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Misfire after a certain throttle point


Z34 Lover
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Hey guys been a while. Im having a weird issue on my 91 Lumina Z34. Recently i had issues with bad misfires and sluggish performance and with the car misfiring on all cylinders (sounds like a 2 cycle revved high) after i depress the pedal about 25 to 35%. It starts decently and runs rough and after a bit when it warms up, it idles with a very slight misfire every once in a while otherwise all 6 are firing and it sounds ok. Throwing 2 codes, O2 sesor and Lean exhaust. Checked all vacuum lines and gaskets and everything seems to be in order. Did plugs, wires, valve cover gaskets (slight oil leak) and didn't do the O2 sensor(hard to reach). So now ir runs far better and i can drive it at low throttle with no misfires but after going about 40% down with the pedal it starts to misfire rapidly again and i lose power. When i let the pedal go and give it a little gas it will misfire once and then fire on all 6 just fine. Me and my friend are completely stumped so i bought a fuel filter and have yet to install it. Pulled my front plug wires when it was idling one at a time and it changed the idle with each one i pulled so i think the coils are ok

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TPS was replaced about 3,000 miles ago i forgot to mention that. Ok O2 sensor ill try and ill do the fuel filter too. Whats the easiest way to do the O2 sensor because even with the upper intake plenum off its still difficult to reach

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with the UIM off, about the only way to get more room is to tilt the engine forward.

 

by the time the O2 code comes on even intermittently, it is quite worn out.

 

fuel filter and pressure/flow in general is a good place to look. if you have a pressure guage, watch fuel pressure while the engine is under load and when it starts misfiring, insufficient fuel flow WILL show up as low pressure under a load. WOT should produce ~43PSI at all engine speeds. if it dips too much, the engine will lean out very quickly.

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Ok did some tests and i checked coils again and now im noticing no spark and very weak spark coming from my spark plug wires. Tested the plugs and wires and they are ok. I think the coils are shot. I have a set of L67 coils laying around, can i use them on my LQ1 for replacement coils? Kinda in a bind for a budget till my next paycheck

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