08 Tahoe misfire
#1
04-26-2022, 06:27 AM
08 Tahoe misfire
So I recently came across a 08 tahoe hybrid. Body is great. Had hybrid batterry replacement still under warranty for another year. Good tires. Carfax shows great maintenance records... bought it everything was fine until about 1hour after I bought it. Naturally I reached out to the owner simply saying the issue was significant enough we're he definitely was aware of the situation. The least he can do is let me know his progress in diagnosis so I don't waist time.. anyways. I bought it and originally I did notice a slightly... and I mean slightly small misfire. Easily plugs and wire or simple tune up most of the time... well apparently not.... get this on the way home the truck is working fine. V4 v8 autostop everything. Until I hit a big nasty hill. Then the check engine light started flashing the oil pressure says zero. I pull over the truck seems to be running fine. Check the oil and there's oil in it. I decide to see what happens. And start it back up. The cel is off the pressure is normal. I proceed another mile and low pressure kicks in. I'm about a block from my house and I decide to just go for it. The truck sounds normal so I assume oil pressure sending unit... do some research and yup I'll swap out the sensor.. pulled the old one screen was filled with junk and I mean filled. New screen goes in drain oil and nothing comes out the drain plug?? But oil on dipstick???? Shove a pic inside drain hole and the amount of sludge that came out was unbelievable. The most I've ever seen ever. (The motor has heads machined and new gaskets installed about 50k ago) so I decide to do a engine flush... 2nd time the oil comes out naturally after another big ole goober of sludge.... wow... drive it no oil pressure issues thus far.. misfire is still there.. replaced plugs and wires.. no difference... trying to stop at a stop sign and now I'm experiencing the lurching jumping about once every 50stops or so.. only have a cheap scan tool and only code that comes up is p0900 random misfire... no other codes .. take it to parts store and their obd tool is broken... so for the heck of it I have her test the 12v battery.... shows up as 12amp do a alt check and it says dios failed.....
Where do I begin on this... i love this truck other than the issues obviously... also when I give it a noticeable amount of gas I hear a crazy roar. It's like it's been bogged down its entire life and it's trying to finally open up.. but at the same time I'm scared it's actually something bad lol.. any thoughts
Where do I begin on this... i love this truck other than the issues obviously... also when I give it a noticeable amount of gas I hear a crazy roar. It's like it's been bogged down its entire life and it's trying to finally open up.. but at the same time I'm scared it's actually something bad lol.. any thoughts
#2
04-29-2022, 07:47 PM
Re: 08 Tahoe misfire
wow. that poor truck had a horrible life.
I'd probably do a compression check on that engine. might be more going on, especially if it's been a part.
oddly mine has one new coil pack, it was done before I got it, but ls packs are usually pretty reliable, so I thought that was odd. your miss could be something like that if you have good even compression.
if they load tested the 12v battery and it came back 12 CCA, probably worth changing that, so you don't get stuck somewhere. mine has a 2016 sticker on it, but still load tested 800 something, so I haven't changed it, even thou normally I consider that well passed time to replace a battery, even a agm one.
for now I'd probably drive it in m4 mode till your sort some of the issues. and probably turn off the 4cyl mode if you plan to keep it, with all the sludge in it, it's probably just a matter of time before you get the famous stuck lifter tick, since the oil is used as hydraulic fluid to activate all that stuff.
I'd probably do a compression check on that engine. might be more going on, especially if it's been a part.
oddly mine has one new coil pack, it was done before I got it, but ls packs are usually pretty reliable, so I thought that was odd. your miss could be something like that if you have good even compression.
if they load tested the 12v battery and it came back 12 CCA, probably worth changing that, so you don't get stuck somewhere. mine has a 2016 sticker on it, but still load tested 800 something, so I haven't changed it, even thou normally I consider that well passed time to replace a battery, even a agm one.
for now I'd probably drive it in m4 mode till your sort some of the issues. and probably turn off the 4cyl mode if you plan to keep it, with all the sludge in it, it's probably just a matter of time before you get the famous stuck lifter tick, since the oil is used as hydraulic fluid to activate all that stuff.
#3
05-02-2022, 09:30 AM
Re: 08 Tahoe misfire
wow. that poor truck had a horrible life.
