the_supernerd

I have a 1998 S10 with a 4.3 that has a problem accelerating. It basically has no power and will sometimes start to surge, and it is difficult to get it above 25 miles per hour. I could not figure out what is wrong with it so I took it to the mechanic and he also cannot figure it out. According to the computer, the right bank is running rich. Here is what has been done to it by me, the guy I got it from, or my mechanic:

New fuel pump with about 15k on it
New fuel filter
New MFI conversion fuel injection spider (all 6 injectors with regulator)
Fuel pressure tests fine
Valve springs tested good
Power balance test good
Vacuum test good
Unplugged O2 sensor with no effect
Cleaned MAF and throttle body
TPS, MAF, MAP, and temp sensors test good
No CEL codes
Exhaust backpressure tested good

Does anyone have any ideas on what could be causing the problem? Any guess would be fine as I am out of ideas and my mechanic is also getting fairly stumped.

the_supernerd

I went to do a compression test and discovered coolant in one of the cylinders, but the compression tested good. Could a bad head gasket somehow leak coolant but still seal enough to create good compression? Maybe a cracked head?

Thelast83inNJ

These things are very sensitive to fuel pressure, they like their 65psi and not less. What do you have? I've had crank sensors go wacky making the engine ping,the tacometer go nuts,and lay down like fuel pressure low.

the_supernerd

The fuel pressure was at the bottom of the spec, so I replaced all the fuel injectors and regulator with an MFI conversion kit. I then took it to the mechanic and he said the fuel pressure was really good. I have never heard the engine ping and the tach seems to work fine. If I remember right, I asked the mechanic about the crank sensor and he said it was fine. I am starting to think it is an intake manifold gasket or a cracked intake, or possibly a cracked head, leaking into the #6 cylinder. I will have to start taking it apart to be sure.

the_supernerd

If anyone is wondering, the problem has been solved.

I took it apart and it was not the intake manifold, so I sold it. The new owner discovered both heads were cracked and replaced them, but the problem was still there. He eventually took it to a mechanic and he discovered the triple-wall Y pipe had collapsed and clogged the exhaust system before the location where the backpressure test was preformed. This had built up enough heat to crack both the heads and enough heat was transferred through the exhaust system to melt the cat and ruin the muffler.