E38 Injector Timing

To give you a little back ground, I have a 2006 Corvette with a LSX 451 ci 12 to 1 compression, 257/266 .649/.627 112+4 FAST 57lb injectors and no cats. I’m fighting the raw fuel smell. You can’t stand to be in the garage when its running, or when you are driving behind me it’s bad enough that you can smell it. I have delayed the injector timing some, but with 37.5 degrees of overlap, I don’t know if I’m fighting a losing battle. On the gen 3 stuff you have something to reference to come up with injection end of target, but I have found nothing on gen 4 stuff.

Is there any reference points, or formulas that I can use to nail this down?


Thanks in advance. :usa:

Any assistance would be greatly appreciated.

Since No one else replied and as fellow newbie to tuning.
Check these links
http://marcintology.com/tuning/
Download the doc entitled "how speed density works"
In this doc the author has derived a number of formulae that relates the GMVE paratmetric values (used the E38 & E67 ECU's) to an absolute VE amongst (used in earlier ecu's) others.
This also a formula to calculate the required fuel mass from a given air mass charge and afr ratio.

I don't think he's talking about the amount of time the injector's open but rather the time that it opens or closes in this case since the ECM uses end of injection as the target instead of starting point.

As for the end of injection pulse on Gen4's from what I've gathered is the Boundary is the latest crang degree possible for injection to end in a 720 degree crank rotation. The Normal ECT and Normal RPM are added together and subtracted from the Boundary to give you a target EOI.

Example:

Stock LS2 GTO has a boundary of 520 degrees. The Normal ECT table reads 110 degree's at operating temperature. The Normal RPM ramps from 0 @ 1000rpm to 92 @ 4000rpm. We'll use idle since that's what is being discussed is idle fuel smell. At 1000rpm the formula for getting the EOIT is this: Boundary - (Normal ECT + Normal RPM). So 520-(110+0)=410 degree's. So basically using the stock LS2 format at 1000rpm the EOIT is 410 degrees.

For whatever reason the EOIT is already later on the Gen4 stuff. Stock LS1 is set to around 300 degree's. I personally like the Gen4's method much better because it give's control of change vs RPM which allow's more tuneability throughout the lower RPM region.

Quote:

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Originally Posted by LSxpwrdZ

I don't think he's talking about the amount of time the injector's open but rather the time that it opens or closes in this case since the ECM uses end of injection as the target instead of starting point.

As for the end of injection pulse on Gen4's from what I've gathered is the Boundary is the latest crang degree possible for injection to end in a 720 degree crank rotation. The Normal ECT and Normal RPM are added together and subtracted from the Boundary to give you a target EOI.

Example:

Stock LS2 GTO has a boundary of 520 degrees. The Normal ECT table reads 110 degree's at operating temperature. The Normal RPM ramps from 0 @ 1000rpm to 92 @ 4000rpm. We'll use idle since that's what is being discussed is idle fuel smell. At 1000rpm the formula for getting the EOIT is this: Boundary - (Normal ECT + Normal RPM). So 520-(110+0)=410 degree's. So basically using the stock LS2 format at 1000rpm the EOIT is 410 degrees.

For whatever reason the EOIT is already later on the Gen4 stuff. Stock LS1 is set to around 300 degree's. I personally like the Gen4's method much better because it give's control of change vs RPM which allow's more tuneability throughout the lower RPM region.

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This is what I am after, and heading in the right direction.

With an EVC @ 17.2 and IVO @ 20.55. with a total of 37.75. How will this effect EOIT? Do you recommend adjusting the Normal ECT over Normal RPM?

The data quoted for is derived from the Timing Diagram for a Std LS2 Cam.

410 degrees from 0 (TDC at the start of the POWER stock) equates to approximately third lift from EVO event and around 20 degrees after EVC.

If it was my engine I would calculate a new boundary timing target for the new cam based the std cams lift at 520 degrees. Calculate a new offset for the corresponding lift at 410 degrees and use it instead 110 Degrees in the ECT EOIT table. Then use the RPM EOIT table to advance/retard the injection end target until the acceptable compromise was found.

