I have a 7747 ecm, BJYM $OD in my 95 GMC Truck. I have been reading tons of threads to find my answer with no luck or consistency. My question is when tuning my (Open Throttle VE vs. MAP vs. RPM) table, what should I disable? Everything I read consistently says to disable the EGR. O.k. I got that. What else?

Thanks,

R.S.

Note: I am using TunerPro RTv5

 

You can not have $0D mask loaded in a 1227747 ECM. The 1227747 ECM was used from 87 to 92 C/K trucks (and astros and other) and used $42 mask. Your 95 truck probably has 7427 PCM which uses $0D mask (BJYM).

As for tuning disable EGR.

//RF

 

Yeah your right. Thanks for correcting me. I have another question, once VE table is correct and EGR is turned back on, is it normal for the BLM to float and move around compared to when EGR off?

 

Yes, I usually see +/- 2 points of BLM movement - considered normal without EGR and about +/- 3 to 5 points with EGR. Keep in mind that this is over wide range of operating conditions.
//RF

 

Great! thank you so much for the info.

I have read to disable the CCP, AE, PE, and others on other sites. None where consistent other than the EGR. I'm taking your word for the law of the land.

 

Hey - I am not an absolute authority on this. The only people that are authority on this were the GM development engineers which devised, built and tested these power train controllers. All we can do is marvel (or question) their work.

My copy of $0D XDF does not show CCP control - it could be incomplete. So I am curious if there is one - I'll have to check my FSM for CCP solenoid wiring. Be careful when disabling AE and PE - engines do not like to be lean at WOT. You can increase the threshold (%TPS) where PE will take place. AE is like a pump shot on a carburetor and designed to take care of sudden transients - delta TPS and delta MAP to keep engine from going lean. During these transients BLM should not change, but the integer may bounce around. If goes high - not enough fuel, and if drops a lot you may be dumping too much fuel. The best way to tune transients is with WBO (dyno is handy, but who has the money??) since NBO does not have accuracy unless AFR is around 14.7 +/- 0.2

//RF

 

I'd disable CCP for VE tuning as well as EGR. Both will affect the air/fuel mixture when active and you want your VE changes to be the only thing affecting BLMs. I'm not familiar with the $0D mask, but if it has highway fuel and highway spark modes you'll probably want to disable those too, as they lean the mixture out under steady part-throttle conditions.

I would NOT disable AE. It's too critical to engine performance. You don't want to lean-spike the engine every time you try to accelerate a little bit.

 

Thanks for the info. I appreciate it!

R.S.

 

Likewise I have never disabled AE. I did disable PE to observe BLM at high rpms but was careful to reenable later. If you are easy on pedal you can stay out of both and witness BLM at higher rpm/map.