What is an Aj tune?
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Cadillac Powertrain Control Module (PCM) Tuning Discussion, What is an Aj tune? in Cadillac Engine Technical Discussion; title says it all, haha. i keep reading about this, but im not sure exactly what it is/does....
  1. #1
    Nakoa's Avatar
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    What is an Aj tune?

    title says it all, haha. i keep reading about this, but im not sure exactly what it is/does.

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    Submariner409's Avatar
    Submariner409 is offline If it won't run, chrome it
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    Re: What is an Aj tune?


    "Northstar Tuning" (AJ Tunes) has been enjoying a long off-Broadway run uptown in Northstar Performance for quite some time now. It is the ongoing musical soap opera of a lonely Cadillac Technician's quest to successfully hack and alter the GM operating parameter codes in the later OBD-II unitized PCM used in the FWD series from around 1997 through 2003.

    Because the PCM is not modular, chips cannot be swapped to change different engine operating conditions: the entire ROM must be analyzed, changed and reflashed, oft-times with weird results. As in: changing the timing curves slightly to improve (?) overall performance and actually losing 1/10 in the quarter.

    It's one of those Catch 22 automotive electronic situations: A lot of reverse engineering has to be done to find the Holy Grail, and it ain't been found yet.

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    gothicaleigh's Avatar
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    Re: What is an Aj tune?

    Could it possibly be that GM actually knew what it was doing with the Northstar and there isn't much to be gained in this way?

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    Re: What is an Aj tune?

    I've seen the AJ tune in action, and it works!
    "They call Alabama the Crimson Tide, call me Deacon Blues."

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    Re: What is an Aj tune?

    Quote Originally Posted by I~LUV~Caddys8792 View Post
    I've seen the AJ tune in action, and it works!
    Me too! High 14 second (if I remember right) FWD DeVille.

  7. #6
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    Re: What is an Aj tune?

    That's the problem. Yes, The Northstar system is very well tuned and analyzed from the factory. But you know how gearheads are. We insist there's more to be had.

    So far I haven't seen any proof that any bolt on or add on item has produced gain. As a matter of fact I've seen a lot of evidence showing losses with all sorts of aftermarket bolt on 'Power Adders"

    I have faith that there's something to be had hear but I'm not sure what.

    Now on this topic of high 14's. I keep seeing this posted. So if we can take a stock DeVille, throw in an AJ PCM and run 14's don't you think I'd be doing that? The only DeVille on this forum that I know of, who's run those numbers also has a custom exhaust, Volant intake, Hi-Stall converter, NO2 and a few other things.

    If you can show me a totally stock 00 - 05 DeVille running 14's with nothing more than a tune from AJ, I'll eat my hat. A Hi-Stall converter alone is good for about .5 sec at best so that brings a stock DeVille from 15.4 to 14.9 at best.

    Quote Originally Posted by gothicaleigh View Post
    Could it possibly be that GM actually knew what it was doing with the Northstar and there isn't much to be gained in this way?
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    Ur7x is offline Cadillac Owners Connoisseur
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    Re: What is an Aj tune?

    Quote Originally Posted by I~LUV~Caddys8792 View Post
    I've seen the AJ tune in action, and it works!
    I have too and it makes SLS cars almost as fast as an STS and it makes speed limited STS's as fast as a unlimited STS... but it has NEVER made any stock car faster then a top of the line STS.

    Quote Originally Posted by codewize View Post
    That's the problem. Yes, The Northstar system is very well tuned and analyzed from the factory. But you know how gearheads are. We insist there's more to be had.

    So far I haven't seen any proof that any bolt on or add on item has produced gain. As a matter of fact I've seen a lot of evidence showing losses with all sorts of aftermarket bolt on 'Power Adders"

    If you can show me a totally stock 00 - 05 DeVille running 14's with nothing more than a tune from AJ, I'll eat my hat. A Hi-Stall converter alone is good for about .5 sec at best so that brings a stock DeVille from 15.4 to 14.9 at best.
    That says it ALL, Codewise is/was a AJ customer, he was one of the rare few who actually did a few back to back tests and now he runs a Stock PCM... and his car is FASTER.

    AJ did share with me that ALL his tune does is take the fuel/spark map and cut off limit from a W rated STS and swap in into the customer supplied PCM...

    The AJ tune is just a Stock tune... and it produces stock like results.

  9. #8
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    Re: What is an Aj tune?

    Quote Originally Posted by Ur7x View Post
    I have too and it makes SLS cars almost as fast as an STS and it makes speed limited STS's as fast as a unlimited STS... but it has NEVER made any stock car faster then a top of the line STS.



    That says it ALL, Codewise is/was a AJ customer, he was one of the rare few who actually did a few back to back tests and now he runs a Stock PCM... and his car is FASTER.

