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post #1 of 5 Old June 21st, 2018, 04:21 PM Thread Starter
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Bucking When decelerating

Hey guys,

So my car developed a problem where when i’m slowing down foot off the gas, the car chugs and bucks back and forth until the rpms get low enough and it stays steady.
My fuel pressure gauge fluctuates from 20-40. While this is happening.
I have absolutely no idle or wot issues. Car runs fine.
I have swapped the tps, iac, fpdm and plugged the egr, none of which made a difference.

What could it be?

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| 2001 GT Automatic | Kenne Bell 2.1L Intercooled | Bullitt Brakes | Magnaflows & O/R H | Mach 1 Hood | Cobra Bumper and IRS | 2010 Gt500 Wheels | Tuned by DGR Performance |
393 rwhp ~ 412 ft/lbs @9psi

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post #2 of 5 Old June 21st, 2018, 09:14 PM
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Generally a bucking like that is usually due to to insufficient fuel. Your fuel pressure readings seem to back that up. If the FPDM has been replaced I would eye the pump or a loose connection (power or ground) to the pump/FPDM.
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post #3 of 5 Old June 22nd, 2018, 08:42 AM
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I used to have these issues and they were caused by the maf backwashing when the tb blade closed.

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post #4 of 5 Old June 22nd, 2018, 09:23 AM
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Quote:
Originally Posted by ChrisJ View Post
I used to have these issues and they were caused by the maf backwashing when the tb blade closed.
If that's the cause it should be pretty easy to see in a datalog.

Then again seeing a datalog with fuel parameters as well would help.
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post #5 of 5 Old June 24th, 2018, 01:04 AM
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I had similiar problems with bucking on decel, datalogged and saw my maf counts bouncing from no reading to pegged. I switched to a lighting maf (because I already had it laying around) and it fixed my issue.

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