I'd probably do a compression check on that engine. might be more going on, especially if it's been a part.
oddly mine has one new coil pack, it was done before I got it, but ls packs are usually pretty reliable, so I thought that was odd. your miss could be something like that if you have good even compression.
if they load tested the 12v battery and it came back 12 CCA, probably worth changing that, so you don't get stuck somewhere. mine has a 2016 sticker on it, but still load tested 800 something, so I haven't changed it, even thou normally I consider that well passed time to replace a battery, even a agm one.
for now I'd probably drive it in m4 mode till your sort some of the issues. and probably turn off the 4cyl mode if you plan to keep it, with all the sludge in it, it's probably just a matter of time before you get the famous stuck lifter tick, since the oil is used as hydraulic fluid to activate all that stuff.
I'd probably do a compression check on that engine. might be more going on, especially if it's been a part.
oddly mine has one new coil pack, it was done before I got it, but ls packs are usually pretty reliable, so I thought that was odd. your miss could be something like that if you have good even compression.
if they load tested the 12v battery and it came back 12 CCA, probably worth changing that, so you don't get stuck somewhere. mine has a 2016 sticker on it, but still load tested 800 something, so I haven't changed it, even thou normally I consider that well passed time to replace a battery, even a agm one.
for now I'd probably drive it in m4 mode till your sort some of the issues. and probably turn off the 4cyl mode if you plan to keep it, with all the sludge in it, it's probably just a matter of time before you get the famous stuck lifter tick, since the oil is used as hydraulic fluid to activate all that stuff.
Reciept shows
machine shop heads x2
head boys
head gaskets
thermostat housing
valve lifters w/dod x8
value lifters wo/dod x8
ignition coil
temp switch sensor
Coolant
labor
So all 8 lifters were apparently replaced. Just 40k miles ago.. I can't believe they are bad again..
#4
05-02-2022, 04:10 PM
Re: 08 Tahoe misfire
I don't know a ton about the hybrid side of these trucks, just what I have read. but that side sounds about right. better than mine, but I'm probably due for a battery. I'm at 130k.
as for the engine, it's mostly a ls, besides being late intake valve closing. which I'm guessing is cam and tuning. I would agree that 40k if they used good lifters, they should be good for a while. but I've seen some posts about using cheap afm lifters failing very quickly. but since it runs OK in 4cyl mode, makes me think they are OK. what makes me wonder and I'd be worried about is how on earth did it have all the sludge in it so quickly. that's crazy. I have a bore scope at work and peeked around in mine and it looks brand new, like not even oil stains on the aluminum. I switched to the longer oil filter with a higher psi bypass to keep the oil filtered as well as I can. being a ls, they most likely have cam bearing wear issues like all ls's do and these use oil pressure from a groove in the 2nd cam journal for the hydraulic cam timing oil and the 4cyl mode. I turned off the 4cyl with hp tuners just incase. I also have the volm block off from this guy to delete manually too, but I haven't pulled the intake yet.
https://www.crazedperformancerepair....lley-feed-plug
he's got a forum and a bunch of YouTube videos about afm, good place to ask about oiling issues too. I honestly don't think there's much mpg in it, but also I have zero motivation to work on this thing after looking around under the hood haha so I'll give up a mpg for not pulling the heads. Lotta extra stuff in the way of everything. but I will if I have to.
be interesting to hear what the compression test says. if looks good, if you have a temp gun you can usually aim at the exhaust ports and tell which one is running cooler for the cyl that missing, then swap the could from cyl to cyl to see if the cooler temp follows, maybe save some money of throwing coils at it. do you have a scanner? a decent one should tell you which cyl is missing too.
weird that it's bad in rev, from what I have read these trucks trannys don't really have a reverse. only the 2nd electric motor goes in reverse and the engine turns the front motor as a generator to power the reverse motor, not that it matters just seems odd it would load the engine enough to feel the missing so bad.
