Today I ran a barrage of test still trying to solve this rough engine running problem. Pulled all plugs again, all are firing although both 1 and 2 are dirty, 3 thru 8 are all buring clean. Not sure if some indicator here. Additional, pulled oxy sensors and did back pressure test both sides, running 1-1.5psi, so I don't think a blockage problem. Did block plate test on EGR, sealing off ports, no change in engine operating so I don't feel the EGR is bad. Checked MAP Sensor checking DC voltage, input 5VDC, output 3.85VDC prior to applying vacuum, thought I finally solved the problem, replaced MAP, no change in rough engine operation. Checked Compression all cylinders, all at 140-145 (not cold), although not the best, truck has 194000 miles, so expected. No change in engine running, idles slightly rough, small surge about 100-150RPM, in drive engine runs very rough, sounds like it's missing off and on. Rechecked all fuel, pressure maintains 55 idle, slight increase under acceleration. Checked complete engine for possible vacuum leak, can't locate any possible leak and can't hear any whistling indicating a leak. Pulled Mass airflow to force service engine light to make sure it would come on, truck has had no fault codes prior to me tripping the light. I'm at a total loss here to solve further, any other help?
Tuesday, April 13th, 2010 AT 8:24 PM