How to monitor if your in closed or open loop?

Without a scan guage hooked up on my 95 jeep cherokee is there a way to monitor open and closed loop? 95 xj 4.0 obd1

Not sure I understand the question - are you talking about the cooling system? Do you mean whether the thermostat is open? If so, that's easy, just feel the upper radiator hose, if it's hot the thermostat is open.

If you want to monitor it while driving, that's a little more difficult. If your probe lead is long enough, you could tape a temp probe on the same place, temps should indicate pretty clearly when it opens and shuts.

Doubt it, why would you want to ?

He's probably not talking about the thermostat but rather the fuel...closed or open loop....warmup mode or warm mode...

I don't think its directly proportionate to the theremostat's fully open temperature.

http://www.scangauge.com/features/

Middle column ("digital gauges"), last item.

I want one of these.

theres not a way to tell unless you have a scanner.

Usually, if the car is at operating temp, its in closed loop, unless you have a cooler thermostat

Yea I am talking about fuel mode, i am OBD1 that scan guage wont work for me thats only obd2, i wanted something on the fly that is always hooked up to monitor jeeps fuel. I do have the 195 thermostat and the adjustable fan i have coming on late around 220 or 215 so it worms up as fast as possible.

I do like that link to autospeed thats exactly what i want but not sure if they sell em.

An ECU detected failure of any of the fuel injection system sensors or actuators would probably cause the ECU to remain in open loop mode, and also turn on your check engine light, which is the tip off.

What I want is a way to know if I'm in open loop mode on my Renix XJ that doesn't have a check engine light.

Will the idle drop when you switch from closed to open? It may just be the newer models, but for a while after a cold start my jeep idles noticably higher, but after it warms up a bit drops back down to normal. :dunno:

http://www.obd2.com/
http://www.amazon.com/gp/product/B000FJQWS0

The "Loop" means a Feedback Loop in the ECU system, it is just the O2 sensor providing feedback on the A/F ratio to the ECU. The switching O2 sensor only supplies accurate information about when the A/F ratio pass's 14.7:1 (going either direction) and only when the O2 sensor reaches operating temp. Thats it.

Open Loop means the ECU is NOT monitoring the O2 sensor, in most systems it goes off stored tables of data on how much fuel to inject based on variables like rpm, ambient air pressure and temp, engine temp, engine load/throttle position, etc. Often, the ECU stores correction factors for those tables, based off what it has learned while operating in Closed Loop with the O2 sensor.

Closed Loop means the ECU is monitoring the O2 sensor, in most systems it still goes off stored tables of data on how much fuel to inject based on the variables, but the ECU then looks at the feedback from O2 sensor to see what the actual A/F ratio is, and then apply a correction to get it back in. Usually the ECU will store that correction in a table based on the variables, so that it will apply the same correction the next time the engine encounters the same conditions. This is often caused the LEARN MODE, in most systems the ECU is always in the learn mode, when people talk about the learn mode, they are usually referring to the quick learn mode. The quick learn mode is simply the table of corrections being cleared (either by a scan tool or disconnecting battery power to dump the memory) and the ECU simply sees bigger correction factors, meaning it stores new values into the table faster.

Obviously, the Feedback Loop or O2 sensor is valuable data, you'd want it all the time if you could so why would you ever want to go out of "Closed Loop"? You'd want to go out of closed loop and into "Open Loop" when the feedback loop or O2 sensor data is unreliable or unnecessary. Since the simple switching (a.k.a. Narrow Band O2 Sensor) only can detect passing through an A/F ratio of 14.7:1, then when you want a different A/F ratio, you can't use the Feedback Loop or O2 sensor. E.G. when the motor is warming up or you're at Wide Open Throttle (WOT), the A/F ratio has to be richer than 14.7:1, thus you go into open loop mode. When the O2 sensor is not up at operating temp or is malfunctioning, you'll go into Open Loop Mode, this will vary from system to system how the ECU determines this and goes into open loop. Often its a set time after start up or an engine temp, some may have a sensor or sense current draw on the heater on the O2 sensor, as well, for malfunction, it depends on the ECU Built In Test (BIT).

A cold engine not only needs a richer A/F ratio, it needs a faster idle to prevent stalling out, the old carb motors did this also. So a motors idle dropping down during warm up probably is a built in function of the engine temp by the ECU, NOT an indication the ECU has gone into Closed Loop Mode.

Other than looking up some specs on your particular EFI system, such as temps, etc, when the system switches, you just have to guess based on how the system operates, whether it is in Open or Closed Loop. You can get one of those scan tools, linked above, or an A/F gauge. The gauge just taps off the feed from the O2 sensor, even that won't tell you if the ECU is in Open or Closed Loop, but it will be a more accurate guess, because you'll see the output of the O2 sensor and if its NOT switching back and forth quickly between just richer/leaner than 14.7:1, then most likely the ECU is NOT in closed Loop.