    AJ did share with me that ALL his tune does is take the fuel/spark map and cut off limit from a W rated STS and swap in into the customer supplied PCM...

    The AJ tune is just a Stock tune... and it produces stock like results.
    I would say 75% are with in stock specs. That is what people asked for.
    Now Codewize's was not and several others aren't

    Again about 75% were straight segment swaps. Everyone was worried that the tune would blow the engine and ASKED for exactly what they got!

  10. #9
    Ur7x is offline Cadillac Owners Connoisseur
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    Re: What is an Aj tune?

    Quote Originally Posted by AJxtcman View Post
    I would say 75% are with in stock specs. That is what people asked for.
    Now Codewize's was not and several others aren't

    Again about 75% were straight segment swaps. Everyone was worried that the tune would blow the engine and ASKED for exactly what they got!
    There ya go... It produces stock like times 'cause it is (at least) 75% stock and that's what you all want.

    It seems to carry more weight in a big bold font.

  11. #10
    97EldoCoupe is offline Owner of Northstar Performance
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    Re: What is an Aj tune?

    I've personally spoken on the phone with AJ and while I have not tried one of his tunes yet, he is well capable of doing what he claims. He knows the Northstar engine better than probably anyone else on these Forums. The day is coming where I'll be having a PCM tuned by him.

    He knows what he's doing with the fuel trim and timing curves. He has given me a bit of inside info on how he alters these tables and what he can do within the PCM. I cannot let out any of this info because I won't reveal his trade secrets. But let me tell you it's nothing short of amazing. To go from a 15 second VIN 9 to a 14 second VIN 9 should not be all that difficult if the factory left some room for tuning (timing advance, fuel trim, knock retard, torque management, etc).

    I've stood by AJ and I will continue to do so because if he was beating a dead horse he would have given up a long time ago. He continues to argue his point because he can do what he claims. Unlike D3 AJ has let out some of his info on what he does. I wish we could rent a track for the Northstar meet and have his tuned VIN 9 car run the 1/4.

    I'm not saying everyone's wrong for having their own opinion. Not at all. Just give the guy some credit. I do believe GM left the room to gain some performance and AJ's the one that can unleash it.

  12. #11
    Ur7x is offline Cadillac Owners Connoisseur
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    Re: What is an Aj tune?

    I wish what you posted is true...

    In every back to back test of stock cars running AJ's "tuned" chips..
    The cars RAN SLOWER...

    Code's car LOST A FULL 10th... in the quarter... It was slower to 60' slower to the 8th and slower in the quarter..
    Code switched back and now runs FASTER on the stock chip... and THAT says it all.

    The "magic" Deville that runs 14's is running nitrous, a LSD, a loose converter, and a hole bag of tricks (including having the drivers headlight removed.)

    Do NOT kid yourself...

    You can NOT plug in a AJ tune into a stock car and suddenly it runs a second faster in the quarter...

    AJ's trade secrets are not at all secret... he has been very open with what he is doing... He is taking the STOCK spark curve and fuel cutoff parameters from a STOCK unlimited Vin9 (W/Z Rated) PCM and replacing that portion of the code in the customer's PCM... Its call segment swapping...

    It yields a stock like PCM that works fine on a stock like motor and produces stock like results.

  13. #12
    NorthStarGXP is offline Cadillac Owners Member
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    Re: What is an Aj tune?

    After datalogging ignition advance and target AFR on my 2005 GXP, I feel there is a large potential benefit if we can get the PCM properly tuned. It would require premium fuel though, with 87, I don't think there would be whole lot to gain. Admittedly, I'm just guessing, but I'd say a .5 second 1/4 improvement ought to be quite possible with just a tune. Look at the ignition timing at WOT on a cold day:

    RPM / Degrees
    3500 / 12.0
    4000 / 13.0
    4500 / 13.5
    5000 / 14.0
    5500 / 19.0
    6000 / 24.0
    6300 / 24.0

    14 degrees of total advance at 5000 rpm on premium fuel? That is leaving a LOT on the table.

    There are a lot of GM V8s out there that are gaining 20 - 30 horses at the wheels and a large increase in mid-range torque and 1 - 2 mpg improvement by running an aggressive custom tune that requires premium fuel.

  14. #13
    Ur7x is offline Cadillac Owners Connoisseur
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    Re: What is an Aj tune?

    Quote Originally Posted by NorthStarGXP View Post
    After datalogging ignition advance and target AFR on my 2005 GXP, I feel there is a large potential benefit if we can get the PCM properly tuned. It would require premium fuel though, with 87, I don't think there would be whole lot to gain. Admittedly, I'm just guessing, but I'd say a .5 second 1/4 improvement ought to be quite possible with just a tune. Look at the ignition timing at WOT on a cold day:

    RPM / Degrees
    3500 / 12.0
    4000 / 13.0
    4500 / 13.5
    5000 / 14.0
    5500 / 19.0
    6000 / 24.0
    6300 / 24.0

    14 degrees of total advance at 5000 rpm on premium fuel? That is leaving a LOT on the table.

