Getting a shudder. This has been present since I rebuilt this motor with the cam. Runs smooth thru 1st, 2nd, and 3rd but then it goes to 3rd lockup and I get a constant shudder at low rpm only between 1400 to 1850, it disapears above 1850 but still feels slightly sluggish, then when accelerating further and it drops to O/D lockup and rpm drops down again the shudder returns. It feels like pre-detonation and can feel the shudder thru the whole truck. It's usually very faint shudder with occasional stronger shudder. Happens with motor cold or hot under load only.

I have routed wires per TSB with insulating plastic conduit where wires cross. Coil wire does not cross any other wires.
I have also detuned the PCM with the death flash to eliminate it as a cause of pre-detonation.

Motor runs and feels great through all gears until TC locks up and then shudders. Trans oil is right at full mark. This is the second trans with about 100k miles on it. TC failed last year and was changed out with PNH low stall, felt great after install. Trans feels and runs great.

Just installed new cap, rotor, and wires. (New Autolite 5224 copper plugs installed 750 miles ago) Checked all injector wires. Still no change.

Few things I think may be causing this are:
*New TC is failing
*CPS is original needs to be changed
*Fuel sync may need to be rechecked, it was set at 0.

What could be causing this low rpm shudder that only happens in TC lockup?

 

And not the plugs? What plugs are you running? May want to pull them to see if there is any difference in color.

 

Installed new Autolite copper 5224 750miles ago when motor was rebuilt. I'm using a 195* thermostat so those should be the correct ones.

Maybe I should try putting back the 180* thermostat with the 3923 plugs like I had before...?

I will pull the plugs and check em, and do a compression test since the plugs will already be out.

 

Sounds like a miss.... they are most apparent when in O/D. Re-verify your firing order.

Are you getting any codes??

If you pulled the motor for the rebuild, did you crunch the crank position sensor when reinstalling??

 

Just rechecked firing order, traced every wire. 1-8-4-3-6-5-7-2. #1 wire is indicated on cap. Looks good.

Motor was not pulled. Checked CPS wire, not pinched.

No codes.

 

I am guessing you had the distributor out? Did you have fuel sync reset?

 

Yes distributor was pulled out. Fuel sync was set at 0, it was fluctuating 0 to +0.5 and tightened the distr bolt down, then rechecked. Was thinking of rechecking it and set it dead on at zero.

What would be the effect of advanced distributor, early fuel delivery?

 

Yep. Although, I am not sure that is a bad thing....... I *think* it is supposed to hit the valve before it opens anyway, so the nice toasty warm valve vaporizes the gas...... (not to mention helps cool the valve.....)

I think resetting fuel sync is where I would start. After that, have a close like at plug wires, and make sure they are routed properly.

 

I pulled the plugs today and they all look fine, all were normal light brown. Regapped at .040 and reinstalled.
Also did a dry compression test(with all plugs removed) and all cylinders are at 150-155ish with exception of cyl 1 at 140 which is still within normal range. Cranked motor 3 pulses.
I added an octane booster to the gas tank and then filled my half full tank with 92 octane to prevent ping if that is what is causing the shudder. So far it hasn't helped but I only drove a few miles since filling.

My next step is to check fuel sync to see if it's still at zero.
Check rear suspension and drive lines for looseness
Pull valve covers and check lifters and pushrods
Ditch the 195* thermostat and switch back to 180* and Autolite 3923 plugs
Replace CPS
If no change after that, will probably pull timing cover and degree the cam like I should have when it was installed.

 

watching this to see what you find out