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Old 04-28-2009, 10:23 PM   #1
keautocenter
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Question Open loop all the time???

I have a 02 SL1 that I have modified for fuel economy. The best I have ever gotten on the highway is 52.4 MPG at 59 MPH WITHOUT HHO running. Today a friend of mine let me use his ScanGauge II. I plugged it in and set it up and then went for a drive with it. What I am baffled by is that it stayed in open loop the whole time I was driving it, which was about 1 hour.

Here are the things I have modified. 1. O2 sensor with an EFIE set to put out .950 volts. 2. MAP sensor controller. 3. Fuel pre-heater heating the fuel to about 180 degrees. 4. IAT sensor repositioned to put out 132 degree reading. 5. Hot air intake without IAT sensor. 6. HHO unit putting out about 4 liters per minute.

Here are some other readings I spotted tonight while going 55 to 60 MPH. 1. Timing advance was 31 to 33. 2. Water temp was 195. 3. MAP was 8 to 10.

The car ran just fine tonight and I have never had a check engine light come on, unless I set the O2 sensor over 1 volt. As you can imagine, I am down on power some.

Here are my questions. Is there any obvious reason why it did not go into closed loop? Maybe IAT temp? Could I obtain better fuel economy if it were in the closed loop? At 50+ MPG Im OK with it being in closed loop mode. However, Id like to get even better MPG if possible!

Any advice would be helpful! Thank you!
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Old 04-28-2009, 10:34 PM   #2
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Default Re: Open loop all the time???

In open loop your O2 sensor is doing Nothing regarding fuel. Fuel is calculated off the MAP, IAT, and ECTS only. It will only go into closed loop when certain parameters are met. Use the search button to find those parameters. I forget
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Old 04-28-2009, 11:07 PM   #3
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Default Re: Open loop all the time???

Disconnect your EFIE and reinstall the O2 sensor. You have this on the front O2 sensor? Drive the car and see if you go to closed loop.
If you have this on the front O2 sensor I am surprised that you've not gotten a code for running rich.
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Old 04-28-2009, 11:37 PM   #4
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Default Re: Open loop all the time???

First off the mileage is impressive, more so for staying in open loop all the time. With the mods you have going it may be best to try unplugging one by one replaceing with the origional part (if you still have it)in place and take a drive with a scan tool to see if it goes into closed loop. I would start with the o2 sensor, the fixed voltage may make it think the O2 sensor isnt warmed up yet and not trusting it. The lack of engine light makes this more interesting cause if the car dosent throw a code for a fixed voltage reading for the O2 sensor. This could partly explain the reasion why the bosh sensors give bad milage cause the ECM only seems to throw a code when it gets a reading out of expected range. But the devices you seem to have in place of sensors sound like resistors in place of the sensor and you found the happy medium of what it seems to like for whaere you live. I dont see this working as well where I live where it goes from -50C to +45C.

Good luck
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Old 04-29-2009, 12:16 AM   #5
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Default Re: Open loop all the time???

The PCM wants to see the output from the O2 sensor varying as load, throttle position etc.. change. My bet is that is why it is staying in open loop. Its "waiting" for the O2 sensor output to vary. I think this is what Ssicarman thinks you will discover if you hook it back up in stock configuration.
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Old 04-29-2009, 12:28 AM   #6
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Default Re: Open loop all the time???

Quote:
Originally Posted by wolfman View Post
The PCM wants to see the output from the O2 sensor varying as load, throttle position etc.. change. My bet is that is why it is staying in open loop. Its "waiting" for the O2 sensor output to vary. I think this is what Ssicarman thinks you will discover if you hook it back up in stock configuration.
Thats a good point. The Front o2 puts out a sinusoidal voltage. If you have a DC voltage coming from it, then it wont go into closed loop since it thinks the front o2 is not ready.
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Old 04-29-2009, 12:37 AM   #7
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Default Re: Open loop all the time???

Quote:
Originally Posted by keautocenter View Post
I have a 02 SL1 that I have modified for fuel economy. The best I have ever gotten on the highway is 52.4 MPG at 59 MPH WITHOUT HHO running. Today a friend of mine let me use his ScanGauge II. I plugged it in and set it up and then went for a drive with it. What I am baffled by is that it stayed in open loop the whole time I was driving it, which was about 1 hour.

Here are the things I have modified. 1. O2 sensor with an EFIE set to put out .950 volts. 2. MAP sensor controller. 3. Fuel pre-heater heating the fuel to about 180 degrees. 4. IAT sensor repositioned to put out 132 degree reading. 5. Hot air intake without IAT sensor. 6. HHO unit putting out about 4 liters per minute.

Here are some other readings I spotted tonight while going 55 to 60 MPH. 1. Timing advance was 31 to 33. 2. Water temp was 195. 3. MAP was 8 to 10.

The car ran just fine tonight and I have never had a check engine light come on, unless I set the O2 sensor over 1 volt. As you can imagine, I am down on power some.

Here are my questions. Is there any obvious reason why it did not go into closed loop? Maybe IAT temp? Could I obtain better fuel economy if it were in the closed loop? At 50+ MPG Im OK with it being in closed loop mode. However, Id like to get even better MPG if possible!

Any advice would be helpful! Thank you!
I'd be interested in knowing your driving habits personally. Your FE is dramatically increased or decreased by that. I hypermile in a 95 Mazda MX-6 5-speed and on a 12.5 tank I can easily get upwards of 80+/gal just by changing the driving habits. Bear in mind, the mazda has been modified for the highest FE possible.

