Having problems getting 99 7.4 Cam retard to zero out

[BRUCE L RUSK]

I've got a 99 7.4 engine rebuilt I'm trying to get up and running. It has a comp towing cam and 411 PCM. Stabbed the distributor properly and I couldn't get it to twist enough to zero out on the scanner. The Spectra GM03 distributor I could only get to -25, I tried a moving a tooth and swinging the dizi the other way but could only get down to +50. I bought a Autozone distributor and it seems closer as I can get it to -7. First I'm confused on the math as the dizi has 13 teeth I would assume 360 degrees divided by 13 each tooth should give me about 27.x degrees of change but it seems like the scanner sees it more as 75. At this point I'm questioning if this is

A PCM tune issue, is there a table that can be adjusted to start with -10 offset instead of 0?
Is this a distributor issue, either the part itself since I have two that give different numbers?
Could this be a cam issue? I verified that the cam timing was at spec with a degree wheel checking a cylinder on each bank

Any help would be great, I'm moving in a few weeks and need this thing drivable for the move.

 

[Schurkey]

The cam is geared to run 1/2 the speed of the crankshaft. One complete turn of the cam (or distributor) is 720 crankshaft degrees. 720 / 13 = 55.x degrees.

A recent post describes an aftermarket distributor having an incorrectly-positioned rotor mounting. This also mis-positions the cam sensor.

Post L29 Build gremlin - need ideas

Well I got my truck all put back together and it hauled an 11,000 pound trailer 1400 miles with 1,000 pounds in the back from Colorado to Michigan. It was 101 degrees through South Dakota and the ole girl did what I asked it to do. Trailer was probably a bit heavy but the brakes and controller...

www.gmt400.com

 

[alpinecrick]

A couple years ago my brand new Summit "billet aluminum" distributor wouldn't zero out even when I brought to two different mechanics with the high dollar GM Tech and Snap On scanners.

What really fried my butt was there wasn't anything wrong with my original in the first place--even the teeth look good (knocking on wood).

I'll sell my hot rod Summit distributor cheap--it's got about 20 miles on it.

Meanwhile, my original GM distributor is back in the truck and still doing just fine with 267k on it.........(minus the 20 miles, of course)

From here on out it's AC Delco or Delphi only.

 

[BRUCE L RUSK]

I've got two but neither one will zero out. I'd hate to pull it as I'm getting tired of taking this thing in and out but I have an OEM in my RV I could try if I can get that one out easily. I was hoping for a way to just update the tune to tell it to be happy with -10 instead of 0, thus doing the math automatically to get back to proper expected timing.

 

[Philip Parker]

The thread mentioned above is my post about this exact issue. I am convinced at this point that the issue is the aftermarket dizzys are not manufactured correctly. I encountered this with a few parts on my 99 7.4 rebuild last fall.

I am in the process of figuring out why my Snap On scanner will not complete a crank relearn to see if that might be the issue as well. I also have a new cam (as well as just about everything else) so if the ECU is not measuring the crank sensor variation correctly it may also not be able to determine the correct cam offset to the crank. This is just a hypothesis at this point though.

 

[smokymtn65]

Have you turned it to the TDC and checked rotor button position?

 

[BRUCE L RUSK]

Yeah it lines up good. somebody elsewhere also mentioned trying to unpin, reverse and repin the gear as that should be me 1/2 a took closer.

 

[someotherguy]

Had an extremely worn distributor in a 240K-or-so mile 7.4, top bushing was so worn out it was letting the rotor strike the terminals inside the cap and was breaking the little ridges off the top of the rotor. Needed immediate repair as it was a wrecker that was expected to be on duty every night.

Only local distributor available -right now- was a Cardone, which I would have otherwise avoided. Was decent though and it had an aluminum body instead of plastic. Stabbed it and got it to zero using a borrowed OTC Genisys scanner, no issues. FWIW

Richard

 

[smokymtn65]

I would loan you a good known take out, but you would have to come to K town to get it, and I am off till next tuesday , obiously don't have it wilth me and I live 50miles NE

 

[BRUCE L RUSK]

Problem fixed, guy on an EFI group recommended taking the pin out of the gear and flipping it 180 and repinning. I can get to 0 now.