Vacuum Gauge experiment help

[Telco]

If there was a way for you to look at the control maps, you should be able to figure out what the relevant numbers are on vacuum vs RPM vs open/closed loop. I can see the computer going open loop on acceleration from a lower start RPM sooner, it would depend on how fast the computer can analyze and adjust the mix. From a lower speed and a lower gear, engine RPM will increase faster than at highway speeds, and during initial manufacturer testing if the computer could not handle a closed loop acceleration without knocking or going overlean, they would have programmed the computer to go to an open loop condition based on engine RPM vs TPS. Newer cars with faster computers should be able to manage this, and stay closed loop longer. Cars with wideband O2s, near as I can tell, are able to stay closed loop even at WOT since the sensor can tell the computer what the actual mix is, so the computer can make sure it doesn't lean out and torch the pistons.

ZugyNA, TPS is not an on-off switch, it is a potentiometer which should have a linear resistance reading. The linear resistance level is what tells the computer how much throttle is present. If your is just showing on-off, then either your manufacturer has a different means of measuring throttle input, your TPS is defective or you're not actually looking at the TPS.

[skewbe]

I've been experimenting, and I'm convinced that there is NOT a simple formula to determine most fuel efficient acceleration with a vacuum gauge in the real world. You throw in a hill or a breeze and the whole equation changes.

Some observations (mpg figures not to be taken literally, sample not controlled):

At 10" vacuum, I HAD to increase throttle to make it up the smallest hills, and was driving down them instead of EOCing to get back to a reasonable speed. 65.4mpg

At WOT (Wide Open Throttle) had the most EOC time, was able to focus on the shift points better, 68.9mpg

6" was a little slow, 67.25mpg, glide time suffered.

2-3" was decent acceleration and glides but was 63mpg.

Side note, ever since focusing on my acceleration so much, I forgot how to get 72 mpg, LOL.

[ZugyNA]

Originally Posted by Telco

ZugyNA, TPS is not an on-off switch, it is a potentiometer which should have a linear resistance reading. The linear resistance level is what tells the computer how much throttle is present. If your is just showing on-off, then either your manufacturer has a different means of measuring throttle input, your TPS is defective or you're not actually looking at the TPS.

In this case...an '86 Nissan engine with early TBI...with the manual trans it is an on/off switch...switches right above idle. The auto does have a carbon track potentiometer.

I haven't figured out all the input sensors yet...but there might not be even a manifold vac signal to the ECU. Havng trouble getting repair info for this TBI system.

[ZugyNA]

Originally Posted by skewbe

I've been experimenting, and I'm convinced that there is NOT a simple formula to determine most fuel efficient acceleration with a vacuum gauge in the real world. You throw in a hill or a breeze and the whole equation changes.

Some observations (mpg figures not to be taken literally, sample not controlled):

At 10" vacuum, I HAD to increase throttle to make it up the smallest hills, and was driving down them instead of EOCing to get back to a reasonable speed. 65.4mpg

At WOT (Wide Open Throttle) had the most EOC time, was able to focus on the shift points better, 68.9mpg

6" was a little slow, 67.25mpg, glide time suffered.

2-3" was decent acceleration and glides but was 63mpg.

Side note, ever since focusing on my acceleration so much, I forgot how to get 72 mpg, LOL.

Very interesting that at least in this series...WOT.... open loop and no vac reading got you the best mpg. Guess you were attempting to P&G with all these?

So...the way I drive...it would be best to just get up it speed reasonably fast and then concentrate on keeping it in closed loop.

72 is just a dream to me...most are getting 20 mixed with this truck...I'm managing 22...hoping for 23 soon with no dragging brakes and new O2.

You CAN increase your vac level at the same TP by shifting down a gear....question being...would this help mpg? This also decreases LOAD (LOD). Should increase MPG?