5ltrBetr

iTrader: (3)

I have a 408 setup, BBK intake, 42# injectors, long tubes, ported 241 heads, .020 milled, etc etc. Makes 442/439 on dynojet.

Recently, I started getting a miss at 4000+ rpm in 2nd. It still pulls, but it seems power is going in and out, sometimes almost "spitting". I ran a log and did not see anything out of the ordinary. I did notice my fuel pressure drop to 50psi during the 2nd gear run. Is that normal? Here is a link to the HP Tuners log file. Any help would be greatly appreciated.

My Log File

SSpdDmon

iTrader: (10)

Fuel pressure shouldn't be dropping. Also, have you checked/cleaned your MAF? Is there a problem with timing (burst knock kicking in)?

brad8266

iTrader: (23)

Check your fuel system first.

5ltrBetr

iTrader: (3)

I can check those tomorrow. Can others chime in as well on fuel pressure dropping to 50psi during WOT? I have a 255lph pump in the tank. Is this enough to support 42# injectors running 65-72% duty cycle on a 408? Also of note, I replaced the TR55 with TR6's tonight. Can't say they helped yet as I had a few beers installing them and won't get to test it until tomorrow

SSpdDmon

iTrader: (10)

The pump should be able to support you motor. The question may be can the factory wiring/power supply support your fuel pump? I know Racetronix sells what they call a hot wire kit.

5ltrBetr

iTrader: (3)

I bought one of those upgrade kits. It seems to work fine until recently. Interestingly, I installed the new TR6 plugs last night and the problem seems to have gone away...

Except for the fuel pressure drop.

Thanks

5ltrBetr

iTrader: (3)

Well, sad to say that my problem has returned. Installed the TR6's and all seemed fine until today, it started "spitting" back, fluctuating power, at 4000+ RPM. I don't get it. I have checked plugs, wires, fuel (seems OK excpept the pressure drops to 50-55PSI at WOT). Does anyone suspect a mechanical failure? The lifters are new LS7 units, the rockers are stock, the pushrods are chrome molly, the spings are comp 918's. I am feeling the frustration mount... I have HP Tuners. Is there anything in particular I should be monitoring while doing a 2nd gear run? Aso, the O2 sensors are less than 6 months old.

Thanks in advance!

Frost

iTrader: (45)

I can't open your log, but what is your MAF looking like? Remember it takes over completely at 4K...

5ltrBetr

iTrader: (3)

Here is a pic of my log file during the 2nd gear run where is is "breaking" up after 4000 rpm.

Log File Pic

SSpdDmon

iTrader: (10)

Is it just me or does it appear his LTFT's are maxed out when he hits WOT???

Frost

iTrader: (45)

your LTFTs are locked crazy *** high, 24-25%... do you have another MAF you could try or one you could borrow and try (though this is just ruling out since the NB O2s stay relatively high? Do you have a code set?

5ltrBetr

iTrader: (3)

I am kind of new at the tuning gig, what are the LTFT's? I have suspected the MAS since at the same time I feel the dips in power, there are corresponding dips in the MAS readings. I don't have any codes set since I have deleted most of the ones in question. Maybe I should re-enable those and get the ones that are being set.

Frost

iTrader: (45)

Your car is adding 25% fuel on top of what it is commanding at WOT. This is indicative of some problem with fueling/airflow.

5ltrBetr

iTrader: (3)

Holy Yikes! I should figure out why. Any ideas of where to start looking? MAS I assume would be a starting point. Where else could I get a command for that much fuel? That would explain the 10PSI drop in fuel pressure at WOT as well.

I just thought of something... One change that I did make was I remounted where my exhaust clamps are positioned to give more ground cleareance. As a result, under full acceleration, the clamps bang the bottom of the chassis a bit. Could the computer be sensing detonation because of that and pulling timing/adding fuel??? I also added a catch can setup for my PVC system. I'll post some pics of that tonight. Just a thought.

Frost

iTrader: (45)

If there is a leak there and outside air is making it to your O2s it could cause a false lean which it would try to over-compensate for...

5ltrBetr

iTrader: (3)

I checked everything and there does not appear to be a leak. I am in the process of cleaning the MAS now. I moved the clamps. I'll do another log run in a few minutes and report back...

Frost

iTrader: (45)

back to looking at the fuel pressure drop/MAF... Do you have old logs that you can look at to see if idc has recently gone up (showing pressure drop) ?

5ltrBetr

iTrader: (3)

Good greif. Nothing seems to change these things. I thought maybe my injector settings might be wrong. They are Bosch 24508208 injectors rated at 36lbs at 43.5psi. They are rated at 42lbs at 58psi. I changed the value to 62psi and then to 52psi with no change in LTFT behavior. I wish I knew more about tuning... I also wish I had an old log. I'll search some more...

5ltrBetr

iTrader: (3)

Am I on the right track here? I read something about porting the MAS causing high LTFT's. I increased my MAS Table by 20% across the board and the LTFT's came down to 21%. Interestingly, my injector duty cycle went from 72% to 91%. Why? Am I on the right path here? Thanks!

5ltrBetr

iTrader: (3)

Frost:

Have you had a chance to ponder this? thanks for your help thus far!