2000 Blazer 4x4 automatic 4L60E

Symptoms:

hard shifting in all up gears, followed by a serious power loss. The only way to get any serious acceleration, is to downshift, which works, but as soon as it upshifts, its bogs down. If I'm going 40 mph in 3rd, and want to accelerate, I gotta downshift to 2nd. Additionally, the Torque converter seems to be confused in 3rd and 4th in the 40-60 mph range. Constantly engaging, and disegaging, hunting for the right spot.


Tranny fluid dirty, took it to Aamco, said tranny will go soon, but operating fine now. They said engine was weak, which is why the tranny was needing to downshift to find power.

Took it to the dealer 3 times, first they claimed CAT was blocked, so I removed it, second they said the muffler was blocked, so I replaced that, third time they had multiple techs look at it all morning and finally declared there was nothing wrong and 'those 4.3 engines are just dogs'.

I'm still not convinced that the tranny is shot. I just drove it from 5200 ft to 9500 ft and back with no problem (except the downshift for power issue).

What could be causing this bogging after every (hard) upshift?

 

possibly, bad tps sensor, weak fuel pressure, in need of a major tune up plugs,wires,cap,rotor,02 sensors pending on how many miles. with out being able to look at it myself very hard to say i would check the things out that i mentioned. the plugs well tell you the story if you know how to read them.

 

Changed tps, dealer checked fuel pressure at idle and driving, new plugs, new plug wires, only code is cat low efficiency, since it's gone.

The dealer had it 3 times, used all their diagnostic tools.....nothing!

 

Changed tps, dealer checked fuel pressure at idle and driving, new plugs, new plug wires, only code is cat low efficiency, since it's gone.

142K

The dealer had it 3 times, used all their diagnostic tools.....nothing!

 

If you did the spark plugs and wires and it is still acting up I would continue with the Distributor cap and rotor as well. Maybe even think about getting the ignition coil and ignition module checked out. Also what did the dealer say about the fuel pressure? They may have said something that might allow War00 or someone else to help you out more.

 

3 things come to mind with a bogging situation fuel issue, spark issue or clogged cat. 1)fuel leak down test needs to be done to see if the system is holding pressure, if it doesnt hold than you could be looking at the fuel pump or the spider asy. does it smell bad when its idling like unburnt fuel or off smell 2) if you havent changed the cap or rotor than do soo, or the dizzy needs to be checked for play and if the gear is worn than it needs to be replaced because the the timing is retarded. Finaly the cat is clogged, pull the o2 sensors and take it for a drive and see if it's better. since you said you had a code for the cat id almost put my bets on that. simple to do your self with a 7/8" wrench.

 

Park & war00 are giving good leads,but I would look into other issues as well... You did not give enough history of the problem. As you know the 4.3s aren't necessarilly dog engines,but the only time I drove one at high altitude (my 87 GMC K15-non-computer controlled) it was very weak over the passes in CO!I suspect transmission solonoid problems above and beyond what the other folks have suggested-AAMCO is probably correct,the tranny does not have long to live:but they are going to say that to EVERYONE!!!! How many miles?Trans maintained? If you do have your trans re-built,take it to an independant ATRA (automatic transmission rebuilders association) shop-NOT a chain-be forewarned! Best of luck! step66

 

Thanks so much for the input, let me go over a more detailed history so I can get some final advice before I start replacing things.

We bought it (for my teenager) used with 139K about 3 months ago, had a rebuilt tranny from a dealer with a 3yr 36K mile warranty (at 96K-2005).

Has 2" body lift, 31"tires, aftermarket radiator, High flow air intake and exhaust.

Car lives at 9100 ft (mother), and 5200 ft. (me). Car spent the first half of it's life in Souix City, IA, and the second half in Boulder, CO, with many road trips to Utah and some hard driving, I suspect.
__________________________________________________ _______________

The following were said to be done by the previous owner (we believe him)

new plugs
new wires
__________________________________________________ _______________

we did the following after purchase.

New brakes, and rotors
new shocks
new serpentine
new tps
new fuel pressure sensor (on top of fuel pump)....funny story here, we got the code for this sensor, and when we checked it out, the ring holding the fuel pump into the tank was disconnected, and the fuel pump was floating out of the tank, but it still ran...we reconnected the ring and the pump. we found the new wiring harness for the fuel pump in the back, so it must have been replaced improperly.

cleaned MAS
cleaned EGR
new gas cap
removed the catalytic converter (replaced with straight piece of pipe)
__________________________________________________ ______________

We have two outstanding issues.

The left front wheel bearing is bad, and the wheel sensor is not working, so the ABS light is on.

The Check engine light is on because the cat is gone (catalyst below threshold)
__________________________________________________ ______________

The original issue was the hunting the Torque Converter (TC) was doing in 3rd, and 4th gears and the lack of uphill power. That's when we took it to Aamco. They originally said the brake switch was inoperable, causing the TC to get confused. We remembered that the previous owner told us he pulled the ABS fuse, when we replaced it, and tested the transmission, it was OK, except the burnt fluid, of course. (That's probably what burnt up both transmissions!) The Aamco owner said it was a matter of time before the tranny died, the rebuilder said maybe, but the tranny was operating fine now, and it was probably a weak engine.

So off we went to the GM dealer. They said there was backpressure before the cat and it had to go. We took it to our exhaust guy, who removed the cat, and it was empty, I mean nothing at all in it at all. And he also told me that no one had checked the back pressure at the dealer, as no o2 sensors had been removed. Anyway, back to the GM dealer we go, they had every tech in the shop scratch their heads over it and hooked it up to every diagnostic tool they had and could not find anything. They declared it a 'DOG' and reminded me that the transmission was bad and sent me on my way.

The reason we took it to the dealer in the first place, was to get a professional confirmation that our spider needed to be replaced, but they said it was not leaking.

So here I am.

 

Nothing there about fuel delivery, fuel pressure is critical on these engines. Check fuel filter for restriction, then check fuel pressure and leakdown: key ON, engine OFF, fuel pump running, pressure must be 60psi to 66psi and must remain above 55psi for 10 minutes after the pump shuts off. The results of these tests will determine if the fuel delivery system is working properly. BTW, no such thing as a "weak" 4.3L, a technician with weak diagnostic skills is another story

 

Hook is spot on about fuel pressure needs espescially at high altitudes!