service 4wd, truck wouldnt turn off, more....

[UpAndComing2k2]

Ok, lets start this at the beginning of "small" problems that sprang up recently that have in time got "worse". List starts at..

-Clank when shifting sometimes. When im on throttle, then let off to take a turn, if i make the truck downshift more than 1 gear i hear some slop somewhere, and sounds like rear end. It does it occasionally, when trq tranfer is anything more than feathering the gas pedal.

-4hi have a front locking diffy? I put my truck in 4 hi and went up a wet, grassy hill. Got to the top doing about 15-20mph and tried to turn and could feel the tire skipping (both axles staying locked). I didnt know 4hi was a locking diffy, ive always thought it was 4lo that should be, but i could be wrong.

-Almost stalls out when you tap the pedal while idleing. Tap the pedal, slight delay, then rpm's drop and lights dim, then it revs up somewhat. I figured i would ask since the tb seems to have some recalls in unaware of. The trucks headlights will also dim for no reason while driving, sometimes when i quit accelerating. Not sure if thats realated or not

-Last but certainly not least... I used 4lo for the first time a few days ago going up my girls almost solid ice driveway. I wasnt revving it high or anything, just spun tires for a couple seconds and realized it was going to work. Pulled Into the gas station today, took the keys out, truck is still running. Looked on the dashboard, service 4wd light is on and i couldnt get the truck off. I messed with the keys, then tried to shift from 2hi, to the other gears, all worked except 4lo. Key in on position, back in 2hi, revved it up and turned if off with the key. Hasnt shown a light or anything since (only been about 5 hours of driving time since then though). When the key wouldnt turn the truck off, you couldnt feel the "clicks" in the ignition when turning the key, that you feel from access. to startup.

Im kinda lost here, with a warranty that is GONE, so any help would be greatly appreciated.

Kevin

[ylab]

I'll take a stab at most of it:

For the clanking, if you have an auto-locking differential first thing I'd do is change the fluid. The noise you describe sounds like it might be the universal joints in the yoke and not the diff itself, they'll cause a clank/clunk when they develope some wear or play in them. I recall hearing a few others indicate that greasing them removes the noise for a while.....worth a shot and shouldn't cost too much to have done. (This is definately something any decent repair shop should be able to do a lot cheaper than the dealer).

The 4WD settings (HI/Lo) on our trucks lock the torque split 50/50 from front to back, without use of a center differential. It relies on sufficient wheel slippage to make a turn and isn't meant for full time use. (Problem is the front wheels want to turn at the same speed as the rear wheels, which is why this occurs). Only the A4WD setting, which disengages the fronts via an electric clutch may be used full time. What you described when making the turn is perfectly normal for this type of system.....its not AWD.

Every Trailblazer/Envoy/Etc with the 4.2 I've been in had the same quirk at idle, where in neutral/park the engine stutters before reving up.....seems to be a common and possibly normal trait. (You should notice that it only does this once warmed up, overnight cold they don't do it until they're nearly warmed up). - Doesn't appear to be a real problem and just a quirk.....I've also had other vehicles (non-GM) which did the same thing. Running a good injector cleaner through, if you've been using cheap gas, might make the effect less noticeable.

I'm thinking the final problem you listed is a bad ignition switch or one which is going bad. I'd be willing to bet the ignition was kept powered, but some of the accessory feeds were not and the transfer case circuitry became confused. I had a very similar issue crop up on an 87 Eldo several years ago and a day or two later wasn't able to start the vehicle to go home....spent the next morning pulling the wheel and replacing the ignition switch and lock. - My advice would be to order one now and have it ready or price out having the switch replaced by a qualified repair shop. (You'll end up having to run the passlock relearn procedure when your done, so leave some time).

Good luck

[the roadie]

-4hi have a front locking diffy? I put my truck in 4 hi and went up a wet, grassy hill. Got to the top doing about 15-20mph and tried to turn and could feel the tire skipping (both axles staying locked). I didnt know 4hi was a locking diffy, ive always thought it was 4lo that should be, but i could be wrong.

I've been spending a bit of time in the service manual lately to understand the system. The G80 Eaton automatic locker in the rear diff. activates below 20 MPH whenever the wheels are rotating at >100RPM difference.

The transfer case clutch is driven by an encoder motor. In A4WD mode, the clutches are not engaged (but are held close to engagement) until the controller senses slippage (an RPM difference between the front and rear drive shafts). Then the clutch is commanded to engage, but it takes time, and that's where the jerky engagement feel comes from.

In 4HI and 4LO, it seems like the transfer case clutch is commanded to go to full torque engagement, but it's not clear from the manual what the breakaway torque is, if any. In other words, there might be an attempt at 50-50 sharing, but it's not truly locked like a hard transfer case available in some Jeeps, etc. I've got to do some careful experiments with jack stands in the driveway to lift my rear wheels an inch, and see what kind of torque gets developed by the front wheels.

I was wishing it could be totally locked, but then I looked at the spiders in the CV joints, and putting oodles of torque through them would not be a good idea.

The manual confirms that the front differential is totally open. No locking. Not even limited slip. If a front tire looses traction, the front tires suddenly become useless and you're back to 2WD. At least in that case, all you need is one rear tire to have traction, and you can continue.

I'm on the road, but I should post some scans from the service manual when I get home.

[UpAndComing2k2]

i c i c. So if i were going over 20mph the tires wouldnt have skipped around the turn?

ill check prices on the ignition switch, since after hearing you say that it could be it and sounds accurate.

Ill also try and grease it, not hard, just cold as crap outside, but time to bear the cold.


Thank you for all the help, and if there is anything else that would be useful to me and you all get into a typing mood or something, let me know. Im not a complete idiot, but the cars ive mainly worked on had not been so computer controlled, or had bad ignition switches, lol.

THANX AGAIN!

-Kevin

[UpAndComing2k2]

one more thing while im at it. I noticed that my guages make a contant noise, almost like small gears moving around. I thought it COULD be normal, or maybe not that big of a deal. I was reading (for an ignition switch) and noticed someone say that a bad ignition switch could cause your cuage cluster to quit working, so i thought i would ask about this. If this is possible, then i think that basically tells me to buy the switch and get ready for some winter fixing upping.


Kevin

[ylab]

Several others have reported ticking sounds coming from their instrument panels and usually, it ends up being the tachometer. The dealers usually pull the unit and send it out for repair and have it back 1-2 days later......problem is that your truck pretty much gets layed up during the repair.

Not sure what they change, lube or adjust.....just that its in the tach portion of the cluster.

[UpAndComing2k2]

i c. The noise doesnt bother me that much, just as long as the guages themselves are accurate.