Dealer not honoring warranty work..2018 5.3 Yukon issues

smokey_mountain · Jan 24, 2020

Thank you. 15% is the tolerance on injectors during the test per GM spec.

SnowDrifter said:
Long ass thread, not going to read 25 pages. So sorry if I'm repeating anything

I'm wondering if it's cycling back and forth between lean and rich, and misfiring on lean. And you might have an injector that's underperforming to the point of misfire. Either rich or lean. Not sure what the GM spec on it is on the new rigs but I seem to recall reading somewhere a while ago that the tolerance for flow on older rigs that +/- 15%. I'm unable to locate that at current to take that with a grain of salt.

Sooo, my thought is this: See if you can find a good scanner. Figure out which cylinder is misfiring, if it's even tripping the misfire monitor. Cross reference that with the commanded fuel flow and/or oxygen sensor voltages.

If possible, see if you can tune or otherwise command the rig to run a bit rich to see if that alleviates the issue.

You might also try investigating your spark plug gaps. Narrow them down a few thousandths. See if there's some weird intermittent weak spark

SnowDrifter · Jan 25, 2020

dvzzz said:
Thank you. 15% is the tolerance on injectors during the test per GM spec.

Nice

So, then next step is to determine which cylinder(s) have a misfire and swap injectors around. You can get some weird shit happening where a lame injector will cause a neighboring cylinder to misfire. What I'd do is swap to a cylinder on adjacent bank as well as the neighboring ones

i.e.

If your engine layout is
1 2
3 4
5 6
7 8

And cylinder 4 is misfiring

You'd swap
1-2
3-4
5-6

Take note of what's what, keep track of it. See if it follows

If it does, then you can do a swap back on 3-4. If it follows, then you've found your issue. If not, then swap 1-2, test again, then 5-6

smokey_mountain · Jan 25, 2020

Swapping injectors on recent engines is crazy hard, requires some special tools, there is a post earlier that explains why, what used to be 20 mins affair is now multi hour if one has tools. It could be done but not by av average weekend warrior.

SnowDrifter · Jan 25, 2020

dvzzz said:
Swapping injectors on recent engines is crazy hard, requires some special tools, there is a post earlier that explains why, what used to be 20 mins affair is now multi hour if one has tools. It could be done but not by av average weekend warrior.

Oh hell are these direct injection?

You might go back to see if you can get it to run rich then. There's no real easy way around those

Kpwweb · Jan 26, 2020

So, crazy thought—what about the in-tank fuel pump? Have you tried a full-throttle acceleration when misfiring at idle? I had to replace my in-tank fuel pump due to slight stumble at idle and big stumble under WOT. Some of the in-tank pumps are questionable, especially when hot. Other thing to check is the fuel pump controller.

The in-tank pump feeds the direct injection pump (think lift pump). If it is borderline, it can lead to problems. Wot start off idle would show this.

smokey_mountain · Jan 26, 2020

Interesting thought... What would be the way to test for it? At this point, I have to try a thing or two but myself, I am done with dealers, they will not help as GM does not accept the problem.

Kpwweb said:
So, crazy thought—what about the in-tank fuel pump? Have you tried a full-throttle acceleration when misfiring at idle? I had to replace my in-tank fuel pump due to slight stumble at idle and big stumble under WOT. Some of the in-tank pumps are questionable, especially when hot. Other thing to check is the fuel pump controller.

The in-tank pump feeds the direct injection pump (think lift pump). If it is borderline, it can lead to problems. Wot start off idle would show this.

smokey_mountain · Jan 26, 2020

I am not a litigious person but I feel really frustrated that GM is not willing to help, I spent now $1890 of my personal money trying to fix the truck that is only 11 months into bumper to bumper manufacturer's warranty. Are small courts effective or are they giant waste of time?

Desperate to get the truck running normal. Now that I drove enough of 2018-20 Tahoes and Yukons trucks, these trucks can run smooth.

swathdiver · Jan 27, 2020

dvzzz said:
Interesting thought... What would be the way to test for it? At this point, I have to try a thing or two but myself, I am done with dealers, they will not help as GM does not accept the problem.

Get your app to show fuel pressure and stomp on the gas to 75 mph on an on-ramp somewhere. If all is well, the pressure will not drop more than a pound at WOT. You guys have a fuel system that I am not familiar with though. Mine runs at 43.5 PSI all the time.

smokey_mountain · Jan 28, 2020

I will give it a whirl and see. I went down the slippery path of arbitration to prep for a court. I am reading in numerous posts that GM's self-appointed "specs" allow up to 3-4 quarts of oil to be added and consider normal... this is out of control.

Bob2C · Feb 3, 2020

swathdiver said:
Get your app to show fuel pressure and stomp on the gas to 75 mph on an on-ramp somewhere. If all is well, the pressure will not drop more than a pound at WOT. You guys have a fuel system that I am not familiar with though. Mine runs at 43.5 PSI all the time.

Mine too has a rough idle. 2018 5.3. The motor mounts were replaced in the fall. In the beginning it seemed to help but it’s back and seems to be getting worse. I’m wondering if it’s destroying the new mounts from the constant movement. I did the fuel pressure test. Got it up to 50 from a dead stop. It didn’t drop. The low reading around 31 was idling in drive stopped. It fluctuated to 45. Do you think this is a fuel delivery problem? I have no issues with acceleration or hesitation.

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Dealer not honoring warranty work..2018 5.3 Yukon issues

smokey_mountain

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