QuestionQUESTION: i have a shudder when the truck is under load in 4th gear at cruising speed. begin to x-celerate slowly the truck
shakes. it seems like the trans should down shift. pressing
the petal farther down it will down shift, shake goes away
and x-cellerates. universal joints good and engine run smooth.
ANSWER: Hey,
When your truck gets into 4th gear the torque converter clutch comes on. The TCC is a method of locking up the converter to a 1:1 ratio with no fluid shear. This is done to lower transmission temperature, increase fuel economy and lower emissions. One problem with TCC's is that they accentuate driveability symptoms. A small misfire or stumble is amplified by the TCC and you begin to feel it. When the truck gets into 4rth the engine is loaded down and RPM is at its lowest. Here are some simple things to check that are common problems you might be able to narrow down on your own.
- Pull coil wire and distributor cap off. Look for corroded ends, green fuzz and moisture intrusion into distributor cap.
- When the symptom occurs very lightly touch the brake pedal just enough to turn the brake lights on. This will send a TCC disengage signal from teh brake switch to the PCM and it will unlock the TCC. If you do this and the symptom completely goes away you can narrow it down further.
- IF you have a vacuum EGR put your fingers under the edge of it and make sure it isn't seized. Excessive EGR densifys the air fuel mixture causing misfires under engine load.
Hope this helps
Wayne
---------- FOLLOW-UP ----------
QUESTION: the shudder i described has not stored any codes, are there
any problems that would not store a code to cause a misfire
AnswerHey,
There are tonnes of things that will cause a miss-fire and not store a code. A 1996 has a poor self diagnosis system and they can missfire right in front of your face and not set a code. They should only be used in a last resort.
Wayne
