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  #1  
Old 10-22-2012, 12:48 PM
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Open Loop

Since I made one thread today, I figured why not ask my other question too!

Anyways here it goes. I was kind of afraid to admit but I may have made a mistake when doing my exhaust, hopefully not, but I'll get your guys opinions.

I purchased a scangauge II which reads tons of things from the OBDII port. One of them is if the truck is running in open or closed loop. The gauge always read open loop when I set it to read which mode it is in.

The thing is, I don't know exactly what would cause it. I know many people say the get 2-3 mpg gain from headers, y-pipe, 3in pipes etc from the stock exhaust which is what I did. However, I am getting roughly the same mileage with the new setup (and I drive it much easier than I did before too which was pretty light. People always pass me because of how light I am on the pedal). I believe this is because of the open loop mode.

Now where I may have made a mistake.. I tried to model my exhaust off of what others have done with the 96 bronco but there aren't too many 'walkthroughs' on the complete setup for a 96.

What I did was go with the Bassani headers, then the Bassani Y-pipe with the O2 sensor bungs welded as high up on the y pipe as I can get them, then have the y-pipe go to a single hi-flow Bassani cat. The third o2 sensor is right behind that, and the muffler and tailpipe follow. What I think MAY be an issue is where I have the air pump tubing. I have that coming BEFORE the cat, and I know with the stock setup, it was in between both cats next to the third o2 sensor.

Here is a very high quality diagram I spent hours on:


Would that be causing my Bronco to run in open loop if the air going to the air pump has not been through the cat? If so, would anyone recommend getting an air-pump delete kit? I don't really like taking anything off I don't need to, but I think it would be easier to delete the air pump then take my truck to a shop to have them re-weld the tubing hose and move it, then get more hi temperature hosing to stretch behind the cat.

If that wouldn't cause being stuck in open loop, what are other things I can check to get it back to going into closed loop? Temperature sensors? Possible exhaust leaks?
 
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Old 10-22-2012, 05:12 PM
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The air injection is there to increase the oxygen level in the exhaust gasses as they enter the cat. This helps the OEM catalytic converter reach the necessary temperature to actually do its job and burn off excess crud. With that said, I know the Bassani Y-pipe with the cat in it has the air injection port in the same location as OEM which is upstream of the cat. I've not actually worked on a 96 so I don't know where the air injection hits the exhaust in stock configuration. But air injection to the exhaust pipe is always done upstream of the cat to help the cat, NOT to alter HEGO sensor readings. What I DO know is that the Bassani cat DOES need the air injection to function just like the OEM setup so what you have pictured there is correct.

There are a number of factors that must fall into place before the system will drop into closed loop operation and regardless of what folks may try to tell you, the determination is made wholly by the computer and will ONLY occur once it is determined that ALL adaptive mode parameters have been met. Since you made recent changes to the exhaust system, the computer is most likely still "learning" the parameters. Closed loop will NOT engage until all thermal sensors are within normal op. temp. range (but thats a huge range) and O2 sensor readings ALL fall within specific ranges. Thermal sensors are polled by the computer first then, the O2 sensors. Since the adaptive control parameters are used by the computer to "write" the closed loop information tables, the adaptive parameters are in constant fluctuation and therefore pinpointing the exact point or criteria that the computer will drop into closed loop is all but impossible. It was once thought that closed loop would absolutely engage at certain temperatures and this has been dis-proven since closed loop has been shown to drop in as low as 140 F or as high as 190 F. It depends on what the computer wrote into the closed loop operation tables during adaptive control operation.
 
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Old 10-22-2012, 08:07 PM
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Thank you for the reply, it is a huge relief knowing my exhaust is set up correctly then.

It has been about 4 months since I put the new exhaust in, do you think that the computer would still be learning the new setup in that time?

If that has been more than enough time for the computer to relearn then:

I know a lot of people say oxygen sensors are often to blame for open loop, but I replaced all 3 sensors when I put the exhaust on too. I don't have any engine codes coming up either so I wouldn't think the sensors are bad, however, I have heard that the heater (or something like that) on the o2 sensors may not be working correctly and not throw codes, but make it stuck in open loop.

If not the o2 sensors, then I have heard also that the coolant temperature sensors could cause this too. Are there two different coolant temperature sensors in these trucks? The reason I'm asking is because my digital gauge (which reads from the OBDII port) usually stays between 180-210 (I adjusted my fan so it only goes up to about 195 now) but it would increase at a seemingly normal rate. My mechanical temperature gauge seems to jump up and down pretty sporadically on occasion. I don't know if those gauges are just garbage, or its getting a coolant reading from a different sensor that may be going bad.

Otherwise, if the computer may still be relearning the parameters for closed loop, is there anything I can do to help it out, or will it just take some patience on my part?
 
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Old 10-23-2012, 01:44 AM
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No, you are right, the computer should "relearn" everything within about the first day of driving assuming you cover the broadest spectrum of driving styles and conditions.

