Just in quick review.
I have a 91 GMC truck, 7.4L, Auto, TBI, and it uses the 7060 PCM.

Other then some exhaust work, and removing the intake choke point it's completely stock. And being a tow vehicle I keeping it that way, but just for the exercise have been tuning it to get the best possible drivibility and MPG.

In oem form the VE table was into the ninties, and in general not even close to what the engine wanted. So with the WB (with the PCM in Open Loop) I've been gradually going thru the table and getting things real darned close. One thing I had played with some was the BPC to drop the table vales into the 80s which seems to be alot closer to what the true VEs are. So the original 132 BPC has grown to 160.

And there was also some work done on the spark tables, but nothing radical there.

So as it turns out, we had things pretty sweet.

But, it was Open Loop. And like they say, an O2 sensor is a terrible thing to waste.

So I set the BL, and Int limits to 128, lowered the C/L temp thershold back to a resonable number, and disabled the code 44 and 45.

How what I'm working on is being able to set the coolant temp as low as possible, and then set the BL and Int limits with JUST enough range to allow the engine to transistion from cold to closed loop with as much accuracy as possible. It seems that you have to run on the rich side to keep the drivibility, as the engine warms up, maybe with a little correction by being in C/L just that much earlier it will get that extra .002 MPG increase.

Just a share in case anyone else is looking for a tuning idea to play with.

 

I tried moving the BL and Int limits around some. With the large BPC, it no longer takes alot of BL change to get to stoich.. So I have the BL+Int., limits set at 122, and high of 132.

Also decayed out the choke a little faster.
At 23dF, and with a 30 sec warm-up the drivibility is just as good as at 190dF. And about the time the decay runs out the O2 is hot and we're in closed loop in what looks to be a little over a minute.

Oh and as not to get the ecm mad, disabled codes 44 and 45.

 

002 MPG increase

to get that much increase you could have added a 1/2 pound of air increase to your tires or took a healthy crap before you leave the house

 

Look at the application again. And if you read up on the various threads about it, it went from 9 MPH to 13+. That's about 50%. It's attention to detail that does pays off.

Excuse me for ignoring the tolling.

 

So.. relatively no difference between closed loop and open loop operation? That's a nice tune you've got going there

 

Bingo.
30 secs or so of running, and things are just as nice as being at 190.
And with the large incremential changes with slight BL changes now, allows it to instantly zero in on being right.

 

Grumpy I have a question . I have a 1227747 ecm and I have been tuning it in open loop and have it pretty close . When I set it to go into closed loop it runs pretty rotten and the blms are high something like 140s to 150s. Is there a setting in tunercat that i could change to bring the blms in line or will it require retuning the ve tables. Also i would like to know if there is a setting that would shift the mixture in closed loop from 14.7 to say 13.5,I realize these are just calculated values but if I want it to run fatter is there a setting that would allow this.You mentioned narrowing the blm setting low and high what effect does that have ,does it hold it to a tighter setting or limit its range of control.

 

As you may recall, closed loop toggles the AFR to average 14.7. So some of the time is lean of 14.7 and some richer then 14.7.

You might look at the O2 limit voltages, and cut down how much the ecm actually toggles things.

I also went to a larger BPC, and then limited the ranges of the BL and Int..

Yes, you can move the commanded AFR around, but it's a combination of things to do that. Just about a must to have a WB when trying that stuff.

 

I managed to bring down the block learn values by going up on fuel table two. You mentioned the bpc ,if i understand it correctly then the larger the number for example 160 = less fuel
the smaller the number for example 120 = more fuel.

Thank you for your help.

 

sorry, total noob, but whats the difference between closed and open loop? open is when the engine has just started up and is getting up to operating temp? and closed is when its at 190*?

-chuck