08 Tahoe 258000 miles hard starting and wet spark plugs

Jkiel84 · Feb 27, 2024

petethepug said:
Where did you purchase the new o2 sensors? I've seen another owner chase issues down a rabbit hole and it came back to non OEM o2 sensors that were prolly counterfeit.

eBay they were expensive so I thought they were good maybe I got hosed

Jkiel84 · Feb 27, 2024

Jkiel84 said:
My 08 Tahoe 5.3 flex fuel all of a sudden on day just had a p0300 random multiple misfire so I changed all the plugs ac Delco iridium’s mind just bought all new coil packs also ac delco it ran fine then the p0300 code checked the plugs they were all black and wet with fuel so I changed all the injectors since they were still oem from the factory still no change it starts really hard then when it starts it’ll idle up and down like it wants to die it also has brand new Bosch o2 sensors and new cats before the misfire thing happened it ran good not great but good was getting 15 miles to the gallon that’s why I say good not great running and that’s highway and then the next day I came out and it would barely stay running fuel pressure is normal with just key on it was 55psi and with it running it was 60psi I know there’s some knowledgeable people here need some help thanks for reading. All cylinders a between 170 and 180 one cylinder is at 160 don’t know if that helps and all coil packs are firing brand new spark plugs just looked in the cylinder with a scope and they all look good gonna do a pressure test to make sure the head gasket isnt leaking but truck wasn’t overheating and never lost coolant need some help buddies

I just wanna thank everyone who helped so far it’s not fixed yet but I’ll get it just nice to know there’s still people that will help definitely appreciate it

petethepug · Feb 27, 2024

Couldn’t find the thread on the counterfeit o2 sensors but I do remember they were Bosch units. Still have the old ones? If they’re compatible you can have my old, known working set from my 09 L9H 6.2 for shipping costs.

You’d have to cross check the part #’s.

petethepug · Feb 27, 2024

Cleaned up a post misplaced post

Jkiel84 · Feb 28, 2024

petethepug said:
Couldn’t find the thread on the counterfeit o2 sensors but I do remember they were Bosch units. Still have the old ones? If they’re compatible you can have my old, known working set from my 09 L9H 6.2 for shipping costs.

You’d have to cross check the part #’s.

View attachment 422456

Definitely appreciate it I’ll go to auto zone and get hopefully a good set lol really do appreciate it thank you

Jkiel84 · Feb 28, 2024

Jkiel84 said:
My 08 Tahoe 5.3 flex fuel all of a sudden on day just had a p0300 random multiple misfire so I changed all the plugs ac Delco iridium’s mind just bought all new coil packs also ac delco it ran fine then the p0300 code checked the plugs they were all black and wet with fuel so I changed all the injectors since they were still oem from the factory still no change it starts really hard then when it starts it’ll idle up and down like it wants to die it also has brand new Bosch o2 sensors and new cats before the misfire thing happened it ran good not great but good was getting 15 miles to the gallon that’s why I say good not great running and that’s highway and then the next day I came out and it would barely stay running fuel pressure is normal with just key on it was 55psi and with it running it was 60psi I know there’s some knowledgeable people here need some help thanks for reading. All cylinders a between 170 and 180 one cylinder is at 160 don’t know if that helps and all coil packs are firing brand new spark plugs just looked in the cylinder with a scope and they all look good gonna do a pressure test to make sure the head gasket isnt leaking but truck wasn’t overheating and never lost coolant need some help buddies

I guess when I said hard starting it’s not like the engine struggles it just turns over more times on the first start and then the only way it will start is for me to give it gas them it will start after the first start it will start after that the other thing I noticed is that the higher rpm it stops misfiring except if n number 8 but u figured that out the injector not firing sound now I gotta figure out if it’s smart wireless by issue or a bad injector like usual. Any say it enough thank mms everyone for the input it’s a little cold here in Wisconsin today but this weekend I’m gonna get at and I’ll keep you guys posted thanks again

Jkiel84 · Mar 3, 2024

Jkiel84 said:
My 08 Tahoe 5.3 flex fuel all of a sudden on day just had a p0300 random multiple misfire so I changed all the plugs ac Delco iridium’s mind just bought all new coil packs also ac delco it ran fine then the p0300 code checked the plugs they were all black and wet with fuel so I changed all the injectors since they were still oem from the factory still no change it starts really hard then when it starts it’ll idle up and down like it wants to die it also has brand new Bosch o2 sensors and new cats before the misfire thing happened it ran good not great but good was getting 15 miles to the gallon that’s why I say good not great running and that’s highway and then the next day I came out and it would barely stay running fuel pressure is normal with just key on it was 55psi and with it running it was 60psi I know there’s some knowledgeable people here need some help thanks for reading. All cylinders a between 170 and 180 one cylinder is at 160 don’t know if that helps and all coil packs are firing brand new spark plugs just looked in the cylinder with a scope and they all look good gonna do a pressure test to make sure the head gasket isnt leaking but truck wasn’t overheating and never lost coolant need some help buddies

So again another update I found that injector 8 isn’t working and all the o2 sensors I put in a shit I’m getting power to all of them the give me readings I just don’t thing the right readings the other thing I found was when it’s at a higher rpm the check engine light will stop flashing anyone know why that is and on my scanner it seems that all the other cylinders that had slight misfires stop misfiring but then when it comes back down to idle it starts flashing again like I said before thanks for everyone input

Jkiel84 · Mar 3, 2024

I didn’t see you couldn’t read what was going on and then here’s what the o2 sensors are doing it’s warm and at idle

Fless · Mar 3, 2024

This was mentioned in previous posts, along with suggested diagnostics, but it's still an issue. Need to clean the MAF or replace it with OE sensor; it's over-reporting at 9g/s at warm idle (if that's a true statement).

The fuel control isn't getting into closed loop so the O2 sensors can't report properly (they probably aren't warming up).

Jkiel84 · Mar 3, 2024

Fless said:
This was mentioned in previous posts, along with suggested diagnostics, but it's still an issue. Need to clean the MAF or replace it with OE sensor; it's over-reporting at 9g/s at warm idle (if that's a true statement).

The fuel control isn't getting into closed loop so the O2 sensors can't report properly (they probably aren't warming up).

Alright I try that thank you for the info

08 Tahoe 258000 miles hard starting and wet spark plugs

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