The P0420 code started over a year ago (August 2011 or so). No negative/adverse driving issues were occurring at the time.

The misfire started when I returned from the Hamptons several months ago (July 2012?). No high RPM driving to/from the Hamptons, just highway through some ****** parkways (Belt, LI, etc.).

Because of the misfire I:

-Replaced the plugs
-Replaced the wires
-Swapped coils around (Problem stayed on #5 & #7)
-Removed #5 injector, replaced with a known working injector
-Checked cats using infrared thermometer & tap test:
----Driver side 450*/400*, no rattling
----Pass. side 350*/300*, no rattling

GOtta run, post more later.

It sounds like you need to check the injectors or injector harness to get that #5 injector firing properly before worrying about the other codes. I saw there is a TSB for electrical harness for 1999 Firebirds TSB 03-06-04-012A to inspect the harness but it doesn't give any specifics. Maybe a good scan tool will show if the #5 injector is truly getting the signal to the injector.

or a simple noid light

That wouldn't cause misfiring.

The 160* t-stat has been in the car for over 2 years. I don't see that causing a problem.

I just got a noid light on it today. Both #5 and #7 injector connectors are pulsing properly.

A guy who is local to me on Yellow Bullet is going to hook his scanner up to it and see what's going on. He has one of those DRB style tools (Really expensive diagnostic ones). Shooting for Saturday.

Okay, so my buddy (He has been building engines for decades) looked at it yesterday. Hooked up one of those super expensive Snapon scanners. The o2's are reading fine, so it seems the o2's and cats are good. He saw that cyl's #5 and #7 were misfiring. At times #8 would hop on the misfire bandwagon, and #6 seemed to be having minor issues as well at times. He swapped out all the driver side coils to some from his LQ4, the problem remained. Injectors seem fine.

At this point he thinks it's either the ECU or wiring in the harness, possibly even a bad ground somewhere. Some random electrical issues pop up such as the turn signals blinking real fast, then real slow, then fast and slow when I activate them. Also my third brake light will light up like a regular tail light: On while the parking lights are on, then when I hit the brake it gets brighter. When revving the Check Gauges light 1/4 illuminates sometimes, which is odd. A few other odd things occur from time to time as well.

At this point I need to find a '98 Camaro SS or Trans Am computer and swap that in there. See if the problem is resolved. Anyone have one to loan out?

99 won't work?

Nope, it seems '98 is unique. Of course. My buddy just told me he has a few spares, including a '98, so I'm heading over there today to grab it.

Borrowed an ECU from my buddy. He had several from his past vehicles. He gave me one out of a '98 Camaro SS. Swapped it in and still runs like crap. Very strong odor of raw fuel.

When I pulled the old ECU I did notice some white corrosion and residue. It was on both the lower wiring harness connector as well as the ECU connector itself. Hard to see here but it's the ECU on the left, very bottom, the flash made it look brighter:
http://pafirefighter11.smugmug.com/p...K2nm3KG-XL.jpg

Sound like an electrical issue. Try and check all the grounds then start looking at the wiring to see if anything is rubbing through somewhere causing it to energize the whole frame/body. Also check the alternator/voltage regulator to make sure it's not overcharging.

It's charging pretty high (not in the red though) 'cause I did the high output Escalade alternator swap. The car blew 2 alternators before I did this. There is a HUGE post over on "Tech" about it.

After re-reading this entire thread I think your next step is to set aside some time and really check out the entire harness. I think you mentioned an aftermarket alarm? If so, locate that and all associated wiring and check it over very well. Could be that one of more of the connections from the aftermarket alarm to the factory harness are failing and causing shorts or other odd behavior.

It sounds like there are too many different issues going on (long term code, misfire, brake light issue, turn signal issues) to be able to point to one specific cause (other than a harness issue).

- Justin

Thanks, Justin. Factory alarm that was always on the fritz, as seems the issue with most factory F-body alarms.

All the electrical things made me really believe that it was an ECU. I'm pissed it wasn't 'cause I had a good deal on this ECU if it did fix the problem.

Speaking of ECU's, does anyone know how long it takes for a replacement ECU to idle well on a new car? i.e. does it have to go through a couple warm up cycles, or just one idle and it'll learn?

Pending the conditions, it can take a few start ups and drives for it to learn all necessary parameters.

Alright, I'll give it a few more starts and drive it too. I didn't want to move it since it was idling so badly.

First I'm going to see if I can get the new computer to learn everything and work. If not, on to the grounds.

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

Second here's the crap that's all over both the ECU and the harness side:
http://ls1tech.com/forums/attachment...ine=1357256003

Kinda looks like the dielectric grease that should be there but its tough to say it is exactly. Does it seem to be consistent with what you would consider grease?

Negative. It's like battery terminal corrosion. It looks as though water has dripped down between the hood/fender, onto the ECU, into the connections, then down further as well.

Ok, well that's not good obviously. Have you checked the seals on the connectors? I can only imagine if you are seeing corrosion there that water has gotten into the pcm as well.

The seals all good great. That's what worries me...

I just spent 2.5 hours working on it. I removed the ECU connectors from the ECU and cleaned them with electrical cleaner spray. Then, 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 all on the "new" ECU from my buddies '98 Camaro SS. Should I be cleaning out my other ECU (Which is remanned it seams) and try to run it again?

Have you checked back pressure on the known bad converter yet? I saw this mentioned on the last page, not sure if its been done yet.

All 4 o2 sensors are operating correctly per my buddy with his expensive SnapOn scanner (He's an engine builder). The temps (Front and rear on the cats) are within range for a properly operating cat. I did not check further than that.

It sounds like the computer is learning and making adjustments, but something is still not reading right (sensor) or the injectors still aren't firing. The reman ECU might be a clue that there has been a problem previously so maybe look for any electrical items that might have been replaced. I still suspect the wiring harness might be messed up at this point. And the corrosion means the seals were leaking at some time, they might have been replaced before you got the car.

Rick, perhaps now is time to start pushing.


Joking aside, I'd start cleaning some of the electrical connections if they look corroded. And check your ground straps just because.