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Recently discovered some new information regarding how the ECU's advance spark timing in relation to the EGR system. Please consider this information if you have already or are thinking about deleting the EGR system.
Disclaimer: The EGR system on the brick noses and OBD trucks is an eye sore, adds complexity to the EFI, and can be a pain to maintain and keep functioning. For those reasons, I've deleted it on my two MAF windsor projects. Bare in mind that for both projects, I utilize the Moates Quarterhorse chip, and Binary Editor software to help tune the EFI for my modifications and needs. Recently I've been researching and trying to understand timing advance and how to utilize the best timing for my 408 MAF build. In doing so, I discovered that there the OBDII ECM's reference EGR position and other EGR factors when the computer's calculate spark advance under several conditions.
Below is a base spark table the ECM references, which the values in each cell can be modified by the ECM using other factors. For my application, where EGR is deleted from the engine, AND disabled in the tune, EGR is not a factor that my ECM weighs when it calculates spark off of this table.
Below is a screenshot of the stock function "EGR Spark Adder" with a description below it. In essence, the ECM adds more spark to the base table above depending on several factors such as EGR position, airflow, load, ect.
If you have not disabled EGR function in your tune, your computer is still using this function and adding spark when the EGR is blocked off, or otherwise deleted. This added spark advance will GREATLY increase pinging under most driving conditions, less idle and WOT. I've experienced this myself on my first 302 MAF build where I deleted EGR but did not disable it in my tune. Engine sounded like popcorn under light load until I gave it throttle (which would tell the the ECM to command less or no EGR) and retard the spark.
Guys, I get it; we wish this emissions system would go away and make our engine bays alot cleaner, and have less headaches. I want us to understand the implications of just blocking off or removing the system though. I'm not 100% certain that if the EGR position sensor is unplugged, the system is disabled in the computer and spark is retarded, but in my experience, I still pinged alot prior to disabling it in the tune.
My EGR and thermactor system fell off my truck while I was driving through potholes that didnt get filled in with my tax dollars and at 12* timing I have no pinging on any fuel or under any load. 95 460 OBD1.
My '88 never pinged with it blocked off, but maybe it depends upon base timing setting, what EEC-IV is being used, and/or the combination as yours is far from stock. I have a C3W1 on that truck (yes, MAF) and it is basically a roller 302HO with an Edelbrock intake, long tubes, and 1.7:1 roller rockers. Nothing wild.
That is wild.
So at 30% load at 2000 rpm when the egr activates....it adds 38 degrees? On top of the 10 base for 48. Then add in whatever the ecm calls for for rpm based advance. You could possibly be well into the high 50 degrees. That seems excessive to me.
That is wild.
So at 30% load at 2000 rpm when the egr activates....it adds 38 degrees? On top of the 10 base for 48. Then add in whatever the ecm calls for for rpm based advance. You could possibly be well into the high 50 degrees. That seems excessive to me.
Not sure about the function adding THAT much timing, but regardless, there's a scaler function that limits max timing. On the A9L (91 mustang) it's default is 45 degrees.
Also, EGR delete will affect each modified engine differently. If it works for an individual, great. Just putting the info out there that I found.
Subscribing to this thread. Always wanted to learn more about Moates Quarterhorse. Also never realized that the ECU changed timing in relation to what it expected from the EGR.
My EGR and thermactor system were lost in a tragic boating accident a few years back, and I had to retard my base timing (which had been previously advanced) to stop pinging. I'd be willing to bet this was exactly why!
Glad to hear I can bump it back up to those previous numbers when I abandon the factory ECM in a few months in favor of a better aftermarket EFI system.
Glad to hear I can bump it back up to those previous numbers when I abandon the factory ECM in a few months in favor of a better aftermarket EFI system.
You mean..glad to know there's an aftermarket ecm available to use if/when the obsolete oem one takes a dump!
Neither of the 2 CBAZ0 strats that I use for my HUG0 ECU even have this table. It looks like it handles it with just a function instead. This may explain why some of them work fine and other not so much
Subscribing to this thread. Always wanted to learn more about Moates Quarterhorse. Also never realized that the ECU changed timing in relation to what it expected from the EGR.
It changes many things in relation to many other things. It is actually a pretty in depth setup.
