unckybob

I have a 1991 Chevy G10 Van and I thought I would optimize the PROM chip for best mileage.

I recently talked to a custom PROM programmer and he told me that if I'm interested in economy and I have a stock engine, I should go with a stock chip.

He says The design of the system makes it nearly impossible for you to adjust the fuel delivery to the engine outside of what the O2 sensor is going to want to see.

Can't the chip tell the computer to adjust the fuel delivery so that you can have any percentage of 02 in the exhaust you want? The O2 sensor is only a sensor.

Also I would think that there are other things you might try to adjust the computer for economy. What about advancing the timing, or running the transmission in a higher gear.

He also says that if you run things outside the stock settings you run a risk of damaging the engine. That makes sense, but couldn't you monitor things like the spark plugs to see that things are going okay?

My thinking is that his market is oriented towards people with more money who are interested in getting performance and aren't afraid of damaging their engines. I think he may be afraid that I'd damage the engine and get mad at him.

Also, he probably has more experience with getting performance out of an engine. He may have little experience getting economy out of an engine and he might be more likely to get me in trouble.

I'm a mechanical engineer and I've worked on many vehicles in my life. I know when you change these things you're taking a chance. But still I'd like to experiment with this. I realise this could damage the vehicle and am willing to take responsibility for my actions.

I'm just getting started in this. I'd appreciate a second opinion.

Do I have a chance at getting better mileage out of my vehicle with PROM programming?

Six_Shooter

iTrader: (2)

There's always room for improvement, even with a stock engine.

unckybob

Can you tell me if the PROM can be set to adjust fuel delivery for a desired level of O2 in the exhaust?

DENN_SHAH

iTrader: (1)

you can indeed gain some fuel mileage with an optimized tune.
there is usually some performance gains too.

even without knock, you can have too much timing which can hurt both performance and fuel mileage.
during cruise, you can lean the fuel out with hiway mode/lean cruise which is already in some chips, but just turned off from the factory.
most stock motors can easily run at 16.0:1, some even leaner.
if im not working on my tune, hiway mode is turned on. i've put well over 100k on my motor running at 15.7 and leaner on the hiway.

doing a search for Grumpy and reading all of his tuning articles is a good start.
you can also search for hiway mode, highway mode, and lean cruise.

when its time for a new motor, using nothing more than a vortec (96~02) short block will yield very noticeable performance and fuel mileage gains.
for more performance, a search for the user Fast355 will turn up some good engine options.
he has one of those driveable brick walls too.

unckybob

Thanks for all the advice.

It definitely looks like I should go on then.

Before going on all the searches you recommended. I'm thinking it would be good to learn more about the capabilities of PROM programming. I'm thinking of reading through:

https://www.thirdgen.org/promintro

and through this:

https://www.thirdgen.org/forums/diy-...uide-book.html.

I found a page on my particular chip:

http://www.diy-efi.org/gmecm/ecm_info/1227747/

And I thought I would work towards getting to the point where I could edit the ASDU PROM image.

Does that sound like a good way to go?

Also, you said, "if im not working on my tune, hiway mode is turned on". Do you have some way of adjusting your PROM while the vehicle is running?

Ronny

iTrader: (1)

Like DennShaw said.

Use hyway mode for economy. If you go too lean you will see surging and increased oil temps. Also your emmisions will increase(NO?).

Bring in deaccelaeration fuel cut off sooner(MPH). Too soon annd engine will die at stop sign.

Tune CL is based on stoich or lambda 1.0. That is perfection. NB02 may not be perfect. A WB02 maybe closer to perfect. you would need to simulate a NB per MFG instructions with WB. Or you can use WB but not simulate but that requires appropriate definition file and possibly a diff ECU. I am not sure on that. I know EBL-ECU offers that option.

unckybob

Thanks for all the advice.

I'm sure I'll come back to that later on.

Ronny

iTrader: (1)

your def file may have hyway mode seperately for A/F as well as Spark.

RBob

iTrader: (1)

Stock '7747 doesn't have a highway lean cruise mode.

RBob.

Ronny

iTrader: (1)

Is there not a patch somewhere on this site? Hint Hint

xch3no2

Yes, the program seeks values that you can change.

Ronny

iTrader: (1)

A couple of years ago I move the rich/median/lean values up first 5% and then another 5%. I also moved the stoich value constant from 14.7 to 14.3 and then again to 14.0.

I was attempting to enrichen my CL A/F.

I was unsuccessful.

WB never changed from swinging14.8/15.1 cruising CL. Not sure why I could not enrichen. I since restored to what I believe are stock values however I kept at 14.3/1 for E10.

This season I reapproched the P gains and feel it is now much improved in all areas of fueling.

Solders18

My tune right now surges a little bit when going downhill with nearly closed throttle. If i take my foot off the gas it will go into DFCO and stop surging of course, and if it gets a little more throttle it will stop surging. Its a very small surge and usually is only going downhill. what would you suggest adjusting?

unckybob

Thanks xch3 and everyone else. I'm moving to a different thread. Hope you'll check it out.

https://www.thirdgen.org/forums/diy-...ml#post5247074

EagleMark

D'oh!

https://www.thirdgen.org/forums/diy-...an-cruise.html

Fast355

iTrader: (2)

5% voltage increase is not enough to really notice. I wanted to richen my stock closed loop fueling and increased the values up to that of a stock L98 Corvette and my closed loop fueling richened dramatically, up to the 14.5-14.7 swing I was looking for. With the Tri-Ys my closed loop fueling was in the 15.1-15.5:1 range.

xch3no2

Yes, I certainly made significant changes to the AFR (FAR) in closed loop.

Anyway using the NB o2 sensor in this fashion can be problematic unless you understand that it is just not very accurate when used far from it's designed operating parameters.

Or to say, I don't think I would be as successful setting CL o2 voltages without the WB to check it with.