Configuring Injector Timing | AEM
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Last seen: 5 years 7 months ago
Joined: 02/19/2015 - 02:13
Configuring Injector Timing
We have a 30-1500 in a Gen 2 Dodge Viper and we want to adjust the timing of the injectors. As far as I can tell I do this here: Fuel / <<Advanced Fuel>> / Injector Phasing / Inj Advance Map / Table
I have some questions though that I hope someone can answer, 
1. The number I write in the table is degrees I assume, but what position of the cam shaft are they refering to? In other words, what does it mean when I write 0? 
2. If I write - (minus) it would happen before 0, right? (maybe obvious but better safe than sorry)
3. Are the numbers refering to when the injector will close or when it opens?
An example. I have a cam shaft where the intake opens 25 BTDC and close 65 ABDC and want my injector to open at TDC (or close at BDC if the number refers to when it closes) what should I write in the table?
Right now the values we have in this table seems very strange to me, it starts at -78,8 at 0 RPM, stays that way until 2500 RPM, then it gradually increases until it reads 0 at 6500 RPM and above.
Kurt's picture
Last seen: 1 month 3 weeks ago
Joined: 06/04/2014 - 17:17
If you want these numbers to

If you want these numbers to make sense in terms of TDC compression, you need to first figure out what Fuel Tooth value = TDC compression.  This is very easy, just use the Ign Fixed and Ignition Fixed options to lock timing at 0° and write down the resulting tooth value from the Ign #01 Firing Loc parameter.  Make sure you turn Ignition Fixed OFF when you're done!  That Fuel Tooth value is TDC compression, so half a cycle from that would be TDC exhaust.  I find it easy to think in terms of this point since it's when the intake valve opens.  

It should be a pretty safe assumption that Injector 1 and Coil 1 are wired to the same cylinder and all inj/coil phasings are in appropriate order.  Your application is wired in wasted spark, so it's possible that your ign phase can be 360° off.  Confirm it's right by 1st turning off Inj 1 in the software and notice the drop in rpm.  2nd, turn off Coil 1.  There should be NO drop in rpm.  Turn them back on when done.

A lot of applications will have 12 tooth cycles, but some will be different.  Your's is 10 teeth.  So, if your TDC compression Fuel Tooth is 4.25, Injector 1 will be OPENING at TDC exhaust at Fuel Tooth 9.25.  You will see when the injector is opening in the Fuel Inj #01 Open channel.  The option Injector Phase and the Inj Advance map are responsible for setting injector open point.  

The Inj Advance map has a range of -360 to +357.  At -360, there is no injector advance and at +357 there is 717° injector advance.  I set the Injector Phase option so that I have a small range to inject after TDC and a large range to inject before TDC.  -180 is my reference point for this table.  Set it all to -180 and adjust Injector Phase until Fuel Inj #01 reaches TDC Exhasut (9.25 in my example above).  

At this point, each injector will OPEN at TDC exhaust.  To open them at 10° BTDC, enter -190.  10° ATDC set to -170.  You could set the reference point at zero or where ever you want in the Inj Advance map.  But, I like to have the range in the map to get all the injection done by the early parts of the intake stroke.

Last seen: 3 years 11 months ago
Joined: 01/31/2015 - 18:00
I was reading this and trying

I was reading this and trying to figure it out. If a wheel is 10 teeth you mean that it rotates twice for a total of 20 teeth per full engine 4-stroke cycle right?

If so, wouldnt the fuel tooth TDC be the same tooth as TDC exhaust, only 360* out (same as the fuel tooth but 360* on the other side) WHich is why the injector advance table has 360* of advance built into it when set to 0*? SO shouldn't we set the phase value to the same as the injector TDC compression tooth?


Edi: I think I understand. The tooth you chose for exhaust TDC reflects the additional -180* of advance you are putting into the adv. table, for a total of 360*.

Only question now is, how do we control when the injector is closing? How can I know how much advance I need to finish the injection event before the intake valve opens? Or is it just a guessing game....

