2004 Suburban 1500, 5.3L Flex Fuel Engine. 196K miles. Code 0300 and 0305. Verified spark, fuel, and compression at idle of 160PSI. Leak down test in #5 cylinder is less than 5%.
#5 cylinder holding 35 PSI at open throttle I believe suggests a lower engine internal failure consisting of either rounded cam lobe or faulty or sticky push rod. Planning to replace the engine with a long block unless the Forum has other suggestions. Am I missing something? Any experience with re manufactured engine company's is also appreciated. Thanks to the Forum!

 

So #5 has very low compression and OK leak down. Not sure how that happens.

I assumed that the 160 psi was on the other 7 cylinders w/ TB held wide open and all plugs removed. At idle confused me.

 

Yes, all cylinders tested between 155 PSI and 160 PSI. Leak down test was performed with #5 at TDC fully seating both valves. The fact that it resulted in less than 5% leakage suggested to me that the valves were seating well and held pressure. Re-installing the compression gauge and performing an engine running compression check and opening the throttle resulted in the drastic reduction in compression. My belief is that either the push rod is sticking a cam lobe is rounded. Either way, I surmised it is a lower engine failure (cam or push rod) and a worthy candidate for replacement.

 

Never heard of running a compression check w/ the engine running so not sure what your results mean.

 

That's funny since I never did either until last week when I was advised to do so. Apparently it's used to narrow compression failures between the heads and below. Seemed logical and the fault is consistent.

 

Let us know what you find when you tear it down.

 

I doubt I will open it up. Planning on replacing with a re-manufactured long block from one of the large national re-builders.


QUOTE=73shark;335929]Let us know what you find when you tear it down.[/QUOTE]