2000 blazer ls, 103,000 miles, 4 button 4wd ,

Is it possible for my truck to get stuck in auto 4wd? A few weeks ago I noticed a steady hum at speeds above 25 mph or so. I suspected wheel bearings, but the standard tests (tire shaking, left/right turns to detect noise changes) turned up nothing. The noise is present in drive, as well as nuetral, at speeds, no clue about reverse, because frankly, I dont go that fast in reverse, lol!

While driving straight, I engaged 4wd, and heard the relay, but no noticeable change in noise. auto4wd produces no noticeable change either. I tested my 4 hi by making a slow turn in 4 hi on dry pavement, NO THROTTLE, and I felt the front diff start to bind to where it was about to hop, but i didnt let it, just backed out of the turn and re-engaged 2 hi. 4 low works, at least as far as the tc shifting into low, and Ive no erratic blinking of lights, service 4wd lights, or delay of tc shifting. (if its in fact shifting...)

Also...fuel economy has decreased by a few mpg...

Shouldn't there be a change in audible drive train noise? Or do I have the quietest front diff on earth? any help is appreciated. Ive searched and found little to no help with my identical problem, if I've missed anything in my search that may help, feel free to direct me towards that thread, I don't mean to repost!

My next plans for troubleshooting are to jack it up and see whats turnin in drive, if the front tires do anything if one is spun.

I should also probably add, the trucks been suffering from an on again off again p0174, along with its evil brother, 0171, on rare occasions...I've found no obvious vacuum leaks, fuel pressure is fine, filter is new, air filter is new, plugs have 3k and all look the same, (no evident lean cyl combustion) and ive swapped upstream 02 sensors to see if the lean code follows one, no go. Not looking for an answer to the codes, merely stating more information that someone may find relevant. (unless you've got a fix for this too, lol)

 

I'm not sure you would really notice any additional noises from the front end when engaged in 4wd or not.

I would suspect the wheel bearings as well. The noise should get worse and give you a better indication of which side is suffering.

 

I had a friend familiar with s10s and blazers (hes had a few of both) drive the truck, he suggested it may be the pass. wheel bearing, I disagreed but still replaced it hoping to fix the problem, and it was no dice. Does the design of these bearings make them not change sound when a load is placed/removed from it? Ive replaced bearings on many a vehicle, and this one is certainly howling like it has a bad one (although personally i think it sounds like its coming from below my feet as i drive) but it isnt failing my bearing tests. I really dont want to throw money at the remaining three bearings to see if it works!

 

When they get bad enough, they definitely change tone when turning towards the side of the bad bearing.

It could be a front drive shaft issue. With the NV236 transfer case, the front driveshaft is always turning although it is not under load when in 2HI so...

 

Is it possible, that my lean codes are a result of, or at least related to, some sort of vacuum problem in my 4wd system?

 

Sure it's possible. Shouldn't be too difficult to diagnose. You may want to just replace all of the vacuum lines. On the Auto-4wd trucks, there isn't much to replace and it is easier than on the NP231/NP233 transfer cases due to the fact that the vacuum lines don't run to the transfer case.

 

New development: taking a gamble, I replaced the front pass. wheel bearing. Now, when I turn right, there IS a change in noise, it gets quieter when I go to the right. I thought, well, this is good, rear bearing, problem solved! wrong. I did the rear pass bearing, the noise is still there, and gets quieter when I turn to the right. I figure I may have gotten a defective front bearing, or I may have an axel issue. No popping or clicking though, so who knows. Are my front pass/driver axels the same length/part number? If so, I may swap them around to see if the noise follows one of them. Any thoughts?

 

anyone?

 

There is a difference between the Left and Right CV axle on your vehicle, as well as if it has the ZR2 High Wider package. I would double check the ball joints while you're looking at the wheel bearing also. It's possible a worn or loose one could be putting stress on your bearing causing your noise, having experienced that with full size trucks with IFS.