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Discussion Starter #1
I have a few questions regarding tuning and adjusting VTEC cross over point.

I have a general idea of how VTEC works. ECU send power to the VTEC solenoid. VTEC engages.
VTEC pressure switch gets grounded and send the signal back to the ECU showing that the VTEC
is correctly activated.

When using a VTEC controller or Piggyback ECU (E-manage, AEM F/IC, VAFC, etc) to control the
VTEC engagement point, obviously the VTEC will be engaged at a point different from the stock
VTEC engagement point, will that trigger off any kind of error code?

For instance, if the stock VTEC crossover point is at 4800rpm. I then adjust the VTEC to activate
earlier at 4000rpm. When this occurs, VTEC will be switched on at 4000rpm and VTEC pressure switch
will tell the ECU that the VTEC is on. However, the ECU will know the VTEC is on when it is not
supposed to. Will that trigger any kind of error code? (Or in the reversed case the VTEC is OFF
when it is supposed to be ON.)

In terms of fuel and ignition. When the VTEC is switched on at the factory crossover point, the ECU
will supply more fuel and adjust ignition to allow the engine to produce the optimal power.
Is this action triggered by the engagement of the VTEC, or is it hard coded into the stock
ECU's fuel map? If let's say I adjusted the VTEC to be off all the time, will the ECU still adjust
fuel and ignition as if the VTEC is on?

For example, if the stock VTEC crossover point is at 4800rpm. I then adjust the VTEC to activate
later at 6000rpm. Will the ECU still start adjusting the fuel and ignition at 4800rpm as if the VTEC
was on?
 

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As I understand it, the PGM-FI/PCM logic has mostly nothing to do with VTEC. It adjusts fuel delivery and timing based on parameters such as air flow, air temperature, baro pressure, knock sensor, etc etc etc that may be changed by VTEC but are not dependant on it. VTEC controls valve lift/duration which has an effect on mass of air, turbulence, swirl, etc, but is independant of fuel mass or timing.

IMO playing with VTEC crossover on a stock J30A4 is a waste of time, and 'tuning' for increased AFR (again, stock engine) will do more harm than any power you'll gain. You'll need a change like cams/fuel injectors/pistons etc to make any of it worthwhile.
 

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Frankv6coupe
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I installed AEM V2 on my 2004 accord v6 coupe automatic.Went to the track on Tuesday and the car ran slower. Stock Best run was 14.97 at 96 Mph. Now i ran best 15.38 at 93 mph. A friend of mine figured that i might be getting too much air and need to adjust fuel. Spoke to Apexi and they have no vtec controller for
automatic transmission. Also spoke to AEM and they told me it should not slow the car down and also no need to tune car. Does this make sense?
 

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Bobby Lane Racing
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5,679 Posts
I installed AEM V2 on my 2004 accord v6 coupe automatic.Went to the track on Tuesday and the car ran slower. Stock Best run was 14.97 at 96 Mph. Now i ran best 15.38 at 93 mph. A friend of mine figured that i might be getting too much air and need to adjust fuel. Spoke to Apexi and they have no vtec controller for
automatic transmission. Also spoke to AEM and they told me it should not slow the car down and also no need to tune car. Does this make sense?
was the weather different? heat, tires wear, humidity, different tracks all play a role in the time you achieve.

there's no point in adjusting your vtec.
 

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Frankv6coupe
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Same tires,same track,the weather may have been a little warmer, but not enough in my opinion to loose three mph. And if the weather may be the cause shouldn't the AEM compensate or at least not loose any mph. This weekend I'll be installing the BORLA exhaust system. Then might install back to original air intake to see if it made a difference. This may take some time to have results.
 

