Slight Hesitation when hittin 3rd

[BLUBYU2]

Does anyone else experience a slight hesitation occasionally when they hit 3rd or 4th gear at WOT? It seems like everytime Im bangin 3rd I get a slight hesitation. I have seen some videos of other cobras and from the exhaust sound it seems others are experiencing this too. Any info would be great. :??:

 

[goodquest]

tttt

 

[BLUBYU2]

ttt

 

[tv's 03]

Yea i noticed it the other day and asked if these cobras pull a bunch of timing on shifts. I think they do. My 99 and 01 cobras would hit 3rd much harder on the shift, even bark the tires

 

[BLUBYU2]

That may be the case, my brother has a Mach 1 and I can bark third and there isnt a hesitation. I am just concerned that it would hurt the car in some way.

 

[BLUBYU2]

Bueler.......................

 

[black03]

I used to have that problem at WOT shifting to 3rd I'd have slight hesitation. Now I dont notice it anymore. This subject was around a while back. I think it has to do with the boost being dumped at such a high rpm.

 

[cobra_4]

I have a little hesitation. My Mach 1 would bark third almost everytime. I can't even get my cobra to bark second consistantly.

 

[NeedForSpeed]

true..... if I think back half a year ago.... maybe longer since I've driven mine.......

it did hesitate..... you bang the next gear, the pedal to the floor, and it hesitates for a split second, then pulls like an animal...

something in the tune I sapose

 

[03soniccobra01]

I think the boost bypass mod bypasses this problem...Also....Is track lock off???

 

[NeedForSpeed]

I had the boost bypass installed at JDM,

and also I always have the trac-controll off

 

[NeedForSpeed]

but I'll be running a completely different set-up & tune this time, so I'll have to see if it still does this then

 

[03'Darin]

I think what you guys are desrcibing is actually fuel starvation. I'll try to explain it the best I can.

With a returnless fuel system like our cars have the fuel pump doesn't run at a constant pressure. Meaning that it's not just off or on. There is a fuel pressure sensor (FRPS) that reads fuel pressure on the fuel rail. This sensor converts pressure to a voltage reading that it sends to the PCM. The PCM takes many factors into account to determine what speed the fuel pump should run. The PCM sends a signal to the fuel pump driver module (FPDM). The FPDM then sends the signal to the fuel pump. This signal "should" be the correct fuel pump speed to produce the correct fuel rail pressure supplying fuel to the injectors.

The problem you are experiencing is after a higher rpm (usually above 6k) wot, quick lift/shift, back to wot run the fuel rail is getting sucked dry of fuel.

What happens is the FRPS sees the spike in rail pressure (wot run then lift) so the PCM shuts the fuel pump speed down to stop sending fuel. When you go right back to wot the fuel in the rail is quickly drawn out and before the FRPS/PCM/FPDM can react to send more fuel, the rail is drawn dry causing the brief hesitation until the fuel pump can recover the rail pressure.

Darin

 

[NeedForSpeed]

that does make perfect sense, and now can we hear from the people like me that have blown the diafram in the FRPS . Possibly the split second changes in the rail pressure going from 0-80 sends a nice hit to that diafram inside the sensor.

Also, going to a larger fuel rail and line, like I am in the process of doing, will increase the fuel rail volume almost 4 times. Should stop the rail from going dry.

???

 

[BLUBYU2]

Originally posted by 03'Darin
I think what you guys are desrcibing is actually fuel starvation. I'll try to explain it the best I can.

With a returnless fuel system like our cars have the fuel pump doesn't run at a constant pressure. Meaning that it's not just off or on. There is a fuel pressure sensor (FRPS) that reads fuel pressure on the fuel rail. This sensor converts pressure to a voltage reading that it sends to the PCM. The PCM takes many factors into account to determine what speed the fuel pump should run. The PCM sends a signal to the fuel pump driver module (FPDM). The FPDM then sends the signal to the fuel pump. This signal "should" be the correct fuel pump speed to produce the correct fuel rail pressure supplying fuel to the injectors.

The problem you are experiencing is after a higher rpm (usually above 6k) wot, quick lift/shift, back to wot run the fuel rail is getting sucked dry of fuel.

What happens is the FRPS sees the spike in rail pressure (wot run then lift) so the PCM shuts the fuel pump speed down to stop sending fuel. When you go right back to wot the fuel in the rail is quickly drawn out and before the FRPS/PCM/FPDM can react to send more fuel, the rail is drawn dry causing the brief hesitation until the fuel pump can recover the rail pressure.

Darin

Thanks for the info. The question that I have then is why do other cars like the Mach 1 arent affected by this problem? Is there another solution to this problem besides changing the fuel rail and lines to larger diameter?

 

[tv's 03]

I have a hard time believing a fuel delivery issue is the cause. The thing would go lean and detonate if that was the case.

It seems more likely that the computer is killing timing on the shift, ford has done this on many stangs in the past. its avoids major shock loads to the drivetrain. Its probably can be corrected by a chip. Its does feel similar to traction control, which also cuts timing, just not as agressive as TC. I always turn off traction control, it been a habit since 2000 when I got my 99 cobra. Those cars with much less power hit third much harder than these cars

Returnless systems are designed to stay pressurized. I have had 4 different cars with returnless systems, and none of them had a fuel starvation problem

One problem that i have is that I am used to reving to 6800 to 7000 rpm on my cobras. I keep hitting the rev limiter.

It sure feels like it wants to rev higher though, its still pulling strong at redline

 

[Tim Lester]

I don't know what RPM your shifting at, but try shifting a little sooner and see if that gets rid of it,you might be getting into fuel cutoff, just my 2cents

Tim

 

[03'Darin]

Originally posted by tv's 03
I have a hard time believing a fuel delivery issue is the cause. The thing would go lean and detonate if that was the case.

It seems more likely that the computer is killing timing on the shift, ford has done this on many stangs in the past. its avoids major shock loads to the drivetrain. Its probably can be corrected by a chip. Its does feel similar to traction control, which also cuts timing, just not as agressive as TC. I always turn off traction control, it been a habit since 2000 when I got my 99 cobra. Those cars with much less power hit third much harder than these cars

Returnless systems are designed to stay pressurized. I have had 4 different cars with returnless systems, and none of them had a fuel starvation problem

One problem that i have is that I am used to reving to 6800 to 7000 rpm on my cobras. I keep hitting the rev limiter.

It sure feels like it wants to rev higher though, its still pulling strong at redline

I have done some data logging trying to trace this problem and have found the fuel pressure to be the issue.

Maybe we are talking about different problems. The problem I am referring to happens after the shift, just after returning to wot, the car briefly comes back to full power then does a very abrupt and violent hesitation (that feels like the ignition was turned of for a split second) then back to full power.

I have been told by a tuner that this is a common problem with the returnless fuel systems on a blower car. I was also told that this problem shows up on earlier returnless fuel system cars when a blower is added.

Darin

 

[Tim Lester]

Originally posted by Tim Lester
I don't know what RPM your shifting at, but try shifting a little sooner and see if that gets rid of it,you might be getting into fuel cutoff, just my 2cents

Tim

Has anybody tried this yet.

Tim

 

[03'Darin]

Originally posted by Tim Lester
Has anybody tried this yet.

Tim

Yes.

I've actually seen the problem happen as low as 5900-6000 rpm's.

Darin

BTW this doesn't happen if you don't lift on the shift.