MY SON WAS USING MY CAR WHEN HE SAYS HE HEARD A LOUD BANG(BACKFIRE) AND GMC 1995 JIMMY 4.3 VOTEC V6 STOPPED RUNNING AND MUFFLER EXPLODED. WITH GREAT DIFFICULTY, I GOT THE MOTOR TO START A FEW TIMES. IF YOU STEP INTO GAS PEDAL HEAVY, IT STALLS. IF YOU START AND STEP IN EASY, RPM WILL COME UP. IF IT DOESN’T START WHEN TURNING OVER, IT SOUNDS LIKE IT IS MISSING, THEN WILL FIRE RANDOMLY, BACKFIRE AND BLEW UP A REPLACEMENT MUFFLER. A RETIRED MECHANIC TELLS ME TO CHANGE THE TIMING CHAIN AND GEARS. HE SAYS THE 160,000 MILES INDICATES ITS TIME FOR A CHANGE OF CHAIN AND GEARS. IS THERE A WAY TO CHECK THIS DIAGNOSIS BEFORE TEARING FRONT OF MOTOR ALL APART?
Yes, turn the crank clockwise. Stop. While observing the distributor rotor and or the camshaft gear, turn the crankshaft a few degrees counter clockwise, until the camshaft gear just starts to move. The difference between the clockwise position, and the counter clockwise position, will be the amount of wear of the timing chain and gears.
OTHER THAN TIMING CHAIN SLACK, ANY OTHER IDEAS? i WAS TOLD THIS MODEL ENGINE IS FAMOUS FOR THE TIMING CHAIN SKIPPING A TOOTH ON ONE OF THE GEARS AND NOT TEA KETTLING LIKE A PLASTIC GEAR THAT STRIPS AND MOTOR BOUNCES AROUND DUE TO CRANK AND CAM SHAFTS BEING WAY OUT OF TIMIMNG
HOW MANY DEGREES ON CRANK GOING BACKWARDS FROM WHEN ROTOR STARTS TO TURN WHEN GOING FORWARD WOULD INDICATE A PROBLEM WITH CHAIN?
ARE THE CAM AND CRANK GEAR METAL TOOTHED FROM THE FACTORY?
DOES ANYONE KNOW IF IT IS COMMON FOR A CHAIN TO SLIP A TOOTH?
IS THERE A CHAIN FOLLOWER THAT TAKES OUT SLACK?
Using all caps is not polite.
The symptoms just about diagnose the problem for you. Taking the front of the engine apart is really not what is done to change a timing chain. It takes about an hour and ten minutes to get the timing chain cover off if you use an air gun and ratchet. But you should be done with the suggestion by hellokit by now. Any slack is an indication. No slack isn’t a positive indication of perfection. Set the timing mark on TDC and if the rotor doesn’t point to where the #1 plug wire is connected to the cap, then your timing chain is worn out and has slipped quite a few teeth. Either way you go, it sounds like you will have to pay a mechanic if changing a timing chain on that engine sounds like real work. The symptoms are classic signs of a dead timing chain and the mileage says it’s true. There is no cheap fix.