Topic: 22re closed loop vs open loop.......

[emsvitil]

I'm going to get around to installing a vacuum gauge....  (watch it for better gas mileage)

I was wondering at what vacuum level the ECU goes out of closed-loop mode and goes into open-loop for power enrichment so I can try to avoid open-loop mode?

Or inversely,  how fast can I accelerate before it goes into open-loop mode.....   

[Fearless-Yota]

the computer goes in and out of closed loop due to the O2 senor activity. The O2 works strictly off of heat. Later model  vehicles has O2 heaters to keep the car in closed loop. Closed loop should be your best bet for fuel milage as the computer makes fuel trim adjustments off of ECT, MAF, O2, and TPS. Open loop the computer ignores most of those

[Fearless-Yota]

Vacum has nothing to do with it. Strictly O2 senor activity

[brainlessfool]

and eng. temp.

[JamesD]

Computer uses engine temp to determine when going from open to closed loop if everything else is working properly. Just install your vacuum gauge and go from there.

James

[BigMike]

emsvitil,

What would be far more useful than the vacuum gauge would be a fuel mixture gauge.

I run an ooooolllllllllllllllllllllllllllddddddddddd  SplitSecond ARM1 Air/Fuel meter found at the following address:
http://www.splitsec.com/products/airfuelmeter.htm
It is very small, like only 2-1/4" wide by 3/4" tall, and is light enough to be mounted to a dash pad with velcro.


I've ran this meter for many, many years on my MR2 with the stock '87 4A-GE engine and with my '91 JDM 4A-GZE engine, and it is currently operating on my '95 3RZ-FE in my truck.

When I have my OBD-II scanner plugged in to my laptop and monitoring my fuel mileage, I can watch my split second gauge above go from rich-to-lean-to-rich-to-lean-to-rich-to-lean... and I'll be making 19-21 miles per gallon at the scanner screen (cruising at normal loads under a closed ecu loop).

Then when I slowly begin rolling into the throttle, I'll see my fuel mileage drop to about 17-18 mpg --the gauge still going lean-to-rich-to-lean-- and then all of a sudden, the split second gauge will go straight to full rich and my mileage will instantaneously drop to 12-13 mpg.

So when I check my mpg, if I averaged down like 17 or 18, then I must have been heavy on the throttle. But if I average upwards to 20-21 mpg, then I must have been driving like a grandma -- one who keeps the ecu in a closed loop.

I also have a vacuum gauge hooked up in my truck, and I do NOT use it for fuel mileage considerations. I use it for engine load considerations.

BigMike

[emsvitil [OP]]

Well,  I have a vacuum gauge which I got on a clearance sale, can't use a scanguage because it's not OBDII, and don't have the money for a A/F meter...............

Just wanted to try to use what I've got...............

[emsvitil [OP]]

Actually, BigMike you may be able to answer the question even though you don't have a 22re......

When the mileage drops and the A/F meter pegs,  what's the vacuum gauge read?

[BigMike]

In general, this will vary between engine to engine mainly based nominal power output, load or drag of vehicle, and valve overlapping (camshaft(s)).

Specifically speaking for my engine, recalling from memory as best as possible, if I am running through the gears accelerating from a green light, then it will go open loop at 5 pounds vacuum and less. If I am cruising on the freeway, then it will go open loop in 5th gear on a flat road with no headwind if the vacuum drops below about 12 pounds. In 3rd and 4th gears, depending on the rpm (higher rpms develop more vacuum with decreased throttle), it will go open loop more towards 8 pounds and below.

Cruising on the freeway in 5th at 70 mph, my gauge reads 15-16 pounds vacuum. So I have about 3 to 4 pounds of vacuum to "play with" if you will, before it hits open loop.

And when I say "pounds vacuum", I am referring to millimeters of mercury vacuum

[emsvitil [OP]]

Weird about 5th being different....

How does it know it's in 5th?

Wonder if it's more a function of the TPS........


thanks

[BigMike]

No, no, the thing is about engine load.

In the figures above, 5th gear is assuming freeway speed, or about 70 mph. And there is far more of a load (wind resistance, rolling friction, losses) at 70 than compared to say 30 mph in 3rd gear. Also, I am more likely to be above 2,800 rpm in 3rd gear than compared to that in 5th gear at freeway speeds, which means I am more into my power band in the lower gears (power band of my 3RZ kicks in hard around 3,100 rpm).

More power + less load/resistance = less load on engine = longer stay in the closed loop

[emsvitil [OP]]

Temporarily mounted the gauge (used one of those big black paper clips) without lighting......   

Doesn't take much throttle to get it down to 0.    And just a slight change in foot pressure to keep it above 10.   

Might have something here to improve mileage   


BTW,  there's another check connector in the engine compartment that's useful.    Single wire, round connector with rubber cap on it.    It's in the same vicinity as the 2 that are plugged into the fender.       It's a direct line to the O2 sensor.   So you can use a digital voltmeter as a cheap A/F meter for temp testing.     Readings jump all over the place when in closed loop mode, but become steady and high when in open loop......

With the voltmeter, I should be able to see under what conditions it goes into open loop, and the corresponding vacuum level....... 
 

[KDXSR5]

Keep us informed, I am interested.

[emsvitil [OP]]

Well so far, a vacuum gauge on a 22re seems to react like an on/off either/or switch.......

Doesn't take much throttle to zero out the gauge.   (little 4-banger moving 2 tons around)


As the EFI system doesn't use a MAP sensor, I think the decision to goto power mode is based more on the TPS.........

I'm breadboarding an  A/F meter with odds and ends I already have , plus some cheap pieces from Radio Shack to learn more........