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View Full Version : Car boggles at 4k rpms



Dvsmx6
01-29-2005, 09:00 PM
We have a t25 on a 4afe (ST) 5th gen and the fuel mods we have is just a vortech 12:1 fmu. Besides those facts, everything else is stock. At about 4k rpms throughout everygear, it boggles. It sounds like it goes Boom. I called up one of my friends and said it could be a sound of detonation. He said we need a msd something and that we should retard the timing. I thought it was the FMU because we hooked up the vacuum inline with the stock fpr. So we routed the fmu to another vacuum source, and it's a little bit better, however, same thing. And when it boggles, a puff of blue smoke comes out. I mean, we're boosting fine until 4k rpms, after that we let go of the gas because of the boom. Could it be the clutch as well? FMU is bad? Do we gotta retard the timing? Do you think it's fuel issues as in we need an upgraded fuel pump as well as an aFPR.

nuclearhappines
01-29-2005, 09:36 PM
What PSI are you boosting to ?
What plugs are you using ?
Does the check engine light come on when you do this ?
Do you have an air/fuel ratio gauge?
Do you have a fuel pressure gauge in the car?
If your car has cooled down, take off your your coolant top off cover and see if you can see oil on top of your coolant?
Take off your oil fill on top of the engine and look to see if the underside of it has a sludgy foggy mess under it ?
Pull your spark plugs and check them against this :

http://www.off-road.com/dirtbike/tech/2002sparkplug/4.jpg

We don't have enough information to help you... yet

nuclearhappines
01-29-2005, 09:51 PM
>>"we're boosting fine until 4k rpms"
If you don't have an EGT or an A/F gauge or you haven't read your plugs then you have no idea that it is fine... it may be detonating or running lean and you wouldn't really tell...


>>"after that we let go of the gas because of the boom"
Is it a loud pop from the exhaust ? are you backfiring ?

>>"Could it be the clutch as well?"
if the clutch is slipping, you'll see the rpms rise and the car won't accelerate as hard...but it won't 'boom'

>>FMU is bad?
unlikely, they are very simple, and should last longer than most cars, depends where/who you bought it from though.

>>Do we gotta retard the timing?
Depends what boost you are running/ what octane you are using... do you have a timing light ?

>>Do you think it's fuel issues as in we need an upgraded fuel pump as well as an aFPR.
You may need a pump but not an Adjustable FPR.

We can help you ... we have a lot of good people here... you should visit ALOT and should've before you did this... don't drive it anymore untill we figure out what your setup is like and give you advice...otherwise i'm afraid you are very close to losing your motor.

If your friend is a honda guy ... don't talk to him anymore either...talk to us first. we know these cars better

-nuke

Dvsmx6
01-30-2005, 05:47 AM
Haven't check the plugs yet, but will do. And the boom sounds like it's backfiring. We're only boosting 3 - 4 psi just for testing purposes. And we're running on 91 octane.

Hooligan
01-30-2005, 06:39 AM
What do the plugs look like? How new are the ignition components?

Trance4c
01-30-2005, 07:13 AM
Haven't check the plugs yet, but will do. And the boom sounds like it's backfiring. We're only boosting 3 - 4 psi just for testing purposes. And we're running on 91 octane.

up the octane!!!! jesus!

nuclearhappines
01-30-2005, 08:11 AM
fuel cut, spark blowout, or running out of fuel flow from your pump

that's what i think for starters.

Jaemus
01-30-2005, 08:23 AM
i just bought a turbo - can u define fuel cut for me?

spoolin_gt
01-30-2005, 10:05 AM
could be a spark problem.....check the ignition coil....had this problem for quite some time..and i changed the ignition coil and boom!!!...problem is gone....first thing that happened was the wires...one of them were cracked....fixed it..then realized that my tps was loose..fixed that....changed the fuel filter.....put some injector cleaners..didn't do nothing....finally change the coil..and there it is..running smooth again.....just try swapping in a better ignition coil and see how it works....

Trance4c
01-30-2005, 06:10 PM
i just bought a turbo - can u define fuel cut for me?

Fuel Cut - where the fuel system cuts fuel going into the combustion chamber due to an excess amount of pressure created by the turbo into the engine. This excess pressure measured in PSI (pounds per square inch) is a by product of making the turbo create more PSI for more horsepower. If you create to much PSI, you'll hit fuel cut.. automatic slow down.

spoolin_gt
01-30-2005, 06:41 PM
i doubt that it can be a fuel cut though...since you're getting a backfire...backfires are caused by unburned fuel...from my experience...you're engine is taking enough fuel..and not getting any spark to burn it...so dont worry about any fuel pump upgrade and such...and try to see if you have a spark problem....

Jaemus
01-31-2005, 11:49 AM
thanks trance

hmm
so if once the turbo has fully spooled up, and the car during acceleration seems to drop in power drastically intermittently, i would be experiencing fuel cut?

spoolin_gt
01-31-2005, 06:57 PM
not necessarily...there are several reasons for the car to stop accelarating while driving...some cars with old/bad ignitions will have this problem as well....while your rpm goes higher...your car is suppose to produce more spark since you're car is putting out more fuel....old ignitions won't be able to produce this spark and burn the fuel due it's bad conditions...making the power drop drastically...

only way to get fuel cut is if you're overboosting...or when the car hits the governed speed it came out from the factory...

Dvsmx6
01-31-2005, 07:58 PM
Thanks for all the replies guys, will look into everything.

Does NGK make sparkplug cables for our cars? I went to the local autoshop and they said they couldn't find any. Anyone have part numbers for the wires?

And do they have ngk 6 series for our cars? Just the v-power ones. Also any part numbers?

nuclearhappines
01-31-2005, 08:45 PM
Iridium
NGK-BKR6EIX (6418) 6.50 6.50
NGK-BKR6EIX-11 (3764) 6.50 6.50

Copper
NGK-BKR6EP-11 (2978) 8.69 8.69
NGK-BKR6EP-8 (2215) 8.69 8.69

Platinum (standard recessed electrode)
NGK-BKR6ES(3783)Box of 10 20.00 20.00 small gap
NGK-BKR6ES-11(5553)Box of 10 20.00 20.00 large gap
NGK-BKR6EY(3696)Box of 10 v-power (if i recall correctly)


wires for a 1991 4afe:
NGK Premium wire set 9835 TE21 --- $78.57

BraveUlysses
02-01-2005, 12:05 AM
thanks trance

hmm
so if once the turbo has fully spooled up, and the car during acceleration seems to drop in power drastically intermittently, i would be experiencing fuel cut?

Fuel cut feels like you're hitting a wall. It is not subtle and should suprise you when it happens.

You've got a 205, so hitting fuel cut is no easy feat, it should be set over 14psi.

Jaemus
02-01-2005, 06:45 AM
gotchya

seems like i should inspect the ignition system then...

im attributing anything strange to the turbo setup atm cos ive never had one before :)