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How to tell if truck had a tune?


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I have a 2003 silverado the only "mods" that I have done is an electric cooling fan, K&N filter (not CAI) and replaced stock muffler with glasspack. My truck seems to have a lot more getty up than other trucks of same year and specs. I have a buddy that has an older Ford with a moderatley built 390 big block and I smoke him in every way and form. I wouldn't expect this small cubic inch chevy to do that also my father in laws 2002 1500hd doesn't hold a candle to this truck. I am starting to think the previous owner might have had a tune done.


Is there any way to tell other than having a dealership read the pcm?

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Hook up some cheapie scantool and see how much spark advance you have at wide open throttle is one way. Shift points, limiters and whatnot can still be stock especially if it's some canned tune off a handheld of some kind. My buddies 05 was that way.... it had no limiter per say and a ton of timing added.... but everything else still stock. Ran like crap honestly lol.


I am assuming you did some kind of "aftermarket" or toggle switch setup for your fan. You can wire the 03 and 04 trucks exactly as the 05+ e fan equipped trucks were done provided you just enable the bits in the pcm to control the fans.


And really..... a Ford 390...... boring, lol. And a stock 1500HD has so many limitations, no timing and power enrichment delay that if you couldn't outrun him your truck would just be sad.


And the premium gas thing is bunk. You can run around 30 degrees of advance on the LM7's on regular with zero knock retard tuned properly..... You only have 9.4:1 compression.... premium is a waste of money.

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If your tires are good, get her out on the open highway. If you can get up to 115MPH, then the speed limiter has been bypassed. AKA, you have a tuned PCM.


You should also only run super unleaded/premium fuel too....



Also your rpm will be up around the 5000 + mark when pegged, closer to 6000 rpm.

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  • 4 weeks later...

So some of the stuff you guys mentioned says tune to me. My speed limiter is still there but she pulls right up to 6k. Yes my fan is off a toggle. The truck also shifts quickly and pretty hard maybe that is nature of the beast but 1st can be sluggish the rest are firm. Guess I just need to get a hold of a scan tool.

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  • 3 weeks later...
  • 4 weeks later...


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