The ACT and ECT sensors are both thermal sensors and as such operate within a range of temperatures that the computer reads as "within acceptable parameters". The problem occurs when one of these sensors gets "stuck" at a low or a high temperature. It may still be "within acceptable parameters" (so no fault Codes) but if the sensor is "telling" the computer that the engine is warmed up when its still cold or vice-versa, you are going to have issues related to this condition. Typically a "stuck cold" condition will cause the kinds of fuel economy "losses" you are seeing. Basically, since the computer is being told that the engine hasn't fully warmed up yet, the computer is dumping more fuel into the system than necessary even after the engine has warmed up. Since the truck starts just fine this way, the only way to tell is with the loss of fuel economy and maybe fouled plugs if the condition is bad enough. A "stuck hot" condition typically manifests with a good deal of hard starting because if the computer "thinks" the engine is already warmed up and its NOT, the computer will lean out the fuel mixture making cold starts difficult. If you want more info, run a search on the ECT. I've posted the temperature range chart no less than a half-dozen times in the past. I think it was b4hntn who actually "baked" (yep, in the oven) his ECT and ACT sensors just to verify that they were changing resistance values in accordance with the chart.

HEGO (O2) sensors, as long as they are clean, connected and not much farther away from their OEM locations, should be fine. Little known fact, O2 sensors MUST be clean and clear of debris and dirt on the OUTSIDE as well as the tip that extends into the exhaust stream. I can explain why but its tedious and complicated. It suffices to say that making certain the O2 sensors are clear of debris and dirt on the outside of the exhaust will help to preserve their lifespan. DO NOT PAINT OR SEAL THE BODY OF THE SENSOR!
 
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Old 10-23-2012, 09:27 PM
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Okay so it could be possible that one of the sensors is stuck then. I did find your chart and copied it for my own reference. Unfortunately, I don't have a voltmeter yet so I can't read the values on the sensors until I get one (which will probably be soon since I always seem to need one).

One question though, if the gauges read normal operating temperature (both the mechanical gauge and the scangauge hooked to the OBD2 port), could the sensor still have the possibility of being bad? The gauges' temperatures don't seem to be stuck, but I don't know if that necessarily means the ACT or ECT sensor could still be reading a stuck cold condition.

I will check the prices of the voltmeters and see if I can get one soon. Otherwise I may just replace both sensors because they don't seem to be too expensive.
 
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Old 10-24-2012, 12:13 AM
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Neither the ECT nor the ACT feed information to the dashboard gauges. The engine temp sensor for the temp gauge in the dash is a completely separate device. So don't assume that because the dashboard gauge reads "normal" that everything is. Your scangauge reader is reading the information that is being fed to the computer so, inaccurate info coming in from the sensors is inaccurate into the scangauge reader as well.
 
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Old 10-24-2012, 06:22 PM
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Oh okay. I'm still learning a lot about the electronics/sensors but I will get the hang of it hopefully soon. I really appreciate the help you've been giving me too.

I went out and bought a multimeter today for $25 (didn't realize they were so cheap) to test the resistances of the sensors. I don't know if I'm just being dumb and can't get the multimeter to work correctly, but I'm not getting a reading from the ACT sensor.

I unplugged the sensor, set the multimeter to 2k ohms setting (and then 200 and 20k), and probed both connections of the sensor and nothing comes up on the screen. I've only used a multimeter a handful of times in circuits labs and don't really remember exactly how to use them, but I did mess around with spare light-bulbs I had in the truck and they gave resistance values when I probed them.

The ACT sensor should provide a reading of approximately 24.27k ohms if its in the mid 80s if I probe both connections with the ohm meter correct (according to this chart I found online Fuel Injection Technical Library Air Charge Temperature (ACT), I left the other chart you posted on my girlfriends computer and not mine)? If for some reason it has infinite resistance like the ohm meter is proposing, then I assume an engine code would be thrown correct?


Edit: Well I must not know how to properly use the multimeter.. With the engine on and the scangauge plugged into the obd2 port, I decided to unplug the ACT sensor and see what the intake air temperature read then. With it unplugged, it reads -40. With it plugged in, it was reading around 87 (when its about 81 out here so that seems about right for the engine bay with the hood open). I still can't get a resistance reading from the multimeter with the method I said but the scangauge is getting info from that sensor.

With the ECT sensor located about the thermostat, the scangauge was reading a value (around 150 when I checked when it was warming up) so I unplugged it and tried to read the resistance with the multimeter there too. I didn't get a reading from the multimeter, but the scangauge read -40 for engine temperature with the sensor unplugged, and continued to give a value to about 188 when it fully warmed up and the sensor was plugged in.

Are there two ECT sensors? If so is it the sensor located close to the lower radiator hose? If so then maybe that one doesn't feed info to the gauge, but is faulty. I would try to test resistance but I don't know how to do that correctly yet... at least now with the sensors. I can test dome lights but otherwise I feel so stupid with the multimeter.

