2003 Cobra supercharger issue

[jdcleve]

I am the original owner of a stock '03 Cobra with less than 19,000 miles that exhibits a slow return of supercharger action after a higher RPM shift--typically first to second. That is, I am running full-throttle within the RPM range for a gear, and the RPMs drop toward idle after clutch release in the next higher gear--even though I have returned to full-throttle; this lasts for about a second after shifting up. The sensation is much like that of a rev-limiter fuel cutoff. Any ideas as to what the cause may be?

 

[Uncle Meat]

Yup! It's a safety feature built into the tune of the car from the factory. It's part of the torque management system I believe. It bleeds off boost between high rpm shifts momentarily to reduce the amount of torque and prevent massive wheel spin or large shocks to the drive-train. It feels as if the car is lagging between shifts. There are a couple ways to remedy this, one is the recommended way, the other is the non-recommended way.

Recommended way - get a custom tune created for your car by a reputable tuner and have the torque management disabled in the tune itself.

Non-recommended method - manually disable the boost bypass valve. The boost bypass valve is there for a reason, it's a safety feature. Manually disabling it in a permanent fashion is not recommended.

U.M.

 

[jdcleve]

Thanks for replying. I assume that you have not had a similar experience on your Cobra. Are you still stock? It seems that my loss of power is due to greatly reduced fuel injection persisting momentarily after I reopen the throttle after a higher RPM shift. I assume the absence of boost during this time is due to the loss of induction vacuum necessary to hold the super charger dump valve closed. I will monitor my max RPMs, the RPM to which the engine speed falls, and the approximate duration of the lost performance during a hard acceleration up-shift. I will pass that info along.

 

[Uncle Meat]

Thanks for replying. I assume that you have not had a similar experience on your Cobra. .

No. I modified my car with a CAI, mid-pipe, cat-back, and a custom tune less than 3 months after purchase in August of '02. I had the boost bypass issue taken care of then. I never personally experienced the issue myself.

Are you still stock?

No. In addition to the mods listed above I've since added a set of JBA shorty headers, a C&L intake pipe, and a 2,93 upper pulley.

It seems that my loss of power is due to greatly reduced fuel injection persisting momentarily after I reopen the throttle after a higher RPM shift. I assume the absence of boost during this time is due to the loss of induction vacuum necessary to hold the super charger dump valve closed. I will monitor my max RPMs, the RPM to which the engine speed falls, and the approximate duration of the lost performance during a hard acceleration up-shift.

As stated earlier, I know the stock tune in the car from Ford will momentarily dump boost between high RPM shifts.

I will pass that info along.

Pass it along to who, Ford? This is a common issue with stock Cobra's and there's nothing Ford will do about it.

U.M.

 

[blueblazes]

it can also be attributed to the pprv system in the car, its a device that acts like a check valve in the fuel tank and has been known to cause the "hesitation" between shifting. Even with the the fix for boost bypass it can still show up.

 

[Uncle Meat]

it can also be attributed to the pprv system in the car, its a device that acts like a check valve in the fuel tank and has been known to cause the "hesitation" between shifting. Even with the the fix for boost bypass it can still show up.

On modified setups yes, but his car is stock and I've never heard of an issue like this being attributed to the pprv on a bone stock Cobra.

U.M.

 

[blueblazes]

I have a friend who did once pprv was out no problem afterwords

 

[Don 95Vert]

First, if you do get a tune for it, be sure whoever tunes it uses the AMZ2 box code - it's the latest '04 code from Ford that uses factiory calibrations to get rid of hesitation. With you combo, a mail order tune would probably be fine - '03 Cobras are about the easiest cars t tune if they are mechanically sound. Second, on really high HP Cobras it may be necessary to remove the PPRV, but first, have whoever tunes the car make the necessary tuning changes to get rid of it. There are a number of things to change, some many tuners know about and a couple hardly anyone knows - we have tuned a ton of '03 Cobras and have successfully gotten rid of the shift hesitation on higher HP Cobras - but to be fair a couple of them have had the PPRV already removed - but not all of them.
Don

 

[jdcleve]

Thanks to all who have responded. My problem is intermittent and is more likely to result after applying power in a turn. This is reminiscent of an old carb problem--such as caused by a sticking float--as I recall. JD

 

[Williesvt]

Non-recommended method - manually disable the boost bypass valve. The boost bypass valve is there for a reason, it's a safety feature. Manually disabling it in a permanent fashion is not recommended.

U.M.

my 04 has cai and pulley, i had it tuned THEN switched the boost bypass hose, i assume the tune took out the factory lag feature....i should be safe right? ive been driving like this for almost a year now

oh, and

 

[Uncle Meat]

my 04 has cai and pulley, i had it tuned THEN switched the boost bypass hose, i assume the tune took out the factory lag feature....i should be safe right? ive been driving like this for almost a year now

oh, and

Most custom tunes cover thedisab,ing of the boost bypass, but check with your tuner to be sure. I'd go ahead and hook up the manual bypass though. Better safe than sorry.

U.M.