1999 GMC Suburban C1500 96000 MILES, BAD VIBRATION

OLEPRO

MEMBER
1999 CHEVROLET TRUCK

WHILE UNDER POWER AT 70 MPH OR GREATER (GOING UP A HILL) AND IN LOCK-UP THE VEHICLE STARTS TO VIBRATE AND THE INTENSITY GETS SO GREAT I FEEL LIKE THE CAR IS GOING TO EXPLODE. AS I LET UP ON THE ACCELERATOR THE SHAKING STOPS. OR IF I DOWNSHIFT INTO PASSING GEAR IT STOPS, BUT GOES RIGHT BACK INTO LOCK-UP AND THE VIBRATION STARTS AGAIN. IF I TAP THE BRAKE TO DISCONTINUE LOCK-UP IT STOPS SHAKING, BUT SHORTLY GOES RIGHT BACK INTO LOCK-UP AND SHAKES AGAIN. WHEN I FINALLY SLOW DOWN TO 55 OR 60 AND NOT UNDER GREAT POWER EVERYTHING IS GREAT. THE PLUG-IN ANALYZER SAID MULITPLE MISFIRES UNDER" CHECK ENGINE SOON". ALL PLUGS, WIRES AND POINTS AND CONDENSER WERE REPLACED ALL TO NO AVAIL. THE TRANSMISSION WORKS PERFECTLY OTHER WISE. I FEEL LIKE ITS A DEFECTIVE SPEED SENSOR, BUT I CANT GET THE CHEVY PEOPLE OR THE TRANSMISSION FOLKS TO AGREE. THEY DONT KNOW! IF THEY PUT A $3000 TRANSMISSION IN AND THAT DOES NOT FIX THE PROBLEM, THEY DONT WANT TO BE OUT $3000. WHAT TO DO?

Thursday, May 17th, 2007 AT 5:25 PM

2 Replies

AACPLUS

MEMBER
60 POSTS

I can't imagine the difficulty involving replacing points and condenser on a 1999 vehicle since it should have electronic ignition, but if the engine was replaced with an older engine and drivetrain, I could see it being done, if it is leaving the country and the DOT gives a waiver to eliminate the 1999 emissions due to leaded fuel at the new destination.
If it is in the trans or transfer case, have a reputable repair outlet diagnose the problem properly.
I have seen such with propeller shaft joints, tailshaft bushings, loose pinion, and many other possibilities including bad torque converter or bad/loose flexplate, restricted exhaust, etc.
If you have misfire codes, it could be a distributor problem, (or bad coil pack if distributorless), even mounts, trans input shaft bearings or an eccentric shaft that walked, bad/arcing ignition wires, bad plug, coil pack, emission component problems, even a coil that trips out when hot or at higher speeds.
A misfire would eliminate most of these other senarios.
The list is too broad without some specific code info or hands on. Find a shop you trust and hope you don't end up financing someones vacation this summer.
Good Luck.

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Thursday, May 17th, 2007 AT 5:58 PM

OLEPRO

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SORRY, IT IS ELECTRONIC IGNITION. I ONLY REPLACED THE PLUGS, WIRES, ROTOR CAP AND DIST. CAP. THE TRANS MOUNTS ARE GOOD, TAILSHAFT BUSHING, GOOD, UNIVERSAL JOINTS GOOD.
YES, THE CHECK ENGINE LIGHT DOES COME ON WHEN THE VIBES GET SEVERE AND THEN GOES OUT IN ABOUT 5 MINUTES. WHEN CHECKED WHILE ON IT DOES SAY "MULITPLE MISFIRES" OR "MISFIRE #8 CYL", BUT THEN GOES OFF, BUT WHY DOES THE TRANSMISSION INSIST TO GOING BACK INTO LOCK-UP UNDER POWER WHEN IM TRYING TO ACCELERATE?

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Friday, May 18th, 2007 AT 10:45 AM