01' Tranny Prob? Rare jolt on highway

[hcary]

I've had this rare problem for the past year or so. While driving on the highway at about 60-70mph, the car will jolt like the tranny just slipped for half a second. The symptom occures about once a month. It happened this afternoon a couple times while heading home. No RPM drop, just a brief jolt.

Any ideas? I though it was electrical and have already changed my plugs, wires, cap, rotor and fuel filter, even though there was no RMP change.

Thanks

[drdd]

are you using cruise control when this jolt happens ?

is this your original drivetrain?

have you ever done a tranny flush or fluid exchange?

Originally Posted by hcary

I've had this rare problem for the past year or so. While driving on the highway at about 60-70mph, the car will jolt like the tranny just slipped for half a second. The symptom occures about once a month. It happened this afternoon a couple times while heading home. No RPM drop, just a brief jolt.

Any ideas? I though it was electrical and have already changed my plugs, wires, cap, rotor and fuel filter, even though there was no RMP change.

Thanks

[hcary]

No, Cruise was not on, though it has happened in cruise.
Fluid changed at 55k @ dealer. Now just passed 100k.
Original drivetrain.

[wolfox]

Mine was doing this before the ignition module went out. However,this was on a '95 with 4.3 CPI Vortec power plant which has HEI with the wires coming out of the top of the distributor. It would hiccup now and again, until it was hiccupping all the time, then stalling in traffic or on the highway. It finally left me for dead in 100 degree heat on a Saturday afternoon, 35 miles from home. Diagnosed it while the engine was still hot, turned out that it was old, and when the plate it mounts to got hot too, would prevent the trasistor pack inside from firing/switching properly. I am not saying that this is your problem, but adding perspective from experience. You might have to find someone that can lend you a scantool to monitor live data streams off of the truck's computer, giving you a good idea of what's going on in there.

Other issues it may be are:

Possibly bad/intermittent electrical contact from throttle position sensor. This helps the computer determine engine load and tranny shift both up and down. THis part can be checked with a volt/ohm meter easily to determine if it's faulty.

Intermittent power to transmission, letting the overdrive solenoid momentarily slip.

Bad Ignition switch - related to above in a way...

Weak/dying alternator that has lost a phase or two - weak charging circuit can lead to computer/driveline foul ups.

Weak/dying battery

Incorrectly gapped spark plugs/fouled plugs/cracked wiring insulation on spark wires, weak/intermittant ignition coil. (Coil will miss-fire if faulty when it heats up to ambient engine temps - it gets hot under the hood)

Partially plugged Injector causing miss-fire.

Partially plugged or blocked fuel filter, causing miss-fire under high speed/power demand from throttle or maintaining cruising speeds on highway. Usually the car will sputter and make like it wants to stall when the RPMs pass 3k or so, regardless of load.

And if you haven't changed your air filter for at least 2 years, get a look at it and swap if needed.

Hopefully you can trace and nail this problem down. Electrical gremlins are very hard to spot and can make you nuts, but these are some of the places I would look and check to help narrow down your problem quickly.

[blazes9395]

I don't know if you have found your problem or not, but does it occur when the engine is under load and in overdrive? Does it do it while cruising, or acclerating?

[hcary]

It occures while highway cruising under normal driving conditions. However, it hasn't happend since I started the post. Go figure!

[srbianats]

I had a 95 Firebird that did the same thing at around 1600 to 1650 rpm's. It was really noticable going up a small incline. I bought it used and didn't know if the tranny was ever serviced. It had about 65000 miles. I decided to take it to Jiffy Lube (yes jiffy lube, I was young) and had the T-Tech done on the tranny. Problem completely went away. Before the T-Tech, I noticed the tranny fluid was a bit discolored. The firebird also had a 4l60e tranny. Just wanted to tell you my experience.

[Bodaggit]

My blazer does kind of the same thing sometimes.

It's been hard to trace down to anything though since it happens so randomly.

It'll do it one day, then nothing again for a month or two, or even three.

It doesn't seem to matter if the engine is hot or cold, same with the weather, it just doesn't whenever and wherever. Nothing in common with the times that it jerks like that.

It's a headache.