Misfire

svensk · July 2, 2008

My problem is an intermittent misfire under load only when in OD with lockup and I begin to accelerate in OD. Does not do this in 3rd or when under WOT. However, it seems to mis once in a while idling when the truck gets warm (It will shake the truck if I'm sitting still). No codes as of yet, but I did get it to mis badly enough one night the SES flashed for like one second. Truck has no performance issues right now, nor am I suffering from poor mileage. I'm actually still getting very good mpg. Kind of a head scratcher.

Info about my bucket; 144K miles, newer ngk tr-55 copper plugs @ .060 gap, newer oem wires so far.

Alright, I've been gathering info from numerous PM's and research on teh intarwebs, and created this check list:

EGR sticking?

Temp sensor?

intake gasket leak? - common issue for LM7's

MAF? -not running an oiled filter anymore, I have an Outlaw intake (dry flow) now.

Injectors? - I run cleaner through tank regularly

O2's - changed them out at 120K

cats? wouldn't i get performance issues if they were plugged?

coil packs? fking expensive I don't wanna have to replace these.

Please add any information you have, or add to the list. Thread jacking is mandatory!

At least I don't have piston slap!

99silverado1500 · July 2, 2008

I have the number 2 piston slap on urban dictionary, im not worried about my number 1 piston slap

svensk · July 2, 2008

I'll give you piston slap

alaska511 · July 2, 2008

perhaps Jeff will throw his knowledge of STDs, and thier spelling, your way...that will help

In my 'hoe, the one miss I had was accompanied by a DTC, coil pack. I assumed they always threw a code when a misfire was detected. Bummer

svensk · July 3, 2008

Picked up the vacuum gauge today. Going to check to see if I have that leaky intake gasket.

merlin5577 · July 3, 2008

My problem is an intermittent misfire under load only when in OD with lockup and I begin to accelerate in OD. Does not do this in 3rd or when under WOT. However, it seems to mis once in a while idling when the truck gets warm (It will shake the truck if I'm sitting still). No codes as of yet, but I did get it to mis badly enough one night the SES flashed for like one second. Truck has no performance issues right now, nor am I suffering from poor mileage. I'm actually still getting very good mpg. Kind of a head scratcher.
Info about my bucket; 144K miles, newer ngk tr-55 copper plugs @ .060 gap, newer oem wires so far.

Alright, I've been gathering info from numerous PM's and research on teh intarwebs, and created this check list:

EGR sticking?

Temp sensor?

intake gasket leak? - common issue for LM7's

MAF? -not running an oiled filter anymore, I have an Outlaw intake (dry flow) now.

Injectors? - I run cleaner through tank regularly

O2's - changed them out at 120K

cats? wouldn't i get performance issues if they were plugged?

coil packs? fking expensive I don't wanna have to replace these.

Please add any information you have, or add to the list. Thread jacking is mandatory!

At least I don't have piston slap!

My first guess would be the distributor but I am pretty sure thats a coil on plug ignition. With the info you have given my guess would be the EGR valve.

svensk · July 3, 2008

My problem is an intermittent misfire under load only when in OD with lockup and I begin to accelerate in OD. Does not do this in 3rd or when under WOT. However, it seems to mis once in a while idling when the truck gets warm (It will shake the truck if I'm sitting still). No codes as of yet, but I did get it to mis badly enough one night the SES flashed for like one second. Truck has no performance issues right now, nor am I suffering from poor mileage. I'm actually still getting very good mpg. Kind of a head scratcher.
Info about my bucket; 144K miles, newer ngk tr-55 copper plugs @ .060 gap, newer oem wires so far.

Alright, I've been gathering info from numerous PM's and research on teh intarwebs, and created this check list:

EGR sticking?

Temp sensor?

intake gasket leak? - common issue for LM7's

MAF? -not running an oiled filter anymore, I have an Outlaw intake (dry flow) now.

Injectors? - I run cleaner through tank regularly

O2's - changed them out at 120K

cats? wouldn't i get performance issues if they were plugged?

coil packs? fking expensive I don't wanna have to replace these.

Please add any information you have, or add to the list. Thread jacking is mandatory!

At least I don't have piston slap!

My first guess would be the distributor but I am pretty sure thats a coil on plug ignition. With the info you have given my guess would be the EGR valve.

