medium-heavy throttle hesitation

[CRTD]

this car is giving me fits. i am missing something here. this is a transplant of an 04 GTO into a 68-72 GM A body.

what it does is has a terrible hesitation if you give roughly 50% throttle or more abruptly. it is somewhat inconsistant. i have gone over the maf and ve calibrations. have tried some crazy stuff and not got it solved yet. it is 100 times better than the stock cal. but is still not like it should be. i spent alot of time on the ve table. i believe i have it pretty close.

while driving you can give it enough throttle to experience the condition. when it does it the afr is higher than commanded. however, sometimes the o2s are high for the duration. sometimes they are low. there is no rhyme or reason to that i have discovered yet. then after a second or two it cleans up like you hit the bottle and goes. when it does this i notice the pe mode seems to have "kicked in" finally. i have experimented with pe rate. it is at 4.0 right now. when the pe mode works properly it seems to runs good.

the log shows it being random. i thought it may be suffering from a misfire. i hooked up my tech 2 to it and there are no misfires on the misfire graphic when this occurs. the -05 cfg shows the commanded afr vs the actual.

please help!

[Pekka_Perkeles]

Stock engine?

[CRTD]

Stock engine?

sorry, stock engine. bolt on are a set of doug's headers (full length) and a custom air intake. made of a 90 degree rubber boot with a radiused turn, and a k&n filter. the problem is present with the maf failed so i figure it is not a maf issue.

[DAVECS1]

I would think your VE table needs adjusted your showing peak fuel load at 2800 RPM, and then your PE looks to be inverse of what it should be. The timing tables are also extremely ruff that can cause running inconsistencies.

I would go into you VCM scanner and enable open loop. Then log your AFR during steady state cruise at 1500, 2500, 3500, 4500, and 5500. These all should be close to 14.7, if not adjust the VE table until they are.

Then re-enable closed loop, and go try some WOT kick downs and log AFR. It should be near 13.0 WOT. If it is not ad PE until it is.

Also work on smoothing your timing table.

[Throttle]

start back over with stock fueling and timing tables thats a very very strange ve table.

[flame]

What is the fuel system setup? pump intank, baffled tank, regulator?

[CRTD]

What is the fuel system setup? pump intank, baffled tank, regulator?

it has a factory tank. a new stock type tank unit with 3/8 supply and 5/16 return pipes. an msd 8225 fuel pump mounted on the frame. an ls1 corvette filter with regulator.

we have been filling it with premium unlead pump gas.

[flame]

I was just thinking it may be a fuel pick up issue. If it does it with the tank fuel then it obviously isn't. I did a 68 C10 and anything under 1/3 tank would do it.

[DAVECS1]

If he is using the tune he posted, it is pretty good chance his VE table is directly responsible.

[CRTD]

i have been using the "tuning school" method for the ve and maf calibration. when i drive with the maf failed the ve table cels are all 0-1-2. except i cannot get the ltft to register any or enough cel hits in the lower rpm high load areas i was having trouble with. so as a desperate measure i tried increasing the cels i was having trouble with in the ve table. it seemed like it may have helped or maybe it was wishful thinking.

is there a better way to get those cels nailed down than the method i have been using?

[CRTD]

ok, so i put the base ve and timing tables back in. start over the ve tuning process. and as you guys suggested it is coming out different this time. ran out of laptop battery for now.

however, this thing still has that nasty hesitation. seems to be at around 6000hz maf and anyhthing over 75% throttle during the ve calibration process. most noticeable at lower engine/vehicle speed. but it is there whenever the throttle angle goes up enough. when it does it it almost sounds like a jake brake on a diesel. and if i lift on the throttle just a little or the engine speeds up enough it comes back alive.

[CRTD]

what about disabling cylinder charge temp>complex model?

or enabling dynamic airflow>WOT entry max airflow?

[kyphur]

interested in if there are any updates

[SICKstySEViN]

noticed on your pe table your minimum torque was 20 percent and no rpm delay, might be trying to hit pe before you need it.