as for the engine, it's mostly a ls, besides being late intake valve closing. which I'm guessing is cam and tuning. I would agree that 40k if they used good lifters, they should be good for a while. but I've seen some posts about using cheap afm lifters failing very quickly. but since it runs OK in 4cyl mode, makes me think they are OK. what makes me wonder and I'd be worried about is how on earth did it have all the sludge in it so quickly. that's crazy. I have a bore scope at work and peeked around in mine and it looks brand new, like not even oil stains on the aluminum. I switched to the longer oil filter with a higher psi bypass to keep the oil filtered as well as I can. being a ls, they most likely have cam bearing wear issues like all ls's do and these use oil pressure from a groove in the 2nd cam journal for the hydraulic cam timing oil and the 4cyl mode. I turned off the 4cyl with hp tuners just incase. I also have the volm block off from this guy to delete manually too, but I haven't pulled the intake yet.
https://www.crazedperformancerepair....lley-feed-plug
he's got a forum and a bunch of YouTube videos about afm, good place to ask about oiling issues too. I honestly don't think there's much mpg in it, but also I have zero motivation to work on this thing after looking around under the hood haha so I'll give up a mpg for not pulling the heads. Lotta extra stuff in the way of everything. but I will if I have to.
be interesting to hear what the compression test says. if looks good, if you have a temp gun you can usually aim at the exhaust ports and tell which one is running cooler for the cyl that missing, then swap the could from cyl to cyl to see if the cooler temp follows, maybe save some money of throwing coils at it. do you have a scanner? a decent one should tell you which cyl is missing too.
weird that it's bad in rev, from what I have read these trucks trannys don't really have a reverse. only the 2nd electric motor goes in reverse and the engine turns the front motor as a generator to power the reverse motor, not that it matters just seems odd it would load the engine enough to feel the missing so bad.
#5
05-15-2022, 05:17 PM
Re: 08 Tahoe misfire
I don't know a ton about the hybrid side of these trucks, just what I have read. but that side sounds about right. better than mine, but I'm probably due for a battery. I'm at 130k.
as for the engine, it's mostly a ls, besides being late intake valve closing. which I'm guessing is cam and tuning. I would agree that 40k if they used good lifters, they should be good for a while. but I've seen some posts about using cheap afm lifters failing very quickly. but since it runs OK in 4cyl mode, makes me think they are OK. what makes me wonder and I'd be worried about is how on earth did it have all the sludge in it so quickly. that's crazy. I have a bore scope at work and peeked around in mine and it looks brand new, like not even oil stains on the aluminum. I switched to the longer oil filter with a higher psi bypass to keep the oil filtered as well as I can. being a ls, they most likely have cam bearing wear issues like all ls's do and these use oil pressure from a groove in the 2nd cam journal for the hydraulic cam timing oil and the 4cyl mode. I turned off the 4cyl with hp tuners just incase. I also have the volm block off from this guy to delete manually too, but I haven't pulled the intake yet.
https://www.crazedperformancerepair....lley-feed-plug
he's got a forum and a bunch of YouTube videos about afm, good place to ask about oiling issues too. I honestly don't think there's much mpg in it, but also I have zero motivation to work on this thing after looking around under the hood haha so I'll give up a mpg for not pulling the heads. Lotta extra stuff in the way of everything. but I will if I have to.
be interesting to hear what the compression test says. if looks good, if you have a temp gun you can usually aim at the exhaust ports and tell which one is running cooler for the cyl that missing, then swap the could from cyl to cyl to see if the cooler temp follows, maybe save some money of throwing coils at it. do you have a scanner? a decent one should tell you which cyl is missing too.
weird that it's bad in rev, from what I have read these trucks trannys don't really have a reverse. only the 2nd electric motor goes in reverse and the engine turns the front motor as a generator to power the reverse motor, not that it matters just seems odd it would load the engine enough to feel the missing so bad.
as for the engine, it's mostly a ls, besides being late intake valve closing. which I'm guessing is cam and tuning. I would agree that 40k if they used good lifters, they should be good for a while. but I've seen some posts about using cheap afm lifters failing very quickly. but since it runs OK in 4cyl mode, makes me think they are OK. what makes me wonder and I'd be worried about is how on earth did it have all the sludge in it so quickly. that's crazy. I have a bore scope at work and peeked around in mine and it looks brand new, like not even oil stains on the aluminum. I switched to the longer oil filter with a higher psi bypass to keep the oil filtered as well as I can. being a ls, they most likely have cam bearing wear issues like all ls's do and these use oil pressure from a groove in the 2nd cam journal for the hydraulic cam timing oil and the 4cyl mode. I turned off the 4cyl with hp tuners just incase. I also have the volm block off from this guy to delete manually too, but I haven't pulled the intake yet.