Yeah, I'm gonna check that out first. Yeah, these 5.3's have coil packs and they're hella expensive!

merlin5577 · July 3, 2008

I'm still guessing its the EGR valve. The valve is designed to operate under light load and part throttle conditions (like idle) and not WOT. If it was a coil pack I believe it would misfire more often. Good luck.

svensk · July 3, 2008

I'm still guessing its the EGR valve. The valve is designed to operate under light load and part throttle conditions (like idle) and not WOT. If it was a coil pack I believe it would misfire more often. Good luck.

Thanks a lot man about that EGR info I didn't know that part about it. I've been wondering why idle and lockup are the only thing affected.

Big_D · July 3, 2008

My problem is an intermittent misfire under load only when in OD with lockup and I begin to accelerate in OD. Does not do this in 3rd or when under WOT. However, it seems to mis once in a while idling when the truck gets warm (It will shake the truck if I'm sitting still). No codes as of yet, but I did get it to mis badly enough one night the SES flashed for like one second. Truck has no performance issues right now, nor am I suffering from poor mileage. I'm actually still getting very good mpg. Kind of a head scratcher.
Info about my bucket; 144K miles, newer ngk tr-55 copper plugs @ .060 gap, newer oem wires so far.

Alright, I've been gathering info from numerous PM's and research on teh intarwebs, and created this check list:

EGR sticking?

Temp sensor?

intake gasket leak? - common issue for LM7's

MAF? -not running an oiled filter anymore, I have an Outlaw intake (dry flow) now.

Injectors? - I run cleaner through tank regularly

O2's - changed them out at 120K

cats? wouldn't i get performance issues if they were plugged?

coil packs? fking expensive I don't wanna have to replace these.

Please add any information you have, or add to the list. Thread jacking is mandatory!

At least I don't have piston slap!

Hey I'm having the exact same problem. When i first start it up and its idling, or if im sitting at a stop light the truck will shake a bit like it's misfiring.... it shudders. starting to piss me off. I tried new plugs, ac delco iridiums gapped at .060. I'm gonna try an egr valve as well, for me it could still be the cats, o2 sensors, or plugwires. But, i'll start at the egr valve i guess....

svensk · July 3, 2008

My problem is an intermittent misfire under load only when in OD with lockup and I begin to accelerate in OD. Does not do this in 3rd or when under WOT. However, it seems to mis once in a while idling when the truck gets warm (It will shake the truck if I'm sitting still). No codes as of yet, but I did get it to mis badly enough one night the SES flashed for like one second. Truck has no performance issues right now, nor am I suffering from poor mileage. I'm actually still getting very good mpg. Kind of a head scratcher.
Info about my bucket; 144K miles, newer ngk tr-55 copper plugs @ .060 gap, newer oem wires so far.

Alright, I've been gathering info from numerous PM's and research on teh intarwebs, and created this check list:

EGR sticking?

Temp sensor?

intake gasket leak? - common issue for LM7's

MAF? -not running an oiled filter anymore, I have an Outlaw intake (dry flow) now.

Injectors? - I run cleaner through tank regularly

O2's - changed them out at 120K

cats? wouldn't i get performance issues if they were plugged?

coil packs? fking expensive I don't wanna have to replace these.

Please add any information you have, or add to the list. Thread jacking is mandatory!

At least I don't have piston slap!

Hey I'm having the exact same problem. When i first start it up and its idling, or if im sitting at a stop light the truck will shake a bit like it's misfiring.... it shudders. starting to piss me off. I tried new plugs, ac delco iridiums gapped at .060. I'm gonna try an egr valve as well, for me it could still be the cats, o2 sensors, or plugwires. But, i'll start at the egr valve i guess....

yeah, mine does that.

merlin5577 · July 3, 2008

I'm still guessing its the EGR valve. The valve is designed to operate under light load and part throttle conditions (like idle) and not WOT. If it was a coil pack I believe it would misfire more often. Good luck.

Thanks a lot man about that EGR info I didn't know that part about it. I've been wondering why idle and lockup are the only thing affected.

No worries man, glad I could help.

svensk · July 4, 2008

Well I got new front rotors and pads today, and then I pulled out the EGR for a look while I was on a roll. The float was fine and I hosed it down with TB cleaner, then scraped off the gasket and replaced it with a new one. While I was in there I also cleaned the MAF again, and hosed out the top part of the intake. Didn't work, still got a few misfires when it warmed up. However, damn...she was running like a raped ape tonight. I don't get it.

BTW- WTF brand new EGR's are like 200 bucks! F that if it's still the problem I'll just raid a junkyard.