08 Tahoe Hybrid no start/ no crank after AFM valve replacement

Disclaimer: Links on this page pointing to Amazon, eBay and other sites may include affiliate code. If you click them and make a purchase, we may earn a small commission.

j91z28d1

Full Access Member
Joined
Feb 28, 2022
Posts
1,964
Reaction score
2,271
Good job on that, but CrazedPerformance has seen oil pressure come from underneath, and this is why the VLOM modification is done. Cant get pressure from above or below that way.
yeah, I cut the gasket too on mine when I had the intake off to do the oil pressure sensor. I just didn't type it out, I probably should have.

I bought his kit, followed his videos and asked some questions on his board. seems like he has the best handle in why this happens and how to work around it.
 

ivin74

05 NBS Nali
Joined
Aug 3, 2014
Posts
2,271
Reaction score
2,325
Location
Htown, Texas
multiple cylinder misfire code. I'm thinking that the misfire
Remove the swap coils between cylinders to see if the miss fire follows the coil.

To clean the injectors follow the y video, that's the best cleaning method because you can actually see the spray pattern before and after.

Glad you got the suv going again, next time you can't turn on a vehicle bypass the computer by putting 12v power to the starter wire and it will fire right up.
 

j91z28d1

Full Access Member
Joined
Feb 28, 2022
Posts
1,964
Reaction score
2,271
Remove the swap coils between cylinders to see if the miss fire follows the coil.

To clean the injectors follow the y video, that's the best cleaning method because you can actually see the spray pattern before and after.

Glad you got the suv going again, next time you can't turn on a vehicle bypass the computer by putting 12v power to the starter wire and it will fire right up.


it's a funny thing. these don't have a starter. or an alternator. basically anything a normal truck has lol. you gotta have 320 ish volts to start these trucks at the right places or they are giant paperweights haha.
 
OP
OP
kenny-or

kenny-or

TYF Newbie
Joined
Jun 24, 2021
Posts
22
Reaction score
27

ivin74:​

Yea, I went through the process of cleaning each injector. I used a 9v battery to activate the injectors so I could spray cleaner through both directions. I took the time to soak the fuel rail in some gas as well and shook out and possible loose debris. Went ahead and replace all the seals on them while I was at it.

I swapped the coil pack and also the plug wire. I have a brand new plug in it but went ahead and pulled the plug just to be sure I didn't smash it down during installation; however, it looked fine. I did find that the plug to the coil itself was damaged and missing part of the casing so ordered a replacement pig tail which I plan to install this weekend. As j9 said... These cars don't have a typical starter. It starts using the electric motors in the trans. It was odd to notice there is no power steering pump, alternator, ac pump and so on. The only thing the belt runs is the water pump. lol

j91z28d1:​

Any idea what to do if the electric motors go bad? Can you just order a new motor and drop the transfer case and trans to replace them?


At this point I am driving the Tahoe. The tick is still there as is the miss on 8. I'm hopeful the new pig tail will fix #8. I did use a small emery board to sand the pins on the plug to the rail for the coils in case there was some corrosion in there. I'm not sure what else could cause a misfire on 8 if everything has been replaced so hopefully this resolves that.

My thought was that perhaps driving the car would add some wear to the lifters and cause them to compress and release properly.... No idea if this will work but at this point I'm going to save for the DOD\VVT delete. Do you guys have any suggestions for a programmer that will work with this kit? I'm debating doing the stage 3. Thoughts on that?

 

j91z28d1

Full Access Member
Joined
Feb 28, 2022
Posts
1,964
Reaction score
2,271
long post ahead.. lol

as I understand it, parts are available to rebuild these trannys. motors (there's 2)and all, but difficult to find a shop to dive into it. there's a book about them and some tear down videos on YouTube.

I was going to say doing a compressing check on that cyl and compare it to others, but not 100% sure how to do that haha. I believe you can pull the injector plugs and it will spin the engine over for a bit with the key, as it spins it very fast and people have confused it with the engine cranking and then dying. turns out it was just the starting sequence and they couldn't tell because there's no starter gear sounds. I believe there's only a set amount of times it will try to start thou before throwing a fault code.
basically other than fuel and spark, all your really need is compression. so be nice to see if you have a valve not sealing for some reason before taking it all apart. also exhaust leaks have gotten a few people thinking it was a tick. but you just had your heads off, so I doubt it's that. unless you used a paper gasket and it blew out. I alway reuse the oem ones when they are multi layer steel.

hp tuners will flash and disable the afm in the computer. that's what I use on mine. not a lot of tuning parameters enabled like on a normal engine and no transmission tuning. top of my head I remember afm enable/disable. tire size speedo cal, wot fueling but no part throttle ve table or maf cal that I saw. there's speed limit cut adjustment to raise the top speed, but a guy on the hp tuners board says hp engineers actually have that location wrong, and it's changing a different setting in the ecm. I've not touched it to try.

