To disable EGR in the 747, the Enable Temp (address 1B3) should be set to 00 not FF (255). I did some testing with a vacuum guage installed in place of the EGR valve. THe first run was a stock bin. Vacuum showed and the engine rattled like 3 marbles in a can. 2nd test I set the Enable Temp to 00; no vacuum on the guage and the engine ran MUCH better. 3rd test I set Enable Temp to 255. Same result as first test. I suspect the other ECM's are the same however, I haven't tested them so YMMV.

During my first test, I tried like mad to get a code 32 but it never happened. I was quite surprised since the bin was stock and the EGR valve disconnected.

 

YEah, I tried it at 255, too, and after a while on a drive, the EGR just starts working again. I can shut the car off, restart and the EGR is off again for a while but starts up again in like 10-15 minutes??? Weird!!! Wonder why 00 works instead of higher numbers???


EDIT: Oops, sorry. Didn't do that but moved the VSS limits to high/unatainable amounts like 240 and 245 for low and high off/on limits and the EGR STILL WENT on as described above. Whaaassssup??? I couldn't find a "test" that would turn EGR on if the VSS limits were not reached??? Confused.



[This message has been edited by FastBroker (edited March 08, 2001).]

 

It just one of the things that makes absolute statements impossible about GM ecms. Thou that mask is the only one *so far* that I know did that.

 

Almost always never a good idea to set anything in a GM file to 00 or FF as sometimes it causes code jumps. The 7747 EGR temp enable is actually inverted and the lower the hex number the higher the temp enable...I gotta equation around here somewhere but you guys get the point. If I remember correctly the 870(85tpi) computer has some inverted stuff as well.
-Carl

 

What I did to get rid of my EGR problems/corrections is to change all the PERCENT EGR vs LOAD vs RPM values to 0%, set the EGR CORRECTION vs LOAD vs EGR DC table to 0 as well and then (most important?) set the EGR %VE Correction vs AF vs EGR DC table to 92.4, which is the "standard" non-EGR BPW multiplier which means that I am running on the Main VE table only (my VE table #2 is set to 0's) and will never have a fuel correction for any EGR signal. Seems to work quite well. Also, EGR spark at set to 0deg everywhere...

I just say this because it would have been easier for me to set the EGR enable temp to "00" instead... Is what I am doing ok???

 

Verified it again this weekend and what I did seems to work ok (EGR function not adjusting VE) but have to keep tuning for the new cam in there.

Question: Would I be better off (ie, ECU be "happier", engine run "better") by setting the EGR ENABLE temp to "00" instead of doing all the table changes that I did to stop EGR operation???