Last seen: 1 month 2 weeks ago
Joined: 09/16/2016 - 18:02
For anyone who may come

For anyone who may come across this older post and wonder how Kurt's math worked out, he was figuring 10 teeth per COMPLETE engine cycle (720 degress of rotation).

720 degress  / 10 teeth = 72 degrees per tooth

4.25 teeth * 72 degrees = 306 degrees for TDC compression

Add 360 degrees to arrive at TDC exhaust. 306 + 360 = 666 degrees

666 degrees / 72 degrees per tooth = 9.25 teeth for TDC exhaust

Last seen: 3 months 3 weeks ago
Joined: 09/12/2014 - 05:29
This seems like the most

This seems like the most helpful thread I've been able to find on this, but I'm still a little confused about the the logic above. If the viper has 10 teeth on the crank pulley why is the logic 720 degrees / 10 teeth? 720 degrees is two crank cycles so wouldn't it either be 360/10 or 720/20?


I'm trying to apply this to my Supra. It has 24 teeth on crank gear, 6 coils and 6 injectors that all have the same phase with injector/coil #1 starting at 4 teeth. I've got my timing synched and the Ignition Sync is 5.539. I locked my ignition at -0.1 degrees (wouldn't let me lock at 0) and my "Ign 1 Firing Loc (teeth)" is 11.93. That would be TDC on the compression stroke as that is when the plug would fire at 0 degrees.

So to get the exhaust stroke I'd want to go 360 degrees from that. If I use the logic I'm questioning that would 720/24 = 30 teeth per crank. 11.93 * 30 = 357.9 degrees Add 360 to that and you are at 717.9. Divide that by 30 and that would put the tdc of the exhaust stroke at 23.93

If you click on Injector Phase in AEM it recommends this "(Unit=teeth) Trim that adjusts the injector firing locations globablly.  Decreasing this value effectively ""advances"" the injectors; increasing this value effectively ""retards"" the injectors.  Good starting values is Ignition Sync minus 1.5 on applications with 24 wheel teeth (assuming coils and injectors are phased the same)."

So if I took my 5.539 Ignition Synch and subtracted 1.5 from it that would give me ~ 4. I played with the timing advance at that and found that -100 gave me some decent idle throttle response. Before I did this just touching the throttle at idle would make it run 17.9 afr. This helps keep it in line. So if the math was right and if I use 4 Injector Phase with -100 timing advance it shows 22.91 "Fuel inj 1 Open (teeth)". That is very close to the calculation I'm questioning.

Someone please help me understand. I think I am so close.


EDIT: I figured it out. The Non VVTI supra has 12 Teeth on the crank pulley and not 24. So it's 24 teeth per Cycle (2 crank revolutions). The math that people outlined above now makes perfect sense. 

Last seen: 21 hours 15 min ago
Joined: 06/06/2014 - 09:31
The Viper has 10 crank teeth

The Viper has 10 crank teeth but they aren't evenly spaced so the Series 1 cals were setup to count the first of each pair of teeth (which are evenly spaced) thus the 10 teeth reduces down to 5 teeth per rev or 10 per cycle.  As you've discovered, a standard 2JZ has 12 evenly spaced crank teeth therefore 24 teeth per cycle. 

The concept of injector phasing and offset from ignition phasing and the igntion sync point is already pretty confusing.  Then add in that everything is handled in teeth and it gets even more difficult to understand.  The recommendation for setting Injector Phase to Ignition Sync - 1.5 came from testing with an oscilloscope to physically see where in the engine cycle the injection event was occuring compared to TDC.  There's a difference in the scale of Ignition Sync and Injector Phase which again further complicates things so my objective was to just figure out what a good baseline number was to get injection in the right spot regardless of what calculations behorehand might try to dictate.  Setting Injector Phase to Ignition Sync - 1.5 gets the start of injection to occur right before TDC exhaust.  This is a good ballpark starting point from which you'd then adjust the Injector Advance table for finer tuning.