https://www.crazedperformancerepair....lley-feed-plug
he's got a forum and a bunch of YouTube videos about afm, good place to ask about oiling issues too. I honestly don't think there's much mpg in it, but also I have zero motivation to work on this thing after looking around under the hood haha so I'll give up a mpg for not pulling the heads. Lotta extra stuff in the way of everything. but I will if I have to.
be interesting to hear what the compression test says. if looks good, if you have a temp gun you can usually aim at the exhaust ports and tell which one is running cooler for the cyl that missing, then swap the could from cyl to cyl to see if the cooler temp follows, maybe save some money of throwing coils at it. do you have a scanner? a decent one should tell you which cyl is missing too.
weird that it's bad in rev, from what I have read these trucks trannys don't really have a reverse. only the 2nd electric motor goes in reverse and the engine turns the front motor as a generator to power the reverse motor, not that it matters just seems odd it would load the engine enough to feel the missing so bad.
#6
05-15-2022, 07:30 PM
Re: 08 Tahoe misfire
so you did plugs wires and coils and still getting misfires? hmm
since you have a scanner now, do you see the short term and long term fuel trims really out of wack? normally they run +/- 5% ish. if your o2 sensors are sending really bad info, it might be adding a bunch of fuel and running badly. o2 sensor usually fail so the car runs richer. causing the ecm to go +% fuel. the trims might be called STFT and LTFT in your scanner data list.
you can also chick for intake air leaks, I once had a 96 that had intake air leaks and ran lean enough I could hear it ping and miss. check from the MAF to the intake too. the ls based engines have o'ring on the intake to head, so they don't normally leak. the old trick from the carb days was to spray brake cleaner around the intake ports and if it was sucked in by a vacuum leak the engine would Rev up. you knew you had a leak. can't really do that these days, the ecm can compensate for the brake clean too fast to hear, but if you have someone watch the scanner. if you can watch the o2 voltage, it will go from switching back and forth to flat lane when you spray if there's a leak.
other than that, I'd still borrow a comp tester. auto zone loans tools out. it's worth knowing if a valve is hanging open just a touch since the engine has been apart at some point.
have you change fuel filter? it could be plugged up, not likely since it doesn't always run badly. you could also run it down low on fuel and try running some 93 octane, see if the misfires are less on that. also something I do to my own cars, but isn't something I normally recommend, but if you have e85 local, a few gal of that won't hurt anything, but the high alcohol content will clean up any varnish in the fuel injectors and its like 110 octane so it might help the miss too if it's fuel related. don't go crazy and fill it up or anything, just a few gal to a 1/4 tank, and then run it out within a few days. to me it's a better version of sea foam stuff haha. which you could also try, I've never used the stuff but I have been told by people I mostly trust that they have had good luck with it on cars that have sat a while.
since you have a scanner now, do you see the short term and long term fuel trims really out of wack? normally they run +/- 5% ish. if your o2 sensors are sending really bad info, it might be adding a bunch of fuel and running badly. o2 sensor usually fail so the car runs richer. causing the ecm to go +% fuel. the trims might be called STFT and LTFT in your scanner data list.
you can also chick for intake air leaks, I once had a 96 that had intake air leaks and ran lean enough I could hear it ping and miss. check from the MAF to the intake too. the ls based engines have o'ring on the intake to head, so they don't normally leak. the old trick from the carb days was to spray brake cleaner around the intake ports and if it was sucked in by a vacuum leak the engine would Rev up. you knew you had a leak. can't really do that these days, the ecm can compensate for the brake clean too fast to hear, but if you have someone watch the scanner. if you can watch the o2 voltage, it will go from switching back and forth to flat lane when you spray if there's a leak.
other than that, I'd still borrow a comp tester. auto zone loans tools out. it's worth knowing if a valve is hanging open just a touch since the engine has been apart at some point.
have you change fuel filter? it could be plugged up, not likely since it doesn't always run badly. you could also run it down low on fuel and try running some 93 octane, see if the misfires are less on that. also something I do to my own cars, but isn't something I normally recommend, but if you have e85 local, a few gal of that won't hurt anything, but the high alcohol content will clean up any varnish in the fuel injectors and its like 110 octane so it might help the miss too if it's fuel related. don't go crazy and fill it up or anything, just a few gal to a 1/4 tank, and then run it out within a few days. to me it's a better version of sea foam stuff haha. which you could also try, I've never used the stuff but I have been told by people I mostly trust that they have had good luck with it on cars that have sat a while.