the cam change would be very interesting. I honestly don't know how it would work out, if there's enough adjustment built in that it would run well part throttle and then you can adjust wot fueling with hp or not. by wide open throttle, it doesn't have to be foot to the floor, just anything above 70% ish tps or 70kpa map will get you out of closed loop fueling and into open loop, where the ecm is no longer looking at the o2 sensors to adjust fuel trims on normal ecm's, again not 100% sure on this one but probably the same.

cam tuning can require some throttle opening adjustments and stuff with the drive by wire stuff so it idles right. which has to be done in the software, not like with the old cable throttle, you could just adjust the throttle stop set screw. I'd find a tuners that was interested in tuning it for you before you do the swap and can't find one. unless you wanna go down the tuning ribbit hole, which while super rewarding is always a steep learning curve. I've tuned a few things from my old diy obd1 prom days to my. 08 c6 with hp and honestly I've avoided putting a big cam in my ls3 because cam swap drivability is the hardest part and I very much dislike driving badly running cars for a few more hp these days, and I have no desire to deal with tuning shops even thou I know it can be done well.
younger I didn't care so much about part throttle issues haha. they do sound cool thou.



I don't want this to sound like I'm trying to talk you out of it, I'm super curious if it would work or not and how it drives. in theory the electric would help a big cam get the heavy truck rolling and then use the extra hp up top. since there's no torque converter, you wouldn't need a higher stall speed one but that said, just for info to watch out for. this has a special cam grind, not just the afm stuff, but it's called late intake closing(Miller cycle).

In theory it gives up off idle tq for efficiency in the mid range, they offset that cyl pressure bleed off from the late valve closing with higher compression ratio, so we have a different piston than the normal 6.0. so make sure you have the needed piston to valve clearance. I don't know if they would clear 600 lift or not. maybe thou, just a question to ask.

the dodge version of this hybrid, the Dodge Aspen didn't have the late intake closing cam. I have always wondered how they drove. they did list lower epa mpg ratings but that could be engine design as well. the ls is a pretty economical v8 when setup to be and gm seems to have done a lot to enhance that here. definitely run 93 in your truck after the cam swap with the higher compression and cam not bleeding off cyl pressure.


super interesting and I would love to try some things with mine, but it's 90% the wife's daily soccer mom van and my tow vehicle a few times a year. so byond trying out the lithium battery change, I've mostly decided to leave it alone. by go the cold air intake with scoop thou. my other project cars take up to much of my time as it is. but I would be lying if I haven't wondered what long tube headers and a free flowing intake would do to help fuel mileage. that and the late intake cams love boost. with the lack of any accessories to deal with, a small roots style blower like the lsa pulled to make say 4psi would be very interesting and easy to run a belt to haha. but they want way to much money for those things. the Ford take offs are cheap, and they make adapter brackets now, but they want 1400$ for a chunk of cnc aluminum. feels ridiculous and you're back at lsa money.

either way, keep us updated with what you do.
 

TollKeeper

Full Access Member
Joined
Feb 21, 2010
Posts
2,725
Reaction score
5,223
Location
Brighton, CO
Didn't read all that... holy long post batman!

I would start a little different, free tests!

First, pull the coil off another cylinder, and swap it with number 8. See if the miss moves. While you are there, pull the spark plug, and just check it for strap issues, and electrode issues.

Next, since this is a DOD/AFM engine, pull the valve cover and check the rockers. Usually it's the intake lifter that fails, but it can be either one.
 

j91z28d1

Full Access Member
Joined
Feb 28, 2022
Posts
1,964
Reaction score
2,271
definitely a long post haha. and I forgot to link the the tranny rebuild stuff.

if it is cyl 8, I believe that's not one of the afm cyl? I read that's 1,4,6 and 7. I have not had one apart thou, but also he changed the lifters with what I believe are a good brand. millings I believe?
 

BG1988

Full Access Member
Joined
Nov 14, 2018
Posts
2,946
Reaction score
1,344
View attachment 395441View attachment 395442


Hey all, I'm looking for some help and thoughts on an issue I have been battling with my 08 Tahoe Hybrid. I recently had an issue with a collapsed AFM lifter so replaced all of the valves. Due to the cathedral heads I needed to remove the valve covers, Heads, Intake, Exhaust Manifolds, and the valley cover. In the process of doing the valve replacements I replaced the valley cover plate, the valves, the spark plugs and the gaskets. I also replaced the water pump as I noticed that there was a leak from the weep hole on the pump. Prior to removing any of these parts I disconnected the 12V accessory battery and then removed the disconnect from the hybrid battery. I had to pull the wiring harness from the top of the engine which runs from the left side to the right and connects to the Hybrid control box on the right side as well as the coils, fuel injectors, and a handful of other devices. There was 3 ground wires that were disconnected in the process which I have verified are all secure back in the original locations.

