Suburban :: 1999 - While Driving After Engine Warm-up Misfires On Cylinder 2 Under Slight Load

1999 Suburban 5.7L Vortec

Symptoms: While driving after engine warm-up the engine misfires on cylinder 2 under slight load (basically whenever maintaining speed, and slight acceleration) between 1500-3000 rpm's. Backfires through exhaust when this is happening. Misfire counts on Cyl. 2 collect rapidly and only a few on Cyl. 1 but no P0301.

History: Purchased vehicle with a blown engine (intake gasket leaked coolant into engine and was hydro-locked) with the intention of using it to pull a boat or camper but never did buy either one. Replaced the engine with a new Goodwrench engine and rebuilt the tranny figuring I would drive it till the body rusted off of it. I honestly never felt that the truck ran as strong as it should have with a brand new engine but just attributed it to being as big as a cruise ship. A couple of years later started receiving multiple codes (don't remember what they were at this time) found the distributor very corroded inside due to the ear on the distributor being broken off.

Replaced the distributor, cap,rotor,plugs and wires and fixed it. About a year later, only in the summer I would start to receive the P0302 sometimes, would not happen in the winter. Did the usual plug swap, wire swap, checked spark to rule out ignition with no change. After a while the catalytic converter failed (big surprise with a missing engine) and replaced it as well as both O2 sensors on the rear bank and one on the front bank. P0302 did not change. Last year the fuel pump failed so I replaced it. This April I took the truck on a road trip to visit relatives, about 80 miles out it started backfiring through the exhaust whenever I got over 70 mph and the CEL would flash. Finished the trip babying it the whole way but now it does this all the time when warm.

Repair attempts:
* Distributor, cap, rotor, wires, plugs. (Due to distributor failure mentioned above.)
* Fuel pump and filter. (Due to pump failure mentioned above.)
* Upgraded fuel injection spider. (Because of GM bulletin regarding misfires and multiple failures found on the internet.)
* Repeated valve and fuel system cleanings. (Grasping at straws.)
* Removed rear bank cylinder head and sent to machine shop, All checked good. (After ruling out ignition and fuel figured it had to mechanical. Compression was good, cylinder leak down test was good. The problem seems to be temperature related so thought maybe the exhaust guide was mis-manufactured too tight causing it to drag when warmed up.)
* Crank sensor with a used one from a u-pull it place, I got too much money wrapped up in this. (Found a reference to this repairing a similar problem on another vehicle.)

One final note: After replacing the fuel injection spider the truck ran extremely well, this only lasted a few days and the problem came back. After replacing the crank sensor the truck again ran extremely well, but only for 1-2 days. What is the connection between the injection spider and the cranks sensor? The only other thing that I can think of that would create a misfire on one cylinder only is the PCM but that gets misdiagnosed so much that I don't want to jump to it unless all other options have been checked out.