open vs closed loop?

[mikekaz1]

curious if someone can tell me what exactly triggers the swap from open to closed loop. ive herd its, time, o2 sensors, temp sensors, a combination, it can go back and fourth.    I just never got a really straight answer and wanted to clarify. 

[fiatslug87]

PM an email address and I'll send you manuals that explain it.

From the JEEP 1991 Sequential Fuel Injection Manual:

 

[mikekaz1]

Hmm that's pretty neat. So "cruising" uses no fuel? It just spins the engine around till you hit the accelerator or 1200 rpm.

 

So it looks like on this it goes back and fourth from open and closed depending on the condition

 

I sent an email for the whole packet. But guess my real question would be... I ditched the clutch fan for a standalone electric fan with its own temp sensor. This has seemed to work very well so far. Other then the fact that my gauge temp fluctuates between 170-210*f but mostly stays closer to the 170 mark. This may be due to a stuck open t-stat as its my understanding that besides initial warm up you shouldn't necessarily drop below the predetermined temp on the t-stat. but I don't necessarily dislike this as I prefer the truck to stay cooler. But alternativey I don't want to be constantly burning rich and stuck in open loop due to improper or "toolow" coolant temps. Which is why I was curious on what exactly controls the in and out of control loops.

[cruiser54]

I have hooked my dRB up to numerous Renix rigs that were dead cold, and started them while monitoring the "open loop/closed loop" readout.

 

They go into closed loop within 30 seconds if the oxygen sensor is working. If it's not working, they never go into closed loop. 

 

The other conditions from the manual above will affect the switching from open to closed. 

[64 Cheyenne]

I have hooked my dRB up to numerous Renix rigs that were dead cold, and started them while monitoring the "open loop/closed loop" readout.

 

They go into closed loop within 30 seconds if the oxygen sensor is working. If it's not working, they never go into closed loop. 

 

The other conditions from the manual above will affect the switching from open to closed. 

 

Quick question, if a Renix stays in "open" loop because of bad o² sensor or other cause, would there be any outwardly identifiable symptoms, ie poor fuel mileage (of course, mine has), fouled/ carbon plugs, hunting or surging....?

[cruiser54]

 

I have hooked my dRB up to numerous Renix rigs that were dead cold, and started them while monitoring the "open loop/closed loop" readout.

 

They go into closed loop within 30 seconds if the oxygen sensor is working. If it's not working, they never go into closed loop. 

 

The other conditions from the manual above will affect the switching from open to closed. 

 

Quick question, if a Renix stays in "open" loop because of bad o² sensor or other cause, would there be any outwardly identifiable symptoms, ie poor fuel mileage (of course, mine has), fouled/ carbon plugs, hunting or surging....?

 

As to 02 sensor, not really. Unstable and low idle a bit with somewhat poor mileage.

 

As to other sensors, they have a bigger effect.

 

In order of highest effect to lowest effect they are MAP, CTS, IAT. These all share the same ground outlined in Tip 5 at www.cruiser54.com.

 

The highest failure in Renix O2 sensors is the heater circuit which is energized with voltage. If the heater is bad, or not getting voltage or ground, it doesn't work.

 

Try this:

Unplug the sensor. Set your meter to ohms and check continuity between the red and the black wires of the sensor pigtail. Should be about 4.2 ohms.Image Not Found  To check for power issues:

 

[HOrnbrod]

 

I have hooked my dRB up to numerous Renix rigs that were dead cold, and started them while monitoring the "open loop/closed loop" readout.

 

They go into closed loop within 30 seconds if the oxygen sensor is working. If it's not working, they never go into closed loop. 

 

The other conditions from the manual above will affect the switching from open to closed. 

 

Quick question, if a Renix stays in "open" loop because of bad o² sensor or other cause, would there be any outwardly identifiable symptoms, ie poor fuel mileage (of course, mine has), fouled/ carbon plugs, hunting or surging....?

