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Junior Member
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63 Posts
Discussion Starter #1 (Edited)
O/K, heres what I mean. When you flip the 3 position switch, from stock to either of the preset tunes,,, does the new programming run through the chip constantly,, or does the chip actually reflash the ecm?

Why do I ask? If a chip was removed after it had been used in a "tune" setting,, would the ecm retain the "tune" or would it reset itself to the stock factory programming?

Chip in question is a diablo 3 position chip. Truck is a 1997 f250 PSD auto 4wd crew.
 

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Premium Member
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4,090 Posts
The chip overrides the PCM so that it reads directly from the board on the chip. The switch just decides which tune it sees.

Once the chip is removed, the PCM should default back to whatever tuning is native to it.

A programmer is different. It loads tunes directly to the PCM.

prt
 

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Junior Member
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63 Posts
Discussion Starter #3 (Edited)
Another question

Is it possible, that on a 3 way tuner,, the "stock" tune is something other than factory oem stock?

Reason for asking; While trying to fix the cold start problem in my truck I noticed that the tuner switch was in the top high power position, but the chip was removed. In the past, I know if I started the truck in the high power setting, it would over fuel, smoke alot, hard start, no power until it warmed up.

After replugging in the chip, and putting the switch into the "stock" position, it fired right up on this mornings cold start.

I figured either the stock setting is something other than "stock" that makes cold start easier,, perhaps its economy? or the ecm must have retained some of the "tune" setting when it was unplugged??? Perhaps the "mechanic" unplugged it with key in ignition and the ecm got confused???

Only way to tell for sure weather or not it was a fluke,, is to wait till tomorrow and go for another cold start.

So, this begs another question: On the diablo chip,, how are the tunes arranged?

3 position switch: Bottom = economy, middle = stock, top = high power?

Or, is it : bottom = stock, middle = economy, top = high power?
 

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Sheep Shearer
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22 Posts
No idea on the Diablo chip having no expereince with it.

But if its a programmer, it re-flashes the PCM, which generally means you cannot hot switch tunes either.

if its a chip, it over rides, as the other guy said, and when the chip is out, its just the PCM in its original format.

The stock tunes on the Chips are updated versions of the stock tunes with the latest programming for sensors and such, like OBD2 upgrades that the 94-97's wouldn't have unless they had a PCM reflash.
 
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