#7
05-16-2022, 11:29 PM
Re: 08 Tahoe misfire
so you did plugs wires and coils and still getting misfires? hmm
since you have a scanner now, do you see the short term and long term fuel trims really out of wack? normally they run +/- 5% ish. if your o2 sensors are sending really bad info, it might be adding a bunch of fuel and running badly. o2 sensor usually fail so the car runs richer. causing the ecm to go +% fuel. the trims might be called STFT and LTFT in your scanner data list.
you can also chick for intake air leaks, I once had a 96 that had intake air leaks and ran lean enough I could hear it ping and miss. check from the MAF to the intake too. the ls based engines have o'ring on the intake to head, so they don't normally leak. the old trick from the carb days was to spray brake cleaner around the intake ports and if it was sucked in by a vacuum leak the engine would Rev up. you knew you had a leak. can't really do that these days, the ecm can compensate for the brake clean too fast to hear, but if you have someone watch the scanner. if you can watch the o2 voltage, it will go from switching back and forth to flat lane when you spray if there's a leak.
other than that, I'd still borrow a comp tester. auto zone loans tools out. it's worth knowing if a valve is hanging open just a touch since the engine has been apart at some point.
have you change fuel filter? it could be plugged up, not likely since it doesn't always run badly. you could also run it down low on fuel and try running some 93 octane, see if the misfires are less on that. also something I do to my own cars, but isn't something I normally recommend, but if you have e85 local, a few gal of that won't hurt anything, but the high alcohol content will clean up any varnish in the fuel injectors and its like 110 octane so it might help the miss too if it's fuel related. don't go crazy and fill it up or anything, just a few gal to a 1/4 tank, and then run it out within a few days. to me it's a better version of sea foam stuff haha. which you could also try, I've never used the stuff but I have been told by people I mostly trust that they have had good luck with it on cars that have sat a while.
since you have a scanner now, do you see the short term and long term fuel trims really out of wack? normally they run +/- 5% ish. if your o2 sensors are sending really bad info, it might be adding a bunch of fuel and running badly. o2 sensor usually fail so the car runs richer. causing the ecm to go +% fuel. the trims might be called STFT and LTFT in your scanner data list.
you can also chick for intake air leaks, I once had a 96 that had intake air leaks and ran lean enough I could hear it ping and miss. check from the MAF to the intake too. the ls based engines have o'ring on the intake to head, so they don't normally leak. the old trick from the carb days was to spray brake cleaner around the intake ports and if it was sucked in by a vacuum leak the engine would Rev up. you knew you had a leak. can't really do that these days, the ecm can compensate for the brake clean too fast to hear, but if you have someone watch the scanner. if you can watch the o2 voltage, it will go from switching back and forth to flat lane when you spray if there's a leak.
other than that, I'd still borrow a comp tester. auto zone loans tools out. it's worth knowing if a valve is hanging open just a touch since the engine has been apart at some point.
have you change fuel filter? it could be plugged up, not likely since it doesn't always run badly. you could also run it down low on fuel and try running some 93 octane, see if the misfires are less on that. also something I do to my own cars, but isn't something I normally recommend, but if you have e85 local, a few gal of that won't hurt anything, but the high alcohol content will clean up any varnish in the fuel injectors and its like 110 octane so it might help the miss too if it's fuel related. don't go crazy and fill it up or anything, just a few gal to a 1/4 tank, and then run it out within a few days. to me it's a better version of sea foam stuff haha. which you could also try, I've never used the stuff but I have been told by people I mostly trust that they have had good luck with it on cars that have sat a while.