Doing things like FAS and D-FAS, pulse and glide (engine braking) where legal, not using the AC and DWL can easily bump your overall FE up several notches. Using the scangauge is the key to target which techniques deliver your best overall FE. Sorry for the semi thread hijack.
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Old 04-29-2009, 08:00 AM   #8
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Default Re: Open loop all the time???

You're on your own as most here don't or won't follow up on your many mods to achieving high mileage. You'd have to answer whether or not the iat sensor is needed as another input for the PCM to decide when to switch from open loop to closed loop. It may be a key to your dilemma.

Whether or not achieving higher mileage results in staying in open loop or not is another question you'll be answering yourself as you continue with hypermiling techniques. Most don't have a clue about the various sensors and their interaction affecting open or closed loop operation and you'd have to read as much if not more to see the correlation of each sensor affecting EFI operation.

One possible misconception is with the O2 sensor where everyone insists that the O2 output vary before the PCM will see it as an input. I tend to think that the PCM will see the O2 sensor when other sensor inputs meets minimums that the PCM needs before it uses the O2 sensor, switching to closed loop mode. In electronic terms this would be described as AND GATES; all inputs must be made before an output is sent. In this case the various sensors are inputs including the O2 sensor but the O2 takes time to heat up to the minimum 600F temperature before it can be used as in input signal. Until the O2 sensor gets to operating temps we're in open loop. Once it reaches operating temperatures it doesn't matter that the signal varies as its at operating temperatures where its performing its job outputting signals according to exhaust make up. The other signals must be at certain levels including the O2 output before the PCM switches from open loop to closed loop. The AND GATE inputs have been met and now outputs a signal for closed loop operation. The signal is for emissions control data gathering for federal emission standards. This is a rough outline of my interpretation of what goes on from open loop operation to closed loop. Understanding all the little details will give a better overall picture of EFI systems. The more you know.......
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Old 04-29-2009, 02:35 PM   #9
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Default Re: Open loop all the time???

UPDATE! I should have been a bit clearer about my O2 setting. I set my EFIE so that the maximum voltage is .950 volts. Meaning that as my O2 voltage fluctuates it never exceeds .950 volts. Sorry for the confusion.

I drove the car to work this morning and within 2 minutes it went into closed loop and never came out. My drive to work is about a 20 minute drive. It takes about that long for the IAT to reach 132 degrees. I will take it on a longer trip tonight to see if it goes into open loop after driving it longer.

I really appreciate the advice so far. After this mornings drive to work, I'm wondering if it was just a fluke last night.
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Old 04-29-2009, 06:45 PM   #10
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Default Re: Open loop all the time???

not sure why u want it in open loop, closed loop is where it reads all the sensors and than gives max MPG it can within its parameters.

Open loop means one of the main sensors doesn't work or the ECU doesn't like how its working and goes into default or it just shuts down the engine.

Default is where the ECU goes off factory programing so the car can run to get home or to the garage - not fuel efficient.


Oh and i know how the EFIE and map sensor enhancer works - I also run HHO - not in my saturn yet but will.
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Old 04-30-2009, 06:41 AM   #11
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Default Re: Open loop all the time???

Quote:
Originally Posted by keautocenter View Post
UPDATE! I should have been a bit clearer about my O2 setting. I set my EFIE so that the maximum voltage is .950 volts. Meaning that as my O2 voltage fluctuates it never exceeds .950 volts. Sorry for the confusion.
There's something wrong with this picture. As I recall, the higher the voltage from the O2 sensor, the more rich the PCM thinks the engine is running. Despite the mumbo jumbo that the efie's sellers claim, all an efie does is fool the PCM into thinking the engine is running rcher than it is which will cause the PCM to lean out the mix. For the efie to do that, it would have to be adding voltage not limiting it.

BTW if I were you, running that setup, I'd get a temp gauge. Running an engine leaner than designed can cause it to run hot and these cars run pretty hot to begin with.

With the way you've mucked with the sensors, I'm not surprised you aren't going into closed loop. Pull your mods and see if it goes into closed loop. Start putting them back one by one till you find the one that's causing the problem. It's probably going to be that efie.
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Old 04-30-2009, 11:33 AM   #12
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Default Re: Open loop all the time???

one more item that might help you get better FE: higher coolant temp.

You indicated a water temp of 195. Try to push it to 205. There is a small range here. If you go too high, you'll start hitting the knock limit, especially at lower speeds/higher loads.

You might be able increase the spring force of your Tstat by adding a spacer, or using a slighly stiffer spring. This should cause your regulating temperature to be higher.
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Old 09-19-2021, 05:03 PM   #13
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Default Re: Open loop all the time???

Hello, I have a 1999 SL2 that I cannot find info on the PCM pinouts. This pcm has two pink and two blue harness connectors. Problem is it is staying in open loop. I installed a new and Denso pre cat one wire O2 sensor as per the no / low activity code on the sensor. Ects is fine. I want to run a dummy line directly from the sensor to the proper pin on the ecm, but all I could find was a 3 connector pinout for a different ecm. (The three connector) Thanks in advance gentlemen. Oh, I also changed out the tstat as the engine was running excessively cool. (Around 3/16ths on the guage. Snap on MT2500 shows fluctuating voltage on post cat O2 but pre at O2 reading 489 and not fluctuating. Tested that sensor and it was fluctuating, but the scanner didn't detect it leading me to a wiring or /PCM issue.

Last edited by AXEMAN1063; 09-19-2021 at 05:11 PM.
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Old 09-19-2021, 09:19 PM   #14
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Default Re: Open loop all the time???

PCM pin-outs have certainly been posted here, but the search function for this forum sucks badly. I will try to find, but no guarantees...
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