What causes the fuel cut feel like 03 Cobras have? - 2003-04 Mach 1 Registry Owners Club

Stopsign32v · 11-06-2011, 12:45 PM

I was amazed but when I powershifted into 4th at the track on the last run I had this happen. The car fell on its face for a split second like it does with TC and also like the 03 Cobras do when you shift hard with a modded one. Does anyone know what I'm talking about?

ASMACH · 11-06-2011, 12:49 PM

Mine has done it since I did an eaton swap. Most of the time it seems to be the pprv that causes this

Stopsign32v · 11-06-2011, 01:03 PM

I've never had a bolt on N/A car do this.

musclemerc · 11-06-2011, 03:08 PM

It sounds like the issue stick shift Cobras have with the PRPS.

There is a mod on KBs website, most issues are associated with SC'ed not NA cars

lxh89 · 11-07-2011, 10:14 PM

The problem is caused by the EEC cutting power to the pumps during hard shifts. Basically what happens, you let of the accelerator, the throttle snaps closed but your fuel pressure spikes momentarily. The feedback loop for the fuel system control interprets this spike as a problem so it tries to control it by dropping the ground to target a lower duty cycle and lower pressure. By the time you hit the accelerator again, it needs some time to get the pressure to build back up. This feels like a second but in reality it's about 500ms (.5 seconds).

The pprv check valve definitely contributes but removing it is not a sure fire cure. My car lacks a pprv valve and still does it. The only real cure is going return style so fuel pressure is constant.

hecdel40 · 11-08-2011, 01:16 AM

Quote:

Originally Posted by lxh89

The problem is caused by the EEC cutting power to the pumps during hard shifts. Basically what happens, you let of the accelerator, the throttle snaps closed but your fuel pressure spikes momentarily. The feedback loop for the fuel system control interprets this spike as a problem so it tries to control it by dropping the ground to target a lower duty cycle and lower pressure. By the time you hit the accelerator again, it needs some time to get the pressure to build back up. This feels like a second but in reality it's about 500ms (.5 seconds).

The pprv check valve definitely contributes but removing it is not a sure fire cure. My car lacks a pprv valve and still does it. The only real cure is going return style so fuel pressure is constant.

He is on the money that is why i went with a return style fuel system.

Mach828 · 11-08-2011, 01:38 AM

You said that letting off the gas is part of the equation. But the OP said he powershifted so he never let off the accelerator.

JeromeMach1 · 11-08-2011, 11:01 AM

My car does this same exact thing. It is present at high rpm WOT shifts when I am on/off the throttle. It does not happen if I do not get off the throttle.

I hate it but have learned to live with it.

Jerome

lxh89 · 11-08-2011, 08:33 PM

Quote:

Originally Posted by Mach828

You said that letting off the gas is part of the equation. But the OP said he powershifted so he never let off the accelerator.

He's not power shifting...

004mach1 · 11-11-2011, 08:52 PM

i had a problem with fuel cut on my 03 when i would really lay into it in the hi rmps and shifting the fuel would slosh, the problem only occured when i was under 1/4 tank as long as i was over that it never happened again!

ModMike · 11-17-2011, 12:15 PM

Quote:

Originally Posted by Stopsign32v

I was amazed but when I powershifted into 4th at the track on the last run I had this happen. The car fell on its face for a split second like it does with TC and also like the 03 Cobras do when you shift hard with a modded one. Does anyone know what I'm talking about?

What kind of mods do you have on your car? Are you NA or SC?

Stopsign32v · 11-17-2011, 04:52 PM

Quote:

Originally Posted by ModMike

What kind of mods do you have on your car? Are you NA or SC?

Mods are in my sig. This is the first time I've ever had this happen on a N/A returnless Mustang.

