96 K3500 7.4l Vortec

[Schurkey]

I didn't realize the cam and crank sensors had to be aligned, they both fastened into place without any engine rotation. I remember seeing mechanics turning the distributor to dial in timing, I was wondering if that needed done, maybe from slightly off timing on reassembly after engine rebuild

On most (almost all) other engines, turning the distributor changes the timing.

On the Vortec, turning the distributor does NOT change the timing, but it does change the alignment of the signal sent by the cam (distributor) sensor, compared to the signal sent by the crank sensor. The computer wants the two signals aligned, so that it can identify WHICH cylinder is misfiring with certainty. If the alignment is too far out-of-spec, the computer still knows when to fire the coil, but maybe not WHICH cylinder is being fired. The engine runs, but the computer is confused. If the alignment is WAY off, the spark might jump to the wrong terminal in the distributor cap, and then bad things happen.


Again--what about fuel pressure? Fuel filter? Which cylinder misfires? Are your cam/crank sensors aligned?
If you didn't clear the codes that were set before the repairs, those codes are now potentially giving you faulty information. Clear them, see what codes come back.

 

[Thomas Augenstein]

On most (almost all) other engines, turning the distributor changes the timing.

On the Vortec, turning the distributor does NOT change the timing, but it does change the alignment of the signal sent by the cam (distributor) sensor, compared to the signal sent by the crank sensor. The computer wants the two signals aligned, so that it can identify WHICH cylinder is misfiring with certainty. If the alignment is too far out-of-spec, the computer still knows when to fire the coil, but maybe not WHICH cylinder is being fired. The engine runs, but the computer is confused. If the alignment is WAY off, the spark might jump to the wrong terminal in the distributor cap, and then bad things happen.


Again--what about fuel pressure? Fuel filter? Which cylinder misfires? Are your cam/crank sensors aligned?
If you didn't clear the codes that were set before the repairs, those codes are now potentially giving you faulty information. Clear them, see what codes come back.

I cleared the codes after the repairs. The fuel filter and pump was replaced 5 years ago, but only 10,000 miles. I am not showing a misfire now after the repairs, just the sputtering and shifting issue. Before the repairs it was #8. I haven't checked fuel pressure yet. Thank you for the help. I did have to bump the starter to get the rotor mount to move a little for the camshaft sensor to fit in the groove, but it ran dreamy for 60 miles after all installations.

 

[Thomas Augenstein]

I have Car gauge pro on my phone and an elm327 wireless module so I set out to see where the timing was, but my set up wouldn't connect to the ecu. So remembering that #1 was tight against the intake when I put the wires on I decided to see if the distributor was loose. Felt snug at first, but with very little effort it spun counter clockwise about a quarter of an inch. I thought oh crap what did I do. So what the crap, I started it and everything was better, snappy throttle response, no popping, and shifted right. I need a scan tool to check where the timing is, but looks like that was the problem. Cam, crank timing. Thanks guys. Do they make a tuner that can also read timing?

 

[Supercharged111]

If it's the original plastic body distributor at 200K it's worn and is highly suspect. If you remove the cap and turn the rotor by hand either direction until it pops up with the helical movement of the distributor gear.. try moving the rotor from side to side. If it moves side to side, replace the distributor. It's toast. Make two very distinct marks before you remove your original: rotor position, and distributor position. Install new one as close as humanly possible to same marks, so you can get it running. Then fine-tune cam retard angle using a scanner that can read that data, hold RPM's at least to 1,000 for good reading, adjust distributor until it's within +/- 2 degrees of zero.

Richard

I tried this on my 27X, *** mile 350 Vortec and got zero sideplay.

 

[badco]

Lol put a timing light on a vortec and move the distributor it does change the timing mechanically. I have a crank trigger on my race truck and if i move the distributor it changes timing on it also even though distributor only has plug wires on it. The crank trigger sends signal to the coil and into distributor and if you move the distributor is will fire before or after the lug in cap changing timing

 

[someotherguy]

I tried this on my 27X, *** mile 350 Vortec and got zero sideplay.

100% certain original distributor? I've found I had to turn/shove/turn/try again but I've worked on several that were absolutely toast at far less miles than what you've got. One at 236K or so was so sloppy it was breaking the plastic ridges on the rotor because they were striking the terminals inside the cap. That's pretty bad.

*Mind you all the ones I replaced were on Vortec 7.4's. They are a different part # than the small block Vortec distributor, though I can't imagine what the difference could be that would make the big block piece any more prone to wear.

Richard

 

[someotherguy]

I have Car gauge pro on my phone and an elm327 wireless module so I set out to see where the timing was, but my set up wouldn't connect to the ecu. So remembering that #1 was tight against the intake when I put the wires on I decided to see if the distributor was loose. Felt snug at first, but with very little effort it spun counter clockwise about a quarter of an inch. I thought oh crap what did I do. So what the crap, I started it and everything was better, snappy throttle response, no popping, and shifted right. I need a scan tool to check where the timing is, but looks like that was the problem. Cam, crank timing. Thanks guys. Do they make a tuner that can also read timing?

There's dozens of different ELM327 bluetooth modules out there so this doesn't apply to all of them, but the few I've tried would connect to my Mopars just fine, Ford work trucks, but not to any of my OBD2 GM stuff. For those, I got the BAFX Products reader. It's about $23 shipped and works like a champ on anything OBD2 I've plugged it into.

Richard

 

[Thomas Augenstein]

Great, thanks.
This is my side work truck, as soon as things slow a bit I'll change the distributor.

 

[Schurkey]

Lol put a timing light on a vortec and move the distributor it does change the timing mechanically. I have a crank trigger on my race truck and if i move the distributor it changes timing on it also even though distributor only has plug wires on it. The crank trigger sends signal to the coil and into distributor and if you move the distributor is will fire before or after the lug in cap changing timing

Firing 'before or after the lug in cap" changes the rotor tip-to-distributor cap terminal alignment. If the alignment gets bad enough, the spark jumps to a different terminal, firing the wrong plug.

It doesn't change the timing otherwise. Timing is determined by the position of the crank sensor in relation to the reluctor teeth behind the torsional damper; and the programming of the computer.

*Mind you all the ones I replaced were on Vortec 7.4's. They are a different part # than the small block Vortec distributor, though I can't imagine what the difference could be that would make the big block piece any more prone to wear.

The "Big-Block" distributors have a "Thermal washer" above the distributor gear. That washer--and what I suspect is a shorter gear to make room for it--are the differences between the Big-Block distributor and the Small-Block distributor.