 

 

You can install an A/F gauge, either a wide or narrow band, and watch the open-to-closed loop transition occur when starting a cold engine. It takes about 30 seconds as Cruiser says, maybe a bit longer when the ambient temp is real cold. The gauge constantly monitors the air/ fuel ratio under all driving conditions and immediately lets you know when the system has gone back to steady open loop like at WOT or when a component fails. It's a real handy tool to monitor the engine overall health.

[cruiser54]

 

 

I have hooked my dRB up to numerous Renix rigs that were dead cold, and started them while monitoring the "open loop/closed loop" readout.

 

They go into closed loop within 30 seconds if the oxygen sensor is working. If it's not working, they never go into closed loop. 

 

The other conditions from the manual above will affect the switching from open to closed. 

 

Quick question, if a Renix stays in "open" loop because of bad o² sensor or other cause, would there be any outwardly identifiable symptoms, ie poor fuel mileage (of course, mine has), fouled/ carbon plugs, hunting or surging....?

 

 

You can install an A/F gauge, either a wide or narrow band, and watch the open-to-closed loop transition occur when starting a cold engine. It takes about 30 seconds as Cruiser says, maybe a bit longer when the ambient temp is real cold. The gauge constantly monitors the air/ fuel ratio under all driving conditions and immediately lets you know when the system has gone back to steady open loop like at WOT or when a component fails. It's a real handy tool to monitor the engine overall health.

 

Don, does your 92 go into closed loop real fast also? 

[HOrnbrod]

Don, does your 92 go into closed loop real fast also?

Yes, 30 seconds to a minute max depending on the ambient temperature.

[mikekaz1]

Ah OK. So a low coolant temp won't have very much input into this process?

[cruiser54]

Ah OK. So a low coolant temp won't have very much input into this process?

Hard to say, but probably not. 

[jpdriver1]

do not wish to hijack thread = is there a way to use the diagnostic connectors? thanks 

[cruiser54]

do not wish to hijack thread = is there a way to use the diagnostic connectors? thanks 

Yes. If you have the DRBII or an MT2500, they have plugs for the connectors.

 

But, technically you can use those connectors with your meter to some extent, providing Tips 1 through 5 have been completed so you get accurate readings. .

[dustyinthedirt]

isnt Comanche club great? so much knowledge being shared!  :bowdown:

[mikekaz1]

PM an email address and I'll send you manuals that explain it.

From the JEEP 1991 Sequential Fuel Injection Manual:

 

 

again, thanks for those documents.

 

so after some browsing and reading, from what I have understood... 

 

the computer uses MAP, coolant temp, intake temp, exhaust o2, crank position(speed), battery voltage, (maybe some other variables?)

 

the HOs will go back and fourth between open and closed at various times depending on sensor signals and driving conditions.

 

open loop is determined by MAP, crank(speed), intake temp and coolant temp (cold curve?).

closed loop is determined by "sufficient operating temperatures and a idle or cruise condition."  using open loop as a base but using the o2 sensors as the primary modifier.

 

the coolant temp sensor constantly monitors "exact" temp but basically gets divided into two categories. cold curve and hot curve. in which cold curve (presumably openloop) looks at temps up to ~125*f and hot curve(presumably closed loop) looks at temps above that ~125*f. 

 

I couldn't find any "proper" air temp requirements for closed loop.

 

MAP sensor looks for high pressure/low vacuum for idle/cruise(closed loop)  and low pressure/high vacuum for WOT  (open loop)

 

low voltage conditions the computer will  increase the injector "on time" to adjust for reduced fuel flow caused by low voltage(low fuel pressure?)

 

 

-so from my understanding as long as your engine operates above 125*f, air temp is "proper", and you are at a idle/cruise speed,  you will (be able to) go into  proper closed loop operation. 

[mikekaz1]

not on the jeep but in my work van, I have an aftermarket gauge cluster and  I did some testing.    I found, in terms of WOT and throttle position,  it would go from closed to open at ~75% throttle.  it also would kick into open on deceleration if I was over 1200rpm and under around 3MAP ( 3map -14.7AP=  -11.7psi?)