just changed my plugs....

commercialfshrmn · Jul 11, 2026

somehow were gapped to .60. they're at .40, now.

what do they look like to y'all? (bad) but ideas?
just changed the evap solenoid front & back.....only other thing it could be is the actual canister itself

Fless · Jul 11, 2026

Any particular reason it's running nickel plugs instead of platinum or iridium?

commercialfshrmn · Jul 11, 2026

Fless said:
Any particular reason it's running nickel plugs instead of platinum or iridium?

not sure, i paid a shop to do it when i was offshore that time. just replaced them with iridium

OR VietVet · Jul 11, 2026

Gaps change over time as the tips get burned away, especially since, like @Fless said, nickel plugs instead of platinum or iridium. How long were the old plugs in there? Unknown? Age of ignition coils? Age of wires?

Since, IMO, looks like a slightly rich concern on all of them, may have been a weak spark or needs some TLC at the MAF/MAP sensors and a thorough cleaning at the throttle body with the correct cleaner and correct procedures for the cleaning and then a possible relearn drive or scanner reset.

commercialfshrmn · Jul 11, 2026

OR VietVet said:
Gaps change over time as the tips get burned away, especially since, like @Fless said, nickel plugs instead of platinum or iridium. How long were the old plugs in there? Unknown? Age of ignition coils? Age of wires?

Since, IMO, looks like a slightly rich concern on all of them, may have been a weak spark or needs some TLC at the MAF/MAP sensors and a thorough cleaning at the throttle body with the correct cleaner and correct procedures for the cleaning and then a possible relearn drive or scanner reset.

about 2 full years (gone half of the year on the boat) - changed maf earlier this week, changed plugs/wires/evap solenoid today...could the MAP sensor make it idle rough/run rich? if so, that's the culprit. it's pissing me off, for sure

OR VietVet · Jul 11, 2026

Ignition coils age? Last time the throttle body was cleaned? I asked this earlier. Likely missed it. There are several videos showing the proper way to clean the throttle body and why you should clean it. Does relate to the concerns you listed.

commercialfshrmn · Jul 11, 2026

OR VietVet said:
Ignition coils age? Last time the throttle body was cleaned? I asked this earlier. Likely missed it. There are several videos showing the proper way to clean the throttle body and why you should clean it. Does relate to the concerns you listed.

2 years. that was the first thing i typed. 3 days ago.

MAP symptoms (minus the smoke) are all there entirely

Foggy · Jul 11, 2026

Those TR55 plugs are very common in the LS world. TR6 is more common: it's the same plug just gapped diff at the factory

They should have been pre gapped from the factory, but you never know
what gets thru these days.
Make sure to just replace them with real NGK or ACDelco plugs per the application
and you'll prob be just fine. Wires would be a good idea at the same time

commercialfshrmn · Jul 11, 2026

Foggy said:
Those TR55 plugs are very common in the LS world. TR6 is more common: it's the same plug just gapped diff at the factory

They should have been pre gapped from the factory, but you never know
what gets thru these days.
Make sure to just replace them with real NGK or ACDelco plugs per the application
and you'll prob be just fine. Wires would be a good idea at the same time

i think it's gonna be a lil deeper than that! check these videos out, tell me what ya think/hear.
1. idle vid (exhaust leak)

2. where the fuel smell's coming from

3. you can hear it misfire when gears are changed

Foggy · Jul 12, 2026

An exhaust leak will cause your oxygen sensors to be off which would
really mess with fuel trims.
Almost 20 years old, anything of course is possible.
I would get the exhaust leak fixed, do the basic maint like plugs, wires,
clean maf, clean TB, etc ..
Then clear all the codes and reset adaptives, fuel trims, fuel composition, etc
and see where that puts you.
The first video I can't really hear anything at all - could just be the video

Foggy · Jul 12, 2026

To add: you have the earliest GMT900 and many had oil ring issues.
I see you've made another post... Try to keep it all in 1 post so we can help better.

