Engine misfire

quite suddenly the engine started to misfire, wont start like the timing is way off. new plugs, wires, cap, rotor installed with no change. 2001 4.3 L v 6 engine

Did you confirm proper operation of the fuel injectors? A mechanic’s stethoscope or a long screwdriver cupped to the ear is the common action to check for ticking at each of the injectors.

Did you check for spark and fuel

Most common problem on this engine is where they put the crank sensor. If you have an intake leak, which a majority of 4.3’s do, it inevitably soaks that sensor and wiring. I have seen a lot of starters broken over this problem as well. Let’s hope that doesn’t happen to yours. by the way, crank sensor located where timing cover meets oil pan. Up front underneath.

I have not, just started working on it, the kids car so if it was a developing problem he was oblivious to any changes in operation, just get in and go. Intake leak would be fuel, oil or air?

Coolant or oil. Or both. GM used plastic framed gaskets for the intake manifold, which deteriorates and no longer holds the sealing part which results in a coolant leak. Of course through the years, I have seen oil in coolant, coolant in oil, and external leaking of both fluids. Just kinda depends on where the gasket gives up on this engine.

OK, the sensor reads 56 ohms, think it’s bad?

Don’t know about resistance specs on that. We always test them with a lab scope. Do know that the majority of GM trucks of that vintage with the 4.3/5.7 with the symptoms you describe are fixed with crank sensor/and or pigtail. Look the connector over real good including the wiring. Is it oil/coolant soaked?

Some oil not a lot. Got a new one am installing it now.

Have you even checked for fuel yet? While a crank sensor problem might be common on this engine, there are plenty of other things that will keep it from starting.

Well that sucks, not it. engine turns over then clunk, like one cylinder is stopping it. guess compression check is in order.

Not hat it doesn’t start but when it does it kicks like the timing is off. new fuel pump last year

Pull the plugs. Maybe you have a blown head gasket and it’s hydrolocking.

I think that is next test

Is Pete still there? I’m wondering if high compression (180 psi, #4 hole) on a cold engine would be an indicator of perhaps a valve malfunction.

A 180 PSI compression is perfectly normal, hot or cold. It does not change a noticeable amount anyway.

Have you scanned the truck for codes before starting the parts replacement process?

Yes, shows no codes. I say unusual high for the 170,000 miles on it.

I should qualify the last, it showed no code after I took the battery out to charge it after goofing around with the plugs, wires, cap and rotor hoping that would miraculously fix it. It did idle like crap when the tow truck dropped it off, but it sounded so bad I shut it off, then changed plugs, ect., after that wouldn’t run at all. The new plugs were fairly wet with fuel, kind of expected that

You should be happy that it’s at 180 for that mileage. That’s good. One of my son’s cars (Camaro 3.8) still carries 190 on all cylinders and that’s with over 250k miles on it. My old Lincoln had right at 250k miles when it got wrecked and a compression test at the 240k miles mark showed 190 on all cylinders on that one also.
Good compression at high miles is not rare if the engine has not been abused in some way.

Since it’s running poorly and the plugs are fuel soaked this could be due to one of several things.
The first thing I would look at would be the fuel pressure regulator. If the diaphragm is ruptured the intake will suck in raw gasoline and cause the engine to run like garbage.
If the regulator is good then I would listen (with a stethoscope or long handled screwdriver to serve as one) to the fuel injectors and make sure they’re clicking as the engine is cranked over or running. (Just wondering here if there is an electronic glitch which is causing the injectors to stay open all of the time. Rare, but I have seen this happen.)

Alright, thanks, I’ll look there next. Guess I’m still thinking of the old '73 chevy pu with last time I checked 10 years or so ago had 90 psi or the old '68 390 ford with 110 psi. Got to update my knowledge base with the quality of newer engines.