OK, I am trying one more time for some solid advice on what could possibly be wrong with my engine. Here's the history:

1. original engine had an MTI Stealth II cam and Comp Cams 918 springs. Valve spring broke, blew engine.
2. Bought 2004 GTO block, HKE machined block for 3.905" Mahle pistons, 4" SCAT crank, line honed, clearanced for stroker. Bought Comp Cams 224/228, .610/.605 lift, 114LSA. .020 milled LS6 heads, LS6 intake.
3. Assembled and started. Noticed low on power, which progressed into a SES code P0300 (multiple misfire). Thought just the tune was off. G-Force loaded a 383 tune, no change.

So, here I am. The car still has serious misfires, which appear to be isolated to the passenger bank. Passenger bank plugs are showing rich, while driver's bank show normal burn. This is a list of what I've tried:

1. Different plugs and wires. Started on NGK TR55's and new MSD wires. Tried another set of TR55's with the stock wires. Got TR6 plugs, some improvement, but still misfires. Even tried Autolite platinums, but no change.

2. Tried a different passenger side coil pack from a running car. No change.

3. Replaced passenger side O2 sensor. No change.

4. Replaced crank position sensor and had G-Force run a crank relearn. No change.

5. Pulled injectors and fuel rail to see if plugged. Nothing obvious. Might try having the injectors cleaned and balanced at the local NAPA.

6. Pulled intake maifold to inspect rear wires, inspect intake gaskets, etc. re-installed. No change.

7. Did a compression check. Cylinders 2 & 4 - 200 pounds, #6 - 195 pounds, #8 - 185 pounds.

8. Did a leak down test. Cylinder 2 - 17%, 4 & 6 - 15%, 8 - 25%. Now, this was on a cold engine (intake was off at the time).


I'm left with bad computer, bad cam position sensor, or sticking injectors.

What do you think? What else can I test?

 

bump - anybody?

 

You said you "had a 383 tune loaded" could you elaborate a little on this? Was the car tuned, or was something generic loaded in?

You are running rich one 1 bank, 9 times out of 10 the culprit is either a bad 02 (which you already swapped), or an exhaust leak near the 02 sensor, drive the car up on ramps and start the engine, run your hand around the pipes down there and feel for leaks.

 

Will try that. Question - would this cause the misfires I'm having??

Another dumb question: when installing the engine, I accidently hooked the positive cable on the starter motor and it touched the solenoid. So, when I put the cable on the battery, it sparked and engaged the starter. Could this have damaged the PCM in any way???

 

Oh, and as far as the tune, I really don't know the details. G-Force loaded it based on similar builds.

 

If you have an exhaust leak near a 02 sensor, it will cause one bank to run really rich, and yes it will cause misfires.

Remember an engine is an air pump, for every exhaust pulse out of the leak, it is going to suck in fresh air. If the 02 sensor senses this fresh air, it is going to interpret it as a lean condition and cause that bank to dump fuel.

 

Well, I finally found out what the problem was: plugged catalytic converter on the passenger side. I pulled the Y-pipe off, fired the car up and there was no flow at all. Remove the cat, gutted the interior, re-installed and fired it up again. Success!!

This was without-a-doubt, the most frustrating problem I've ever had with a car!! I'm just glad I finally could figure it out!!

 

Old post but we are having the same trouble. We did have a serious leak near an O2, fixed but driver side bank still dumping an *** load of fuel. Funny thing is that on one start up passenger side was dumping a lot of fuel. Also noticed the driver side o2 (which was new) was not reading like it should at idle. Rev the car up a bit and it will start reading. Also upon 1st connecting to car noticed a Crank position sensor code. Cleared it and has not come back since. So car runs rich has a definite miss on 3 or more cylinders. Temp read on each header pipe from front to rear Driver: 340, 350, 140, 150. Passenger: 360, 140, 340 350. We have spark changed injectors still same thing. Sometimes car will load up and abruptly shut off like it want to hydro lock and will let a big plume of smoke out from engine bay. most coming out from airlid.

 

Update fixed exhaust leak(s) new Crank sensor, new wires and connector to sensor, new plugs, new wires, new stock injectors. When we left the shop yesterday tuner said he put where it will not add fuel. After all this it runs worse and now there is white smoke coming from the tail pipes. Could it be because it needs more fuel and is not getting any? We and stumped and money is depleting fast, any suggestions..

List of new parts after tune
plugs
wires
o2 sensor
offroad y
Crank Position Sensor
Connector (pigtail) to crank position sensor.
27# injectors

Sputters
white smoke from tail pipe
miss
no knock

Maybe washed out cylinder, bad spring I will check thos next if no one chimes in. Right now I am headed back to the tuner

 

just talked to my brother. He is over at tx speed last 2 cylinders are dead on driver side passenger side is ok. What can cause this? They have spark.

 

bad injector, open valve (broken valve spring, bent valve, etc.), or damaged pistons and/or cylinders.

Good luck.

 

I am having similar problems. but the condition changes with the temperature(of the engine, and ambient air, warmer better in both cases). Sometimes it almost goes away completely and I get full performance and no noticiable signs of misfire. Other times its unbearable. This couldnt be a mechanical issue, if it is temperature dependent correct?