    There are a lot of GM V8s out there that are gaining 20 - 30 horses at the wheels and a large increase in mid-range torque and 1 - 2 mpg improvement by running an aggressive custom tune that requires premium fuel.

    Ignition timing was/is/and will aways be a bit of a black science. But one thing that most can agree on is that there is no perfect timing number that you can apply broad brush across all engines and have it yield positive results.

    On old school, slow burn, 2 Valve, long stroke, cast iron headed engines a good starting point was 34 degrees of total mechanical timing with most of the timing "all in" by 3500 RPM. On a NorthStar that would likely cause a "kaboom" situation.

    The point is, the timing needs to match the motor... A long stroke old dinosaur motor like an Olds 455 will need at least 36 degrees of timing to get max performance, whereas on a fast burn LS1 in a short stroke 5.3 most tuners will start (and finish) around 28 degrees of timing...

    Is the combustion chamber of the NorthStar more efficient then the LSx's? Does it have a shorter stroke? Cam timing, etc etc... All of these things contribute to "optimal" timing.

    Or simply, just because it looks like there is lots of timing left on the table doesn't mean there really is... and worse, even if you add a bunch of additional timing to the base table doesn't mean that once all of the calculation are complete that the computer will actually apply all of that additional timing to the final curve.

    The old school POV that you should just add timing until an engine detonates and then back off two or three degrees has now been proven to cost more power then it gains.

    And as AJ and others have posted the NorthStar PCM is a freaking Monster with dozens and dozens of tables that it uses to add, subtract, truncate, maximize and minimize the timing...

    There is a reason that on all of the turbo and S/C work AJ has abandoned the NorthStar PCM and is focused his effort on the LS1 and aftermarket LS1 PCMs...

  15. #14
    AJxtcman's Avatar
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    Re: What is an Aj tune?

    This is from a 4.6L 3 Valve FORD and it has a BLOWER!






    FWD Northstar
    Different X & Y for the chart, but you get the picture.


  16. #15
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    Re: What is an Aj tune?

    Timing isn't really a black art, but without the sophisticated test equipment like in cyl pressure sensors and a load bearing dyno. It is actually simple with a start of modeling software to model the chamber design, burn rates, etc, to get a good base map. Once that is done, in cyl pressure testing on a load bearing (and likely temp controlled) dyno. Then the optimal timing mapping begins to determine actual MBT, Minimum Timing for Best Torque. Being the average joe tuner doesn't have all the GM goodies, we have rely on other things to detmine what is best. Controlled acceleration runs, keeping all conditions as close as possible, show the changes. Datalogging is cruical to that. Do one pass, say 10-100 mph. Note the acceleration rates in 5 mph increments. Now, change something, go back, do it again. See what changes. You can see it much better that way.

    The more efficient the cyl, the lower the ignition timing is for MBT. Which is why we used 38 degrees on a Camel Hump Small Block head and only 30-32 on a 10:1 LT1 iron head on 87 octane. Careful measurement of EGT's is also helpful in determining MBT, as when timing is lower than most efficient, EGT's will climb, which if left uncontrolled can lead to cracked heads, burned seats and damaged cats. O2's and WBO2's are helpful, but use it really very limited.

    GM shoots for MBT and then puts in some buffer, or headroom as we call it to ensure it isn't too close to the "other side" or where it is too far advanced. MAF tables (read by LTFT's and or AFR with WB) will even show the changes in the timing. As the more complete combustion, less is left to go out tailpipe. So removing the headroom is where the power lies. When engines are modified, things need to be changed. HOW you change it to get the desired result is irrelevant. If you need more timing, fine, there are several places that it can be added at. But the right one is key. GM characterizes about everything, and is adding more as time progresses. You have base maps for low octane, high octane, you have coolant temp scalers, intake air temp scalers, PE Mode timing vs commanded AFR adders, the list goes on. My 1994 LT1 has 17 spark tables. My 2000 Park Ave Ultra has 33. This isn't even covering constants or diagnostic settings. Just tables. Being the NorthStar is a premium engine, I would not be surprised if there was more, it is after all a 4 valve engine (granted, mine is supercharged) and at the time, one of the most advanced engines out of GM, if not THE most advanced.

    http://www.freshpatents.com/Method-a...0060042355.php
    http://www.innovatemotorsports.com/f...ad.php?t=10210
    http://www.ecutek.com/tuning/ignition/

    I highly recommend anyone who is questioning what tuning is or wanting to learn more, grab Greg Banish's book on Advanced Engine Tuning. This I feel is required reading for everyone on the list. I have read it 2-3 times and need to read it again.

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