They also had some piston slap issues. May be time for an engine pull to replace
bearings, rings, pistons
You'll have to decide the value vs. $$$

commercialfshrmn · Jul 12, 2026

Foggy said:
An exhaust leak will cause your oxygen sensors to be off which would
really mess with fuel trims.
Almost 20 years old, anything of course is possible.
I would get the exhaust leak fixed, do the basic maint like plugs, wires,
clean maf, clean TB, etc ..
Then clear all the codes and reset adaptives, fuel trims, fuel composition, etc
and see where that puts you.
The first video I can't really hear anything at all - could just be the video

well, someone decided they needed my cats more than i did. so, i bought replacement, but i think the leak is where it's not sealed entirely on the pass side flange. it shouldn't be THAT bad, though. when you put it in any gear it goes to stumbling/falling on it's face.

maf/wires/plugs/coils/both front & rear evap were replaced all this week. also took the tb off and cleaned it.

the first video is just it idling (which is absolutely fine), as long as the ac isn't on. it idles perfect.
it's just when it goes in gear/you turn the ac on, it wants to fall on it's face, which is the 3rd video.
i might have to use my wifes phone to take it, because mine is all messed up lol.

the entire video sequence is a cold start, and the "tick" sound goes away pretty quick when it warms up. however, its a strong smell of fuel coming from that side of the engine.

from what i've been reading, a failing MAP sensor describes to a T every single thing that it's doing. bad mileage, stumbling, etc. i'm not sure, though.

i will say, before this, it ran 100% perfectly fine!

Foggy said:
To add: you have the earliest GMT900 and many had oil ring issues.
I see you've made another post... Try to keep it all in 1 post so we can help better.

They also had some piston slap issues. May be time for an engine pull to replace
bearings, rings, pistons
You'll have to decide the value vs. $$$

yeah, sorry about that. thanks for your reply, by the way.

RET423 · Jul 14, 2026

I say this a lot but for a rich/misfire condition my 1st diagnostic move is to unplug both primary (upstream) 02 sensors and drive it at highway speed for 5 or 10 miles

This will throw a code but if tthe rich condition & misfire go away you know 1 or both upstream sensors were sending a false lean report to the ECM

If that is the case on your rig try cleaning your 02 Sensors first as the replacements available today are like playing roulette; very difficult to get good 02 Sensors these days

Good luck!

hagar · Jul 14, 2026

I run tr55 or tr6 in everything I run or build. Granted most of the stuff i do is running much higher than stock cylinder pressures, so i want the copper core as a last resort fuse, but i still huck them in even basic stuff. I can do 4 plug changes for the price of one plug change in iridium, and it only takes a half hour. Maybe I am getting old. Looks like the plugs were running just fine to me.. just time to change them.

LsHart · Jul 14, 2026

It's just me but I run Acdelcos iridium. No gapping needed. Plus AcDelco is factory heat range plug.

hagar · Jul 14, 2026

I have noticed lots of the engines with previously plugged pcv systems (the common valve cover issue) will have ring lands blown out of them if people ignore it.

Makes me wonder sometimes if it would be so prevalent if the plugs weren't impossible to burn up. An iridium plug will fire no matter what is going on for heat, its the charm of its longevity that it is nearly impervious to heat, and thus wear.

Or maybe it makes no difference, not sure. I know it makes a difference when you have a bad overboost or lean condition with aftermarket cylinder pressures.

LsHart · Jul 14, 2026

All these different plugs are made and classified for heat range and spark ease. So plug quality does matter. Take the E3 plug, platinum plug with 3 prongs. If the plug isn't rated for said condition, it will blow out all 3 sparks!

hagar · Jul 15, 2026

LsHart said:
All these different plugs are made and classified for heat range and spark ease. So plug quality does matter. Take the E3 plug, platinum plug with 3 prongs. If the plug isn't rated for said condition, it will blow out all 3 sparks!

The gap will be the reason for blowing out the spark, not the heat range. The heat range being too hot, in a higher heat cylinder, turns the tip into a hot spot that can light things when the piston is in the wrong position.

LsHart · Jul 16, 2026

As I said quality does matter. If u put a copper plug in an engine that was blue printed from factory with a double platinum or just a platinum plug.iridium plug is better. Engine performance will be poor. Gas mileage, idle quality and more carbon on the cylinder. But to each is own I guess.

just changed my plugs....

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