Need bigger gears

[shorepatrol]

That tire could be close to 34" tall. That effectively changes your gear ratio to around 3.08:1. In and of itself that shouldn't turn your truck into a turd, but mixed with say a gunked up fuel filter, a crudded up air filter, and other possible tune up parts that aren't it great condition (distributor cap, plug wires, etc) I could see it giving you problems.

It is closer to a 34 inch tire. I have the same size tire and the same gears. My truck without a trailer will scream up hills at 7k altitude. Loaded with tons of camping gear and trailer with a 660 grizzly I can still keep it at around 60 up hills floored in 2nd gear. All maint has been done including MPFI uggrade and blackbear tune. I will be regearing sometime in the future though

 

[DallasTahoe]

Ok so I get what everyone is saying, here is what I do know, with the other wheels and tires I had on it they were right at 3inches shorter than my current wheels and tires which are exactly 33in tall and I had no issues. My rig is very well maintained, new fuel pump, new filters, regular oil changes, tune-ups etc, cats are less than 5 years old, new heads, flow master 50, updated mpfi, no check engine, doesn’t smoke, and I have no tune. The difference between the wheels and tires is what leads me to believe it’s a fearing issue


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[slowburb]

Well then. So you know, 35's and 4.56's is equivalent to 4.10's and factory tire height.

 

[Christian Steffen]

Well doing front and rear gears would probably be a nice improvement, but it definitely isn't easy or cheap. Either way a tune will be an improvement, so I would recommend trying that and seeing if it helps enough to keep you happy. If not then you can regear and have it returned for those gears.

 

[Ken K]

I am sure you would have mentioned a check engine light, but I guess nothing.
Yes, installing larger diameter tires effectively changes the final drive ratio and re-programming for proper tires size would be correct action.

However, one thing that is alway over looked, is the MAP sensor. Even though you have the same issue in low ground Texas, when you key on, it takes a screen shot of barometric air pressure to adjust timing and fuel. High altitude should make timing go high as air decreases reducing the possibility of engine knock. Less air pressure, the ability to fill the cylinders with air drops. This is the definition of volumetric efficiency.

I am sure the fuel you're burning requires stopping and shutting off the engine, so at this point the MAP should take a new reading. Bet it's not.

I have had MAP sensors fail and you only see it on a scan tool with key on / engine off. The values don't change as 98-100 KPA engine off, drops with altitude, but idle, values run between 36-42 KPA if the MAP sensor is functioning. May not set code or turn on CEL with incorrect KPA during KOEO.

Using GM's electronic service information would point out a check of the MAP sensor reading under the heading of "Symptoms / No Malfunction Indicator Lamp" Loss of power. But it does not include fuel trim, fuel pressure, spark retard, etc. as they would set a code the enable criteria fails twice over a period of time...Class B codes. Too Lean example.
Retired ASE Master Tech

 

[DallasTahoe]

I am sure you would have mentioned a check engine light, but I guess nothing.
Yes, installing larger diameter tires effectively changes the final drive ratio and re-programming for proper tires size would be correct action.

However, one thing that is alway over looked, is the MAP sensor. Even though you have the same issue in low ground Texas, when you key on, it takes a screen shot of barometric air pressure to adjust timing and fuel. High altitude should make timing go high as air decreases reducing the possibility of engine knock. Less air pressure, the ability to fill the cylinders with air drops. This is the definition of volumetric efficiency.

I am sure the fuel you're burning requires stopping and shutting off the engine, so at this point the MAP should take a new reading. Bet it's not.

I have had MAP sensors fail and you only see it on a scan tool with key on / engine off. The values don't change as 98-100 KPA engine off, drops with altitude, but idle, values run between 36-42 KPA if the MAP sensor is functioning. May not set code or turn on CEL with incorrect KPA during KOEO.

Using GM's electronic service information would point out a check of the MAP sensor reading under the heading of "Symptoms / No Malfunction Indicator Lamp" Loss of power. But it does not include fuel trim, fuel pressure, spark retard, etc. as they would set a code the enable criteria fails twice over a period of time...Class B codes. Too Lean example.
Retired ASE Master Tech

Ok so I did notice the the regular gas in Colorado is 85 octane, I put one tank and noticed it ran ok but no power, after I noticed it I stopped using it and began running their mid grade which is 86-87, depending where you are, power was better, and once I got back to Texas it ran better, but still takes a while to get up to highway speeds. So what should I be looking at? New Map sensor?


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