BattelWagun
Full Access Member
Okay, let me start off by saying I haven't been on here in a while due to being an engineering major in college... not much time for this crazy aspect of life called 'fun' 
But anywho, I have this really bad misfire going on that I cannot get to the bottom of...
99 tahoe 5.7, 160,***. 4 door 4WD.
It started 3.5 years ago after I replaced my intake gaskets. But nothing major, truck made 100% power and had a virtually unnoticeable lope at idle. No other issues, no codes etc.
About a year later, I noticed the truck would really struggle in the summer heat with both A/C units running and steering pump in use. Every 30 seconds or so the engine would fall flat on its face. Not stall, just drop to about 350rpm, ECU would idle it up for a few seconds and it would be fine. THIS is when I wanted to take care of it, but being a college kid at his father's mercy, I gained no ground on fixing it. I would get an occasional P0305 on the highway, usually accompanied by a slight loss in power. Couldn't feel a misfire though.
Fast forward about six months. Dizzy went out, replaced that, tranny went out, rebuilt with beast sunshell(kept original TC), rebuilt rear axle(bad pinion bearings), and replaced some seals on front axle. All pretty much not related to engine.
THEN, it got worse, terrible misfire on the highway. Loses some power, obviously. The misfire is generally above 60mph, flashing SES almost guaranteed. TC unlocks, maybe due to ECU sensing misfire? I also notice that it 'bucks' every once in a while, right around 45mph, like the TC is going out. Hold like a rock though under power. Im honestly afraid to take the thing above 50, because I'm not going to risk misfiring it to death like some idiot. I get misfire codes all over the place... But NEVER below 65mph.
Tested for vacuum leaks, none...
EGR seems fine.. no codes.
All cylinders compressing to 150PSI (+/- 2 PSI)
No other codes whatsoever....
Eats a bit of oil, nothing crazy for 160K miles...
Doesn't eat coolant...
Plugs look fine as well. They were all a nice even color.
No rattling in cats either. But exhaust makes a ton of condensation. Not sweet like coolant, no colors, just condensation.
Smells like its running a little rich.
any help guys? Im at a loss here.
But anywho, I have this really bad misfire going on that I cannot get to the bottom of...99 tahoe 5.7, 160,***. 4 door 4WD.
It started 3.5 years ago after I replaced my intake gaskets. But nothing major, truck made 100% power and had a virtually unnoticeable lope at idle. No other issues, no codes etc.
About a year later, I noticed the truck would really struggle in the summer heat with both A/C units running and steering pump in use. Every 30 seconds or so the engine would fall flat on its face. Not stall, just drop to about 350rpm, ECU would idle it up for a few seconds and it would be fine. THIS is when I wanted to take care of it, but being a college kid at his father's mercy, I gained no ground on fixing it. I would get an occasional P0305 on the highway, usually accompanied by a slight loss in power. Couldn't feel a misfire though.
Fast forward about six months. Dizzy went out, replaced that, tranny went out, rebuilt with beast sunshell(kept original TC), rebuilt rear axle(bad pinion bearings), and replaced some seals on front axle. All pretty much not related to engine.
THEN, it got worse, terrible misfire on the highway. Loses some power, obviously. The misfire is generally above 60mph, flashing SES almost guaranteed. TC unlocks, maybe due to ECU sensing misfire? I also notice that it 'bucks' every once in a while, right around 45mph, like the TC is going out. Hold like a rock though under power. Im honestly afraid to take the thing above 50, because I'm not going to risk misfiring it to death like some idiot. I get misfire codes all over the place... But NEVER below 65mph.
Tested for vacuum leaks, none...
EGR seems fine.. no codes.
All cylinders compressing to 150PSI (+/- 2 PSI)
No other codes whatsoever....
Eats a bit of oil, nothing crazy for 160K miles...
Doesn't eat coolant...
Plugs look fine as well. They were all a nice even color.
No rattling in cats either. But exhaust makes a ton of condensation. Not sweet like coolant, no colors, just condensation.
Smells like its running a little rich.
any help guys? Im at a loss here.
