Hi, I recently bought a 97 blazer 4x4 with a 4.3 that had a bad rod knock. If I would have known the dificulty of removing the engine, I probably would have rethought it. Long story short, I rebuilt the engine, replaced the sensors at the back of the engine (hard to get to), new timing chain, cap, rotor, plugs, wires and oil pump. all other external parts are original, including the intake manifold and associated parts. I now have a p0300 code that I have not been able to correct. I have cleaned out the egr, replaced the temp sensor (The one in the front), one O2 sensor(All of these were codes i was getting, even though they were showing up one at a time, fix one code, drive it and another one would show up) The truck ran a bit better with every thing I did to it, but I still have the loping engine and random backfire. It runs like it is just slightly out of time, so I have tried setting the timing one tooth forward and then one tooth back on the distributor with no success. It would not even start either time. I really want to get this thing on the road. Anyone have any ideas? Is it possible I might be a tooth off on my timing chain or could it be that injector malfunctioning? Any help will be vastly appreciated. Thanks.

Yea, thats what I will check next. I installed the chain while the motor was out of the vehicle, so I had a pretty good look at it, but that doesn't really mean I set it right. Looks like I will tear the front down and verify that it is right. Thanks.

 

Well, I finally was able to take the front of the engine apart to check my timing chain alignment. It was spot on. That's another possibility knocked off the list. Once I put everything back together, I checked the fuel pressure. It went to 55 psi with the key on and stayed at around 54-56 psi with the motor running. Another possibility knocked off. Does anyone have a clue as to why the engine shakes at idle and backfires when running? I'm running out of possibilities. All i have left is possible distributor timing gear, which looked ok with no play when I installed it and the injector system, which may be bad. The only code I'm getting is the p0300, random misfire. Am I missing anything else? Any help is appreciated. Thanks.

 

Does the fuel pressure hold with the key off?

Mike

 

Yes, it does. It stays at 55 until I release the pressure.