Misfire on Cylinders 5, 7, 8 (FIXED! Broken Valve Spring)
 

Slight Update: When I unplugged the MAF the misfire code and blinking CEL disappeared. It still has a misfire, but nowhere near as bad. I tried installing a used MAF out of a working vehicle. Plugged it in and the CEL blinking, misfire code, and horrible drive-ability came right back.

I've been posting on my Trans Am / LS1 specific forums and so far no luck. So, I figured I'd post here for the hell of it.

This is on my '98 Trans Am. On July 25th, 2012 I was driving in to work and I noticed some hesitation in 6th gear at 65 MPH. Wasn't a big deal I thought. Then, I noticed it at lower gear, and now while accelerating in every gear. It's like a full auto AK-47, for example, in terms of rate (not loudness). It idled fine.

My SES light has been on for a year now now. It's telling me the driver side cat is bad. On my drive to/from the Hamptons (On the weekend prior to 7/25/12) I hit 2389048923480234 bumps, pot holes, etc., mainly on the Belt Parkway & Staten Island Expressway. Is it possible it rattled my cat apart and is now clogged up?

Fast forward to a couple weeks ago. Things are MUCH, much worse. Car won't idle properly. Can barely drive it. It's missing BAD. Above 35 MPH the CEL blinks, which as we all know is not a good thing. Here is are two crappy videos to demonstrate what's happening (at idle at least):
http://www.youtube.com/watch?v=_n_8yLhQNtU

http://www.youtube.com/watch?v=4sOfqrMLJlc


2 weeks ago I drove the car to a guy on Yellow Bullet. He is an engine builder and has done several LS1 and other cars over the years. He hooked it up to a SnapOn scanner to monitor the car while running. I think it's the SnapOn Solus. Hooked up fine while the car was off. Then when the car was running it had several issues trying to connect. Finally it worked and we got this...

-Cyl #5 misfire
-Cyl #7 misfire
-Random Cyl #8 misfire
-Random Cyl #6 half fire

CEL is on. Codes are only showing P0420 (Catalyst efficiency below threshold on bank 1). However, o2 sensors are reading as normal. Cat temps are running within normal ranges as well (Checked with an infrared thermometer). Other code is "Cylinder misfire detected".

Other issues:

-Third brake light sometimes illuminates like a rear tail light. On while lights are on, then brighter when the brakes are applied. I have an LED 3rd brake light installed btw.
-Turn signals are also acting weird. They blink quickly, slowly, normal, and anything between.

I changed the plugs to NGK TR-55 plugs. Wires are brand new as well from Vengeance Racing. We have checked the injectors & coils. Used some from other working vehicles and they did not change anything. They are fine. Also got a noid light on the injector wiring harness. Checked fuel pressure and it's good, in the green at 55 psi. So I am thinking harness or computer? I am borrowing a computer from my buddy who removed it from a '98 Camaro SS.

2 interesting things. First, I just noticided this on the ECU I pulled from my car is a reman:
http://ls1tech.com/forums/attachment...ine=1357256003

Second here's the corrosion that's all over both the ECU and the harness side (I cleaned this all up since the photo):
http://ls1tech.com/forums/attachment...ine=1357256003

Also figuring maybe grounds? I removed the 4 easily accessible grounds: Driver side strut tower, driver side front next to the intake, passenger side strut tower, passenger side front next to the intake. I filed down the grounds metal contacts and wire brushed them as well.

Started up the car and it ran basically 99%! I took it for a 0.5 mile drive and it slowly got worse. At stops it would almost stall. I brought it back and parked it. It seemed to get worse the longer it was running. However, overall it seems much quieter and seems to run much smoother as well (This is with the other ECU).

Should I just replace the driver side cat and see if that fixes things?

I REALLY want to be able to enjoy my car again, but I haven't been able to drive it in months 'cause of this crap. Thanks!

Did you wiggle the cat to see if anything is loose in it?

Can't wiggle it, it's in there good lol. I did a knock test on it and there was no rattling of the innerds that I could hear.

Even though you mentioned changing plugs, from the way you described your sequence of events I can't tell if you changed plugs and the misfire was still there.

Also, if / when you pulled the first set of plugs out that were misfiring, how did the plugs look? Any pics of the electrode end of those plugs?

interesting its the total 4 rear cylinders on two banks, and I know those two suck to get to in the rear on your car. Id disconnect the battery, unplug the ECU and clean they terminations at the ecu, and at the coil pack to harness, and coil harness to main harness connections. The LS coils have 4 wires Power 12V, Gate drive, ECU ground, and chassis ground. I would then put it together, put it in the on position and check voltage to both grounds at the 4 wire plug to the coil.

The other thing is your code can also sometimes be associated with crank position not learned, have you seen this code at all?

I have 109,XXX miles and do not think that the prior owner changed the wires. The plugs are half and half. I just changed the wires to Vengeance Racing:
http://pafirefighter11.smugmug.com/p...-bCMPT8c-L.jpg

Also running new TR55 NGK plugs gapped to .055. The gap of the old plugs was at .085!

These are the plugs, set up in cylinder order. Top plugs are the front of the vehicle:
http://pafirefighter11.smugmug.com/p...-kLNnwFP-L.jpg

I was unable to reach cyl #8. I changed the plugs and wires after the misfire began. It did not change anything after the plugs/wires were installed.

I've never had any other codes than:
P0420 - Catalyst efficiency below threshold (original code I've had for some time)
P0300 - Random misfire detected
P0140 - o2 circuit blah blah (from when I disconnected the driver side downstream o2 sensor to check it)

Dude change your ****ing cat.. it could be causing all of this sending false readings to your adaptive learning and making it run rich or lean and messing all your crap up. Those plugs are pretty burnt up too, are you burning oil? Did you clean any of them? Your running a bit rich and not getting enough spark by the looks of the plugs too.

those are his old plugs with 108K but yea he needs new wires for sure

possibly a distributor cap and rotor also, but he really needs to change that cat and by now the o2, if you have a laser thermometer point it about an inch before the cat (At full operating temp) and then an inch after the cat and you should see significant temperature difference

There is no distributor

Coil pack then lol

See above. And yes, no distributor. I have a coil pack on each cylinder. Swapped them around and the issue did not move.

Ordering up a Walker Y-pipe now.

Take same infrared, get to operating temp, check temp on each header to see if their misfiring or your getting a false reading.

They def. are misfiring. Car barely runs/idles and shakes. It sounds like it has a nice cam haha. I'm just going to do a new Y pipe and see what happens after that.

I had a similar issue with my mustang. wound up replacing the camshaft position sensor and the crank angle sensor. Solved all my vehicles issues.

Codes are you best friend

Hmm, never crossed my mind since I am not getting those codes. Doing research on LS1 Tech and other LS forums now on the cam & crank sensors. It seems the symptoms my car is having could be the crank and/or cam sensors or a host of other issues. ..............

Gonna just do the Y pipe first and go from there I guess.

my car never threw codes for the sensors. after reading up on symptoms and some diagnosis I decided to shoot in the dark and replace them.

wow. i see you giving me bad advice than good, give up.

those plugs look BEAT, but thankfully no signs of oil or coolant. if you put new plugs in pull them again and see if they are loaded up. also, to check for a clogged cat, pull the front o2 sensor and check for back pressure with a gauge, if its more than 2 psi you have a problem.

What was that? I cant tell if there's a typo in there or your missing a comma.