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GM Trucks Maladies And Cures - Kopycinski's Brain

Posted in How To on April 1, 2011
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General Motors fullsize trucks and SUVs have been sold by the millions, and there are plenty of high-mileage ones running around these days. As they age, parts wear, deteriorate, and break. This month we'll give you a quick run-down of four common problems and potential cures for the ailments.

If you own a '99-to-'08 fullsize GM truck, SUV, or Hummer, you may have encountered the common clunking, groaning, or creaking that emanates from somewhere forward of your steering wheel. In some cases, the annoyances reveal themselves as early as about 10,000 miles. The stock GM steering shaft contains a splined slip joint that comes from the factory with grease in the slip portion. Over time, this grease slowly works its way to one end of the joint and the slight play in the shaft pieces causes the noisy condition.

A few years back, we installed a replacement shaft from Borgeson Universal. The beefy shaft with needle bearing joints is really smooth, cured all our noise problems, and made the steering feel more solid overall.

The GM vehicles use an in-tank fuel pump to supply the fuel injection rail. Past history shows that the typical life of these pumps is about 80,000 to 100,000 miles, sometimes shorter and sometimes longer. There are two ways to access the pump for replacement. One way is to drop the gas tank out of the truck to remove the pump from the top of the tank. If this method is used, it's best to run the gas tank as low as possible on fuel to lighten the weight of the tank.

A second method that we've used successfully is to lift the bed off the chassis high enough to pull the pump out. This requires either the help of a couple of friends or a means to hoist the front of the bed from above. The fuel level sender is part of the pump assembly that you pull from the tank. You can buy a new pump and reuse the old sender, but it seems the senders get somewhat intermittent as they age as well. Frequent fuel filter changes seem to make the pumps last longer.

The multi-port fuel injection engines such as the 4.8L, 5.3L, and 6.0L models have a small fuel pressure regulator located on the driver side of the engine (shown here). They have a tendency to fail on occasion. Symptoms typically show up as a hard to start engine (and sometimes stalling or hesitating on acceleration), especially after the engine has been turned off for more than a few minutes or overnight. The regulator is connected to a vacuum source through a hose connected to it.

The common failure for this regulator occurs at the seal between the fuel and vacuum sections. A quick check is to pull the vacuum hose off the regulator after the engine has been turned off. If gas is present at the vacuum hose, the regulator seal has failed. Replacement is easy and only takes a few minutes.

One other malady you may encounter is on an ABS-equipped GM truck or SUV. There is an electronic module that is attached to the main ABS (anti-lock braking system) module on the driver side framerail under the cab. The modules can be prone to failure, resulting in the lighting of the ABS dash lamp and a buzzing or humming noise coming from the ABS pump (constantly running) under the truck.

Module replacement cost from the dealer seems to run $700 or more. Another alternative is to have your module internally upgraded to fix the circuit problem that causes these modules to fail. The module can be taken off the truck by removing several electrical connectors and unbolting the electrical module from the ABS solenoid housing. There's no need to disconnect any brake fluid lines and the brake system remains functional, but without the ABS function. Modules can be upgraded by a number of auto electronics companies for about $100 or so.

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