New motor stumble from idle/WOT below 3K RPM

[marshall_mosty]

Guys,
I've put together a new motor and am having issues with a off idle stumble/miss.

It will idle fine, but when you matt the gas in neutral it will hesitate and then "catch up". Same goes with throttle application in gear.

I go for a dyno tune on Friday, but want to know if I should hold off until I can correct this, or if it's something they can "tune out". Here is what is new:

new bottom end (331, 10.5:1 Forged Pistons, Zero Balance)
injectors (24lb to 30lb)
MAF (75mm-24lb calibration to 80mm-30lb calibration)
T-body (65mm to 75mm)
Bigger air filter for the new MAF
New plugs, cap, rotor
New fuel filter

Timing is at 14-degrees BTDC
Fuel pressure is "in range" at approx 40psi with vacuum line pulled. Anything over 35psi is "good enough". I've run as high as 50psi on smaller injectors.

The previous combo had a "no name" chip in the computer that I pulled since I'm having a chip burned to drop the power levels.

Once the car is over 3K, it runs like a scalded ape. I'm just concerned with throttle response, in general.

All the cylinders are firing, but #4 (passenger rear) and #5 (driver's front) are "colder" than the others. I don't know if this is a Ford thing, or part of the problem...

Ideas?

[GlennCMC70]

Move the #4 and #5 injectors to see if the "cooler" temps move w/ them. If so, likely time for new injectors or have them cleaned.

[Casey_SS]

It sounds like you've made some significant changes (injector size, MAF, & TB) which probably require PCM adjustments but don't have the new chip yet? Is that right? Are you having a custom chip burned at the dyno or are you doing the mail order thing?

[marshall_mosty]

Glenn,
The injectors are Ford Motorsport units which are brand new out of the box. I've already swapped them around once and the cooler temps remain.

Casey,
The chip will be dyno tuned. No mail order "stuff". I was "scary fast" over 3K when it cleaned up, so I'm expecting some significant tweaking will be required.

[edrock96GT]

Maybe do a compression check. I had a bent valve give me similar symptoms. It stumbled down low, but cleaned up around 3k. Mine idled like crap though which yours isn't doing, but still something easy to check.

[Fbody383]

All the cylinders are firing, but #4 (passenger rear) and #5 (driver's front) are "colder" than the others. I don't know if this is a Ford thing, or part of the problem...

Is that just an effect of scavenging efficiencies of the manifold? Just reminds me of either a Roush or Saleen article about individual cylinder CRs to try and optimize some of that. Would be interesting to know what you find.

[cjlmlml]

try putting in smaller jets..

[marshall_mosty]

Can I have your left over ones to see if I can cram them in the injectors??

I called the dyno shop and they aren't concerned. They said "bring it"... Appointment is at 11am tomorrow morning, so I should be good by early afternoon.

[way2neary]

Marsall,

I suspect the issue ralates to your MAF calibration being out of sync with your new chip. Only way to fix that is on a dyno and watch the AFR.

Good luck tomorrow!

[marshall_mosty]

I will let you guys know how it goes. I'm going to get a "raw" baseline and then have them flatten out the curves to my AI numbers.