Hi I've got a 1996 C1500 with a 5.7 Vortec. I recently got a tune along with other mods Ive noticed a weird shuttering since I've gotten the truck originally chocked it up to my loud exhaust but now I can view my cmpret parameter and it sits at around -27 to -32 degrees. From what I've seen it looks like my dostrubtor is going bad I tried to adjust my distributors cap and it still has incredibly retreated offset. Any help is appreciated or if anyone knows it's 100% a bad distributor gear.
Greetings TStowell,
In the old days where there was plenty of room to swing the distributor around, it could get installed
(stabbed) one tooth off, and a lot of times we could just twist away the error, get it running right, and
call it a day.
But on your '96 there's very little room for twisting the distributor. It sounds like the previous owner/mechanic
got the dizzy stabbed one tooth off? Here's the kicker: since the actual base timing comes from the Crank
Position Sensor up front, the truck will actually run alright
some of the time, but depending upon the total
advance computed, you start getting misfiring due to the rotor being closer to the wrong distributor cap
terminal. (ie: spark sent to the wrong cylinder)
Enough of the theory. Pull the engine through until the engine is at #1 on the compression stroke. Pull
the distributor, advance the distributor one tooth worth. Since the bottom of the distributor drives the
oil pump, you will need to take a long screwdriver and also twist the oil pump drive the same amount in the
same direction in order to allow the distributor to drop back in.
Tighten the distributor back down and recheck the cmpret. Try to get it within the specs in the FSM:
0° +/-2° at 1000-1100 rpm.
NOTE: High mileage dizzys are known to have a lot of wear in their driven gear. In the first attachment
is the picture of a brand new one -- notice the uniform gear tooth thickness. In the 2nd attachment is
a picture of a worn gear, exhibiting what some refer to as a 'knife-edge' look.
While you have the dizzy out, check to see how much play there is between the spinning distributor
shaft vs the bushings in the housing.
My hope is that with the 1 tooth adjustment that you can now get the cmpret to adjust properly. But
if after this change you still can't get it within spec, then we'll have to take it to the next level. But for
now let's keep it simple and with any luck we'll get this sorted out on the first try.
Hope this helps!