The problem I am currently facing is that upon reassembly the vehicle will not crank over. I get the radio and all other systems as though there are no problems. When I try to crank the engine I get no crank. I checked the power in the accessory battery which tests out at 13.2v. According to my scanner the hybrid battery has 12.4V (assuming that its the hybrid battery voltage that its showing me).

I get a Service Hybrid System on the DIC and no codes currently on the scanner. I have pulled and replaced the disconnect as well to ensure it was seated and clean.

Prior to the AFM valve issue the hybrid system was working flawless. Even during the AFM issue it had no problems.

Currently the scanner for voltage with key on shows:
vpwr ($00) 11.355
vpwr ($01) 11.355
vpwr ($02) 11.355
vpwr ($03) 11.355
vpwr ($05) 11.355
vpwr ($07) 11.355

With key off shows:
vpwr ($00) 0.049
vpwr ($01) 0.032
vpwr ($02) 0.000
vpwr ($03) 0.000
vpwr ($05) 11.562
vpwr ($07) 11.670

I believe that the first 5 of these vpwr are the hybrid battery banks and vpwr07 is the accessory 12v battery. These have lost some voltage since the last jump and testing.

I did jump the vehicle and used my multimeter to measure the voltage on the accessory battery at 13.4v and the vpwr ranged between 12.4-12.8v

I read that jumping the vehicle with the key on can cause the system to think that there was a collision which disables the crank. When I jumped the vehicle the key was off; however, I did turn it on after about 10 minutes charging to get the voltage levels. I can't imagine that this would have caused it to go into safety mode could it? I didn't jump the vehicle prior to trying to turn it over unsuccessfully. Only after it would not crank thinking that the voltage in the batteries may have dropped in the week it was disconnected while I was replacing the valves. I did check all the fuses with a multimeter to verify they were good and did not come across and bad fuses. I also disconnected and reconnected the plugs to the hybrid system after a visual inspection for corrosion or bent pins. Everything looks great.

I am at a complete loss on what to check or where to go from here besides finding a tech2 scanner to put the system in jump mode and disable the collision detection (if its on)... The scanner is fairly expensive and there are a lot of warnings about buying these and getting china knockoffs so thats obviously a concern.

Can anyone help or throw me some ideas on where to go from here?

Sorry for the long write up. I just wanted to give as much data as I could in hopes someone may have experienced similar issues or has some idea on what to do besides the tech2. I love this car but am pulling my hair out at this point.
A: you set off the collision crash sensors which will need to be reset
B high voltage disconnect is not fully seated.. this is pretty common :)


make sure the 12v is disconnected before resitting the connection
 
Last edited:

MRT3678

TYF Newbie
Joined
May 11, 2023
Posts
1
Reaction score
1
Hey Kenny, there are some very sharp edges on the engine block where the harness gets routed through, so they reinforce that part of the harness with a piece of conduit. If the conduit is not position properly, or if the harness isn’t routed just correctly or even correctly without the conduit there it can cause the harness to get cut, grounding and shorting wires. The twisted wires being 5v communication wires, which would keep the engine from cranking or the power wires if there’s any electrical issue at all in that area it pretty much keeps the car from starting. The harness runs open to the right side of the engine as well. They can have major areas over there by the inverter. It sounds like the wiring harness or wires are the issue. There is a service bulletin out there somewhere that describes and has pictures pinch points/cut points.
 

BG1988

Full Access Member
Joined
Nov 14, 2018
Posts
2,946
Reaction score
1,344
Hey Kenny, there are some very sharp edges on the engine block where the harness gets routed through, so they reinforce that part of the harness with a piece of conduit. If the conduit is not position properly, or if the harness isn’t routed just correctly or even correctly without the conduit there it can cause the harness to get cut, grounding and shorting wires. The twisted wires being 5v communication wires, which would keep the engine from cranking or the power wires if there’s any electrical issue at all in that area it pretty much keeps the car from starting. The harness runs open to the right side of the engine as well. They can have major areas over there by the inverter. It sounds like the wiring harness or wires are the issue. There is a service bulletin out there somewhere that describes and has pictures pinch points/cut points.
photos would be great even a TSB because i see bad conduit on my engine went bad ( bought brand new OEM conduit :D )
 

Forum statistics

Threads
129,203
Posts
1,812,067
Members
92,305
Latest member
DefiantOne
Top