Major Drop in Mileage, but no loss of power.. Totally stumped
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Member
Joined: Dec 2009
Posts: 33
Go stupid with it, knit pick...
1.) tire pressure them same on all 4 tires?
2.) fuel system gone over?
3.) intake system cleaned thoroughly including air filter?
4.) how is she idling? Excessive play in the needle while driving? i.e. bouncing from 1500 to 3000 rpms?
5.) that cargo box been on all along?
Anything else you can think of?
1.) tire pressure them same on all 4 tires?
2.) fuel system gone over?
3.) intake system cleaned thoroughly including air filter?
4.) how is she idling? Excessive play in the needle while driving? i.e. bouncing from 1500 to 3000 rpms?
5.) that cargo box been on all along?
Anything else you can think of?
Fuel system has been cleaned several time with lucas cleaner
Intake, KN filter are always kept spotless and clean
Idiling is spot on and smooth as can be, no power loss or misfire, no needle bouncing
The cargo box is NEVER On.. that was just for the pic, I have only used it once.
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Joined: Dec 2009
Posts: 33
Are you saying you are running 92 Octane? Unless you had the PCM tuned for high octane that is not going to do anything for you.
Have you always had a roof rack and carrier?
Where are you located?
Check the brakes, corroded calipers = brake drag.... you know what I mean.
When you changed the trans fluid, how did the old stuff look?
Have you always had a roof rack and carrier?
Where are you located?
Check the brakes, corroded calipers = brake drag.... you know what I mean.
When you changed the trans fluid, how did the old stuff look?
Carrier is NEVER USED. Only for the pic,
Brakes are all brand new, no hang up and in perfect shape!!!
Adn as stated above, all fluids were done at 60000 to GM Specs..
Thread Starter
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Joined: Dec 2009
Posts: 33
PCMforless tunes your PCM, so you can't remove it and continue to run the truck. You could swap it for another with the VIN for that truck in it like talusfan suggested.
However, you bring up a good point.... did anyone of those shops that checked it out scan or flash the PCM?
However, you bring up a good point.... did anyone of those shops that checked it out scan or flash the PCM?
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Joined: Dec 2009
Posts: 33
Thanks for chiming in!! I was thinking this too, but we already replace the o2 sensors trouble shooting, Brakes are new and have been triple checked, no drag, and as far the the troque converter, I would have no reason to thing is locked up.
Truck is driving, shifting, excelerating, idiling, running perfect. The only change is the drastic drop in fuel consumption.
Like I said to the other dudes. I have had it everywhere and had second, third, forth etc opinions, no one can find anything wrong.
I am DREADING the dealership, cause I know they will F**K it up and flash the PCM and charge me an arm and a leg and look at me like a dumbass,
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Joined: Jul 2007
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From: Boat Town USA MI
No, I have only tried the 92 octane a few times and it runs much better on it with much better mileage but its almost $5 a gallon compared to $3.50 a gallon of etheynol added fuel,
Carrier is NEVER USED. Only for the pic,
Brakes are all brand new, no hang up and in perfect shape!!!
Adn as stated above, all fluids were done at 60000 to GM Specs..
Carrier is NEVER USED. Only for the pic,
Brakes are all brand new, no hang up and in perfect shape!!!
Adn as stated above, all fluids were done at 60000 to GM Specs..
I saw you changed the trans fluid, just was asking about what the old trans fluid looked like. There was a reason for that, but you know so its all good.
Sincerely, best of luck.
Thread Starter
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Joined: Dec 2009
Posts: 33
My bad, if you have all new calipers (including liners and pistons) then brakes couldn't be it.
I saw you changed the trans fluid, just was asking about what the old trans fluid looked like. There was a reason for that, but you know so its all good.
Sincerely, best of luck.
I saw you changed the trans fluid, just was asking about what the old trans fluid looked like. There was a reason for that, but you know so its all good.
Sincerely, best of luck.
Thanks Doc, the fluid that came out looked great, normal wear for 55000 miles, no issues there.
Like I said, we are totally stumped, I guess I will just wait till its drops to 1 mpg and finally take it in... lol.. kidding. I just DO NOT want to take it to the dealership!!
I know they will Eff it up and flash my PCM which will cost me another $350... So at this point I am about ready to send her down the road before I dump stupid amounts of money into her.
I love her but, if I am gonna be dumping money into a rig that gets 10mpg, I will go back to a lifted Tahoe and get my V8 back so I can at least tow a trailer or haul stuff..
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Joined: Jun 2010
Posts: 1,042
I have noticed that after a fun day in the mud that the e-brake cables/pedal will bind up and not fully release (if it all). Try lubing up the rear brake mechanism with some WD40 where the cable attaches at both wheels and seeing if the e-brake pedal comes all the way back so the brakes arent dragging all the time.
When you changed fluids, did you use synthetic or dead dino? Do you use your H3 for short trips that dont allow the fluids to fully warm up? Check your fuel tank bash guard to see if its all dented up and pushing on the tank causing a loss in volume (wont explain the bad mpg's, but maybe the 200 mile range). Your 315's, are they a mud tire? Being driven in winter weather, they could be harder in the cold and not flexing enough, robbing power.
When you changed fluids, did you use synthetic or dead dino? Do you use your H3 for short trips that dont allow the fluids to fully warm up? Check your fuel tank bash guard to see if its all dented up and pushing on the tank causing a loss in volume (wont explain the bad mpg's, but maybe the 200 mile range). Your 315's, are they a mud tire? Being driven in winter weather, they could be harder in the cold and not flexing enough, robbing power.
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Joined: Aug 2009
Posts: 1,461
From: Rochester Hills, Michigan
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Joined: Apr 2011
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First, I'd look at the LTrims. If the LTrims are high (i.e., 15-20%) then the PCM is adding fuel. The PCM assumes that the precat O2 sensor is the "truth" and at part throttle, adjusts the injector pulse widths until the precat O2 sensor indicates there is essentially no oxygen in the exhaust. If your new O2 sensor is bad or the pigtail where it samples outside O2 has an issue, your new O2 sensor could be feeding the PCM wrong exhaust O2 information causing too much fuel to be added.
Do you have your old precat O2 sensor to try?
You can look at your new plugs? Does it look like you are running rich?
If your Ltrims are hovering around 0% (i.e., -5% to + 5%), then there is an increased load. This can be the parking brake mechanism freezing and causing the shoes to rub. The parking brake mechanism has been know to rust and freeze.
Could you new water pump be going bad?
Does your H3 coast like it did before?
Maybe its time to switch to light beer ;-)
Do you have your old precat O2 sensor to try?
You can look at your new plugs? Does it look like you are running rich?
If your Ltrims are hovering around 0% (i.e., -5% to + 5%), then there is an increased load. This can be the parking brake mechanism freezing and causing the shoes to rub. The parking brake mechanism has been know to rust and freeze.
Could you new water pump be going bad?
Does your H3 coast like it did before?
Maybe its time to switch to light beer ;-)