Guys, I'm still learning here so bare with me. A little history. I have an 89 IROC, 40 over 350, vortec heads, ZZ4 cam, ported TPI, screens/some fins out MAF, shorty headers, LT1 28 lbs/43 psi injectors, and $6E with modified ARAP. I was having some trouble getting the BLMs nailed down. Tried for 3 months. Got it to run fairly well by setting the Injector constant to 24 and uping the lower gms/sec in MAF TBL to improve idle. BLMs where close, but just could not get them nailed down. Most of MAF Tbl 1 showed lean while Tbl 2 showed rich. Also the BLMs would become erratic at times. YES I had a Bosch O2 in it. Bought it BEFORE I became a member of this site. So I just recently installed an AFS-74 heated. I can tell you that the new O2 settled the BLMs down to where one can tell what's really going on. (So I agree Bosch is trash) The new O2 showed I was running leaner then the Bosch was telling me. Across both MAF TBL 1 and 2. I lowering the Injector constant down to 22.3 and the BLMS settle right into 128, 129, 130 range. Nice and steady with smooth transactions between the BLMs across both MAF 1&2 tables. The motor and car even FEELS healthier and happier. Open loop idle is even smoother. However, based on some threads, by setting the injector constant to 22.3, I lied to the ECM and lieing to the ECM is not good. I'm concern I've kludged it to make it work. I tried 28 lbs, but it was way to lean and it took major changes to the Scalars (Scalar 1 upped from 17 to 20, Scalar 2 upped form 30 to 38) just to get the BLMs out of the clouds. still lean so I have a lot of work ahead if I go down this path. So here are my questions.

1) based on the research and information that RBOB has provided. Can you reverse engineer the MAF tables and scalars by datalogging my currrent configuration and use the Injector pulse width values to calculate the math backward for the Scalar and MAF table values using 28 lbs as the injector constant? This might be an easy way to get the MAF tables/scalars close. Has anyone tried this?

2) Is there a way to modify the XDF file to datalog the MAF voltage output instead of the gms/sec? This might make it easyer to nail down points in the MAF TBLs that need changed.

3) Per the BIN, The Injector constants are based on 40 psi. Is this with vaccum connected to the Fuel Pressure Reg or vaccum off? When cruising, vaccum is on and my pressure is around 35-37 lbs. So I'm wondering if setting my constants to 22.3 lbs is compensating for the lower Fuel pressure at cruise?

4) Does any of this really matter? BPW is BPW. All these tables seem to feed off each other. Modify the MAF tbls to cruise. Causes you to modify the AE and PE tbls. As long as the BPW is correct for a specific motor condition, does it really matter how you got there? It may be more critical for MAP, but for MAF, does it really matter?

 

The easiest way is to use a wideband to tune. You have the airflow that the MAF is reporting, and you have the wideband output. If your getting, say, 10 grams/sec reported and an AFR of 16:1 on the wideband when you want 14.7:1, then to approximate the actual airflow, you multiply the reported airflow by (16/14.7), which would give an airflow of 10.88 grams/sec. You then go to the MAF tables, and find the cell that has 10 grams/sec in it, and enter that new value of 10.88 grams/sec in that cell instead.

Id also set the injector constant to match the actual injector size, and work off of the tables.

As for the MAF scalars, you should really adjust them only when you have to. Do a search. There is some really good info here on what the scalars do, and when you should adjust them. Generally, you want to leave them alone as you have to rescale the values in the entire table when you change a scalar, or there will be large gaps between adjacent tables. I dont know if this is automated in any of the tuning packages or not.

 

Also, to answer your question (i think), if you want to change the injector constant to what it should be without messing with the cars fueling, you can just scale all the tables. Say you have 24 g/s entered in as the injector flowrate when you really have 28 g/s injectors. To change the injector flowrate to match the 28 g/s injectors without changing how the car runs, you divide the actual flowrate you entered by the fake flowrate you had originally, which would be (28/24). You then multiply all the values in each of the six tables by this. The ammount of fuel delivered will not change when you enter 28 g/s in as the injector flowrate.

 

One other thing - I don't believe there is such a thing as an LT1 28# 43PSI injector. If you're using the LS1 28# injectors (narrow body, all light gray, need to check your part number), they really only flow 24#/hr at 43 PSI. They've been tested and proven at that rate.