More expensive vehicles with more sophisticated EFI systems may use "Wide Band O2 Sensors" which can sense the actual A/F Ratio Accurately in a band that the engine actually operates. These Wide Band O2 Sensors also have built in heater to get up to temp right away, in these systems, you'll operate in the Closed Loop Mode almost all the time.

I have OBD1 since i am a 95 xj, do you know of a obd1 site for a cable to connect to a labtop ortuning device

So here's a question - would there be a fuel economy advantage to tricking the computer into going into closed loop mode earlier than normal? Possibly by faking the voltage it gets from the ECU temp sender when actually warm. What would be the disadvantages to that? Higher levels of pollutants?

sjkimmel99 said:

So here's a question - would there be a fuel economy advantage to tricking the computer into going into closed loop mode earlier than normal? Possibly by faking the voltage it gets from the ECU temp sender when actually warm. What would be the disadvantages to that? Higher levels of pollutants?

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Highly, Highly Unlikely. Remember the manufacturer wants the engine to get as much fuel mileage as possible also. OEM setup the ECU to go into Open Loop only when necessary, either because the O2 sensor is unreliable or the engine needs a richer than 14.7:1 A/F ratio. Remember, the narrow band O2 sensor can only tell the ECU when its "passing" through the 14.7:1, it can tell it anything else reliably about the A/F ratio.

If you trick the ECU into going into Closed Loop early, e.g. warm up, the A/F ratio would be leaner than needed and you'll likely suffer poor drive-ability and stalling out. At WOT, you'll get less power, detonation and probably damage the engine. When the O2 sensor is NOT fully warmed up, you'll probably get erroneous readings and really screwed up A/F ratios, resulting in poor mileage, poor drive-ability, stalling or engine damage, if NOT all four. NOT to mention, since the ECU is always "LEARNING", i.e. storing correction factors from the feedback from the O2 sensor, you'd likely suffer poor performance and mileage in the regular Closed Loop Mode due to bad data being stored while you tricked the ECU into closed loop mode when it should have been in open loop.

95cherjustin said:

I have OBD1 since i am a 95 xj, do you know of a obd1 site for a cable to connect to a labtop ortuning device

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Do some research, you might have OBDII or a hybrid of OBD1 & II. 1996 M/Y is only the date the government mandated that all manufacturers had to switch to OBDII. The standard had been out for years, and the manufacturers began implementing it before 1996 M/Y. Chrysler, which was using its EFI system in Jeep by 1995 had started to use OBDII features in their ECU's before 1996.

I don't know about the XJ in particular, but research the different options for scan tools out there, a lot of OBDII readers can also read OBDI or at least read cars of certain makes, models, years before OBDII was mandated (because those makes/models/years had implemented OBDII features a little earlier).

Okay where is your OBD connector on your jeep i cant find one ill take photos

You can use an analog volt meter, high impedance version, wired to read the voltage across the O2 sensor(s), to detect open loop and closed loop operation.

I may take pics of under my dash i cant find a connecter anywhere i know what obd2 looks like, alll that is next to the ecu is a l shaped connector off the wiring harness on the drivers side fender

Rick Anderson said:

Highly, Highly Unlikely. Remember the manufacturer wants the engine to get as much fuel mileage as possible also. OEM setup the ECU to go into Open Loop only when necessary, either because the O2 sensor is unreliable or the engine needs a richer than 14.7:1 A/F ratio. Remember, the narrow band O2 sensor can only tell the ECU when its "passing" through the 14.7:1, it can tell it anything else reliably about the A/F ratio.

If you trick the ECU into going into Closed Loop early, e.g. warm up, the A/F ratio would be leaner than needed and you'll likely suffer poor drive-ability and stalling out. At WOT, you'll get less power, detonation and probably damage the engine. When the O2 sensor is NOT fully warmed up, you'll probably get erroneous readings and really screwed up A/F ratios, resulting in poor mileage, poor drive-ability, stalling or engine damage, if NOT all four. NOT to mention, since the ECU is always "LEARNING", i.e. storing correction factors from the feedback from the O2 sensor, you'd likely suffer poor performance and mileage in the regular Closed Loop Mode due to bad data being stored while you tricked the ECU into closed loop mode when it should have been in open loop.

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The manufacturer cares about fuel mileage, but you can be sure it's not at the top of their list: performance, reliability, cost, and a host of other issues matter a lot more to them than mpg.

As for "tricking" the ECU into closed-loop, I think it's safe to say that it's effectively impossible. The decision to run in closed or open mode involves logic checks from a variety of sensors, so you'd have to fake a whole set of conditions, not just the O2 sensor. However, as you said, there's no reason at all to attempt to fake it, and the FSM for a 1993 suggests that the OBD1 ECU stores rolling data for ~40 key cycles, so it is constantly learning, in a way.

That said, I think the original poster was just interested to see whether it was in closed or open, to use as a diagnostic check. I can't think of any good way to detect that state by monitoring the sensors, just by interfacing to the ECU. You could check the O2 sensor, which would tell you if it's running rich, but that's conditional on having a properly working sensor, and a defective one might have been the reason for an open-loop condition in the first place...