Vacuum Gauge experiment help

[skewbe]

My hypothesis was that once trained on pulsing and gliding, that one could focus on the accelerating portion with something like a vacuum gauge, or an enrichment detector and not require a scangauge like computer.

So far i've managed about 67.25 MPG after 129 miles. That is with holding the vacuum at 6 in-hg while accelerating, same shift points as before, and lots of eoc gliding. I can do 70+ with noticably more throttle and the scangauge, so I must be losing a lot across the throttle plate.

Does anyone have a metro fuel-psi map diagram or otherwise experience with using vacuum gauges to optimize the acceleration phase that can get me on the right track?

[mrmad]

I can't help you with a Metro, but here's a stock Civic VX's fuel map table. Hope it helps. The #'s in the tables are injector duty cycle

[CoyoteX]

When I had the stock computer in mine I had a wideband o2 and it would go rich at 5 inches vacuum. So as long as it was over 5 it was trying to maintain 14.7:1

My car had lots of mods at the time so it never was able to make it to 14:7 but it was obvious when I looked at the voltage on the o2 it would go real rich when it dropped under 5 in. It was pretty uniform across the rpm range, at least as far as I went with it. So if you keep it at 6 or higher you should be in good shape

Another great advantage to a vacuum gauge is you can easily tell the health of the engine. The smoother the needle at speed and at idle the better the engine is running. A perfectly running engine will have a smooth needle at idle and at all constant speed/load running. With the new computer in mine the needle is almost dead smooth but I have a vacuum leak somewhere making it bounce slightly ~.1 in at a constant 60mph. I always use a vacuum gauge to help tune and diagnose a car, even a obd2 car

[skewbe]

Very cool chart mrmad, it doesn't look like the VX ever does a lot of "enriching". Thanks for the tips coyote.

Ok, I've been more agressive on the throttle/vacuum (like ~ 2") and the past 320 miles have resulted in 63MPG. I've got an el-cheapo mixture gauge en-route, will see if that helps.

I might just have to install that PC in the metro But the responsiveness of the analog gauge is real nice compared to the scangauge or the diy mpg gauge.

[Telco]

For general reference, GM vehicles usually go open loop at about 75-80 percent throttle. You might install a voltmeter on the TPS, find out what the voltage reading is at WOT vs idle, and calculate what the 75 percent point would be. Once you have that, don't let the throttle move beyond the 75 percent point. GM TPS voltages run anywhere from 0.5v - 1v to 4.5v - 5v, and every one is a little different requiring a TPS learn when the TPS is replaced. This is a linear operation, so if your TPS reads from 0.8v to 4.8v, 75 percent throttle would be 3.8v. With a 0-5v gauge in the dash wired in to the path, you'd know where max closed loop throttle is.

The only thing I'm not sure about is how well it would work to tap a voltmeter onto a reference voltage like this, since a voltmeter is a pack of resistors. Since it would effectively change the resistance on the circuit, it might interfere with operation, but I'm sure there is a way to do it. My circuitry knowledge is a bit dated as I've not had to mess with circuitry at the component level since the 1980s.

[ZugyNA]

I've been testing monitoring the O2 sensor using a digital multimeter* while watching a vac gauge at the same time.

* less voltage reduction than analog...I use 10ths reading to keep it simple...pickup O2 reading somewhere on O2 wire that isn't shielded

While I don't have a realtime mpg readout....I'm assuming that MORE closed loop (O2 cycling) = greater mpg than running in open loop.

With a 4x4 4 cylinder (' 86 Nissan TBI)...I notice the relationship between O2 cycling...vacuum...throttle position...and rpms.

* O2 cycling and vacuum are highly correlated feedbacks?

* throttle position and rpms are related to the previous 2 in that......to see the higher vac and O2 cycling...many times I need to drop into a lower gear and into higher rpms....allowing less throttle position...and sometimes being able to accelerate or go up a slight grade and still see O2 cycling.

* when cruising at say 55 mph...at times it is necessary to drop into 4th to continue to see O2 cycling...wind or a hill

* this engine will go into open loop with a vac reading of around 10 or 12" hg.

* put in a new O2...and it now cycles more often...$20 cost

* in winter and for short periods in warm weather...alum foil covering this unheated O2 sensor should allow it to cycle more often?

* could be that short shifting...where you just use maybe 1/3 throttle...lower rpms... and open loop to get up to speed would be more efficient?

* once I get a few bugs worked out of the ECU sensor system...I'll test an EFIE.

[skewbe]

Originally Posted by ZugyNA

...
* O2 cycling and vacuum are highly correlated feedbacks?

I noticed that too when I had the scangauge, it would go open loop with not much throttle at low rpm. Which coincides with Coyotes car going into enrichment @ 5". The fuel maps I've seen are MAP based too.

Originally Posted by ZugyNA

...
* could be that short shifting...where you just use maybe 1/3 throttle...lower rpms... and open loop to get up to speed would be more efficient?

My first vacuum test was ~68mpg, that was keeping it about 6", this one had a lot more time around ~2-3" and was 63mpg. With the scangauge I get ~72mpg and that is with it on an average reading for the current drive, no realtime acceleration feedback, but better results, and my butt-o-meter remembers accelerating faster than 6" of vacuum produces

With the scangauge, I would basically "set" the throttle to about 2/3 and focus on the glide portion. Which kinda coincides with what telco said, though I thought best mpg was a lot more complicated than that.

[ZugyNA]

I'm not really into pulse and glide with this truck. Just trying to drive "normally" ...but in the most efficient way.

Sort of doubt that I'll be able to stay in closed loop getting up to speed in day to day driving. So I'll be using 1/3 throttle or so to get up to speed and then use 4th and 5th to stay in closed loop most of the time.

Not sure why this 4x4 goes into open loop at so high a vac reading...early TBI setup? 4x4 transfer case and wind drag?

Might still have a few sensors that aren't feeding the right data. TPS is just an on/off switch right above idle...manual trans.

[skewbe]

Update:
Man, my $8 Fuel Air gage arrived, it is CHEEE ZEE I was suprised at how slow the computer cycles the mixture, like once a second at idle.

I'm going to borrow the scangauge back from the Mrs. for a bit to help sort things out. It looks like it doesn't go into open loop until about 2", which is about where the FA gauge stays on the rich side.

I'm totally confused How the hell do I take this info and figure out the best way to accelerate? I think I just ignore the FA gauge, and do some experiments with the vacuum gauge and the scangauge and try accelerating at different vacuum levels and see what happens.

[ZugyNA]

Originally Posted by skewbe

I'm going to borrow the scangauge back from the Mrs. for a bit to help sort things out. It looks like it doesn't go into open loop until about 2", which is about where the FA gauge stays on the rich side.

I'm totally confused How the hell do I take this info and figure out the best way to accelerate?

If it takes 2" hg to go into open loop...then you should be able to stay in closed loop under most situations?

Use lowest LOD or highest MPG?