Rough idle

90

Asked by May 12, 2015 at 09:28 PM about the 1999 GMC Yukon SLE 4WD

Question type: Maintenance & Repair

I have a 99 Yukon with a 5.7L vortec engine.
It had a slight knock since we bought it but
it never was a problem. We had some out of
town trips planned for this summer so we
figured we should fix the knock. The pistons
for some reason were not where they
should have been. We got used pistons to
replace them. Once it was together it had a
rough idle and eventually wouldn't start
anymore. The timing was set dead center.
The spark plugs are showing signs of a
misfire. Valves were adjusted but it still
won't idle right. The ignition control module
got so hot it burned out while trying to find
the problem. Any suggestions we're running
out of ideas and our race is this weekend!?!

9 Answers

20,715

Pistons not where they should be??? That makes no sense. Used pistons make even less sense. You mean to tell me you went through the effort to take apart the motor to use used parts, and the cylinder wasn't even bored to match?

90

Pistons were not in there correct cylinder #5 in #2 spot with a #5 in #5 spot. 3 of the pistons and rods were doubled 2 #5 2#7 and 2 #1 were in the engine. I hope that makes more sense. Now we have the correct # of pistons and rods in the correct order. It is not an issue with the pistons/rods because it's turning over the idle is just rough after all our adjustments. It seems like it's not firing on all cylinders but we can't figure out why.

1 of 1 people found this helpful.
20,715

The number order doesnt matter as long as the rod and cap match. Do a compression test. Someone was inside that motor before to do that. They may have bored a cylinder to correct damage, if a stock piston is in a bored cylinder you get low compression = miss

90

Ok we'll check that, thanks for clarifying! It also has this whistling noise like it's sucking too much air.

90

Do you know what the compression should be?

20,715

Compression maybe around 120ish. Your really looking for even numbers across the board. Vacuum leaks can cause problems but you should still get spark

90

We checked the compression cylinders #1,3,2,8 compression was 130. Cylinders #5, 7,4, and 6 compression is 120 does the 10 psi make a difference?

20,715

No, that won't do much. there has to be a wire pinched somewhere. You got all the grounds back on? Even the elusive one behind the head?

90

So we got the engine out, looked it over. A couple wires needed mending. Got the motor back in, it started for a while. It seems like it's not getting enough fuel to the cylinders. Got the injectors cleaned and back in. Started up it was the same sputtering. While trying to figure out the problem it got the control module so hot it burned out. New wiring harness you think?

Your Answer

Yukon

Looking for a Used Yukon in your area?

CarGurus has 19,421 nationwide Yukon listings starting at $1,995.

ZIP:

GMC Yukon Experts

  • #1
    clayduster71
    Reputation
    2,780
  • #2
    David Boccabello
    Reputation
    920
  • #3
    Drpsychmom
    Reputation
    750
View All

Related Models For Sale

Used Chevrolet Tahoe
813 Great Deals out of 40,150 listings starting at $1,900
Used Cadillac Escalade
279 Great Deals out of 12,217 listings starting at $2,995
Used GMC Yukon XL
297 Great Deals out of 13,431 listings starting at $1,750
Used Chevrolet Suburban
509 Great Deals out of 23,421 listings starting at $2,700
Used GMC Sierra 1500
1,139 Great Deals out of 61,783 listings starting at $1,295
Used Ford Expedition
487 Great Deals out of 20,334 listings starting at $2,388
Used Chevrolet Silverado 1500
2,720 Great Deals out of 157,558 listings starting at $1,000
Used Ford F-150
3,014 Great Deals out of 230,527 listings starting at $1,300
Used Jeep Grand Cherokee
892 Great Deals out of 71,775 listings starting at $900
Used Ford Explorer
1,085 Great Deals out of 67,954 listings starting at $1,200
Used Dodge Durango
266 Great Deals out of 24,893 listings starting at $1,500
Used Toyota 4Runner
348 Great Deals out of 29,246 listings starting at $1,500

Used Cars For Sale

2018 GMC Yukon SLE 4WD For Sale
506 listings starting at $47,170
2017 GMC Yukon SLE 4WD For Sale
4 Great Deals out of 114 listings starting at $37,933
2016 GMC Yukon SLE 4WD For Sale
48 listings starting at $35,943
2015 GMC Yukon SLE 4WD For Sale
9 Great Deals out of 198 listings starting at $28,989
2014 GMC Yukon SLE 4WD For Sale
7 listings starting at $17,995

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.