with 126K on the motor, would a leaky injector cause a backfire above 3500rpms....

 

possible, but i would lean towards ignition issues.

 

coil was replaced...new fuel filter,pcv valve, tps, egr

what would u look into? any way to dectect a bad opti

 

Its most likely plugs. As the rpm goes up, its harder for bad plugs to keep the spark at the necessary rate. You can take a few off and look at them.

You can look at wires and see if there are any cracks or burns.

Opti... if you have a scanner, scan to see what rpm the pcm is showing you. Spikes or dips in the rpm can be a result of all kinds of things, one of them is your opti giving wrong info to the pcm (eg. you see dips to zero rpm when you're actually at 4000). Best way to check it is to open it up and look at it. If its full of oil, black stuff, or the rotor doesnt turn, or the disk is rubbing against the sensor, you know it needs to be changed.

Sometimes, even the distributor cap maybe the problem. If you see burn marks on the inside of it, you know its not conducting electricity well, and that can cause a high rpm misfire.

I hope this is enough to help you solve the problem, let us know how things turn out.

 

new GM plat. plugs and Taylor 8mm wires were installed 10K ago. would a GM Tech 1 do me any good? Reason im asking bout leaky injectors is because when in 1st and 2nd gears i will slowly increase the throttle to 3500 before shifting to the next and it feels like my motor has this huge miss. it will shake your body you feel it so much. even in 3rd gear at 1500rpms you will feel the motor have the "repetive miss" as you leave your foot steady at 1500rpms. i was thinking maybe an injector could be clogged and not letting the piston fir properly??? im boggled!!!
But when i stomp on it from 2500rpms, really there isnt any problems

 

I cannot imagine a fuel injector causing a "miss". A miss, in my understanding, is when the car loses and regains power so fast that it feels like a vibration. If you had a leaky injector, you might have a hard time starting the car because the fuel pressure in your lines would go down to zero.

It is not hard to check if a fuel injector is leaking. Check the fuel pressure after shutting the car off. If it drops minimally over 10mins, you have no leak. If it drops alot u have a fuel leak somewhere. You can pull the injectors out but leave them connected to the fuel rail. Turn the key into the on position but do not crank, and if an injector leaks under fuel pressure... its leaky.

Plugs are obviously not the problem. A wire can burn in less than 100 miles if it's close to or touching a header. I would at least look at the wires on the passenger side to see if they got cracked by sharp turns or if they are touching something they are not supposed to be.

If the car will miss even in neutral, get somebody to make it miss at night while you watch for arcing.

Gm tech will help if he knows what he is doing. My experience with them has been terrible. When my plugs were bad, they were telling me to replace my MAF sensor, they disconnected and reconnected my EGR, they told me my exhaust backpressure was too high, they replaced my distributor cap. They checked my fuel pressure, scanned it a zillion times, and charged by close to $1000 in the end and STILL did not fix the problem. They would call me up an tell me the problem is gone, and I would take the car back and it would still miss batly and backfire at WOT. I changed the plugs and the problem went away.

I have other stories like this. It really depends on how intelligent the mechanic is, what equipment he has and how he uses it (or she

1) How does your car idle?
2) is the miss always there or only under certain conditions?
3) describe the "miss" as accurately as you can