CEL light comes on when I travel and use different gas?

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boba1111

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I have 2003 Yukon Denali in very good condition. Drive less than 5000 miles per year now semi-retired.
Just finished a trip from Fenwick Island DE (my retired home) back to Lancaster PA (my 45 year working home) and its about 165 miles.
Gassed up in Lancaster PA and about 40 miles in CEL blinks and then solid.
I have traveled this route since i bought the Denali in June 2003 and the CEL issue started probably 8 years ago when gassing up.
My mechanic cleaned the MAF sensors and it was ok, but comes back..
About 2 years ago we replace MAF sensor (no idea which one, I only work on 1960's carbureted motors<g>) and it stopped.
So now its back. We then leave Lancaster Tues for Harrisonburg VA for a business client visit down RT 81 (BAD road) and its off for miles, then blinks, then solid.
Gas up down there and withing a mile of driving back to Lanc PA Wed north 81 goes off. 50 miles later blinks and eventually solid last 50 miles.
Today I gassed up again Lancaster about 15 gals and within a mile CEL goes off and thats how it is now.
Now throughout ALL of this there is NO loss of power, mileage is consistently at its 15mpg.
FWIW 100,000 major service was done at 85,000 and it runs fine.
As soon as used prices drop to reasonable levels I plan to replace it with maybe 2018-2019 Tahoe/Yukon/Esc
Recent work past few years includes stainless brake line replacement ($985), key lock repair ($650), water pump, hoses, belts,
new drive side heater blend door (yea! foot heat back), read view mirror from ebay temp/direction was out, new GMC driver side power window, mirror controller.
What about an additive like cataclean or other?
Thoughts?
Thanks, Bob
 
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boba1111

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I have a code reader but its not with me in Lancaster. We are her for our only daughter's first BABY, due this Tues!
Our first and only grandchild. We are all past READY!
The last code I read was August p0300. I will read them again when I return to Fenwick in Jan.
I have always used 87 octane and Wed used 89 in VA for 15 gals. Today I filled up with 15gals 87.
And I can be in either Lancaster or Fenwick and after a full tank through the CEL stays off and no codes stored or current.
HTH
 

MassHoe04

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Hmmm... So, in the recent past you had a P0300 after a flashing CEL popped up that stayed on for a bit.

Misfire could be attributed to not enough fuel or fuel not being combusted.

Fuel delivery could be injector issue spraying too much or too little.
Could also be fuel pump not sending with enough steady pressure to the fuel rail/injectors.

FYI - I was getting random single cylinder misfires on my 05 Jeep.
The cylinders (1 or 2) were at the end of the fuel rail. Came and went.
Then, my fuel pump died a few months later.
New fuel pump and the issue never returned on that vehicle.

This may not necessarily be your fuel pump or pressure regulator in your case.
Just something to consider on the list of possibilities.

Ignition-related causes for misfires could be momentary disruptions to spark at the coil pack(s), wires or spark plugs.

My gut is telling me your issue is not what kind of gas you are using or where you are getting it.

When you are getting it, could be a possibility.
If your code comes up when tank is lower and not when it is full... Maybe there is a crack in the fuel pump assembly that prevents the pump from pushing all it should to the injectors.

See what you have for codes and see if you can get fuel pressure readings on the test port at different times and at different levels in the tank (F, 1/2, 1/4, 1/8). See if there is anything wonky on fuel pressures.
 
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boba1111

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MassHoe04: Thanks for the reply.
What I really find odd is the CEL disappears right after I fill the tank from 1/2 empty?
This happened multiple times past 6 months. And if I stay in 1 location and SAME gas station, it clears on its own.
Then code reader shows no codes stored or current.
What in the emission system controls how it responds to different gas blends?

Some years ago, before the MAF sensor replacement, it was like clockwork.
Leave PA full tank no CEL. Drive to beach house in DE and fill up tank there, about 50 miles later SOLID CEL.
Then take tank back down to 1/2 and fill in DE and 50 miles later CEL goes off.

I will follow your suggestion and check fuel pressures at different tank levels.
 

Donal

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The computer monitors the fuel tank pressure. Study the system and see what component could be interferring with normal operation. Reading the code each time the CEL light is on is a good thing.
 

rockola1971

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I have 2003 Yukon Denali in very good condition. Drive less than 5000 miles per year now semi-retired.
Just finished a trip from Fenwick Island DE (my retired home) back to Lancaster PA (my 45 year working home) and its about 165 miles.
Gassed up in Lancaster PA and about 40 miles in CEL blinks and then solid.
I have traveled this route since i bought the Denali in June 2003 and the CEL issue started probably 8 years ago when gassing up.
My mechanic cleaned the MAF sensors and it was ok, but comes back..
About 2 years ago we replace MAF sensor (no idea which one, I only work on 1960's carbureted motors<g>) and it stopped.
So now its back. We then leave Lancaster Tues for Harrisonburg VA for a business client visit down RT 81 (BAD road) and its off for miles, then blinks, then solid.
Gas up down there and withing a mile of driving back to Lanc PA Wed north 81 goes off. 50 miles later blinks and eventually solid last 50 miles.
Today I gassed up again Lancaster about 15 gals and within a mile CEL goes off and thats how it is now.
Now throughout ALL of this there is NO loss of power, mileage is consistently at its 15mpg.
FWIW 100,000 major service was done at 85,000 and it runs fine.
As soon as used prices drop to reasonable levels I plan to replace it with maybe 2018-2019 Tahoe/Yukon/Esc
Recent work past few years includes stainless brake line replacement ($985), key lock repair ($650), water pump, hoses, belts,
new drive side heater blend door (yea! foot heat back), read view mirror from ebay temp/direction was out, new GMC driver side power window, mirror controller.
What about an additive like cataclean or other?
Thoughts?
Thanks, Bob
A flashing CEL means you have active detonation(AKA Misfire, preignition, spark knock) happening. A P0301-0308 denotes which cylinder(s). The P0300 is just the basic engfine misfire code. You need a scanner to review while this flashing CEL is happening and look at misfire counts for each cylinder. It will tell on itself and lead you to atleast which cylinder(s) are the problem child. The misfire can be ignition(coil, plug wire, plug) or fuel (injector, pump) delivery related. The 2 clues that I see that stick out, the rough road and when you fill up in a certain town leads me to believe either you have a loose connection or the MAF elements are being affected OR "bad fuel"/too much alcohol content possibly. Is your engine a Vin Z or T? I own (2) 2003 VIN Z Tahoe LT's.
 
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