Mechanics

CHEVY MAJOR VIBRATION PULLING HILLS

1999 Chevrolet Suburban

Engine Performance problem
1999 Chevy Suburban V8 Four Wheel Drive Automatic 94,000 miles

Within the last few months, we've experienced an intermittent major shudder/vibration, primarily when pulling hills. Traveling at interstate speeds (50-60 mph), as the suburban starts up the hill, it struggles to maintain power and speed begins to drop. The whole car shakes violently under the load and rarely gears down for more power. Even if the transmission does gear down, that lower gear isn't generating enough power to accelerate up the hill, and the vibration continues. For the record, we primarily drive in 2WD.

The 'check engine' light came on during one episode, and the code indicated 'random misfire'. So, we had a complete tune-up, since the mileage was approaching 100K. However, it's experiencing the same symptoms.

We've also changed the fuel filter, serviced the transmission and added a transmission additive to improve performance of the torque converter. Nothing has helped, and since the check engine light no longer illuminates under these conditions, there are no codes to help.

Could it be something in the valve body? Is this a common problem with this generation Suburban?

Since receiving the engine tune-up, it occasionally idles rough when warm. Any connection? Ideas of what to try next?

Thanks!
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ElCheapo
May 20, 2010.



Sounds like a possible fuel pump issue. You need to hook up a fuel gauge to it and monitor the fuel pressure when the symptoms are present. I am expecting the pressure is out of spec.

Thanks for the suggestion. It sounded to me like a low pressure issue with the fuel pump.

What bothers me is that the fuel pump was replaced < 14,000 miles ago, and the fuel tank sending unit was replaced < 29,000 miles back. Is there something else causing the fuel pump to fail prematurely?

I'll check the fuel pressure before proceeding.

Thanks.

Tiny
ElCheapo
May 21, 2010.
A plugged fuel filter can kill a pump. We ALWAYS replace the filter when a pump is done. I have seen many aftermarket pumps that are low quality.

That's what I was afraid of. Unfortunately, the GM dealer was responsible for replacing the fuel pump WITHOUT replacing the fuel filter for the previous owner. At least the dealer said the pump was GM.

Thanks for the responses and suggestion. I'll let you know how it turns out.
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Tiny
ElCheapo
May 23, 2010.
Hi-

Here is an update on the suburban diagnosis. Fuel pump seems to be working properly, and they checked for misfires, etc. Diagnosis is replacement of the torque converter.

My big question of the day is will replacing the torque converter fix the problem, or is there an underlying problem causing the torque converter to intermittently malfunction? Any thoughts?

Thanks.

Tiny
ElCheapo
Jun 1, 2010.
It may be. I would have them make sure that the software has the latest and greatest updates.
They can do that here:http://tis2web.service.gm.com/tis2web
Just need to get what calibration it has.

Not sure if a valve body would cause a shudder, but can give a hard shift. Transgo makes kits for this.

Same shudder under load or after a continious highway speed 55-65. I am no professional but from what I researched and what others said one of the lifters may be sticking. It happened to me on a couple of occasions. I purchased a can of SEAFOAM. Poured 2/3 of a pint in my crankcase and reserved a 1/3 for the intake. Get the car hot park it with engine running pull the vacuum line off the master cylinder power booster you may have to hold the accelerator down to keep it running. I used a hair dye bottle to measure the ounces around 5-6. Slowly squirt the seafoam into the vacuum line be careful the line has a very strong pull and will rip the bottle out of your hand if too close. Shut car off and let sit for 5 minutes. Do it at night because after restart get out of your neighborhood it SMOKES! You won't be able to see behind you run the car till smoking stops take it on the highway it dissiaptes pretty quick. Problem solved same EXACT issues you are having are gone. Change oil after a couple of days. You can also add some to gas read the bottle. Hope it helps and saved you some $. 99 sub 115,000 miles original owner, new AC fuel pump installed few months ago in addition to fuel filter

Tiny
Eddiet20
Jun 12, 2010.
This is the second time I am doing this, the first time I went for about 8 months before re-occurence. In addition to the problem going away there is a noticible performance increase faster pedel response smoother idle, etc.

Tiny
Eddiet20
Jun 12, 2010.
Hi and thanks for the detailed reply. Obviously I forgot to check for new responses!

I took the car to a local trans shop, and the owner was quite helpful in trying to pinpoint the source of the problem. Since it didn't shudder for him, he was hesitant to change parts based on just a guess -- refreshing.

I'll call him tomorrow and mention your theory about the lifter. It sounds plausible, given my other symptoms.

Thanks again, and I'll let you know how it turns out.

Tiny
ElCheapo
Jul 28, 2010.

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