NEED HELP! LQ1 starts, runs rough, lacks power.

[MOTORHEAD86]

I recently picked up a 1991 Grand Prix GTP with the LQ1 3.4L DOHC. The car is in excellent condition, but the engine runs like a harley. (sounds like a v-twin)
The owner before said he had this car parked for 5 years, so I understand what the condition of the engine would be like. I've been working on it the past couple of days, checking the upper intake, injectors, spark plugs, wires, compression test, the basic tune up. fortunately, it turns over. but after all that work it still sounds like not all cylinders are firing.
The exhaust is broken before the catalytic converter. Im working on replacing that soon. When it does run, I looked underneath and there is fire blowing out the exhaust. Cool to watch, but I'm under the assumption that its not right.
My next job is to clean out ALL the old fuel and try a fuel injector cleaning method as well as fill it up with some new fuel. I was told gasoline breaks down, or isn't as volatile over time (5 years past due).
Im posting this forum to get any suggestion or information on what I should do next before I go into PLAN X (ENGINE REMOVAL). I have a donor GTP that runs perfect with the same engine that I might swap out. please leave your comments and thanks for viewing.

Motorhead86
1991 Pontiac Grand Prix GTP (OEM)

[bszopi]

Welcome! If it doesn't sound like its firing on all cylinders, check the spark plug wires and routing, and also swap out coils packs (especially since it sounds like you have a good set on the donor engine).

[MOTORHEAD86]

Yes Im checking that today. Also I was told at work that since it backfires when running, I should check the timing. Is there ways of checking the timing or that it can be adjusted anyway? Im thinking more towards the timing instead of the fuel delivery. Fuel pump and filter is the next to check.

[RedZMonte]

check the basics... Spark, Fuel. Any codes? my car wouldnt barly drive without the catback attached (downpipe only). Definatly check the Timing belt, if its old and or worn it would explain what your having as well.

Pull the plastic cover off the front of the valve cover and inspect the timing belt.... i bet you will find it to be warn maybe partially missing.

S

[MOTORHEAD86]

Well, I'm please to say, she is finally running 100%. It was the ignition coil the whole time. Good thing I had a spare pack from my other engine. My next job is to burn all the old fuel, instead of draining it out manually. I figured the injectors aren't too bad so I'm going to leave them be for now.
The Timing belt is still pretty good. no tears, scuffs, or pieces missing on the belt except for the common dustyness. No codes are present either. I am extremely satisfied with the work put into it. All I got to do now is install a new catalytic converter and mufflers. Mabye wash all the dirt n grease under the hood as well.
Thanks everyone for your comments and suggestions. I should have mentioned before that this is my first time using this forum. So far, its been a lot of help. Thank you very much. Ill continue to post updates if there are any other concerns.

John -Motorhead86
1991 Pontiac Grand Prix GTP -OEM (for now)

[bszopi]

Good to hear it was just a simple fix! And glad the site was useful for you, as that is what it is here for.

[pocket-rocket]

Just be sure to get it as empty as you can before filling it up with new gas. If you fill up at a half tank, that's still a half tank of crappy gas diluting the good gas. Then if you fill up at a half tank again, that's a quarter of a tank of crappy gas. If you do decide to just remove the old fuel, you could disconnect the supply line (the larger of the two) at the fuel rail and hook some hose to it running into a gas can. There is a fuel pump lead by the relay on the drivers side strut tower that will turn the pump on when hooked to 12v so you can use the fuel pump to pump it all out of the tank before adding fresh fuel.