Lurching 40 to 50 mph slight hill

[Dave LV]

Recently my H3 AT with 7700 miles has started to lurch climbing slight hills at 40 to 50 mph. Dropping it into third gear does not make it go away nor changing to premium gas. I have also added three bottles of Techron from Chevron. Still no change.

Anyone else experiencing this?

Never experienced this in 17K miles so far.

S.

[f5fstop]

How's the idle? Is the engine light on?
Does it only happen when going up a hill?
Sounds like the torque converter clutch to me, which is engaged in 4th and 3rd gear, is going between locked and unlocked.
Could be an engine miss, but three cans of Techron won't help if it is. Techron is good for keeping the engine and injector clean, as well as the fuel sending unit (if using the right Techron).
Can't help much with a long distance diagnosis, suggest a dealer visit.

[Dave LV]

Since it doesn't go away when I drop into 3rd gear, I figure it can't be the AT torque converter locking/unlocking.
No check engine light.
No idle problem.

How does the center dif work? Engine compression problem? But then why only uphill?

Yep, visit to dealer is called for, but I expect they will say "Problem not found".

Can leases be ended due to fundamental flaws such as this if it can't be repaired - i.e. GM says it is normal?

[f5fstop]

Your third gear theory is wrong, 4L transmissions will lock in manual 3rd gear, as well as in overdrive 4th gear.
Possibly an engine compression problem, but if it is the cylinder head issue, it would cause a rough idle, and the PCM would pick up a misfire after certain counts and turn on the idiot light.
As for buy backs, is this your first problem? Call your lease company. But if it natural, it is between your lease company and GM.

I really don't know of any heavy vehicle with an automatic and limited HP that will not do some shifting around on mountain roads. But then again, I don't know if it is a shifting problem or a TCC problem, or something entirely different. Good luck.

[Dave LV]

Interesting. I did not realize that the H3's AT would torque lock in 3rd gear. My other cars only did it in top gear.

But I now believe you are right about the torque converter lockup being the problem. Today I kept the speed going uphill below the 40 mph where it locks up and sure enough there was no lurching.

Lease is with GM and it is the first shop visit - but not where I bought it.

Shifting is no problem with the transmission. I expect it to with the H3's weight/power ratio. Seemed fine until lately.

Still surprised that putting on the brakes doesn't release the lockup. My '01 Camaro did and it made it much more drivable.

[deserth3]

Originally Posted by Dave LV

Recently my H3 AT with 7700 miles has started to lurch climbing slight hills at 40 to 50 mph. Dropping it into third gear does not make it go away nor changing to premium gas. I have also added three bottles of Techron from Chevron. Still no change.

Anyone else experiencing this?

I had something like this in a 95 Blazer I owned. Turned out to be the throttle postiion sensor.
I finally figure it out by downshifting od flat land so the throttle was in the same position as going up hill. At that throttle point it would stumble or lurch depending how you look at it.

[NEOCON1]

i have a noticable surge too , but only when going down hill with cruise-control . it feels like slack in the 40-60 split in high range unlocked . feels like theres a load then no load , back and forth till hill flattens out . then seems as smooth as ever .

[marin8703]

Hey Dave,

I would love to try this out on my truck to see if I got the problem too, but I need some pretty exact info.

Can you tell me what you mean by a slight hill, about how many degrees. And again tell me at what speed I should drive. Also if there is anything else special that i should do. I wana do everything exact, is AC on, is Traction Control on or off, when climbing the slight hill at around how many rps is your ingine.

I live in chicago, not many hills around here, but if you get me this info so that i can repeat it, i am willing to go out to hoffman estates, about 20-30 miles out, theres some pretty nice hills out there.

Im one of those people that like to know if and when their vehicle has a problem even if it really doesnt effect them, thats why i wana check this out. Thanks!

[Dave LV]

Just above 40 mph with the torque converter locked, flat or slight hill (2-7 degrees), slight throttle that keeps torque converter locked but puts some load on drivetrain. AC on, but I don't think it makes a difference.

Jerks longtitudinally, like poor gas with engine miss but no engine light comes on.

Local dealer has requested GM to send an engineer to look at it. They have seen it on on several H3's but none as worse as mine.

[f5fstop]

Just did some extreme ascents in CO, and had nothing like this happen. Didn't downshift as fast as I would have liked, but overall, it ran the mountains surprisingly good.