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Discussion Starter · #1 ·
i have been fight this 408 from the start. it runs great now but only at like half throttle. when i go to wot it loses power and gets jerky. Could i maybe have the fuel sync wrong or what. The truck is using a sct tuner by PIE. Any thing would help. Thanks
 

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Is it backfiring when you open the throttle up?

You should be able to set the fuel sync pretty close by bringing the engine to TDC #1 compression, and lining up the centerline of the rotor with the notch in the cam sensor under the dizzy cap.

Try that first.
 

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You'll need to put it on a scanner to fine tune it. You'd be surprised how far off you can get it by lining up the notch, because getting a perfect TDC with the heads on is a hit or miss thing in itself. I have been as far off as -22 degrees, where it should be roughly +4. It totally ran like shit too.
 

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You'll need to put it on a scanner to fine tune it. You'd be surprised how far off you can get it by lining up the notch, because getting a perfect TDC with the heads on is a hit or miss thing in itself. I have been as far off as -22 degrees, where it should be roughly +4. It totally ran like shit too.
Dial indicator down the spark plug hole FTMFW. You can get pretty exact by doing that.
 

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Discussion Starter · #9 ·
so i got the fuel sync set the closest i can w/o a scanner. The truck runs better but still makes no power at wot. any other thoughts? I will call the guys at pie and ask them too.
 

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There are so many variables it will be nearly impossible to guess, but I always start with the simple stuff.
First, check all wiring harnesses, grounds and vacuum hoses.
Next check the firing order, plugs, wires, etc.
Make sure the 1/2 shaft (distributor drive) is lined up right, because that factors in to fuel sync vs the ignition firing on time. It should point at the drivers side, front, inside corner of the valve cover (about 5 O'clock or so, as you look down on it).
If everything is right, then I would look at the cam vs crank timing. Was the cam degree'd in? Installed straight up, mark to mark?
Does it have adjustable rockers? What procedure and how much pre-load did you use to set them up?
 

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Discussion Starter · #12 ·
If everything is right, then I would look at the cam vs crank timing. Was the cam degree'd in? Installed straight up, mark to mark?
Does it have adjustable rockers? What procedure and how much pre-load did you use to set them up?
Im pretty sure i put the cam in mark to mark.

No the rockers are set to 1 1/2 turns past 0 lash. They are hughes 1.6 rr.
 

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Im pretty sure i put the cam in mark to mark.

No the rockers are set to 1 1/2 turns past 0 lash. They are hughes 1.6 rr.
That's a 1/2 turn tighter that what I would normally run, but if you like it, I like it.
What procedure did you use to set up your adjustable rockers? I use a lash chart. Some like it, some don't. I'm curious to know exactly how yours are set up.
 

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I'm not up on all the late model fuel injected stuff but 1 1/2 turns past zero lash seems like too much preload to me. I've never gotten by with more than 1 turn. Sounds like the valves may be hanging open at higher rpm. Again like others have mentioned there are too many variables to give a exact answer. I'd change one thing at a time and start with what is easiest. Good luck with the fix.

Mike
 
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