mostly going uphill and when i would punch it from approximately 2000 rpm to about 3000 rpm. What would happen was it would start stumbling heavily and lose power significantly.
The first thing i started with was the cheapest....plugs, wires, cleaned MAF sensor. Still no change. Inspected cap and rotor and all checked out fine. I assumed i was having an injector problem and put off the costly repair for a while. Meanwhile the car would run fine going on the freeway, just had the uphill power problem.
After running a scan at my local mechanic, we found out that four of the injectors on the original assembly were bad. The poppets were stuck open and just pouring fuel. So i went ahead and replaced the injectors with the newer MPFI spider assembly from ACDelco. After reassembly and started the truck again it started misfiring under normal idle.
After running a compression check on all cylinders, two were dead. The compression on the two dead cylinders came in at 60 psi. After performing a wet compression test, squirting oil in the cylinder to see if the compression would increase, this ruled out a cylinder or piston ring problem as the compression barely changed. So the problem is in the head.
After pulling the head we find that two of the valve seats were leaking causing the loss in compression.....Took the heads to a machine shop for a complete valve job. Reassembled with new gaskets and the new spider assembly and it's running like new now.
Just thought i would share this with anybody that might be experiencing a similar problem. My ride is a 1999 Chevy Tahoe LT 4WD with approximately 140,000 miles.
The first thing i started with was the cheapest....plugs, wires, cleaned MAF sensor. Still no change. Inspected cap and rotor and all checked out fine. I assumed i was having an injector problem and put off the costly repair for a while. Meanwhile the car would run fine going on the freeway, just had the uphill power problem.
After running a scan at my local mechanic, we found out that four of the injectors on the original assembly were bad. The poppets were stuck open and just pouring fuel. So i went ahead and replaced the injectors with the newer MPFI spider assembly from ACDelco. After reassembly and started the truck again it started misfiring under normal idle.
After running a compression check on all cylinders, two were dead. The compression on the two dead cylinders came in at 60 psi. After performing a wet compression test, squirting oil in the cylinder to see if the compression would increase, this ruled out a cylinder or piston ring problem as the compression barely changed. So the problem is in the head.
After pulling the head we find that two of the valve seats were leaking causing the loss in compression.....Took the heads to a machine shop for a complete valve job. Reassembled with new gaskets and the new spider assembly and it's running like new now.
Just thought i would share this with anybody that might be experiencing a similar problem. My ride is a 1999 Chevy Tahoe LT 4WD with approximately 140,000 miles.
