08 Tahoe 258000 miles hard starting and wet spark plugs

[j91z28d1]

what ended up being the fix? injectors?

I don't remember off the top of my head if you have the more normal old style fuel pump system, I know 07 did but at some point they split to a returnless style system with a module just for fuel pump speed. if you have that, you should have a requested fuel pressure number in your scanner somewhere and a actually fuel pressure from the sensor. if those 2 don't match it might be a sign the pump isn't keeping up.

just for future info, injectors have a common postive side from a fuse in the fuse box and they are turned off and on by the neg/ground wire from the ecm. so to test that you gotta have a test light across both with it running or cranking. I've seen people get caught out by having the test light ground lead on a ground like engine block and seeing postive on one side of the injector plug. but that only tells half of the story.

 

[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

Alright like I said it’s running still have a little misfire on 8 but it m guessing that has to be due to it not firing so it probably fouled out a bit I’ll change that I got some more info from driving it but all of my o2 sensors have heater resistance codes I’ll post them just curious if these maybe aren’t the right o2 sensors I could see 1 having a problem but all four with the same problem I’ll post some more info I got from the scan tool just so you guys can see if everything is looking good thanks again for everything and I get that p0300 code but the only misfire is on 8 and the only other issue is the first start after sitting awhile it take awhile for it to start and then kind of chugs to life but the after it’s started it’ll start right up and idle fine it’s just the first start after sitting for awhile could that have something to do with the o2 sensors I thought maybe fuel pump but then you think it would do it every time thanks for reading I really appreciate it

 

[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

Up date so it’s running good but I have a little misfire on 8 but only at idle driving it around no misfire but idle it’s misfiring only on cyl 8 I check the plug it’s got the right resistance and I’m still getting the stupid o2 sensor code for heater resistance any info will be awesome thanks a lot

 

[Jkiel84]

what ended up being the fix? injectors?

I don't remember off the top of my head if you have the more normal old style fuel pump system, I know 07 did but at some point they split to a returnless style system with a module just for fuel pump speed. if you have that, you should have a requested fuel pressure number in your scanner somewhere and a actually fuel pressure from the sensor. if those 2 don't match it might be a sign the pump isn't keeping up.

just for future info, injectors have a common postive side from a fuse in the fuse box and they are turned off and on by the neg/ground wire from the ecm. so to test that you gotta have a test light across both with it running or cranking. I've seen people get caught out by having the test light ground lead on a ground like engine block and seeing postive on one side of the injector plug. but that only tells half of the story.

Yes it was the injector it’s running decent but still having o2 problems all four say they have a heater resistance problem and I have a misfire on cyl 8 but only at idle you have idea it would be appreciated

 

[j91z28d1]

so I'm honestly not sure what you have going on.. I looked up your o2 codes, and it's kinda a pain to test them. I normally hate to say throw money and parts at something without being able to test. especially when they are new already but maybe some non Bosch ones. oem is the standard go to, but pricey and don't trust Amazon acdelco parts. they are mostly fakes.

at this point, I think I'd atleast replace the front 2 o2's and hope that fixes the resistance codes. there's also mentionedof calibration of the o2 heater using a scan tool but I've never once seen that on our trucks and I have a tech 2 and about 3 other ones.

for the #8 miss. I think it might be time to do a compression check in that cyl to check its not a mechanical issue. you've kinda ruled out not having spark or fuel. you might still have to much fuel, as I doubt the o2 codes are helping giving data to the ecm it can trust or is trusting.

 

[Jkiel84]

so I'm honestly not sure what you have going on.. I looked up your o2 codes, and it's kinda a pain to test them. I normally hate to say throw money and parts at something without being able to test. especially when they are new already but maybe some non Bosch ones. oem is the standard go to, but pricey and don't trust Amazon acdelco parts. they are mostly fakes.

at this point, I think I'd atleast replace the front 2 o2's and hope that fixes the resistance codes. there's also mentionedof calibration of the o2 heater using a scan tool but I've never once seen that on our trucks and I have a tech 2 and about 3 other ones.

for the #8 miss. I think it might be time to do a compression check in that cyl to check its not a mechanical issue. you've kinda ruled out not having spark or fuel. you might still have to much fuel, as I doubt the o2 codes are helping giving data to the ecm it can trust or is trusting.

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I checked compression already 170 on 8 all cylinders had awesome compression all the cylinders looked good I even did a pressure test to see if the head gasket was leaking and scoped all cylinders they all looked good better than I thought for having 258000 miles on them but I was thinking the same thing with the o2 sensors I’ll got to the parts store and get oem ones thank for the look buddy appreciate it

 

[j91z28d1]

glad it's got good compression.

 

[Jkiel84]

glad it's got good compression.

I think I figured out the mis on 8 also I bought some plugs off of Amazon and I think they were counterfeit I changed the plug and it seems like it’s running smoother the only thing is it cranks for a bit before it starts that’s the only thing that’s still wrong and the o2 heater circuit yet but I’m gonna go to auto zone and get some oem ones and see if that makes it go away thanks again everyone’s been super helpful I’m glad I got it driving again cause I like the Tahoe it’s a great ride I’m definitely gonna buy another when this one craps out

 

[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 last update I hope the only problems I have yet are the 02 sensors all 4 saying the heater circuit the truck won’t start after sitting for awhile I have to put my foot on the gas to get it to start I noticed if I cycle the key a few times it starts better which I learned from a forum on here so thanks and I get a misfire on cyl 8 but only at idle my guess for the misfire is vacuum leak in the intake maybe just hoping you guys can point me in the right direction again thanks for all the help much appreciated

 

[Fless]

Do the circuit system testing that was detailed by @j91z28d1 in Post #65; report results for all four heater circuits.