No Rev Limiter, Add to XDF?

Hello Gents!

Recently picked up an Auto-Prom and have been tuning a 2.8L LL2 V6 from a 1992 GMC Sonoma, swapped into a Chevy Vega. $4E mask, 1228062 ECU.

Anyhow, the car is used to road race, and with my factory pulled BIN and the XDF found on this site and others, there does not appear to be any code for a rev limiter.

I realize this may be factory, (the stock engine VE died off quickly after 4000 rpm in the truck), but his car now has a cam, ported heads, and headers. I am trying to find a way to put a rev limiter on the car for him, but have no experience with modifying XDF files. I've been in the tuning world for a bit with HP Tuners and Megasquirt, but flash chip based tuning is new to me :thumbsup:

Is it actually in the ECU, and just not shown in the code I can see? (the XDF files only say for years 89-91, this is a 92)
Can I do a "ghetto" rev limiter by pulling fuel in the VE adder table at 6400 RPM?

Thanks for the help!
Eric,

Quote:

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Originally Posted by UglyBoost91

Can I do a "ghetto" rev limiter by pulling fuel in the VE adder table at 6400 RPM?

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DO NOT DO THIS!

the table's values are interpolated, so if there were a value of 0 in the 6400 row, starting at 6025RPM, that would be used in proportion to RPM, causing the engine to start shooting VERY lean after 6000.

being a C3 ECM, patching the code to add in a rev limiter(assuming there isn't one already) will be difficult/impossible without some interesting hardware hacks. reason being, the 2732 PROM that the calibration resides in only contains calibration and sometimes a small amount of code. the rest of the code is stored elsewhere on a ROM in the ECM. i can think of at least one person who was successful in removing the ROM portion of the ECM and had everything stored on a single PROM where code could be changed if desired.... but i think it is a fairly involved process if i'm remembering it correctly.

Quote:

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Originally Posted by RobertISaar

DO NOT DO THIS!

the table's values are interpolated, so if there were a value of 0 in the 6400 row, starting at 6025RPM, that would be used in proportion to RPM, causing the engine to start shooting VERY lean after 6000.

being a C3 ECM, patching the code to add in a rev limiter(assuming there isn't one already) will be difficult/impossible without some interesting hardware hacks. reason being, the 2732 PROM that the calibration resides in only contains calibration and sometimes a small amount of code. the rest of the code is stored elsewhere on a ROM in the ECM. i can think of at least one person who was successful in removing the ROM portion of the ECM and had everything stored on a single PROM where code could be changed if desired.... but i think it is a fairly involved process if i'm remembering it correctly.

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I appreciate the insight to my stupid question, haha!

It seems as if a lot of the knowledge on these ECU's is scattered throughout the internet, and not just in one place. The day everyone learned about them, I must have been "out of town" :doh: It was difficult to even find information like what a Mask is, how to use Tuner Pro, etc. I would pay money to read a book on the basics of the GM ECU's! Any leads? I guess I'm just spoiled by the customization and documentation you get from building Megasquirt systems. These GM ECU's sure are more robust, though.

Anyhow, sounds like i'll just have to tell him no on the rev limiter, and if he really want's one, to add a MSD box.

So, on the newer ECU's then, the actual computing code is found on the PROM as well as the tables, etc? I'm guessing that's how Code 59 could be created...

All the best
Eric,

Just a second thought, is there a newer ECM you can think of off hand, that I would be able to use with his TBI harness, but with a much better code base, larger tables, etc?

The MSD box is probably the best choice for this situation as it cuts spark.

There is a fairly easy upgrade to better PCM 16197427 and it has cutoff, but it is fuel. So you can go lean!

A step up from factory ECM but still uses factory ECM would be Dynamic EBL system. You'll like everything about it for this race car.
http://www.dynamicefi.com/

if i were going to stick with a C3 for whatever reason, the EBL system is certainly worth looking at.