Hey all,

Been searching through old threads to dig up some info on how to adjust my EOIT to get rid of that raw fuel smell at idle and possibly even help out my fish-biting in cruise under 1800 rpms whens the converter is locked up. I understand you can achieve some more low end torque too! The Texas Giant cam I have on a 112 lsa equates to 27 degrees of overlap. I understand the concept that I need to have it setup to have the EOIT somewhere around BDC to prevent raw fuel from going out the overlapped exhaust valve. So, what that means is I need to change my Normal Injection Target (ECT and RPM) tables to DELAY my end of injection. How do I do that?

The boundary starts at 520. 520-110 is 410 (normal op temps). I have no idea where that is in relation to what stroke I am on. Therefore, I don't know which way to move the numbers to DELAY my EOIT. If I change the normal injection target vs ect to 150 from 110 that gives me (520-150) = 370. Is that making my EOIT closer to BDC (therefore delaying it) or further from it?!!

In short, do I add or subtract from the normal injection target tables to delay EOIT? I can only find info on how to do this with LS1's which is different.

410* is earlier than 310*, thats why stock table injects earlier at lower temps. So if your cam is 10* larger, than take 10* off the whole table, completely trial and error dont over complicate. Larger cam = inject later.

So I pulled 20 degrees out of my Normal table thus theoretically subtracting or delaying EOIT to 430 degrees from 410 stock. The car doesn't run any different with the exception of more positive STFT's and a bouncier idle when cold (perhaps I'd need to fine tune that if I stick with these numbers).

I'm going to try the Normal table at 130 instead of 110 (stock) now to see if things sway the other way. I believe this would be advancing the EOIT though....unless I'm looking at this backwards!!

I determined with my Texas Giant cam on a 112lsa and 27 degree overlap the intake valve opens 16BTDC and exhaust valve closes at 11ATDC...27 overlap. I'd like to get my EOIT sometime after EVC so I'm not wasting gas but still atomizing properly. However, I'm confused on where this is in relation to crank angle degrees (0-720).?!!!

In relation to crank degrees do I use the GM or Ford graphs?

Using the GM graph 410 crank degrees is well after EVC for my cam. Using the Ford graph its before IVO and and before EVC. Thus pulling 20 degrees out my table would just be advancing or making EOIT even earlier((which I did in the first test by subtracting 20). If I knew what graph to refer to I could get this right!

So after looking at the stock tables and realizing that you wouldn't want (GM probably thinks the same) to spray cold fuel on a cold valve in a cold engine, thus spray it into the chamber after the intake valve opens. So with this logic, 520(boundary) - 245(normal COLD) = 275 degrees. Therefore, this has to be well after TDC and after the intake valve opens to not be spraying on the valve when cold. The intake valve opens on a stock cam at 18ATDC...or 360-18 = 342. When the engine is HOT(520(boundary) - 110(normal)=410) the fuel is sprayed on a hot valve to help with atomization, but GM doesnt have to worry about wasted fuel out the exhaust valve because there is no overlap with a stock cam! So...the HIGHER then number in the normal table equates to a LATER EOIT.

While later EOIT will help, I'd highly recommend getting rid of those FAST injectors and getting some SD 60lb-ers. Having proper injector data is going to ensure the proper AFR and will help with the fuel smell. I know from experience.

I just pulled a set of FASTs out of a H/C Procharger car and replaced them with shorty SD 60's. Noticeable difference in the idle quality as well as part throttle driving.

You won't regret spending the $300.

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Originally Posted by redgto4u

So I pulled 20 degrees out of my Normal table thus theoretically subtracting or delaying EOIT to 430 degrees from 410 stock. The car doesn't run any different with the exception of more positive STFT's and a bouncier idle when cold (perhaps I'd need to fine tune that if I stick with these numbers).

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During testing some of the cars I've tuned I found you sometimes have to make BIG changes to see the difference, then step backwards closer to stock in smaller increments to get what you really want. I had to move the EOI time 60 degrees to see a noticeable change in the AFR reading from more fuel actually burning instead of going right out the exhaust (temporarily forced open loop for tuning purposes).