I was driving my 95, 5.2L at about 40 mph up a grade and suddenly lost power. It starts, but won’t idle or accelerate. At idle it surges from about 750 rpm to 1200 and will die after about 20 seconds if I don’t try to accelerate a little. I’ve checked everything I can think of:

Fuel pressure 40 and steady, no fuel leak down
plenty of gas in the tank
injectors tested and cleaned, connectors tested
Removed the plugs and tested each one for spark
intake manifold vacuum 18, can’t find any leaks
compression for each cylinder between 170 and 180
no coolant in the oil, no oil in the coolant
tested the IAC, throttle position sensor, MAP, crank position sensor, cam sensor, EGR and PCV valve
Distributor, rotor and spark plug wires are new and look good
cleaned the throttle body
it has 170,000 miles on it so I put in a new timing chain. There was a lot of slack in the old one.
power splice and wiring under fuse/relay box look good

The only odd thing I find is some black soot and a little water came out the tail pipe. The cat is only a couple years old and I had the exhaust pipe and muffler replaced a couple months ago. I was thinking of disconnecting the exhaust Y pipe from the exhaust manifolds to see if the Cat is plugged. I wouldn’t think a plugged Cat would cause a sudden loss of power, but it would gradually cause problems.

Any other ideas?

 

Power Control Module?

 

Disconnect the O2 sensor, see if anything changes. If not, physically remove it from the exhaust, and try again. (easier than dropping the Y pipe)

 

Also - check ALL vacuum lines and your plenum gasket.

I'd almost lay odds on the plenum gasket having catastrophically failed; but not being there, I can't check it.

If not, I'd SURE look for a massive vacuum leak elsewhere.

RwP

 

I took off the O2 sensor but it didn’t help. So it’s probably not a clogged Cat. Could be the PCM but I hope not.

I took off the intake manifold. The plenum gasket looks great but I’ll replace it. It looks like about 1/2 to 3/4 inch of the front crossover/end gasket is gone. The entire right side of the gasket was brittle. It’s possible that the missing was was sucked inside. I’ll look for it. My family told me I had to quit working on it tonight and tomorrow. I can’t understand why. Women!

 

That much gasket missing could easily be causing a severe enough vacuum leak that the motor can barely run ... which is what you're describing.

RwP

 

You have an OBD1 PCM. It’s plug n play. No need to get a dealer involved. Your OBD1 can also easily be analyzed, repaired, or replaced that doesn’t cost your first born. There is a variety of options. You can even unplug and replug the harness in the event you have a bad connection…the first step in the RalphP procedure for all things electrical and good advice.

BUT, you have raised other known issues that need to be chased down first and the PCM may have nothing to do with it. I just know the PCM can do squirrely things when it messes up but it is far from a death sentence if it goes bad.

 

How many miles on the engine?

 

170,000 miles on the engine.

 

How old is the timing chain? I would check the chain for slop to see if it jumped a tooth. Remove the distributor cap and mark the position of the rotor. Use soap stone or marker, NOT a pencil. (It will cause ignition shorts.) Mark the harmonic balancer at the timing tab. No rotate the engine backwards by hand. How far does he balancer move before the rotors does? If it moves almost immediately, you're good. If it moves 10, 12 or possibly more degrees, it may have jumped a tooth. It will still run but have no power.