Long flat hesitation on acceleration


B

BRUCE DALEY

New member
Jun 20, 2008
4
Has anyone else experienced a long, flat,(vehicle neither accererating, or decelerating) hesitation upon applicatication of between 1/2 through full throttle. Note: If durring the hesitation under full throttle, you let up to less than 1/2 throttle, the vehicle will accelerate normally.

Any help in this matter will be greatly appreciated.

Feel free to call Bruce at (520) 444-0580 if prefered.
 
$2 fuel pump relay?

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Xcentric said:
$2 fuel pump relay?

Sent from my HTC One using Tapatalk
Click to expand...

Could be. Best bet would be to hook up an OBDII monitor to see what is going on.
 
boost dump
 
How does that happen? We don't have BOV's in these cars. Does he have a boost leak?
 
sorry, was thinking of whipple superchargers. not sure what type of supercharger the OP is running, but a stock one does not dump boost....
 
Sounds like 2nd fuel pump is dead. Recent posts on this. The relays are cheesy. Easy and cheap diagnostic.

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Do you have a stiffener in upir air tube? It can collapse when you punch it. Acufab makes one. Does this happen when the car is standing still and you rev the engine? Watch the tube for collapse.
 
I went thru this and there is a long post about it. Save yourself a bunch of time reading and writing. Just switch out the seconadry fuel pump realy and I bet it goes back to normal. They're about $10 to $12 ea. . For what it's worth I would change them both it's a wear item.. The relay box is in the front trunk under the tray..
 
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Hi Bruce,

1. It would be an unusual set of circumstances where the fuel pump relay would fail and the ECU wouldn't notice and trip a fault code. Percentage-wise I would doubt the failure is here.
2. Our cars do have a boost bypass valve (as do the Whipples) and the ECU has sole command authority to trigger the bypass if/when it thinks anything is amiss.
3. I will put money on that it is not a collapsing intake issue. (Marketing hype vs reality.)
4. Using an OBD2 monitor to evaluate what's happening is a good idea but requires a skill set and a propensity to want to know how to do this stuff -

With the assumption that you are NOT triggering a CEL, my bet is on 2) above. With no CEL, the ECU believes he is saving the world and all is good. But, for this to happen the ECU is somehow mis-informed and he's taking action to dump boost needlessly. To hone in on this problem, can you safely re-create the symptom while watching your boost gauge? The most obvious reason that the ECU triggers the bypass valve is when he thinks an over-boost condition exists. But, keep in mind that the ECU calculates boost - it doesn't measure it directly. One of the main inputs in the boost calculation is the volume of air that the MAF sensor is reporting. If the MAF sensor reports (incorrectly) that too much air is coming in the ECU boost calculation goes too high and the ECU triggers the bypass to save the world. OK, long story short...... I think it is your MAF sensor. Do you have K&N filters? The oil from the K&N's can corrupt the MAF reading. You can try cleaning or replace the MAF sensor. I'll call you this morning to chat through this stuff......
 
nota4re said:
Hi Bruce,

1. It would be an unusual set of circumstances where the fuel pump relay would fail and the ECU wouldn't notice and trip a fault code. Percentage-wise I would doubt the failure is here.
2. Our cars do have a boost bypass valve (as do the Whipples) and the ECU has sole command authority to trigger the bypass if/when it thinks anything is amiss.
3. I will put money on that it is not a collapsing intake issue. (Marketing hype vs reality.)
4. Using an OBD2 monitor to evaluate what's happening is a good idea but requires a skill set and a propensity to want to know how to do this stuff -

With the assumption that you are NOT triggering a CEL, my bet is on 2) above. With no CEL, the ECU believes he is saving the world and all is good. But, for this to happen the ECU is somehow mis-informed and he's taking action to dump boost needlessly. To hone in on this problem, can you safely re-create the symptom while watching your boost gauge? The most obvious reason that the ECU triggers the bypass valve is when he thinks an over-boost condition exists. But, keep in mind that the ECU calculates boost - it doesn't measure it directly. One of the main inputs in the boost calculation is the volume of air that the MAF sensor is reporting. If the MAF sensor reports (incorrectly) that too much air is coming in the ECU boost calculation goes too high and the ECU triggers the bypass to save the world. OK, long story short...... I think it is your MAF sensor. Do you have K&N filters? The oil from the K&N's can corrupt the MAF reading. You can try cleaning or replace the MAF sensor. I'll call you this morning to chat through this stuff......
Click to expand...

What he said... #2

I would ask what gear you are experiences this in? Higher gear usually have more torque demand = more air demand. I had an issue where my boost bypass valve would be pulled open by the massive vacuum on frontside of the throttle body. You can test this by zip-tying the bypass closed or disconnecting the vacuum line from the intake. There was some lengthy discussion about it in this thread: http://www.fordgtforum.com/forums/showthread.php/15866-whipple-4-0/page3
 
nota4re said:
Hi Bruce,


3. I will put money on that it is not a collapsing intake issue. (Marketing hype vs reality.)
..
Click to expand...

It may indeed not be the intake boot in this case, but it should be checked for the internal stiffener to eliminate the option. The OEM boot can absolutely collapse under hard acceleration without reinforcement and the driver will experience a sudden and momentary loss of power I posted a video demonstrating this about 2 yrs ago. This is especially true if the car has been boosted even by a simple pulley tune. Just squeeze the boot (the big black thing between in air filter box and the throttle body).
 
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I remember a few posts about air filters getting sucked in, may be worth a look.
 
Hi there,

Today, I read your response to my question about a hesitation on acceleration for the first time, because right after I posted the question, it fixed itself, that is until today!

I notice that you also live in Tucson!

If you wouldn't mind, please give me a call, as I would like to learn more about what you believe the cause to be.

Thanks,

Bruce (520) 444-0580
 
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