Overkill tune at altitude
06-07-2011, 09:43 AM
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Overkill tune at altitude Wondering if I'm going to run into trouble @ altitude (4500+ ft) on a 91 octane mail order tune from Will @ Overkill. The TCM tune should be just fine, the timing advance is what I'm concerned about, I've heard that people run into problems when using tunes made for sea level vs altitude. I've also heard that more timing can be pulled at altitude to help compensate for the oxygen density losses (indirectly).
I'm planning on feeling it out and seeing how the new ECM, TCM does, possibly get Will to tweak. Shipping and reshipping to get this right isn't the most time effective process. I could probably tweak the tune on a dyno ($$$) looking at another 300+ unless someone knows a cheap dyno tune in Utah. I guess I should have thought about this before I dropped 350.
If altitude is an issue how would it manifest itself?
I'm planning on feeling it out and seeing how the new ECM, TCM does, possibly get Will to tweak. Shipping and reshipping to get this right isn't the most time effective process. I could probably tweak the tune on a dyno ($$$) looking at another 300+ unless someone knows a cheap dyno tune in Utah. I guess I should have thought about this before I dropped 350.
If altitude is an issue how would it manifest itself?
06-07-2011, 12:31 PM
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The PCM already adjusts fueling for altitude. It does this because the less-dense air at 4500 feet will cause the O2 sensor to see a rich condition, so the PCM will compensate by pulling fuel.
To my knowledge (and Lew, Will, or JDMC5 will need to jump in if I'm wrong), there's no timing adjustment needed for altitude. A standard 91 octane tune should work just fine. If you get knock, then yes, timing will probably need to be pulled from the tune, but this will be due to fuel quality rather than altitude.
In general terms, you can somewhat mitigate the lost power with a good PCM tune. Depending on the condition of your car and the fuel available, this could mean that timing will need to be pulled and the fuel tables adjusted. However, pulling timing from what you call a "sea level" tune that is matched to the car (no KR, good power), will simply cause you to make less power and get worse mileage.
To my knowledge (and Lew, Will, or JDMC5 will need to jump in if I'm wrong), there's no timing adjustment needed for altitude. A standard 91 octane tune should work just fine. If you get knock, then yes, timing will probably need to be pulled from the tune, but this will be due to fuel quality rather than altitude.
In general terms, you can somewhat mitigate the lost power with a good PCM tune. Depending on the condition of your car and the fuel available, this could mean that timing will need to be pulled and the fuel tables adjusted. However, pulling timing from what you call a "sea level" tune that is matched to the car (no KR, good power), will simply cause you to make less power and get worse mileage.
06-07-2011, 03:51 PM
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Hey well I appreciate the thorough response, I'm planning on following the scanning instructions in the package that Will provided, I guess if anything is out of the ordinary I'll have to shoot it back to him to be adjusted. Just not the most efficient in terms of time I guess. Considered having it dynoed to tweak out but that would probably be a waste of money at this point.
It would be nice to get some of that power back at altitude definitely noticed a difference in Utah vs Michigan. Fuel economy has went up significantly but what fun is that...
It would be nice to get some of that power back at altitude definitely noticed a difference in Utah vs Michigan. Fuel economy has went up significantly but what fun is that...
06-07-2011, 06:43 PM
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never tuned a car in colorado but my instinct is telling me you'll be fine.
The MAF compensates for less dense air. Hench the name MASS air flow, you need density to find mass.....
Timing is based on load, which is calculated by taking many things into account, MAF is one of them.
The MAF compensates for less dense air. Hench the name MASS air flow, you need density to find mass.....
Timing is based on load, which is calculated by taking many things into account, MAF is one of them.
06-07-2011, 09:01 PM
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I'm impressed you could actually get Will to respond to you to sell you a PCM....I emailed him at least three or four times telling him repeatedly that I wanted to buy one and he never responded to me....I can't believe anyone buys anything from him with the complete lack of response/correspondence that he seems to exercise with the vast majority of the people that I see mention overkill online. It seems like most never hear back from him and the ones who do it takes weeks to get a response from him....and of course, no phone number on his site 
Last edited by jrhartman; 06-07-2011 at 09:14 PM.
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06-07-2011, 09:28 PM
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I'm impressed you could actually get Will to respond to you to sell you a PCM....I emailed him at least three or four times telling him repeatedly that I wanted to buy one and he never responded to me....I can't believe anyone buys anything from him with the complete lack of response/correspondence that he seems to exercise with the vast majority of the people that I see mention overkill online. It seems like most never hear back from him and the ones who do it takes weeks to get a response from him....and of course, no phone number on his site
06-07-2011, 09:49 PM
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Well he was able to put a rush order on the tune, salvage an 08' gxp core and have it out to me the next day so I can't complain too much. He even upgraded shipping for me to get it to me and took some of the cost himself. Still I can see where you are coming from it's been hit or miss, I've asked a lot of questions that I didn't get an answer to which eventually were answered in his tune documentation. Not too thrilled about the no phone number thing, although one did come with the bill of sale. Installing tomorrow so I'll give a candid assessment on the tune for anyone who cares.
06-09-2011, 11:09 AM
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Set a CEL on install (crank relearn), fixed it, drove around for a bit to familiarize, afterward I got on it of course to see what I paid for. Threw a CEL for P1516:
"The commanded throttle position, based on accelerator pedal position and possibly other limiting factors, is compared to the Actual throttle position. The 2 values should be within a calibrated range of each other. Both the PCM and the TAC module redundantly monitor the Commanded and Actual throttle position. This DTC sets if the TAC module detects the problem."
Took back to GM, they performed an idle learn process, the sensed vs actual throttle position was off by 13%...
CEL cleared, I was happy, later in the day I went WOT again, car threw the SAME P1516 CEL...
Anyone ever experience this? I'm guessing it's the tune not my TAP circuitry, I'm going to plug in the old ECM, TCM and see if it sets again. I'm guessing it wont.
"The commanded throttle position, based on accelerator pedal position and possibly other limiting factors, is compared to the Actual throttle position. The 2 values should be within a calibrated range of each other. Both the PCM and the TAC module redundantly monitor the Commanded and Actual throttle position. This DTC sets if the TAC module detects the problem."
Took back to GM, they performed an idle learn process, the sensed vs actual throttle position was off by 13%...
CEL cleared, I was happy, later in the day I went WOT again, car threw the SAME P1516 CEL...
Anyone ever experience this? I'm guessing it's the tune not my TAP circuitry, I'm going to plug in the old ECM, TCM and see if it sets again. I'm guessing it wont.
