motor hesitates then takes fuel

[jonb8]

Went mud racing last night and we lost a second off are regular time. I have a 4.6 with a 505 202 valve head, 512 solid lift cam and bullit rollers. I just installed a 68mm Dakota throttle body and true 3in exhaust. When she stomps the throttle to WOT at the line it heasitates for a second then takes fuel and screams away...I also have a low idle problem since installing the throttle body.. if anyone has any idea's I'd appreciate any suggestions.

[FlyinRyan]

Jon, could be simply lean at lower rpms, or it could be acceleration - enrichment related .With a bigger TB you are going to see a greater change in MAP per given unit of time.

I would expect that you are lean across the board with the current config.

[jonb8]

Yea I'm wondering if the stock computer is having trouble dealing with all that air dumped into it. Do you see anything wrong with this setup Ryan? Here's the header when I started and the throttle body's,



Took me awhile but I got the header modded to a 3in collector



The muffler



Then the 3in exhaust,

[jonb8]

Then the intake system, it's a 68mm throttle body from a 02 dakota then I built this cowl box and I sealed it to the hood with garage door trim





Then I built a cowl hood to get cool air.



Then bored the stock intake to 68mm, not much is left



Here's a video of the truck in a previous race with a 63mm throttle body and stock exhaust, it has no trouble taking fuel and we won with a 4.1 second pass. This weekend we ran a simular pit and the best she did was a 5.3 and it literally shuts off on the line. I'm running 24 inj on a 50lbs rail which makes it a 27lbs inj.

http://vid311.photobucket.com/albums/kk ... 8b9786.mp4

[jonb8]

Took it to the field today and launched it about 20 times and it's working flawlessly. Only difference is I have to launch uphill alittle in the field and when she races the nose is alway's pointed down. I'm just wondering if i'm having a pickup problem in my fuel tank....

[SilverXJ]

Aside from the hesitation issue you could benefit from a larger air filter.

When you launched in the field, are you sure you didn't notice the hesitation due to loss of traction?

[jonb8]

Biggest filter I could get under the hood, I bought a different style to make sure. And yea loss of traction isn't the problem, the pit we ran at last had 6in of mud on the start line. I'm getting more traction in the field. Went through everything and found I didn't get the vac line on the bottom of the Dakota throttle body sealed very well so I fixed that and checked the range of the TPS and modded throttle cable bracket. Gonna try it tomorrow and see how it does. I'm taking my 63 mm throttle body with me and swap them out between runs, Just to see what changes if anything.

[jonb8]

Jeep ran great this weekend, lots of power and finished first in 4/6 and 4th in the street class out of 52 trucks. Pit was deep with only 6 trucks in the class actually going the distance.

https://www.facebook.com/photo.php?v=10 ... =2&theater

[SilverXJ]

The hesitation is gone? What do you think was the cause?

[jonb8]

Not sure Silver xj, I did find the throttle body vacume port that had a hose that was a little too big on it. I had meant to hose clamp it and forgot. I'm wondering if it just took a little running and a few key strokes for the computer to fiquer out what to do about all the changes...

[beiwulf]

maybe try switching the cone air filter over to a box design like the original one that came in most of them. You can probably just cut it and fit base around existing tb and crop box to fit under hood. the raise hood might just be more for show depending on how high you go with it… just a thought - Pep boys sell an after market box one with reusable mesh like the K&N.

not that it was an issue with the air intake.

[jonb8]

Good idea I got to change it, it does seem to small. I could prabably fab a box to accept any flat K and N filter that's easy to get....I gotta pull air out of the hood though, way to much mud enters the engine compartment .....