11-06-2011, 12:45 PM	#1
Stopsign32v Registered User Join Date: Nov 2007 Location: Greenville, SC Posts: 2,554	What causes the fuel cut feel like 03 Cobras have? I was amazed but when I powershifted into 4th at the track on the last run I had this happen. The car fell on its face for a split second like it does with TC and also like the 03 Cobras do when you shift hard with a modded one. Does anyone know what I'm talking about? __________________ 03 white Mach1 JLT RAI \| 1/2 spacer \| Catback \| 4.56s 7.76@87.8mph

11-06-2011, 12:49 PM	#2
ASMACH Registered User Join Date: Feb 2008 Location: Carbondale IL Posts: 478	Re: What causes the fuel cut feel like 03 Cobras have? Mine has done it since I did an eaton swap. Most of the time it seems to be the pprv that causes this __________________ Black 03 Mach 1 IUP. MMR 900sb 8.5:1 Eaton swapped JLT RAI, MAC Prochamber, SSS Terminator catback, MGW Shifter, MM Coilovers & Panhard Bar, 4.10's, X3 tune by Amazonracing, Pro Motion 3650, 04 Cobra Clutch, and SPEC Alum Flywheel

11-06-2011, 01:03 PM	#3
Stopsign32v Registered User Join Date: Nov 2007 Location: Greenville, SC Posts: 2,554	Re: What causes the fuel cut feel like 03 Cobras have? I've never had a bolt on N/A car do this. __________________ 03 white Mach1 JLT RAI \| 1/2 spacer \| Catback \| 4.56s 7.76@87.8mph

11-06-2011, 03:08 PM	#4
musclemerc Registered User Join Date: Jan 2010 Location: Byram,MS Posts: 285	Re: What causes the fuel cut feel like 03 Cobras have? It sounds like the issue stick shift Cobras have with the PRPS. There is a mod on KBs website, most issues are associated with SC'ed not NA cars

11-07-2011, 10:14 PM	#5
lxh89 Registered User Join Date: Jan 2003 Location: Houston, Tx Posts: 1,530	Re: What causes the fuel cut feel like 03 Cobras have? The problem is caused by the EEC cutting power to the pumps during hard shifts. Basically what happens, you let of the accelerator, the throttle snaps closed but your fuel pressure spikes momentarily. The feedback loop for the fuel system control interprets this spike as a problem so it tries to control it by dropping the ground to target a lower duty cycle and lower pressure. By the time you hit the accelerator again, it needs some time to get the pressure to build back up. This feels like a second but in reality it's about 500ms (.5 seconds). The pprv check valve definitely contributes but removing it is not a sure fire cure. My car lacks a pprv valve and still does it. The only real cure is going return style so fuel pressure is constant. __________________ 2015 Ruby Red Mustang GT Premium Bone Stock 03 Oxford White Mach 1 - SOLD 1.72 60',10.932@131.60MPH, 3800# Raceweight

11-08-2011, 01:38 AM	#7
Mach828 Dark Knight Join Date: Nov 2009 Location: Albuquerque, NM Posts: 5,759	Re: What causes the fuel cut feel like 03 Cobras have? You said that letting off the gas is part of the equation. But the OP said he powershifted so he never let off the accelerator. __________________ Vortech V2 S-trim, E85, A2A Treadstone, Comp cams, built engine, full exhaust, built rear, built 4r70, more mods. Tuned by me with SCT Advantage

11-08-2011, 11:01 AM	#8
JeromeMach1 Registered User Join Date: Aug 2003 Location: Simi Valley, CA Posts: 1,383	Re: What causes the fuel cut feel like 03 Cobras have? My car does this same exact thing. It is present at high rpm WOT shifts when I am on/off the throttle. It does not happen if I do not get off the throttle. I hate it but have learned to live with it. Jerome __________________ 03 Mach1 5spd BB/Stroker built by Eddie Rios Addiction Motorsports P&P 03 Heads by Al P Custom cams by NASVT Nazty PSR SAE 420rwhp SAE 387rwt 1.56 60ft 11.44ET 122.1mph 1700 DA

11-11-2011, 08:52 PM	#10
004mach1 Registered User Join Date: Jul 2009 Location: NH, rochester Posts: 19	Re: What causes the fuel cut feel like 03 Cobras have? i had a problem with fuel cut on my 03 when i would really lay into it in the hi rmps and shifting the fuel would slosh, the problem only occured when i was under 1/4 tank as long as i was over that it never happened again!

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