How is injector timing calculated?

[carlrx7]

What is the purpose of the makeup pulses and how much time or degrees need to be allowd for it?

when the ecm wants to add fuel after the main pulse has already happened and there is still time left, it doesn't have to wait until the next cycle.

-Carl

[Kyne]

If you zero out the adders, you leave no time for the makeup pulse.

So just leave 30* for the make up?

[DSteck]

when the ecm wants to add fuel after the main pulse has already happened and there is still time left, it doesn't have to wait until the next cycle.

-Carl

This.

So just leave 30* for the make up?

Realistically, that's probably sufficient. GM leaves over 100* though. That's for small injectors though. Bigger injectors mean your window can shrink.

[HRD]

Have you guys ever tried switching the makeup mode from multiple to single or none? Any difference?

[Kyne]

So I guess with multiple you need to do multiple 30* make ups? Now I'm starting to understand why the ECT is there and how it comes into play.

I need to send Dave a 6 pack...

[DSteck]

Nah, you don't. Everything I've said has already been stated on this forum.

[Kyne]

Did you take a look at my spreadsheet? Which model is correct, carlrx7 or mine?

[DSteck]

Haven't been home long enough to look.

[Kyne]

Haven't been home long enough to look.

When you email back send me your address and beer and cigar choice

[IDRIVEAG8GT]

I need to send Dave a 6 pack...

Nope he likes wine coolers.

On a side note its really too bad that the GM set value isn't an accurate representation of each specific cam whereas you could simply find the difference between intake and exhaust valve open times between that cam and your new one, then simply adjust the firing of both intake and exhaust in reference to crank degrees of movement.

But that would warrant another mass of sensors to tell the injector when to open on each cylinder versus RPM.

In essence though, the best way to start tuning would be to warm the engine up to its usual operating temp and then specifically adjust the boundary normal table overall, then fine tune with the other tables?

[Jamz]

Is everyone just adjusting the injection timing down in the lower RPM's and idle or right through to the higher RPM's?

[carlrx7]

Is everyone just adjusting the injection timing down in the lower RPM's and idle or right through to the higher RPM's?

depends on two things, what values are already in your tune, some cars are different, and how big your injectors are, over 80% IDC and changing the EOIT wont do anything. but running ID1000's on 93 will.

-Carl

[IDRIVEAG8GT]

So if you find the idle and just off idle boundary is it safe to simply interpolate the rest of the table?

[Jamz]

Bump

[carlrx7]

for me, i added 24.5 to the normal rpm table starting at 0 and took it all the way up to the values until the stock ones took over.

[DSteck]

Carl, that advances EOIT.

[Jamz]

Well for the 6litre engines with cathedral heads i.e. ls2 I've notice the boundary is 520 across the board. 110 in ect.

In my l98 / l92 head tune. It tapers from 520 to 360 in top end. And 110 in ect.

Reason why I want to play with my eoit. Is I have some fuel short circuiting due to a new exhaust system with tuned headers. I.e. Fuel smell and light idle misfires. I'm sure it will improve economy in idle during traffic conditions also.

Quick question for you dsteck. With 360 during the high rpm In the std l98 tune. Could this be related to the larger and slower velocity in the bigger head intake ports? Or to just to give more time to evaporate the fuel on the back of the intake valve for a better burn and Emmisons.

I also know that during high rpm gm sprays the back of the valve to reduce cylinder bore wash also for better cylinder distribution.

Thanks

[carlrx7]

Carl, that advances EOIT.

That's the point right? to advance the eoi to after the evc point.

the z06 tunes have 32.5 at the lower rpm stock.

-Carl

[carlrx7]

Well, another reason i did that because in Greg Banish's #2 dvd he adds 20 to the ECT Normal table, but that's on a 99 Camaro.

Bigger cams can exhibit a phenomenon known as "short circuiting" of the fuel where the vaporized fuel cloud gets blown right out the exhaust valve during overlap. To reduce the chance of this happening, one can DELAY the end of injection event so that there is less chance of this happening. To accomplish this, you would effectively INCREASE the values.

The downside to this is that you don't give the fuel as much time to evaporate, so combustion quality may suffer. It's still better than the misfire associated with dumping the fuel out the exhaust instead of trapping it in the cylinder. Also, since the fuel is now being injected across an open intake valve (it's normally early enough that it hits the closed valve), there is an opportunity for bore wash at low speeds until port velocity is sufficient to carry the fuel charge dominantly. For this reason, we only try to delay as little as possible to avoid the short circuiting.

I bet you don't find info like that in your average class or internet post.

[Kyne]

Advanced is earlier while with a big exhaust duration the exhaust closes later so you want it retarded I think. And in Greg's stuff he says just to the opposite way of the cold setting on ETC which on gen4 would to subtract it. Again all this is is what I think