08 Tahoe 258000 miles hard starting and wet spark plugs

[Jkiel84]

sounds like that ethanol percentage reset thing.

do you have a scanner you can see o2 sensors voltage and fuel trims?

Yes I’ll get the trims and o2 voltage all the 02 sensors are brand new Bosch ones cause I thought it was the cats cause I got the code for the cats performing under threshold so I changed them and the cats looked good I also did a compression test lowest compression was 165 and the highest was 180 I did the pressure test to see if the head gasket was leaking and that was normal but I get a code now for the fuel pump command module that comes and goes I changed the plugs now it’ll start right up and all I get is a p0300 code I’m at a lose I’ll get the o2 sensor voltage and fuel trims and it’s never had e85 in it I’m the second owner and my boss was the first other thing it ran fine one day then the next it wouldn’t run at all unless I pushed on the gas pedal

 

[Jkiel84]

Well, hopefully the OP will come back and see some of these comments and suggestions. Hopefully not a hit and run.

I would say to verify the fuel trims and the MAF reading, as well as the alcohol content with a decent scanner, and see if that shows anything. Eric O does that here:

Sorry guys I’ve been away at work at haven’t had time

 

[Jkiel84]

To get it running like it was prior to changing parts, you’ll need a hand with somebody who has a bi directional scanner and knowledge of the LS motor.

You’re throwing parts at it. An LS pro will hook up to it and ask questions like…

* Is it running e85 or pump gas?
* When’s your last tune up?
* Tell me anything you done to the truck in last 6 Mo’s.
* Let’s verify your new plugs are compatible and gap’d etc..

Pump gas tune up was 6 months did coil plugs wires oil changes are around 5000 cats are new o2 sensors are new I did the newer style valve cover there’s no leaks compression lowest is 165 highest is 180 head gasket doesn’t leak

 

[Jkiel84]

To get it running like it was prior to changing parts, you’ll need a hand with somebody who has a bi directional scanner and knowledge of the LS motor.

You’re throwing parts at it. An LS pro will hook up to it and ask questions like…

* Is it running e85 or pump gas?
* When’s your last tune up?
* Tell me anything you done to the truck in last 6 Mo’s.
* Let’s verify your new plugs are compatible and gap’d etc..

Pump gas 6 mos ago tune up plugs wires coils oil every 5000 truck is stock new cats and Bosch o2 sensors plugs are ac delco platinum gapped at .040 I checked before I put in and ac delco coils and wires one day it ran fine next morning go to work and it would start then die but only start if I feathered the gas codes were lean bank 1and 2 cars below threshold p0300 and a intermittent fuel control module loss of communication I have a bi directional scanner I’ll get trims and o2 voltages today 02/25

 

[petethepug]

I forgot to ask about -/+ battery cable replacement history, if any. Has it had e85 in it since this started? No biggie if it has. When new cats & o2 sensors go in it needs to run pump gas for 3-4 tanks to calibrate baseline off petrol. It can not calibrate off e85.

 

[Jkiel84]

258000? Non afm?

It’s arm but all that works correctly there’s no noises coming from it there was no knocking or any rattling coming from the motor itself it ran quiet and then the happed all the shark plugs are black and damp with fuel I’m lot losing any coolant I’ll get numbers today for the fuel trims and o2 sensors and post it thanks again

 

[Jkiel84]

I forgot to ask about -/+ battery cable replacement history, if any. Has it had e85 in it since this started? No biggie if it has. When new cats & o2 sensors go in it needs to run pump gas for 3-4 tanks to calibrate baseline off petrol. It can not calibrate off e85.

No e85 ever I e never replaced the cables never knew that needed to be done I learn so something new all the time on here that’s why I posted here with my problem

 

[petethepug]

Im guilty @ 180k mi of my Orig batt cables too. I’ve replaced OE injectors & o2 sensors last year.

I am getting DTC related to both and didn’t blink replacing them simply based on the fact they are wear items and both improved perf & milage. Did the OEM fuel pump, carbon canister, evap purge valves the year prior to blow out carbon pellet contamination.

Batt cables & front suspension rebuild comes in next few Mo’s. My smog is due in 1 year so when it comes time for diagnostics I’ll have a somewhat clean baseline for accurate fuel and electrical diagnostics on my P0420 / P0430 that comes about on e85 only.

I’ve run e85 exclusively for last 3 years. Here in CA it means a better performing 75-$85, 31 gal fill up vs $180 for 91. I’m laughing all the way to the bank.

 

[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

 

[Jkiel84]

Yes I’ll get the trims and o2 voltage all the 02 sensors are brand new Bosch ones cause I thought it was the cats cause I got the code for the cats performing under threshold so I changed them and the cats looked good I also did a compression test lowest compression was 165 and the highest was 180 I did the pressure test to see if the head gasket was leaking and that was normal but I get a code now for the fuel pump command module that comes and goes I changed the plugs now it’ll start right up and all I get is a p0300 code I’m at a lose I’ll get the o2 sensor voltage and fuel trims and it’s never had e85 in it I’m the second owner and my boss was the first other thing it ran fine one day then the next it wouldn’t run at all unless I pushed on the gas pedal