QuestionI have a 1998 gmc 4x4 4.3l automatic. The problem is that the engine loses power and spark knocks like crazy when it is under a load on the highway. The truck will actually surge when it is about to shift into drive and continually spark knocks over 3500 rpm The problem is worse when i am towing my utilty trailer. I have no check engine light on and the truck has about 55000 miles on the odometer. please advise! Thanks!!
AnswerOk ,
When was the last time you had a decent tune-up ..
A 98 with 55,000 is nothing , Sounds like you might have a fuel and a spark issue . Do the following
Gas Filter :
Spark Plugs
Spark Plug Wires
Cap
Rotor
Although i have seen bad vacuum cause the same thing .
At night time look for sparks jumping across to the frame . Start the engine , be careful , dark . And look for sparks jumps.
This is usually an indication of spark jumping ALL THE TIME.
Has the engine always pinged , while acceleration ?
When you tow , of coarse you are putting a load on the engine and trans as well .
You can have all these issues and have no engine light on !
You can check spark with a ( spark wire tester ) on every wire . This tool costs onlt a few dollars at Autozone etc, It will give you a GOOD indication on spark .
