Truck vibrates/shudders 55-70 4th gear 3/4 throttle
Asked by Jared Sep 19, 2017 at 01:41 AM about the 1994 GMC Sierra 1500 C1500 SLE Extended Cab LB
Question type: Maintenance & Repair
I have a 94 GMC sierra 5.7 V8, during a cold start I
will get a random miss fire but goes away with a
touch of throttle. At speeds in 4th gear around 50 -
70 mph. The truck will vibrate/shudder as like I
snap the throttle shut when I depress the throttle to
the 3/4 spot..
I have done: plugs, cap, rotor, wires, egr valve, map
sensor, rebuilt the TBI,
I'm thinking this is a vehicle to lean issue and the
cat is possibly plugged causing exhaust to pool at
the o2 sensor tricking the PCM to think its to rich.
I temped the cat at operating temp idle...and I had
336 going into the cat and 256 coming out.. I
thought regardless the out flow temp of a cat
should be hotter than the intake of the cat
7 Answers
That was one of the things I replaced but forgot to mention... I'm down to faulty injectors, fuel pump, cat, o2 sensor, distributor unit, cam and crank sensors, and tcc solenoid
It started after I replaced the egr, so I think by fixing one thing I've started a snowball effect..and I'm seeing the damage done from the lack of care that the previous owner had. But the problem has gotten progressiy worse, this morning I couldn't get past 70 because if I pushed the petal further it would shudder miss and back fire but it 3rd gear everything runs perfect, but only if I select 3rd my self
I had the trans rebuilt recently and thats really when this all started...to torque converter and all the parts are new but they didn't replace the tcc solenoid in the transmission because it only comes with the internal wiring harness for the trans. I'm thinking that maybe the solenoid is leaking or malfunctioning some how...I've got the two bottles of shudder stop in It still only does the jerking in 4th only
OK I had a shop record engine data with a tech 2 scanner, they didnt see anything out of the normal..I've had it at 8 different shops and they all come up with different ideas...the only thing I noticed is when it bucks and jerks and I apply even more throttle it will stay bogged into third until I back off the pedal..so I'm going to try changing the knock sensor and tcc solenoid and distributor and see what happens
Well I did more self diagnostics.. And pulled the 15 amp fuse turn B/U which also powers the TCC solenoid. Truck only jerks and bucks only in 4th gear . if I force the pedal into the kickdown spot the engine will stay bogged down untill I come off the throttle. Last night while just looking for wiring issues I found insulation on the wire going to the knock sensor was exposing the copper wire but not touching any metal. But I think I've gotten it down to a engine fuel/air or ignition issue. What is the likely hood of the coil only failing at operating temp and in the given driving scenario. Diagnostic rates are killing me 100 bucks an hour
I found the problem, it was a faulty icm, I put a new one in and the truck is running 90% better..I'm going to take it in for a final timing adjustment and see if it gets to 100%