The Emissions System is not performing as expected. An issue has been detected in the Exhaust Emissions System which monitors and controls exhaust gases released into the air from the engine. If the vehicle is continually driven with this light on, the emission controls might not work as well, the vehicle fuel economy might not be as good, the engine might not run as smoothly and could lead to future repairs
#8
05-18-2022, 04:38 AM
Re: 08 Tahoe misfire
Could this by chance be a bad catalytic converter? When I floor it it does make God awful almost gurgling sound. It also I don't know... anyone in the PDX area want to make some money and fix this thing?
#9
05-20-2022, 12:55 AM
Re: 08 Tahoe misfire
so you did plugs wires and coils and still getting misfires? hmm
since you have a scanner now, do you see the short term and long term fuel trims really out of wack? normally they run +/- 5% ish. if your o2 sensors are sending really bad info, it might be adding a bunch of fuel and running badly. o2 sensor usually fail so the car runs richer. causing the ecm to go +% fuel. the trims might be called STFT and LTFT in your scanner data list.
you can also chick for intake air leaks, I once had a 96 that had intake air leaks and ran lean enough I could hear it ping and miss. check from the MAF to the intake too. the ls based engines have o'ring on the intake to head, so they don't normally leak. the old trick from the carb days was to spray brake cleaner around the intake ports and if it was sucked in by a vacuum leak the engine would Rev up. you knew you had a leak. can't really do that these days, the ecm can compensate for the brake clean too fast to hear, but if you have someone watch the scanner. if you can watch the o2 voltage, it will go from switching back and forth to flat lane when you spray if there's a leak.
other than that, I'd still borrow a comp tester. auto zone loans tools out. it's worth knowing if a valve is hanging open just a touch since the engine has been apart at some point.
have you change fuel filter? it could be plugged up, not likely since it doesn't always run badly. you could also run it down low on fuel and try running some 93 octane, see if the misfires are less on that. also something I do to my own cars, but isn't something I normally recommend, but if you have e85 local, a few gal of that won't hurt anything, but the high alcohol content will clean up any varnish in the fuel injectors and its like 110 octane so it might help the miss too if it's fuel related. don't go crazy and fill it up or anything, just a few gal to a 1/4 tank, and then run it out within a few days. to me it's a better version of sea foam stuff haha. which you could also try, I've never used the stuff but I have been told by people I mostly trust that they have had good luck with it on cars that have sat a while.
since you have a scanner now, do you see the short term and long term fuel trims really out of wack? normally they run +/- 5% ish. if your o2 sensors are sending really bad info, it might be adding a bunch of fuel and running badly. o2 sensor usually fail so the car runs richer. causing the ecm to go +% fuel. the trims might be called STFT and LTFT in your scanner data list.
you can also chick for intake air leaks, I once had a 96 that had intake air leaks and ran lean enough I could hear it ping and miss. check from the MAF to the intake too. the ls based engines have o'ring on the intake to head, so they don't normally leak. the old trick from the carb days was to spray brake cleaner around the intake ports and if it was sucked in by a vacuum leak the engine would Rev up. you knew you had a leak. can't really do that these days, the ecm can compensate for the brake clean too fast to hear, but if you have someone watch the scanner. if you can watch the o2 voltage, it will go from switching back and forth to flat lane when you spray if there's a leak.
other than that, I'd still borrow a comp tester. auto zone loans tools out. it's worth knowing if a valve is hanging open just a touch since the engine has been apart at some point.
have you change fuel filter? it could be plugged up, not likely since it doesn't always run badly. you could also run it down low on fuel and try running some 93 octane, see if the misfires are less on that. also something I do to my own cars, but isn't something I normally recommend, but if you have e85 local, a few gal of that won't hurt anything, but the high alcohol content will clean up any varnish in the fuel injectors and its like 110 octane so it might help the miss too if it's fuel related. don't go crazy and fill it up or anything, just a few gal to a 1/4 tank, and then run it out within a few days. to me it's a better version of sea foam stuff haha. which you could also try, I've never used the stuff but I have been told by people I mostly trust that they have had good luck with it on cars that have sat a while.
Idling in park
here is a bunch of the readings when in park idling. Next set is when in reverse with foot on brakes.
