HELP!! with a miss that I can't resolve!!

[mattlwright]

My 87 350 has a miss that I cannot make go away even after replacing parts multiple times. Truck has recently replaced 350 with Vortec roller cam and EDB MPFI conversion and DynamicEFI ecm. This thing has a miss that is the most evident at around 1200 rpms and vibrates the truck. When checking with a timing light the timing jumps around 4-5 degrees in this area. I have replaced the distributor now 3 times, coil twice, wires and cap and rotor now 3 times with the new ACDelco distributor I installed Sunday. When I first installed the new distributor after the truck had sat for 5 days it ran smooth like it should. I then drove the truck about 15 miles and the miss started to come back and is now as bad as it ever was. Brian @ tbichips has been helping with tuning and this problem but I thought I might post here and see if anyone has ever experienced anything like this. I am losing my mind and hate driving this truck!!

[454Man]

The distributor gear to cam gear "mesh" can cause timing to jump around. A loose timing chain can as well. are you using the correct bronze distributor gear for your roller cam? Hope you get it fixed so you can enjoy your ride.

What's under the hood??? If you have to ask maybe we shouldn't race...

[454Man]

Or "cam walk"

What's under the hood??? If you have to ask maybe we shouldn't race...

[mattlwright]

454Man, it's a stock hydraulic roller that uses a plate at the front of the block to retain it. It also uses the same type of gear as a flat tappet so that isn't the issue.

[454Man]

Have you checked for a loose timing chain by rotating the crank shaft back and forth watching the rotor? Glad to here you have faith in the cam not being the issue.

What's under the hood??? If you have to ask maybe we shouldn't race...

[mattlwright]

Motor has less than 7k on it and I've been fighting this issue for about 5k that I put on it.

[454Man]

Only other thing I know to make timing bounce around like that it's the mechanical advance springs in the dizzy. Rare but maybe someone else could pin point this. Id still rotate the crank and watch the rotor. There's something funky going on...

What's under the hood??? If you have to ask maybe we shouldn't race...

[bd]

My 87 350 has a miss that I cannot make go away even after replacing parts multiple times. Truck has recently replaced 350 with Vortec roller cam and EDB MPFI conversion and DynamicEFI ecm. This thing has a miss that is the most evident at around 1200 rpms and vibrates the truck. When checking with a timing light the timing jumps around 4-5 degrees in this area. I have replaced the distributor now 3 times, coil twice, wires and cap and rotor now 3 times with the new ACDelco distributor I installed Sunday. When I first installed the new distributor after the truck had sat for 5 days it ran smooth like it should. I then drove the truck about 15 miles and the miss started to come back and is now as bad as it ever was. Brian @ tbichips has been helping with tuning and this problem but I thought I might post here and see if anyone has ever experienced anything like this. I am losing my mind and hate driving this truck!!

Verify the firing order, plug wire routing/looming (to eliminate crossfire as a cause) and check cylinder compression.

Did you check and set the ignition timing with ESC bypassed?  Some timing light inductive pickups can cause a light to mistrigger, so it appears the timing is unstable. 

Have you isolated the misfire to a particular cylinder?  You may have an issue with one of the injectors.  Have you physically removed them recently?  The Pico injectors are easily damaged.  Or, the injectors may need cleaning.

As 454Man suggested, don't assume the timing chain is in good shape.  Check it for looseness!

As a precaution, service all of your ECM grounds and the harness connections to the ECM.

[mattlwright]

If the timing chain was loose and worn the miss shouldn't have "gone away" with a new distributor. Something is causing the pick up assembly to fail and I suspected grounds also and added another ground from the intake by the temp sensor. I have also tried the old ECM to eliminate that. I even disconnected the alternator as I've heard of them allowing some AC voltage to leak by the diode trio and cause driveability problems and that made no change.

[bd]

It might surprise you how well electronic injection can mask mechanical problems. 

...Something is causing the pick up assembly to fail....

Have you verified that this is what's happening?

[bd]

Any chance your DynamicEFI ECM needs an ignition filter, because it's mistriggering?

[mattlwright]

Any chance your DynamicEFI ECM needs an ignition filter, because it's mistriggering?

That I don't know. I could fire Bob an e-mail and see if he's seen this happen before. The most baffling part is that replacing the dist with the Delco unit made it run like a champ, briefly! Brian @ tbichips advised that if the stator/reluctor assembly made contact due to expansion from heat it would be toast. I plan to do a LS swap in this truck but I'm not quite ready, and I need a place to go with all of this gear and it would be nice if it worked properly!

[bd]

...The most baffling part is that replacing the dist with the Delco unit made it run like a champ, briefly! Brian @ tbichips advised that if the stator/reluctor assembly made contact due to expansion from heat it would be toast....

I'm skeptical.  Had this actually occurred you would likely 'see' physical evidence of it.  Why not pick up some Prussian Blue and lightly dye the ridges of the reluctor vanes?  If it's colliding with the pickup, it will be visually obvious.

[bd]

Are you running an ignition box?

[mattlwright]

No external ignition box like an MSD or anything. Just stock ignition.