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Frankv6coupe
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MY best 60ft time is 2.29 and on tuesday it was 2.48. The problem is not the 60 ft time. The problem is the mph has dropped. So when mph drops, horsepower drops. If mph rises the et will follow, meaning it will drop. Plus i have a hard time peeling my tires at the track because it sticks. The torque on these cars are not high especially with automatics compare with manuals you can rev higher and take off. The reason i don't have a 6speed is because the wife can't drive manual. Plus my other car is a Buick Grand National, but unfortunately the connecting rod bearing let go. So for now I like to try and make this accord coupe faster. Will see what happens when I will be installing the borla this weekend. thanks fs
 

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Buckwildly Racing
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132 Posts
I have a AEM v2 intake and UR crank pulley. But when I set my parameters for 12v switched function I get a CEL and the car goes into limp mode. Anybody have any thoughts? I'm using AEM FIC software and everything works good and MAP voltages look good "haven't done a dyno yet" but everything stays good through 4500 rpms in the low cam but when it crosses over I fall on my face.
 

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The real test would be putting the car on a dyno, the track times have so many different variables to be considered a true test of one performance mod.

From my personal experience I have an injen cai and the borla cat back system for a 2004 accord v6 automatic tranny and it is putting down 202hp at the wheels, without a tune.
 

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Track time are more ideal since it deals with real word situations. Your car is only as fast as the person driving it. But a dyno doesn't hurt.
 

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I have a AEM v2 intake and UR crank pulley. But when I set my parameters for 12v switched function I get a CEL and the car goes into limp mode. Anybody have any thoughts? I'm using AEM FIC software and everything works good and MAP voltages look good "haven't done a dyno yet" but everything stays good through 4500 rpms in the low cam but when it crosses over I fall on my face.

You have to use a relay so that the car doesnt throw a code. Hopefully paul can draw up a quick schematic for you.
 

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This is exactly what paul told me when I asked how to wire in the relay

"VTEC- On the ECU side, wire the VTEC Pressure Sensor to ground thru a "Normally Closed" relay contact, then use the VTEC Solinoid control to drive a relay that will "OPEN" when VTEC is active, this will keep the ECU from throwing a CEL when IT expects VTEC."

Maybe you can understand it better than me..OR Maybe you can draw a quick schematic and post it up lol
 

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Buckwildly Racing
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132 Posts
Agreed! Yes it was the relay. I had Pins 22&23 crossed {VTS&VTPSW} Now that its fixed I no longer have the CEL. Thank GOD for PAUL! Yes the wires have to go through the relay for the ECU to not throw a code. Now for the Dyno... I'm still having some Tip in stumbles when I go form 0-25% on the throttle and back out. Other than that she pulls like a beast!
 

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Buckwildly Racing
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I could get to 4300 or so with no CEL but when vtec cross over threshold was met under whatever it would fall on its face. Although, one interesting note probably for another thread is my stock map readings read something like 15.8-15.9 Atmospheres! That means that I had to somehow be reaching some sort of resonance charging effect because it read 14.7 with ignition on but engine off. I just remember reading something about having a supercharging effect from the plenum. Check your Map voltages and make sure it matches with a Wideband so that you aren't leaning out or running to rich. Ive learned the hard way how TOUCHY a honda ecu can be. Once I corrected my outputs to match everything worked perfectly. With A LOT of HELP of course.
 

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Buckwildly Racing
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132 Posts
Did you wire in the relay yet? NVA-AV6 fixed mine for me. You need a relay that is normally closed to be grounded and run through the "VTS" and "VTPSW". Once that is done make sure your 12v switched input is properly set for load; TPS; and rpm.
 

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Work hard, play later.
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657 Posts
I installed AEM V2 on my 2004 accord v6 coupe automatic.Went to the track on Tuesday and the car ran slower. Stock Best run was 14.97 at 96 Mph. Now i ran best 15.38 at 93 mph. A friend of mine figured that i might be getting too much air and need to adjust fuel. Spoke to Apexi and they have no vtec controller for
automatic transmission. Also spoke to AEM and they told me it should not slow the car down and also no need to tune car. Does this make sense?
? There is a local guy running a LS/VTEC Auto (Integra) supercharged on a non vtec ECU to activate VTEC he is using a Apexi V-AFC.
 
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