99 5.7 vortec

Asked by Sep 28, 2017 at 12:55 PM about the 1999 GMC Sierra 2500 3 Dr SLE Extended Cab SB

Question type: Maintenance & Repair

I have a 99 gmc c2500 with a 5.7 vortec. I pulled
the motor and dropped 4000$ into parts. Corvette
crank cam pistons and heads. Got it running great
till last week when I cold start and try and take off
it starts to sputter real bad for a couple seconds
then launchs, the second issue when I'm giving it
gas and let off at my cruising speed it pops and
back fires every time I left off the gas. Any ideas
what it could be? My MAS just went out  ordered a
new one. Do you think this is related to my MAS?

6 Answers

105,355

Could have been, Mass Air Flow sensor can cause a bunch of varying driveabality problems, replace it first clear the computer run the drive protocol and see what happens after that. You may want to consider a reprogramming unit like BullyDog so you can take advantage of all that money you spent one the engine. HTH

The mas will be here tomorrow and yes I was planning on clearing before I put the new one on. I had my buddy erase the ECU and completely rewrite everything to this new motor from the old ecu to the new it's night and day between the two. But after going threw everything the mas is the only part faulting and not sure if it could cause an issue like this

105,355

I have personally felt a MAF sensor causing a lurch during gradual throttling up, but not a backfire, so I'm with you on replacing it, backfire is usually fuel introduced when it should not be but there too it could be the ECM getting a false input from the MAF. Hope that's all it is.

Shoot if this mas only fix s the sputter I'm happy with that hopefully it will fix the back for too if not I'll have to go threw it again and see if I can figure out what s going on causing the back fire. I will keep you posted tonight and let u know what happens with the new mas

Put the new mas on cleared n reset ecu, it's still doing the same thing but not all the time only half the time is doing the popping and sputtering

105,355

The only thing I can think of right now is check the TPS sweep, it could still be sending a ohms signal when in the closed position so the ECM thinks it still has some throttle and is still delivering fuel instead of shutting off, now this might be intermittent so test it a number of times. Also rechecking the systems grounds that were all undone when your had all that work done might also be a good idea.

Your Answer

Sierra 2500

Looking for a Used Sierra 2500 in your area?

CarGurus has 7 nationwide Sierra 2500 listings starting at $12,995.

Postal Code:

GMC Sierra 2500 Experts

  • #1
    Rowefast
    Reputation
    160
  • #2
    tennisshoes
    Reputation
    90
  • #3
    JOHNG123
    Reputation
    60
View All

Related Models For Sale

Used GMC Sierra 1500
249 Great Deals out of 10,495 listings starting at $1,775
Used Chevrolet Silverado 2500
4 listings starting at $6,995
Used Chevrolet Silverado 1500
194 Great Deals out of 10,047 listings starting at $1,995
Used Ford F-250 Super Duty
26 Great Deals out of 709 listings starting at $2,475
Used Dodge Ram 2500
4 Great Deals out of 88 listings starting at $6,990
Used Ford F-150
655 Great Deals out of 10,077 listings starting at $2,995
Used Ford F-250
3 listings
Used GMC Sierra 3500
5 listings starting at $17,888
Used Toyota Tundra
41 Great Deals out of 1,286 listings starting at $5,925
Used Dodge Ram 1500
50 Great Deals out of 492 listings starting at $3,488

Used Cars For Sale

2004 GMC Sierra 2500 For Sale
1 listings starting at $12,995

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.