Thanks!
Yea the biggest issues for me will be the AFM. The pack not as much, since I know it's been replaced at least once before.
I'm thinking an inspection of the VLOM, the VLOM filter, and the lifters might be in order if I buy it and bring it back. I know it's not a popular system, but I think on these hybrids it ends up being more useful since the motors can pick up the slack.
RockAuto thankfully has the parts (they don't have the compressor, hence my question). Is there anything hybrid specific I would need to know about the AFM, or just make sure I get the right parts and follow the repair guide for a GMT900 non-hybrid?
if you ever need a compresor, I'd just find a ebay one. since they aren't a high failure point, it should be good. I've seen them for 500 ish.
oh, the charcoal canister at least on the non hybrid Suvs is a huge failure point. like clock work they dump carbon pellets in the fuel vent system and it's a nightmare. I don't know if it's an issue on these hybrids or the trucks, but I replaced mine anyways. they are a specific hybrid part number thou and getting hard to find oem. I bought one off rock auto clearance, ended up being bad but I didn't know till after the return period ran out. found one more on ebay that was new left over stock somewhere. that one has been good. worth keeping an eye out for one.
the afm vlom system is honestly a nightmare. I know you want to keep it, I did too but it's just not good for long term use. even if the lifters don't fail and eat the cam up, over time those cyl that aren't used build up varnash from the oil all these Gen 4 ls engines eat. which sticks the rings and they start to burn even more oil. there's a guy here that has done gm's tsb for unsricking the rings with good results. some special surff you pour in the spark plug hole, let set for a while. his stopped burning a good amount of oil after that but the cylinder that cut out seem to build up faster. I personally believe it's the pvc system. older ls1s had a pvc valve in the vacuum line into the intake. at some point gm stopped that, put a not very good baffle in the valve cover and let it suck full bore. even with the updated valve cover like your newer one has, it still drinks a lot of oil. to fight that it's common here to install a aftermarket catch can inline. I have one and it gets more oil then I expected in it between changes for a engine that really only sees 2500rpm max. Definitely do a search for catch can here. I have a 35$ Amazon one, I feel it's totally worth it.
but back to afm, so these lifters have a few reasons they fail besides the obvious wearing out. they release internally for the valves to stay closed by a separate oil port in the lifter. that oil is fed from the vlom. if they get oil sent a little late or a little early, it's ******* the lifter and the vlom is electronically controlled solenoids that open to send the oil pressure down. if they are worn, leaking or sticking, that alone can damage the the lifter. the lifters themselves either gall up inside and get stuck, usually lack of lubrication, or dirty oil/varnash builds up from following gm recommended oil change of up to 10k miles and they stick down and won't release. throw in its actual fairly common we see posts about non afm cyl lifters tapping. gm seems to have lost the ability to build a lifter that lasts forever like thes old engines for some reason. but when any of that happens, the lifter wipes out the cam lobe and you need to either replace everything, cam, lifter, vlom if you want afm to work, or a delete kit. but here's the hybrid part. we don't have a normal cam grind, there's no delete kit with this grind, I don't even know if the oem cam is available anymore. hptuners does support the truck a little bit, I have it. but I don't know that I see enough parameters defined to tune for a cam swap, or what kinda tuning would even be needed to go from our late intake valve cam grind to a normal one. plus we then would have a higher compression ratio and no hybrid cam to bleed off the extra compression, so probably need 93 to keep knock away.
I've seen 2 posts about guys putting normal delete kit cams in, I've asked how they run or if they have any problems and no one ever replies. I personally don't want to be the first to do it haha.
so if you're dead set on keeping afm with your mileage, I would replace all the afm lifters with oem gm afm lifters only, they are expensive but there's many posts about the cheap mostly made in China lifters failing in days. millings is also said to be good ones and some say they are actually the manufacturer of the oem gm ones. but I don't know forsure, about the same price thou. oem lifter trays and new oem vlom cover with new solenoids.
personality it is not worth the risk for what might be 1mpg, but I can't say I noticed any difference. I disable my afm in the ecm with hptuners, remove the vlom cover and there's a oil passageway block off you install under the oil pressure sensor, that eliminates any chance of oil getting sent down to the lifters if a solenoid were to leak. and then on the lifter side of the solenoid, there's a gasket where oil pressure is sent down into the the block to the lifter to release it. you cut that gasket so that it vents any oil that might find itself from the normal lifter oil port around a slightly worn lifter bore back up into the afm release port and release the lifter. at that point along with good oil changes every 3-5k miles, you've done all you can to limp this Gen 4 ls valve train along as long as you can. I like to keep my cars into the 300k range. fingers crossed it gets me close, I honestly don't want to pull these heads lol.
as for mpg, there's really no free lunch, these aren't plug in hybrids. the only really free energy is the regen braking charging the battery. besides that the engine charges the battery either way, and it's not going to be able to keep the truck moving, since afm doesn't work at idle and charge the battery. I live in hot tx with the ac blasting even with the engine idling it's using a little bit of battery power to run everything, only about 500w but it's still gotta be put back into the battery with gas.
the tranny design, the cam type, being lighter weight and atleast for the Tahoe having better aero is what really brings the mpg up, especially when cruising. I'm actually testing out the hood adjar switch trick right now, with the hood open the truck doesn't go into auto stop where it runs off the battery pack, I have a switch on the hood to tell the ecm the hood is up when it's not. from what I see, it uses more fuel idling the truck at red-lights but since the battery is kept at a much higher state of charge, say 65% instead of 50 ish of normal, it seems to discharge more power to the electrical motors whole accelerating at light throttle. this saves fuel but also feels much nicer driving as it just feels more effortless and I haven't been able to do any hand math yet on milage but my dash hasn't started dropping yet. so doing everything "wrong" no afm, no auto stop the truck is still showing good to me mileage of about 18 in soccer mom hell of city traffic and school pick up lines. plus the ac runs cooler with the engine running. you can pull up the compressor rpm and even thou it's electric when you stop without the engine running the slows down the compressor speed. something you might never notice, but it's 112deg here in the shade lol.
don't let me discourage you, just sharing what I've seen over the few years of owning one and researching as much as possible.
