Well i posted a thread about this a little while back, About my car missing at around 5 grand ... I was thinkin it was the opti-spark but then i was told that it would have trouble starting while it was warm and not cold , well mine hs trouble starting cold ? and now it breaks up around 3 grand pretty bad it wont even go wot , It will start spitting and backfiring ? I ran it under obd but it wasnt pulling anything up so that kinda elimenates the o2 right ? im kinda at a rough spot here as i dont have the resoursces anymore to diagnose this thing and im farliy new to lt1's so b-4 i go ripping into this i just wanted to see if the veterans here had a good idea were to start .... i just had anew plugs and wiresdone last month .. Could it be a fuel filter ? ..If i run it real gently and keep it under like 3,200 it dosnt miss only when im on the highway in od under a load i can feel it missin just a small amount ? Thanks for taking the time to read this and possibly helping me .... My z is sick and its killing me lol ....

 

I would check the wires to make sure they are not burned/melted.

 

Yeah check the wires first and if that doesn't work check the MAF sensor. The one on mine was giving off a low voltage so it was failing. After I replaced that it worked liked a charm. Actually it ran better than before.

 

I probably told you before, it's probably the Opti, especially if the car is slowly degrading. The backfiring is common when the opti goes out as is the missing at high rpm. If the SES light isn't lit it's not one of your sensors (MAF, O2 etc.). You can replace the fuel filter and do other general maintenance sort of things, but it sure sounds like a bad opti to me.

 

My SES light wasn't on and it was one of my sensors. The computer has a fault level for their sensors. My MAF was reading low but it wasn't at the fault level to throw a SES light.

 

It still does sound like it's an opti issue. I heard of guys buying new opti's and those were bad too.

My car has had misfireand backfire issueslike you twice while I've owned it.; once when it was the opti, and the other was a fuel issue cuz once I replaced the fuel pressure regulator, it went away. Also, while I was searching the fuel problem, I found my plug wires were too close on my passenger side and may have been arcing, so I put wire separators in three places. That got rid of some of the misfire.

 

oh and another thing , if its cold it really dosnt do it that bad but afterit warms up or if i make it miss then it gets real bad , now its doing at right off idle but i will go out in the moring and have troble starting it then it wont miss till aroud 3 grand .. but once it starts missing then it gets real bad ..

 

If a sensor is malfunctioning to the point that it's causing a misfire you should be throwing a code. As I said before, double check all the normal fuel and ignition related components, make sure your plugs are gapped correctly etc.

 

Check to see if the O2 sensors are working alright

 

I had a similar problem with my lt. It started missed at wot, then it started missing if i ever went about halft throttle or trying to drive up hill. I checked fuel pressure, changed plugs, changed wire, then changed he fuel pressure regulator. It ended up being one of the metal tabs that hold the metal tip down on the rotor in the opti broke so it wasn't aways making contact to fire. bought one of ebay for 30 bucks now the car runs great.