08 Tahoe 258000 miles hard starting and wet spark plugs

[Jkiel84]

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]

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]

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]

Cleaned up a post misplaced post

 

[Jkiel84]

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]

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]

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]

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]

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]

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

 

[j91z28d1]

on a side note.. the 8th injector isn'tf firing? is that plug not wet?

it is the one that's hard to get to, are you sure it's been checked and or changed out? it gets skipped alot because of its location

 

[Jkiel84]

on a side note.. the 8th injector isn'tf firing? is that plug not wet?

it is the one that's hard to get to, are you sure it's been checked and or changed out? it gets skipped alot because of its location

No I just found out I wasn’t firing I did the injector test and that was the only one that didn’t make any noise I checked the wiring with a noid light and it’s getting power to the injector I must have got a faulty inject there all brand new so are the plugs and wires and coils all that’s brand new and o2 sensors and cats all brand new I’m gonna recheck my fuel pressure at a higher rpm and see if it goes down with the key on engine off I’m getting 55 psi with the key On engine on at idle I’m getting 60psi but I never checked it under load so I’m gonna get a new injector and then check that thanks for the input man I really appreciate it

 

[j91z28d1]

so I was just looking at some fuel trims on a different car after a catch can install. but I noticed this and it reminded me that sometimes gm ecm's, especially when it's flashing the check engine light. as that's gm code for you're engine is eating itself alive. it will turn the fuel injector off in that cyl to try and save washing everything down with fuel.




so that might complicate your trouble shooting if the replacement injector doesn't fix anything. it might be spark related or valve train

 

[Jkiel84]

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 I got it running decent but my fuel trims are out of wack I have the numbers from my scan tool with the o2 sensor numbers and my fuel pressure dips to under 40 psi when bring up the rpm’s my mass air flow is at 5.74 g/s that seems right just wanna know why my trims are out of wack thanks again for everything at least I’m getting closer

 

[Fless]

It's taking away fuel, probably since it's been over-fueling for a while. Lots of fuel left where it shouldn't be, and you may want to check your oil for fuel contamination. Hope you didn't ruin a cat.

Warm it up and run it for a while (several days, maybe) to see if the short term trims come down. If they do, the long term trims will follow.

 

[Jkiel84]

It's taking away fuel, probably since it's been over-fueling for a while. Lots of fuel left where it shouldn't be, and you may want to check your oil for fuel contamination. Hope you didn't ruin a cat.

Warm it up and run it for a while (several days, maybe) to see if the short term trims come down. If they do, the long term trims will follow.

I just changed my oil it did smell like fuel and the cats a brand new just curious if everything else looks good like the o2 sensors I don’t have any other codes all the codes went away

 

[Fless]

The mv values for the O2 sensors will be high when there is too little oxygen (fuel rich) in the exhaust. So they do seem to be reading the exhaust as rich now.

Reading O2 sensor voltage ranges in Live Data

The voltage output of an oxygen (O2) sensor in a properly functioning vehicle can vary depending on the specific engine and the operating conditions.

www.innova.com

 

[Dustin Jackson]

@j91z28d1 I think in this situation that isn't the case since power is being sent to the injector but it just isn't firing

 

[j91z28d1]

@j91z28d1 I think in this situation that isn't the case since power is being sent to the injector but it just isn't firing

yeah if that's what's happening and he had power and switched ground at that injector then the ecm hasn't shut it off but I was never quite sure what he was doing to check. sounded like he was just running an injection test on the scanner one at a time. which turns off the injector and if the engine doesn't run rougher you know you've found one with an issue.(old days we'd do this by pulling a spark plug one at a time off) at that point it's one of the 3 things, eother spark, fuel or compression. he doesn't have a tick so hopefully it wasn't a compression issue. so I was just thinking of the ecm already had the injector shut off because of a blinking check engine light, the injector test might not have worked because the ecm already had it off.

sounds like it's fixed thou?

like said, drive it a bit.. the trims don't look crazy bad.. like I believe they will go as far as 25% plus or minus for both short and long term. so they are able to keep it under control right now. give it a bit and see if it clears up.


the fuel pressure dips below 40 under throttle could be a signs of things to come. it should probably be steady all the way to redline. it will very with vacuum thou, so if you let off vac will go high lowering the pressure for a bit.

 

[Jkiel84]

yeah if that's what's happening and he had power and switched ground at that injector then the ecm hasn't shut it off but I was never quite sure what he was doing to check. sounded like he was just running an injection test on the scanner one at a time. which turns off the injector and if the engine doesn't run rougher you know you've found one with an issue.(old days we'd do this by pulling a spark plug one at a time off) at that point it's one of the 3 things, eother spark, fuel or compression. he doesn't have a tick so hopefully it wasn't a compression issue. so I was just thinking of the ecm already had the injector shut off because of a blinking check engine light, the injector test might not have worked because the ecm already had it off.

sounds like it's fixed thou?

like said, drive it a bit.. the trims don't look crazy bad.. like I believe they will go as far as 25% plus or minus for both short and long term. so they are able to keep it under control right now. give it a bit and see if it clears up.


the fuel pressure dips below 40 under throttle could be a signs of things to come. it should probably be steady all the way to redline. it will very with vacuum thou, so if you let off vac will go high lowering the pressure for a bit.

It’s still has the original fuel pump that’s why I was wondering about the fuel pressure and yeah I checked the injector at the wire with a test light to make sure it was getting power thanks guys for all the help I we lost but I said I’d get it going again but with help do thanks again