Truck is jerking alot.

TIREDMOM33

MEMBER
CHEVROLET

My name is Beth and and our truck is really running rough. We have a 1997 Chevy Cheyenne King Cab. We purchased it used but until now it has run great. Lately it is jerking ALOT! So my husband gave it a tune-up. It runs alittle better but still jerks.
The mileage is 114000. We took into the garage and they said nothing came up on the diagnostic.
HELP. I have to use this vehicle to take my kids around and I just don't feel safe.
Signed
tiredmom : :roll:

1 Reply

INDYUKE

MECHANIC
416 POSTS

When you say nothing came up on the diagnostic, do you mean they scanned the computer for fault codes and got nothing?

Check these things first.
1) check fuel pressure at the fuel rail. There should be a schrader valve (like a tire valve) that you can screw a mechanical pressure guage into.
2) check to make sure spark is getting to each and every spark plug. Unscrew the spark plug, plug it back into it's wire and hold the spark plug against a clean bare section of the engine block and crank the engine. You should get a series of sparks. Careful you don't zap yourself.
3) check compression on all cylinders and compare them with each other. All the values should be fairly close to each other.

Fuel delivered in the right ratio at the right time, spark delivered at the right time and good compression are the three things an engine needs to run. Additionally check such things as the fuse panel, relay box, ignition timing, wire connections you think might receive a lot of abuse, etc. I hope this helps.