Recently bought this truck and I'm new to Rovers but I have turned a lot of Jeep and Chev wrench. This has me stumped. Idles good and smooth with a slight surge and will rev without load fine. As soon as I think I figured it out and test drive it will putter out of the driveway but as soon as I try to throttle up to speed it falls on its face and backfires into the exhaust. Since I have been working on it and test driving it seems the problem is getting worse. When I bought it I had it delivered to town then drove it the 20 miles home. It was not running good but it was dark so I didn't realize how slow I was going until my wife asked me why I was going 30mph all the way (the speedo said 50-55). Anyhow, on my most recent test drive it wouldn't have made it half that distance.

Cleaned/replaced: MAF - before I cleaned the old one it would die when I unplugged, after I cleaned the old one it doesn't seem to matter if its plugged in or not, runs the same. Replaced the MAF - No change. New fuel filter, new cap and rotor, pulled and checked the plugs, they look good, cleaned the stepper valve, fuel pressure stays at a steady 33psi under load, timed, and rechecked and rechecked. I rotated all the plug wires one hole each way, when they are not in the proper position it won't even start. PO replaced the vacuum advance just before I bought it and the ignition module as replaced with the Chevy HEI style and is mounted next to the coil. PO said it has run that way for a while. Any suggestions please.

 

Would you cat or exhaust be blocked?
Check pre cat and cat temperature. I have seen up to 380Cª!!!

check air filter.
how does it fire.. backfiring sounds it might only run on 6 and half cylinders

 

I checked both cats but neither had the telltale rattle, I'm thinking about replacing both with pipe anyway. Air filter is new. I discovered the fuel pump was on its way out so I replaced it, mostly fixed the problem. After driving it to work a couple days (22 miles) I discovered it seems to now start running badly (mostly stalling) at mile 21 or so depending on the weather that day. It reminds me of a coil slowly dying, I bought a new coil and will give it a try. Thanks for the help.

 

Replaced the coil, didn't help. It runs good for about 20 minutes or so then sputters and dies. If I let it sit for about 10 minutes it will start right up and run good for about 5 minutes or so. Finished the front axle rebuild yesterday and took it for a test drive, about 20 minutes in it sputtered and died. Let it sit for a few minutes and it fired right up and ran good to within about 50 feet of my driveway where it again died. I coasted into my driveway and let it sit, now it will not start. It seems to be something that starts acting up when it gets hot, that has now quit altogether, any suggestions. Thanks

 

massage all the coil/plug wires, try the old "get an IACV from an 89 chevy astro and swap it in" trick, check for vacuum leaks, etc.

A while ago I had a neat trick where if you stalled the car it wouldn't restart unless you popped the hood and fiddled with the plug wires

 

quitting when hot sounds like a coil or the ignition module (amplifier)...may be worth a second look at those two

 

Coil is a new MSD. Someone converted to a GM 4 pin HEI ignition module which may be the problem. It's mounted next to the coil on an aluminum piece. I read somewhere that it should have some kind of heat transfer compound between it and the mount or it will over heat and die. I'm going to try that this morning when I get home, we'll see what happens. If I can figure out how the rewire/modify was done I may attempt to reverse it and go back to stock setup. Thanks for the help.

 

fyi...the stock mounting for the stock ign amp was on that aluminum bracket by the coil...earlier models had it mounted to the distributor....where the heat destroyed it

 

 

Would you cat or exhaust be blocked?