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00'Yukon

Just Did A Tune Up..

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I just completed a full tune up on my 2000 gmc yukon w/ the 5.3. It has new a/c delco iridium plugs, a/c wires, a/c fuel filter, a/c air filter, pcv valve, mobil 1 full synthetic tranny fluid, a/c tranny filter, amzoil 75W90 severe gear lube for front and rear differentials, autotracII transfer case fluid, and all new gaskets.

 

The truck had 120,000 miles on all the stock parts(including plugs) and right now the new parts have about 700 miles on them. The idle and shifting seemed to smooth out a bit but i did not notice any gain in performance at all and gas mileage has noticably suffered. Today i just took off the battery cables and left it for 45 minutesx before reinstalling since i have heard of this trick helping by resetting the computer so we'll see how that goes.

 

Anyone have any instight in this? Anyone with similar problems or possible solutions? I thought atleast id get better gasmileage and noticeable improvements in performance but as of now, nothing.

 

Thanks, 00'yukon

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i dont know of any codes. no check engine light or anything and i haven't had the codes checked. Where would i get them checked? also, no i did not check the O2 sensors... The plugs i left at .040, which came from the factory like that and i knew that since they were iridium's and $9 a plug, i didnt want to screw up the electrodes. I also saw the service bulletin gm posted about these new plugs which gm stated were to stay at the pre-gapped .040.

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I dont think your supposed to re-gap these plugs.

The PCM will need some miles with the tune up on it to take affect. 700miles should of done it. It has to re-learn its tables, but you should of had some gains already.

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correct draenor. I took the battery cables off to see if that would change anything too...just thought that after all that work i would see some gains..or at least more than what im seeing.

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Drew, I would tell you to drive it for a little while since disconnecting the battery. I wish I could offer more info but it appears you did all the stuff you needed to. I would say you may be getting a lazy O2 sensor but if any of them were bad, I would think you would be getting a code.

 

One caution, was the PCV valve a fixed orfice design or a regular check valve type PCV? If it is not a fixed orfice design you could get a little oil consumption. Even if the one you removed was not a fixed orfice PCV valve, it is my understanding that is what you should be going back with. To my knowledge, the F/O PCV can only be bought from GM or an AC Delco Supplier.

 

Hope you see your MPG improve.

 

PS The only other suggestion would be to run Chevron Techron through the tank at 1 oz per gallon and clean the Throttle body. You may need to run the Techron through 2 tanks to get the full benefit.

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I agree with replacing the O2 sensors. Have you tried putting some fuel injector cleaner through your fuel system?

 

Phil

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I would also lean towards the o2 sensors being as you have 120,000 miles and chances are they have never been replaced. As o2 sensors get old, they will produce less voltage. When the computer sees low voltage from the o2 sensor, it thinks the engine is running lean and compensates by adding extra fuel (ie, poor fuel mileage and no check engine light).

 

When you do replace them, make sure you are replacing the pre-catalytic converter sensors. The post-cat sensors only check for converter efficiency, they do not affect the amount of fuel going into your engine.

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thanks guys...the pcv valve sits inside a rubber grommet with a vacuum line(?) attached to the top of it. It justed pulled the old one out, put the new one in, and connected the hose. I bought all the a/c stuff(everything except tranny oil and front and rear diff oil) from the gm dealer including the PCV valve.

 

I did have a professional fuel injection cleaning at about 40,000-50,000 miles (don't remember) so they should be ok and i do run seafoam through it once in a while. also, the performance feels to be the same as it was before (which is and was good-i just expected a little more).

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Drew, one more idea. Is your temp running cooler than it has been? If the thermostat sticks open, it will kill your MPG.

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not, looks to be right at 195-200. thanks for the suggestion though...Oh well, i guess we'll see how the battery reset does...It kinda shocks me though that having all these new parts results in no noticeable gains..

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think of it this way.... take into the fact that your motor is 7 years old. Lets say your motor, all the new wammy bamy like you did at 120,000 miles vs. a brand new motor. with all new parts. The old one won't perform at the same level as the brand new one exactly as a carbon copy of eachother. there is acount of 120,000 mile wear and tear, not saying its all beat up.

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yea i understand that but one would think that the new stuff would at least help it perform better. I do believe that my engine is in great shape since i make sure to take good care of it w/ mobil 1 full synthetic, seafoam, ect. It has always performed great and hasn't missed a single beat, i guess i was expecting a little too much.

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