1dirtyZ

iTrader: (1)

i finally got to tunning my car on a mustang dyno . but now it seems to having a small issue under wot and a load:

as soon as i floor the car and the rpm reaches about 5k rpm a big miss or a small bog happens for a fraction of a second, then the car continues for a second or two real good then the bog happens again at about 6400 rpm .

these are the symptoms: map sensor ( 3bar) shows a drop in boost from 15ish to about 10 when the bog happens , injector duty cycle as well as fule pressure drop momintarily to about 65 psi - ( understandable since the injector duty cycle is related to what the 3 bar map is seeing and the fuel regulator is boost refrenced ) it almost feels like the car hit the rev limiter , but it is set at 6800 rpm . afr is at around 11.3 all the time , changes just a bit when the bog happens

now more on the combo : 427 , 8.7:1 copression , F1-R blower with sdce tensioner kit , vortech mondo bov ( about 5 years old) , th-400 with a huge stall.


what do you think is going on?? the car was strapped on the dyno pretty well , we also did the fat man in th trunk mod as well as used the pull down straps under the car. the car had the slicks on too.

i think i narrowed it a bit down to either the bov popping open under load ( vortech says that its good from 0 to 10 psi) - but why does it do it once or twice only and not all the time during the run??
or could it be the belt slipping ?? same argument as the bov, why only once or twice during the run?
another thing i thought of is that it could be blowing the spark , but why would the boost drop ?

any ideas ? suggestions ?

94blownz281

iTrader: (12)

i would check on the BOV since its pretty old. what plugs and cold range and gap? what pulley do you have that could cause the belt to slip? maybe upgrade to a better one. maybe a TB sensor is acting up?

94blownz281

iTrader: (12)

Long shot also but maybe boost is leaking out somewhere? but that wouldn't cause a bog down just pressure lose.

1dirtyZ

iTrader: (1)

plugs are tr6's gapped at .035 . i'm also running c16 gas.
i removed the intake manifold just to check if it was leaking from the rear , but no luck .

94blownz281

iTrader: (12)

I have no clue then man. have the car scanned and see if that shows anything.

CHRISPY

Try narrowing the gap to .023 and try again. How much RWHP are you seeing through the unlocked 400? ~700? Are you running truck coils?

If that doesnt work try testing another BOV

Cheers,
Chris

NicD

iTrader: (7)

Does it happen at the EXACT same RPM every time or does it vary a bit?

DeltaT

iTrader: (5)

What pump setup are you running? Are you turning on a 2nd point at some boost level?

Jim

1dirtyZ

iTrader: (1)

the issue happens at exactly the same place every time .
sometimes its not as noticable as otheres . problem is that the rpm is kinda constant ; i have a huge stall and as soon as i get on it it flashes to about 5000 ish rpm and rpm starts climbing to 6kand settles at about 6300 rpm , its when it just starts going flat on the rpm curve that the bog happens and then about a second after that ( note that the rpm is constant throughout the run )

i'm currently using twin external walbro's on all the time .

it has truck coils on ( the older version ) and i will try gapping the plugs a bit narrower .

i slapped on a new BOV - godzilla one , rated from 10 to 35 psi - will see how it does today.

Schantin

iTrader: (6)

Sure you know that a lot of things can cause that prob. One is fuel loading. What was the AFR at the bog point? Too much fuel will cause it to fall flat on it's face......and then recover higher in the RPM range.

Floating valves (due to inadequate springs), improper spark (from gap), and boost leak can all cause similiar probs. I'll assume that the car is being logged during these runs. So, my $0.02 is check the fuel delivery and see if it's spiking high (or even low) where the stutter occurs). Good luck

1dirtyZ

iTrader: (1)

well i think i figured out what it is , but first let me answer your questions , the afr was around 11.5 to 11.2 even when it bogs it stays at around that afr. you also have to note that the bog is momentary almost liek a back fire - a long backfire- it lasts about 1/2 second.
springs are adequate, they are good to .650 lift.
fule pressure never drops, and climbs linearly with boost.

now back to what i think is the issue :
i noticed that there was a clanking noise from under the car when i turned it off. and the last dyno pull the car made no boost !!
upon further investigation it sounded like it was coming from the blower. and when i tried to move the impeller with my hands , the pulley would move a bit then stop.
from what it seems like the impeller has stripped its teeth/ splines on the shaft
that could explain the strange bog that was happening .

1dirtyZ

iTrader: (1)

has anyone ever heard of this happening before ??
any idea how much it would cost to repair?