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Weird 'Fuel Cut' Like Problem: Help!

MidnightRun

Proven Member
47
0
Aug 28, 2002
Dallas, Texas
1993 Eclipse GST
6 bolt JDM Motor
No Check Engine Lights

I am having a weird problem with the car that seems a lot like fuel cut. I had a little fun last night with a GST on the freeway, from a roll in 4th, and everytime we ran, I hit a brick wall in 4th at 5900rpm and had to switch gears prematurely. What could this be? EGTs were never higher than 800*C or so, and the car still pulled and boosted fine(12psi). Here is a list of mods that could pertain to this problem...

Big 16g(only 12psi)
510 Injectors
Walbro 255 High Pressure Fuel Pump
SAFC with settings at zero across the board
2g MAS
Spoolin Up AFPR
Brand New Knock Sensor(6 months old, 4000 miles)
Magnecore Wires(Almost new like knock sensor)
NGK copper plugs one range colder

I have other substantial supporting mods as well, but figured these would be helpful to list in hopes of attempting to diagnose the problem. Could too much fuel be causing this problem as well? I have the B&M FP gauge mounted on the filter, and it shows 46 0r 48 psi at idle with the vaccum hose on like normal. Thanks for any help everyone!
 

sential

Proven Member
185
0
Jan 27, 2003
Fullerton_Ca
It definately sounds like fuel cut. Fuel cut I believe occurs when you are running too much fuel. However, I wouldn't think that 510 injectors would be too much. I'm having problems with fuel cut myself but its at like 17 lbs on a 16g. I tried to lean it out a bit, but I don't have an egt to tell if I'm leaning it out too much, so I'm still running a little rich. Some one with some fuel cut knowledge.... Please.. Help us out...
 

boosteddsm

Proven Member
33
0
Jan 1, 2003
Ellicott_City_MD
Originally posted by sential
It definately sounds like fuel cut. Fuel cut I believe occurs when you are running too much fuel. However, I wouldn't think that 510 injectors would be too much. I'm having problems with fuel cut myself but its at like 17 lbs on a 16g. I tried to lean it out a bit, but I don't have an egt to tell if I'm leaning it out too much, so I'm still running a little rich. Some one with some fuel cut knowledge.... Please.. Help us out...
No, fuel cut happens when the ECU sees too much air. Hacking the MAS and using an AFC can pretty much eliminate fuel cut.
 

nine5raptor

Proven Member
1,855
0
Oct 3, 2002
Kansas City, Missouri
why are you running a b16g @12 in the first place?? crank that #### up! wait--do you have a turbo'd nt or a turbo motor and what is your compression if nt? (i saw you said "turbo conversion")
 

MidnightRun

Proven Member
47
0
Aug 28, 2002
Dallas, Texas
LOL. I'm only running 12 because I'd rather be safe than sorry. I'm completely untuned and am new to tuning. I want the car running close to perfect before I turn the boost up. I have a JDM 6 bolt Turbo motor in it though, so it can handle the power if I choose to turn it up.
 

boosteddsm

Proven Member
33
0
Jan 1, 2003
Ellicott_City_MD
Originally posted by MidnightRun
I understand Fuel Cut, but I don't think that is the problem in my case. I should have plenty of fuel with the Walbro 255HP and 510s for my Big16g on 12psi! Anyone else care to jump in here?
I don't think you do. Fuel cut doesn't have anything to do with "how much fuel you have". Fuel cut happens when the ECU sees too much airflow, trust me. Do you have an afc? Leaning out with an afc tricks the ecu into thinking there is less air coming in. DSM maf's can only flow so much without dropping counts. If you still have a 1G maf, get a 2G maf. If you have a 2g maf and you're hitting fuel cut, then you most likely have a boost leak. If you have an afc, how many hertz are you hitting?
 

MidnightRun

Proven Member
47
0
Aug 28, 2002
Dallas, Texas
I see... I'm on a 2g MAS. How many hertz should I be hitting on the SAFC at a given rpm point? I'll take a look next time I drive the car. At idle I believe it's usually about 55-60 on a cold start, but after it warms up it moves from 39-42.

Vaccum on my boost gauge at idle is at almost exactly 500mmhg or just above.
 

boosteddsm

Proven Member
33
0
Jan 1, 2003
Ellicott_City_MD
Originally posted by MidnightRun
I see... I'm on a 2g MAS. How many hertz should I be hitting on the SAFC at a given rpm point? I'll take a look next time I drive the car. At idle I believe it's usually about 55-60 on a cold start, but after it warms up it moves from 39-42.

Vaccum on my boost gauge at idle is at almost exactly 500mmhg or just above.
It depends on what turbo you're running, boost, etc. Do you have an afc??? If you're overrunning the 2G MAS, then you're either running lotsa boost on a big turbo or you have a sizeable boost leak. Do a pressure test on the intake and I bet you find a good leak.
 

nine5raptor

Proven Member
1,855
0
Oct 3, 2002
Kansas City, Missouri
Originally posted by MidnightRun
LOL. I'm only running 12 because I'd rather be safe than sorry. I'm completely untuned and am new to tuning. I want the car running close to perfect before I turn the boost up. I have a JDM 6 bolt Turbo motor in it though, so it can handle the power if I choose to turn it up.

turn the boost to 16-18 and watch your egts for tuning the afc. if your egts never got above 800C then your ecu is seeing too much air and adding in the extra fuel (thus keeping the egts low). this is why you are hitting fc, your ecu is seeing too much air (and hitting the limit of calculated airflow that the stock fuel system should be able to support)
 

pneumo

Proven Member
3,763
57
Oct 19, 2002
Bay Area, California
You could be getting major hesitation from a combination of being too rich and bad plugs. Without a logger it's tough to know for sure. Try leaning out the AFC high settings by 2- 3% and check your plugs and plug gap, they should be gapped to 0.28 to 0.30" The colder plugs might not like being run so cold with only 12 psi, and could be fouled. Wait until you go over 17 psi boost before getting colder plugs. The fuel pressure is about 15 psi higher than stock turbo cars, which will add a lot of fuel. At 12 psi boost you have enough of a safety zone for tuning without fear of doing damage.
 

j.d.roost

Proven Member
55
3
Sep 19, 2002
NEPA, Pennsylvania
Boost leak . I agree.
I had an ic pipe that only leaked at 14 +psi.
I would check for leaks 1st with the "home depot" setup.
 
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