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2005 Yukon SLT 5.3L fuel system problems


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kwag
Novice

Mar 30, 2017, 8:04 AM

Post #1 of 10 (187 views)
2005 Yukon SLT 5.3L fuel system problems Sign In

A few months ago I noticed a weak start after I had driven for a while stopped then started again after only 10-20 mins. Its completely random and wont do it for a long time then do it for a few days in a row. The symptoms are a little different than anything I can find online. The engine will fire before a full starter revolution and then sputter to idle up like it has too much fuel or not enough. then a few times it cranked a long time before it started.
It has always started but afraid its going to strand me soon.

I checked the fuel pressure and it reads around 48 psi pump on/engine off, 60 psi engine running. When I shut it off it the pressure drops immediately quite fast down to 40 then slowly keeps dropping off.
I am thinking possible fuel pressure regulator or leaking injector into the cylinder maybe

I don't notice any hesitation or acceleration problems at all while driving.
It is also giving me "Tighten fuel cap" message every week or so pending fault code of P0455 then goes away without the check engine light ever coming on.


kev2
Veteran
kev2 profile image

Mar 30, 2017, 8:36 AM

Post #2 of 10 (176 views)
Re: 2005 Yukon SLT 5.3L fuel system problems Sign In

Check for codes even f light is off.
A scanner might help ID a bank or cylinder without a scanner I would -
think an injector leaking,
At the least I would add a can of 'techron' or 'sea foam' fuel treatments...
then checking above and reading plugs you may isolate the injector.
FYI: THe fuel regulator is in the tank.
I will need to double check that fuel pressure spec.
The p0455 is a large evap leak... in the trade a smoke machine is used to locate the leak.
Asside from the cap you could check vent valve and related hoses not a easy thing to spot without a tracer..


(This post was edited by kev2 on Mar 30, 2017, 8:38 AM)


kwag
Novice

Mar 30, 2017, 9:28 AM

Post #3 of 10 (164 views)
Re: 2005 Yukon SLT 5.3L fuel system problems Sign In

I have a blue tooth OBDII scanner and have checked quite a few times for codes. The only one that shows up is P0455 only after the tighten fuel cap message appears and it says pending fault code and it clears itself I think before it actually throws the code. Tha'ts why I thought it may be related. I have used sea foam quite a few times and 93 octane fuel and it starts much better when I do. The fuel pressure dropping off makes me think there is a small leak somewhere. I have searched online for similar problems and heard people say it should hold pressure much longer than that after the pump is turned off.


Tom Greenleaf
Ultimate Carjunky / Moderator
Tom Greenleaf profile image

Mar 30, 2017, 9:51 AM

Post #4 of 10 (158 views)
Re: 2005 Yukon SLT 5.3L fuel system problems Sign In

Quote from top ">
I checked the fuel pressure and it reads around 48 psi pump on/engine off, 60 psi engine running.<"


That's too much deviation IMO. Can't find fuel pressure without knowing which engine there were two 5.3s used. 8th digit of vin# would help. "T" is the common one and Flex Fuel another letter designation.


60 is borderline too low for some of these but while cranking if lower would really give you a hard time,


T



kwag
Novice

Mar 30, 2017, 10:06 AM

Post #5 of 10 (154 views)
Re: 2005 Yukon SLT 5.3L fuel system problems Sign In

The 8th digit is a "T", I did a VIN report that says the engine model is LM7


kev2
Veteran
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Mar 30, 2017, 10:41 AM

Post #6 of 10 (146 views)
Re: 2005 Yukon SLT 5.3L fuel system problems Sign In

LM7 is basic small block no flex or displacement on demand. :)
You should NOT need to spend money on 93 octane should run fine on 89.
As mentioned fuel pressure - 55-62psi. And dropping to 40psi is an issue.
The EVAP code may be pending, it may take several trips, as well as fuel quantity to run tests. let's not celebrate yet.
Do you have a scanner able to see live data?


kwag
Novice

Mar 30, 2017, 11:49 AM

Post #7 of 10 (140 views)
Re: 2005 Yukon SLT 5.3L fuel system problems Sign In

Yes, I use a blue tooth OBDII scanner and an app on my phone.


kev2
Veteran
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Mar 30, 2017, 12:29 PM

Post #8 of 10 (132 views)
Re: 2005 Yukon SLT 5.3L fuel system problems Sign In

OK then - check for codes - post all here.
With scanner look at, fuel trims FT's, eng coolant temp ECT, o2 sensor voltages B1S1 and B2S1, mass air flow MAF, and manifold pressure MAP.
that will give us a picture of what is going on... and hopefully narrow down the fuel pressure leak.


kwag
Novice

Mar 30, 2017, 1:04 PM

Post #9 of 10 (127 views)
Re: 2005 Yukon SLT 5.3L fuel system problems Sign In

Thanks for your help, I set up my app with all those sensors and I should be able to log it all and have some info tonight.


kwag
Novice

Mar 31, 2017, 6:22 AM

Post #10 of 10 (106 views)
Re: 2005 Yukon SLT 5.3L fuel system problems Sign In

I am still learning how to use the torque app and only got the gps to log last night. I will try it again this weekend. I was watching the real time gauges and only a few were constant values. the rest fluctuated up and down continuously so don't know if that is normal. From my memory The 02 voltage range was .2 - .8, fuel trim was like -4 - 3.5, coolant temp 190-195, MAF 60-500 cfm, intake manifold pressure was between 3-8 i think, there were fuel pressure sensor options but no values shown.






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