Edit 2: Okay wow I am dumb. I thought I read the resistance values wrong on the multimeter and apparently didn't try all settings even though I though I did. The ACT sensor reads 29.5k ohms inside my house around 75 degrees which seems reasonable. I bet I can get a reading from the ECT sensor about the thermostat also.
 
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Old 10-24-2012, 06:54 PM
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Alright my ECT sensor near the thermostat read roughly 3.6-3.8k ohms at 181 degrees which is also the proper range on the chart. If there is a second ECT sensor either that is the Open Loop problem or it doesn't deal with the ACT or ECT sensors.
 
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Old 10-26-2012, 05:18 PM
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I've been determined to figure this out myself, but this seems to be defeating me. If I can't get this figured out I'll have to take it to a shop.

The ECT sensor on the thermostat housing tested out good, and the ACT sensor on the filter intake tested out good also (as far as I know with the multimeter).

I couldn't test the O2 sensors with the multimeter, but I programmed the scangauge to read the first two O2 sensors (bank 1 and bank 2) and they seem to range from 0-99% (slow update speed on the gauge but it fluctuates from high to low which I believe the percentage means from .1 to .99 volts). If the voltage is fluctuating, I think this means the O2 sensors are good. Could the heaters on these O2 sensors be faulty and not throw a code but cause open loop? I bought Bosch O2 sensors because that's all Oreilly's had at the time and heard they are notorious for faulty heaters.

Maybe the MAF sensor could be causing an issue too? I don't have surging idle, but sometimes after driving a while on the highway, the Idle stays around 1000 instead of 600.

The only other sensor I think that could possibly cause open loop would be the TPS sensor. However, my idle isn't surging and there is no random bucking under acceleration (previously I did have that but I replaced plugs/idle air control valve, and cleaned throttle body and it went away).

My problem seems pretty isolated from most Broncos, especially since I have a 96 and OBD2, but if anyone may have any more advice I'd greatly appreciate it!
 
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Old 10-26-2012, 08:15 PM
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If you are still concerned about it because of 2-3 mpg, try an oil change. The Bronco is still a rolling brick. Open loop/closed loop operation is the ECM's decision entirely. If you are not seeing any fault Codes and the ECT and ACT both check out through the full engine temperature range (dead cold through op. temp.), the system is fine. Closed loop doesn't stay active and will more likely engage in "Drive" while cruising. Closed loop basically is the ECM's "auto-pilot" that engages when the ECM doesn't really have any major adjustments to make. "Open loop" is usually referred to as "Adaptive Mode" anyway. During "Closed Loop" operation the ONLY thing that the ECM does in respond to O2 sensor readings and attempt to maintain optimal stoichiometeric fuel/air ratio. There is no way to determine exactly when "closed loop" will be engaged/disengaged. Not seeing it happen doesn't mean there is something wrong.
 
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Old 10-26-2012, 09:39 PM
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Well if staying in open loop won't cause any damage then that's good. When I plug my reader into my friend's/parents vehicles, their system goes into closed loop, but when I keep it on that mode the whole time I'm driving (usually 30+ minutes), it never switches once to closed loop. I was worried that after a prolonged period of time, staying in open loop might start to be harmful to more than gas mileage.

I definitely would like to get it fixed so I can get better MPG since I do drive 50 miles a day though... but it's not the end of the world. I am about due for an oil change, but it hasn't quite been 3000k miles yet. I make sure to use full synthetic oil too to help clean things out.

I'll still keep messing around with this and post if I ever do figure anything else out, but knowing it isn't bad at all (besides gas mileage) makes me less stressed.
 
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Old 04-27-2018, 10:50 PM
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Originally Posted by Bubba Jones View Post
Well if staying in open loop won't cause any damage then that's good. When I plug my reader into my friend's/parents vehicles, their system goes into closed loop, but when I keep it on that mode the whole time I'm driving (usually 30+ minutes), it never switches once to closed loop. I was worried that after a prolonged period of time, staying in open loop might start to be harmful to more than gas mileage.

I definitely would like to get it fixed so I can get better MPG since I do drive 50 miles a day though... but it's not the end of the world. I am about due for an oil change, but it hasn't quite been 3000k miles yet. I make sure to use full synthetic oil too to help clean things out.

I'll still keep messing around with this and post if I ever do figure anything else out, but knowing it isn't bad at all (besides gas mileage) makes me less stressed.
Did you ever find the problem and get it to run in closed loop?
 
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Old 05-30-2018, 08:41 PM
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Originally Posted by Cummings Guy View Post
Did you ever find the problem and get it to run in closed loop?
I never found a definitive answer. If I recall, some more expensive scanners read that the motor went into closed loop, but my scangauge never did. I'm wondering if the scangauge wasn't reading right. The motor was in great shape when I pulled it to swap for the 7.3.
 
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