why carb loading and backfiring when let off throttle on my 85 f-150 300 6cyl.

Asked by Jul 07, 2013 at 12:08 AM about the 1985 Ford F-150 STD Standard Cab SB

Question type: Maintenance & Repair

runs good when accelerarting when letting off fuel throttle carb loads up and backfires.
when idling rpm revs up and down.and starts anytime!

1 Answer

26,625

Typically, if it's backfiring out the exhaust on deceleration, it's because of a diverter valve for the air injection that is stuck or not receiving the proper vacuum signal. It could be dumping fresh air into the exhaust when it shouldn't be. The Idle: some possible causes are an idle set too high causing the EGR to open and close and perhaps float settings. It sounds as though it needs a little TLC. Often, the exhaust manifold warps causing the intake to warp with it and creates a vacuum leak along with the exhaust leak. Both manifolds are bolted together and are quite heavy to hang off the side of a motor without checking the torque of the nuts a couple of times a year. Someone sets the idle high to try to keep it running with a vacuum leak and the EGR activates. Kind of a cascade effect.

2 of 2 people found this helpful.

Your Answer

Ford F-150 Experts

  • #1
    OJ
    Reputation
    9,730
  • #2
    dandyoun
    Reputation
    4,660
  • #3
    tennisshoes
    Reputation
    3,370
View All

Related Models For Sale

Used Ford Mustang
460 Great Deals out of 42,890 listings starting at $1,488
Used Ford F-250
417 listings starting at $2,900

Used Cars For Sale

2018 Ford F-150 For Sale
15 Great Deals out of 134,224 listings starting at $18,092
2017 Ford F-150 For Sale
210 Great Deals out of 17,544 listings starting at $18,000
2016 Ford F-150 For Sale
245 Great Deals out of 7,665 listings starting at $16,997
2015 Ford F-150 For Sale
513 Great Deals out of 11,170 listings starting at $9,000
2014 Ford F-150 For Sale
778 Great Deals out of 14,968 listings starting at $7,000

Content submitted by Users is not endorsed by CarGurus, does not express the opinions of CarGurus, and should not be considered reviewed, screened, or approved by CarGurus. Please refer to CarGurus Terms of Use.