Home Forums Gear Hunting Trucks and Four-Wheel Drives Suburban 1999 170K miles

Okay previous problems having been addressed, this is the latest. When you kickdown on the accelerator, as if passing or climbing a steep hill, the RPMs go up but the speed doesn't. If you accelerate slowly, all is well. The transmission guy says it's not the transmission. Engine guy changed the fuel filter (not that dirty) and the plugs and we ran about 500 miles of Sea Foam through it. Seemed to help at first. but back to square one about 1K miles later.
The truck is in real good shape so I don't mind spending some money on it. The cost of a new one gives me apoplexy.

I don't see how the rpm's can go up with speed not changing unless either the transmission is downshifting, the clutch is slipping (if manual) or the torque converter is slipping (if auto)

If the engine is simply getting louder but making enough power to accelerate that's a different issue. Might be worth doing a compression check to see if the engine is still healthy, also check the plugs to see if any of the cylinders look like their running off.

How is oil consumption?

I can't imagine a transmission guy dismissing the transmission and not letting you know about a clutch, transfer case or torque converter. I had a suburban with a manual transmission and when the clutch went out it acted just as you describe. There weren't many manual transmissions in the late 1990's so I suspect the converter or transfer case. Physics says it's impossible to gain RPM but not speed unless something between the engine and tires is slipping. You don't hear your differential sounding like a rock crusher do you?

Check the kick down cable they stretch.. Check the timing .Could also be a fuel delivery system problem. I had to change
my fuel pump last year due to cutting out on my 2000 Silverado

Fuel pumps were an issue in that model year - I speak from experience, only in my case they WANTED to change out the transmission 😃. Kind of a pita , pump is in the tank.

My bet is the pump

Good units

Thoughtful ideas. Thanks for the suggestions.
It's auto transmission. When I try to accelerate fast, the RPMs go up, the noise level goes up but we don't travel any faster. I'll have to try this again but I tried manually dropping a gear and, IIRC, it was more normal. Reluctant, somewhat, to try it again when the RPMs are racing.
The truck uses less than a quart of oil between changes, usually around 5,000 to 6000 miles. Differential is quiet.
50,000 miles ago a very similar problem was cured with a fuel filter change. Tried it again didn't fix it.
I agree something must be slipping or not engaging. I was surprised by what the transmission guy said. On the other hand their neighbor had just shot and killed himself before I got there. They may have been a bit distracted although it didn't seem like it. After all, they are transmission guys.
Everything is "normal" unless I really kick it pretty hard.

This sounds like a rental car I had a few years ago, a Nisson Altima. If I needed to accelerate in a hurry, it would drop 2 gears, the engine would race and it would veeery sloooowly accelerate.

I had that with a bad aftermarket torque converter in a 2001 corvette, A Yank torque converter fixed it.

Just FYI

Took it into the shop today. On the way it was misbehaving as per usual. The head guy drove for a test and it ran perfectly. Ran great on the way home too. Now I have to wait until it acts up again.

Hate those intermittent problems.

Good luck.

Have a smart phone?
Video it the next time it acts up. Show tach and speedo.
Then you have something to show mechanic.

Different year but had a suburban a 93 that was acting similar. Thought it was the tranny. Normal driving was fine but when getting on the freeway or anytime I really had to put my foot in it all show no go. Thought for sure the tranny was slipping. Would drop a a gear and things would be fine or it would eventually slip into the next gear and all was fine. Ended up being the speed sensor for the tranny. Tranny was not shifting correctly.

intermittent sounds like an electrical problem...maybe something with the torque converter lockup...........

I had a 1996 GMC truck that did that. Step on the gas pedal and it would rev up but didn't go any faster. Let off the gas and then apply slowly and it ran fine.

It was the 700R4 transmission that was causing the problem.

I had the same deal with a '96 (305 ci), only it would cough/sputter whenever the accelerator was pressed. If you feathered it lightly, you could eventually get it up to speed. 'Twas the plug wires.

FC

You should take it to GM spend the 60 bucks and have it scoped. They will tell you within a couple minutes exactly what is wrong.. It will save you time and money in the long run. I'm the last guy to recommend a dealer but it will eliminate the headache of guessing. Then do the repair yourself or take it to a mechanic you trust.

Could the catalytic converter be clogged ?

Fuel pump

That's what's I would bet on also

Come on guys. He says rpms increase but truck does not speed up.
If he is right, everything back to the flywheel/flexplate is working fine,
There is slippage somewhere between the end of the crank and the tires
on the pavement. Most likely this is an automatic, if so, thats the prime suspect.
It perfectly describes a manual clutch about to die.