Cylinders misfiring

20

Asked by Jan 31, 2015 at 04:19 PM about the 2003 GMC Sierra 1500 SLT 4WD Extended Cab LB

Question type: Maintenance & Repair

Cylinders randomly misfires when hot. Manifold gaskets, fuel injectors on the odd
number cylinders, M.A.F. sensor, crank shaft sensor, spark plugs, and O2 sensor
were replaced. The funny thing is, after every items were replaced [in these order] on
test runs, truck runs fine, until engine gets hot. The latest diagnoses was cylinders
were slightly misfiring truck could still run good and catalytic converter not performing
up to par which maybe due to it being plugged. Did as recommended fuel treatment
were placed in fuel tank. Truck ran really smooth for a period of time where I thought
problem was solved until it started major misfiring again. Any thoughts or suggestions?
I would appreciate it.

7 Answers

105,465

Sounds like an injector problem, try putting in a bottle of Techron injector cleaner, then when fuel gets to a 1/4 tank fill it with Chevron or a fuel that contains Techron, after that you can go back to your regular fuel but keep adding the Techron every other tankful. That should help, it did my Tahoe.

35

Tz

20

Appreciate your answer. At the suggestion from a mechanic, I did fill my gas tank which was half empty w/chevron techron gas. Also added a packet of X-treme fuel treatment at his advise I guess to mix w/the present fuel? As I mentioned, truck did run smooth after running it a couple of miles. It continued to run smooth for I estimate another 2-3 miles and started misfiring again?

1 of 1 people found this helpful.
72,455

Have you checked the ignition coils? Sounds like they may be breaking down when hot. HTH. -Jim

20

Thanks. That's my next move. The misfiring are randomly happening with all of the cylinders when hot. It started with 1-3-5-7 cylinders, jumped to 5 and 6, now and then 2 and 4 would pop up. The last read out was most of the cylinders including 8. It's just jumping around at random.

1 of 1 people found this helpful.
105,465

Did you check the plug boots for hard spots or cracks? Did you put a little dielectric grease around each plug boot when you replaced the plugs?

20

Yes, the boots seemed to fine. Did not see any cracks or signs of wear. No, I didn't know that the boots needed to be greased?

Your Answer

Sierra 1500

Looking for a Used Sierra 1500 in your area?

CarGurus has 64,603 nationwide Sierra 1500 listings starting at $999.

ZIP:

GMC Sierra 1500 Experts

  • #1
    dragonflyoffshore
    Reputation
    5,470
  • #2
    John Saffrahn
    Reputation
    3,780
  • #3
    Glenn Clingenpeel
    Reputation
    3,470
View All

Related Models For Sale

Used Chevrolet Silverado 1500
2,704 Great Deals out of 174,506 listings starting at $955
Used Ford F-150
3,333 Great Deals out of 221,765 listings starting at $1,200
Used GMC Sierra 2500HD
109 Great Deals out of 14,261 listings starting at $2,799
Used Toyota Tundra
710 Great Deals out of 34,288 listings starting at $1,500
Used Chevrolet Silverado 2500HD
381 Great Deals out of 30,661 listings starting at $2,995
Used Dodge Ram 1500
425 Great Deals out of 11,102 listings starting at $1,495
Used Toyota Tacoma
719 Great Deals out of 45,626 listings starting at $1,000
Used GMC Yukon
608 Great Deals out of 20,728 listings starting at $2,500
Used Chevrolet Tahoe
806 Great Deals out of 42,074 listings starting at $1,987
Used Ford F-250 Super Duty
404 Great Deals out of 49,117 listings starting at $1,899
Used Cadillac Escalade
289 Great Deals out of 11,900 listings starting at $1,200
Used Chevrolet Colorado
361 Great Deals out of 38,262 listings starting at $1,595
Used Chevrolet Camaro
467 Great Deals out of 31,602 listings starting at $1,450
Used GMC Canyon
156 Great Deals out of 13,805 listings starting at $1,500

Used Cars For Sale

2018 GMC Sierra 1500 For Sale
26,123 listings starting at $23,419
2017 GMC Sierra 1500 For Sale
84 Great Deals out of 10,992 listings starting at $20,369
2016 GMC Sierra 1500 For Sale
166 Great Deals out of 4,089 listings starting at $16,404
2015 GMC Sierra 1500 For Sale
183 Great Deals out of 5,605 listings starting at $14,995
2014 GMC Sierra 1500 For Sale
217 Great Deals out of 4,945 listings starting at $9,900

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.