After a bunch of time and $$$, I'm at a loss. I've got a 4.2L, 97 F-150, 5-speed with 187k miles. The intake manifold gasket breached, pulling coolant into cylinder #1 and bent the rod. Pulled the engine and did a complete re-ring kit / had the heads resurfaced, valve job, new timing gear and chain - basically tore it down and rebuilt it. It idles a bit rough, but quickly smoothes out. But when driving it is quite rough with poor acceleration. Occassionally, I used to get (and still do every once in a while) DTC codes for running too lean (both banks) and an occassional Cyl-3 misfire. I've already replaced the coil-pack, wires, plugs, MAF sensor. I've checked for vacuum leaks on the intake and all is good. Tested the EGR and the valve works well. I can disconnect the battery for 15 min and the engine will run better, but give it a 10-15 minute drive and it goes right back to running rough with power loss.

I've tried running injector cleaners through it without success. Interesting enough, when the DTC codes appear, the engine actually has better power (still rough) than it does when the DTCs aren't there. Also, I have the exhaust system where the tailpipe is in front of the rear wheel. It appears to be running real rich due to discoloration of the tire lettering in comparison to the other tires.

Any help (other than a gallon of gas and a match) would be a GREAT help!! I'd like to keep the truck for a while. It's still driveable, but with all of the work that's gone into it, it should run a lot better than it does! Many thanks!!!

 

Since the engine was rebuilt, it sounds like something was not put together properly, the valves may not be seating properly or something like that. I would suggest a compression test. they should be around 120 psi and equal. If not equal the book gives a equation to do to figure out if there is a issue. But again you just rebuilt it so it should be excellent if not then there is a problem.

Lance

 

Thanks - I'll check it tonight. I would assume the problem would be around Cylinder 3 since that's always the DTC that comes up. It idles very smooth and quiet once all codes are reset - it only gets rough (and not extremely bad, just "not right") when the engine is under load. It's particularly so at the low RPM of each gear. Once the RPM is in the mid to high range of each gear - it's pretty smooth, but still no power to speak of.

 

Every time you reset the cpu the cpmputer goes to a default setting and after you do the drivability test, the CPU sets it self up to what the sensors are telling it to do. Does that make sense. deffanitly do the compression test though to rule out the valves and piston problem. If you do have low compression in a cylinder then spary a little oil into the low cylinder, then compression test that cylinder if the compression goes up then it is a ring problem, if the compression stays the same then it is a valve problem.

You did not mention it but did the heads get redone when you had all the work done?

Lance