94 LS 140k miles, Misfirng, Bogging Down, Backfire as engine is getting warmer. When the engine is cold it will almost never do this. Usually after it's warmed up, on accelerating the engine will misfire like crazy. It does this the most in 2nd gear, starting about 2200 rpms, all the way up. The only way to make it stop is to let off on the throttle to about a eighth of the way down, then it will quit misfiring and regain it's power. But if I was to hit the gas hard again it would just start misfiring again. It does it in other gears as well but it is the most noticeable in 2nd. Another thing, If I do not let off of the throttle it will eventually just backfire. I have replaced the MAP sensor, fuel pump, plugs, rotor cap, plug wires. It is throwing no check engine light codes. I have taken it to different mechanics and I keep getting told different things, and to be honest I really do no want to just keep replacing parts until I eventually fix it. I was told that it is the crankshaft position sensor now, but before I go out and spend more money I would like some different opinions on it. Thanks for your time guys.

 

You should be getting a CEL with all that misfiring. What are the codes you're throwing?

 

ok that could be a number of things. so most likely your getting to much fuel so check your timing make sure its right and check your temp switch and if those are good. let me know and will go from there

 

Or not enough -- lean conditions can cause misfiring and backfiring too.

 

It is throwing not a single code. I had a friend of mine check the codes and nothing. We unplugged the MAP sensor to make sure the CEL was working at all, and sure enough it came on. I am no mechanic myself, but to me it seemed like the engine was not getting enough fuel, that was my first guess. I told my mechanic and he agreed and thought it was the fuel pump. So we changed it and the fuel filter and no difference at all. Then I let him drive it when it was warmer out, and he told me that it was misfiring like crazy and thats why it was bogging down. So I am stuck as of right now.

"ok that could be a number of things. so most likely your getting to much fuel so check your timing make sure its right and check your temp switch and if those are good. let me know and will go from there "

I will get this checked out this weekend, got a busy day tomorrow. Again thanks for the help guys.

 

Timing is a good thing to check. The problem is just that any number of problems with the fuel system or ignition system could lead to this issue. Strange that there's no codes. Perhaps timing is to blame.

 

Check your valve clearances

 

Well I took it to a specialist, they thought it was oxygen sensor, so we changed that, still messed up. Now they think it is the computer itself. Would a faulty computer cause it to misfire/ bog down when the engine is warmed up?

 

That is a possibility swap ecu w/ a known good one. A clogged cat can cause this same problem to. Bad ign coil also. As head builts up in the coil it can cause a failure

 

I had similar issues with a 98'' gsr, i replaced the cap rotor wires ect.. still had a power loss and bog but i was told to reset the ecu when you do all this so when i unpluged the ecu for 2 mins and repluged it the power was back and it ran great, also check inside your dizzy for damaged wires and also look for a leak near the header and cat or cat back.