As for setting the fuel pressure - you have to disconnect and plug the vacuum line going to your AFPR to set the fuel pressure.

Hope this helps!

 

I am running the $6E ARAP in my 86 Vette. I have vortec heads, hotcam, lt4 intake, and the gray ls1 injectors I got from SLP. The stock BIN was really close (after I found the vacuum leak by spraying starting fluid around the throttle body) The only fuel mods I had to make was to tweak MAF table #1. I set the injector constant at 25# and run the stock pressure. The only problem I have is closed loop idle sounds good but the motor likes to shake. I think it is the cam overlap causing the o2 sensor to read rich so it takes out fuel. (even when the BLM says 128) I think I will try to run open loop at idle to see if this corrects the problem. In open loop it will idle great at 600 rpms.

 

dimented24x7... I understand. Stay away from the scalars. Apply the percenage difference between my injector constant setting and the actual injector flow rate to the MAF tbls. Update all entries in all 6 MAF tbls. Then I can use the actual Inject flow rate for the constant and fine tune from there.

vernw...Good question on the injectors. They are the medium gray skinny injectors. Yes they are LS1. Purchased from SLP about a year ago. I thought they were advertised as 24 or 25 lbs at 43psi, but could not find receipt nor fine them on the SLP site anymore. Number on injector is 12561462. I looked number up on internet and multiple sites say this is a 28 lbs/43psi injector. One site says Delphi/Lucas. Another says Delph/Bosch. Are these the ones you refered to as actualing flowing 24lbs/43psi? If so, then it explains why I'm so lean when I set the injector constant to 28lbs.

 

All I can tell you is that exact part number injector was tested by Rich at Cruzin Performance to try and settle this debate once and for all. It tested out as a 24# injector at 43.5 PSI (our normal fuel pressure). Duplicated thie on 2 different injectors. Do a search if you want, it was all posted on here.

 

BTW the 98 ls1 were the only ones to have 28 lb injecters. And I believe the zo6.

 

As I recall 98, 01-02 had 28 lbers, while the 99-00 had the 26.4s

 

dimented24x7...I tried your suggestion below but the last entry in each MAF Tbl. maxed out:

[To change the injector flowrate to match the 28 g/s injectors without changing how the car runs, you divide the actual flowrate you entered by the fake flowrate you had originally, which would be (28/24). You then multiply all the values in each of the six tables by this. The ammount of fuel delivered will not change when you enter 28 g/s in as the injector flowrate]

I used 24 as the real injector size (because that's what these LS1 injectors really are at 43.5 psi) / 22.3 (which was the injector constant entry that worked the best)= 1.07. I multiplied each entry in each MAF tbl by that amount. The last entry for ARAP in MAF tbl #1 is 22.28 * 1.07 = 23.98. The highest that the Tbl would accept is 22.91. If you tried to enter anything larger it reverted back to 22.91. If I upped the MAF SCALAR 1 from 17 to 18, then it would take 23.91. MAF Tbl 2 last entry is 47.63*1.07=50.96. I had to up Scalar 2 from 30 to 34 in order for it to take 50.98.........Thoughts?

 

in the MAF systems, you have two choices for what you are doing there, you can either leave the injector constant at the value that gives you the best performance, or you can do what you are trying to do, and rescale the MAF tables. You have to be very careful at this point, since you are finding out that there are limits to each table that you are exceeding with a lower scalar. If you change the scalar, this changes EVERY value in the table, since it is a mulitplier. The best thing to do is to build the tables in excel and play around with them to get what you need. basically, the main thing to remember is that the first and last entry in each table should match the first and last entry of adjacent tables(respectively), in reality, they will be very close(not necessarily the exact values, even with factory bins).

I posted a document on moates.net file manager that starts to dig into the MAF system, and gives a breakdown on how the tables are made. take a look at that document. Its labeled something like '32 maf tuning' or something like that.

 

Well, they are rated at 28.55, but at 4 bar (58 psi). I learned the hard way, I picked up a set for my LT1, and changed the injector constant to the larger size and it ran like doo doo. I fought with it running lean all the time until I finally set it back to 24.87, and it ran great, and BLM's came back to where they should be. Before they were all over the place.

 

LT1 injectors are in fact 24#'ers at 43.5psi. I was running them up until this year. LS1's got 28's.

Anyway, interesting topic here.