Reader Question My truck really starts to jerk when accelerating. My check engine light doesn’t come on. Can a mechanic still read the computer without a alarm to do so? I thought that maybe it was trash in the gas, plug wires look ok. I just don’t know. 1989 GMC S-15. 4.3 replaced two years ago. New plug, wires, converter, etc.
If you think this is an engine miss type of problem and not a transmission problem I would take a closer look at the spark plug wires, distributor cap and ignition rotor. I would also check the fuel pressure with a manual fuel pressure gauge you can rent from your local auto parts store.
See if you can power brake the engine (one foot on the brake while giving some gas to the engine to raise RPMS) so you can watch the fuel pressure gauge while you experience the problem. You can also have someone watch the spark plug wires while you power brake the engine to see if a spark plug wire arcs.
You can also spray some water like from a plant water mister bottle on the spark plug wires with the engine running. If there is a hole or break down in the wire it will produce a ground when it comes in contact with the water and an engine miss will be obvious.
If you suspect a transmission problem rather than an engine problem, try driving in another gear besides overdrive to rule out a problem with the overdrive converter clutch. If you don’t have this problem in normal DRIVE, you might have a transmission problem.
In any case, yes the mechanic can read the codes, and watch the engine performance with a scope to track down an engine miss…but the engine will need to misfire in the shop with some equipment on it to find it.