Bucking/Hesitation during accelerating downshift

[SBGT]

Searched the iternets and found a TSB for the '05 fuel pump describing a similar symptom as what I am experiencing. Wanted to get some opinions as to whether or not I can attribute it to fuel pump replacement or tune. With being boosted and running a KB BAP I can't decide which. Basically what I'm experiencing is upon downshifting at highway speeds to accelerate after I engage the gear and step on it I get a hiccup or hesitation that just feels like then engine sort of shuts down then goes right after. Boost level stays the same so I don't think it's a BBV or vac leak issue. Don't have an FP gauge to check but it feels like it either loses spark or fuel for a second then goes back to it. What do you guys think FP or tune?

 

[blue3v]

I know it sounds weird but is the alternator stock. If so I ran into that with mine. Im not boosted but it would hesitate like you are saying

 

[BruceH]

Searched the iternets and found a TSB for the '05 fuel pump describing a similar symptom as what I am experiencing. Wanted to get some opinions as to whether or not I can attribute it to fuel pump replacement or tune. With being boosted and running a KB BAP I can't decide which. Basically what I'm experiencing is upon downshifting at highway speeds to accelerate after I engage the gear and step on it I get a hiccup or hesitation that just feels like then engine sort of shuts down then goes right after. Boost level stays the same so I don't think it's a BBV or vac leak issue. Don't have an FP gauge to check but it feels like it either loses spark or fuel for a second then goes back to it. What do you guys think FP or tune?

To me it sounds like the tune. Did it just start after doing something to the car? Has it always done this? You mention being boosted, is it a pd blower with a different intake manifold?

 

[SBGT]

I know it sounds weird but is the alternator stock. If so I ran into that with mine. Im not boosted but it would hesitate like you are saying

Yes, I believe the alternator is stock

To me it sounds like the tune. Did it just start after doing something to the car? Has it always done this? You mention being boosted, is it a pd blower with a different intake manifold?

I haven't had it for very long but I noticed it when I bought it. I haven't don't anything to it other than change the blower and engine oil, and put in some new plugs. It's a KB setup with the intercooled manifold.

 

[BruceH]

I haven't had it for very long but I noticed it when I bought it. I haven't don't anything to it other than change the blower and engine oil, and put in some new plugs. It's a KB setup with the intercooled manifold.

Did it come with a handheld tuner? Do you know what tune is on it? Provided that you know everything else is working correctly I'd start with a new tune.

 

[SBGT]

Came with a dinosaur of an SCT but the original owner had it tuned with a Diablo and it came with that as well and I believe that is the tune on it now. I'm such a noob with these cars I am scared to fiddle with anything to be honest. It only boosts to 8.5-9lbs and had a conservative tune from what the owner informed me when I bought it.

 

[Uncle Buck]

My nearly stock 06 does the same thing and has done so with three different tunes, one being a dyno tune. My best guess is its relates to the TSB on these car on the fuel pump getting little air bubbles around the pickup when cruising for a while. I find if I downshift and run in the lower gear for a few seconds before I punch it, it doesn't hesitate. Be careful, this hesitation is a lean condition. Add boost to the situation and you could hurt your engine in a blink of an eye. I'd drive easy until you sort it out.

 

[michael.konor]

- Have you hooked up your tuner and checked to see if you have any fault codes? If yes, what were they?

- In either of your tuners, and specifically the datalog selection, can you look at the streaming data? If so, look at your fuel pressure PIDs.

- If everything looks normal, then remove your MAF sensor and clean it using MAF cleaner, then clean your throttle body.

- When's the last time you pulled your spark plugs and checked their condition?

Mike

 

[05roush0090]

My car had similar symptoms but only when the car was not up to operating temp. Tuner had to make some adjustments to my tune and cleared it up.

 

[SBGT]

- Have you hooked up your tuner and checked to see if you have any fault codes? If yes, what were they?

- In either of your tuners, and specifically the datalog selection, can you look at the streaming data? If so, look at your fuel pressure PIDs.

- If everything looks normal, then remove your MAF sensor and clean it using MAF cleaner, then clean your throttle body.

- When's the last time you pulled your spark plugs and checked their condition?

Mike

No codes, not quite familiar with the tuner but I'll check to see if the diablo has the ability. I'll clean the MAF just for GP. The plugs were changed out less than a month ago.

 

[07 Boss]

I think it is the fuel pump. Had a guy with similar issues after cruising on the freeway at a constant speed. Car would lose power and sometimes die. I sent him my old pump and he hasn't had that issue since.

here's a link to the thread. http://www.moddedmustangs.com/forums/2005-2010/438570-hesitation-mid-range-rpm.html#post8323898

Maybe see if you can get a hold of him and see how sililar your issues are.

 

[SBGT]

Bingo, that's the same thing happening to me. Damn thing almost died completely in the middle of an intersection after getting off an offramp. Do you know what pumps are compatible and after what year would alleviate the problem? Thinking that with me being boosted I might want to just dump the KB BAP and go to a dual setup. I don't know but it's annoying to say the least.

 

[07 Boss]

I think that TSB was for 05-06. I gave that guy my old pump from my 07. I PMed him today just to make sure the issue hasn't reared it's head again and he told me the new pump got rid of it.

If you're gonna get a new pump you might as well just get the dual pump and ditch the BAP. I don't know what the price difference is but I think it's worth it regardless. Unless you can find someone like me who had one sitting around after installing the gt500 one.