Performance 1FZ part throttle bog help

[bjowett]

I'm posting this in hopes that someone might recognize the problem or have some idea's on what it could be before I jump in deeper than needed.

The problem is what I refer to as bogging, at more than say 20% throttle and from about 1800 rpm to about 3000 rpm the engine wil bog. Increasing throttle dosn't help until high 2k - 3k and then it will start to pull strong and well right up to redline. If I advance the ign. base timing it reduces it, and if I bring it up past 15 degrees the bog begins to disappear... but it still dosn't pull like it should.

My 93 FZJ has a mildly built engine. The basics, it is bored to a 4.6L, the block and head were shaved/resurfaced and brought compression ratio is roughly 10.5:1. The head has a basic porting job, polished combustion chambers. The intake manifold is ported, with a little work to the exhaust manifolds, custom dual exhaust.

Things that were done during build.

Moddified timing chain guide to remove slack from the chain created by shaving and keep stock cam timing.

Had 12 injectors, checked spray pattern on all 12, installed the 6 best.

New wires, cap, rotor.

Plugs are one range cooler and gapped. Pulled all 6 to read and things look to be burning well, maybe slightly lean.

There are no codes, just the quick flash for all is good.

I plan to check TPS, air flow meter, cam timing, etc etc. Any other idea's? There are no vacuum leaks...

[Cattledog]

Try pluging the FRP to manifold hose, and taking it for a 20 to 30 minute ride.

Sounds like you are running lean to me in closed loop and the ecu is pulling timing lots of advance out to avoid preignition. Strange. Once you are in open loop you end up runing rich and timming is per the ecu's map plus correction factor and all it well then. Maybe you are out of the mapped fuel range with the rebuild.

The idea is to run the injectors at full pressure off idle. Worst that will happen is that the truck will run too rich or nothing will happen.

Other thought you may need to adjust the AFM if possible, I remember this from my minitrucks AFM. Not sure if that is possible on a 1993 80 AFM. The mod/adjustment made the 22rec run richer for improve torque.

BTW, I want to see that truck sometime. I have been following your build for ages. Amazing work.

[turbocruiser]

I'm thinking Throttle Position Sensor. It is relatively easy to check with an ohmmeter / voltmeter. I'd start there. HTH.

[landtank]

Fuel pump/ fuel pump relay. Isn't 3k about the time the relay flips over to the high side.