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Steve M. Samba Member
Joined: July 30, 2013 Posts: 6798 Location: Fort Lauderdale, Fl.
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Posted: Fri Sep 24, 2021 6:06 pm Post subject: 2.1 WBX RPM surging - Diagnosing with the new "WBX Emulator" |
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So I have had this problem with gas mileage dropping off about 4 miles a gallon and the engine is just jumping up and down a few hundred RPM.
I did the Digifant diagnosis and did not see any smoking gun to isolate the source. It is not a leaking injector and all the other readings were in spec.
So now with the most excellent "WBX Emulator" by DigiMatrix I was watching the "Real Time Data" display and on that it has the O2 Sensor display with 3 ranges of LEAN, Rich and the one in the middle is the Goldilocks setting I assume of "just right". I say that because I never saw it.
My O2 sensor was jumping from Lean to RICH constantly without stopping and it was doing it at all RPM ranges from Idle to 4000RPM.
Also on the same "Real Time Data" display there is the 2nd line from the bottom that says "Fuel"
This says "Start" or "Run" depending on which is active.
Mine was jumping back and forth between START & RUN.
So I'm now wondering what the relation is with the O2 sensor? Obviously the fuel flow is going up and down, but what is causing this?
My TP WOT setting was not showing a response either when I put the pedal all the way to the floor just sitting there with the ignition on and the engine not running. The TP Idle Setting is working just fine. I'm not worried about the WOT right now because the only time I'm at full throttle was checking it out today.
Seems to me what ever is causing this could be the solution to my problem.
So any good thoughts on where this might lead me to fixing the idle surge?
Let me just add that I did do a Injector spray and leak test,
Temp 2 sensor was showing within the parameter ranges when the problem started.
All the vacuum lines were good, but I did change some of the tubing connections at the vacuum ports anyway just to have new ones on them.
I'm going to run through the DigiFant Diagnosis again to compare readings I got from the last time I did it. _________________ This free advice is worth exactly what you paid for it.
There are seven days in a week. Someday is not one of them. |
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Wildthings Samba Member
Joined: March 13, 2005 Posts: 50255
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Posted: Fri Sep 24, 2021 7:28 pm Post subject: Re: 2.1 WBX RPM surging - Diagnosing with the new "WBX Emulator" |
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How old it your O2 sensor? Their response time slows as they age. |
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natejohn Samba Member
Joined: February 20, 2020 Posts: 57 Location: Vancouver, BC
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Posted: Fri Sep 24, 2021 7:59 pm Post subject: Re: 2.1 WBX RPM surging - Diagnosing with the new "WBX Emulator" |
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Having never had the ability to view real time data like this to diagnose, I think we're going to be breaking all kinds of new ground when we start discussing problems with our engines and following up with readings from the ECU. Very exciting. I think it's going to take some time to build a knowledge base of what things should and should not be reading and displaying. _________________ 1990 Vanagon Westfalia |
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Steve M. Samba Member
Joined: July 30, 2013 Posts: 6798 Location: Fort Lauderdale, Fl.
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Posted: Fri Sep 24, 2021 8:15 pm Post subject: Re: 2.1 WBX RPM surging - Diagnosing with the new "WBX Emulator" |
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Wildthings wrote: |
How old it your O2 sensor? Their response time slows as they age. |
Replaced it with a new one when I did the DigiFant testing. _________________ This free advice is worth exactly what you paid for it.
There are seven days in a week. Someday is not one of them. |
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Steve M. Samba Member
Joined: July 30, 2013 Posts: 6798 Location: Fort Lauderdale, Fl.
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Posted: Fri Sep 24, 2021 8:17 pm Post subject: Re: 2.1 WBX RPM surging - Diagnosing with the new "WBX Emulator" |
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natejohn wrote: |
Having never had the ability to view real time data like this to diagnose, I think we're going to be breaking all kinds of new ground when we start discussing problems with our engines and following up with readings from the ECU. Very exciting. I think it's going to take some time to build a knowledge base of what things should and should not be reading and displaying. |
Yes, it is going to be a new range of causes and effects shown to write down in out bibles! Actually it will not be a lot because of the knowledge base accumulated from people who know the system inside and out and are just talented with remembering what happens when inside the system. _________________ This free advice is worth exactly what you paid for it.
There are seven days in a week. Someday is not one of them.
Last edited by Steve M. on Fri Sep 24, 2021 8:28 pm; edited 1 time in total |
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ohhorob Samba Member
Joined: September 26, 2013 Posts: 212 Location: Santa Cruz
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Posted: Fri Sep 24, 2021 8:24 pm Post subject: Re: 2.1 WBX RPM surging - Diagnosing with the new "WBX Emulator" |
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Here's my basic understanding and would be happy to be corrected–
The lambda control of the fuel injection isn't chasing a perfect "goldilocks" (or stoichiometric) air-fuel combustion ratio. Instead, it's trying to swing between a narrow range rich and lean, either side of stoichiometric. I believe one main reason for this is to keep the chemistry in the catalytic converter functioning correctly. (I'm probably forgetting other reasons)
Quote: |
My O2 sensor was jumping from Lean to RICH constantly without stopping and it was doing it at all RPM ranges from Idle to 4000RPM. |
So that is what I expect. When I've monitored my Digijet controlled Fuel Injection while driving, the Air-Fuel Ratio and injector pulse width is swinging lean to rich and back again. I'll dig out an old capture file to see what the typical timing of that is.. something around a second or two from memory.
On regular cheap O2 sensors, they are very sensitive to that narrow band either side of stoichiometric and saturate their reading quickly and are (almost?) impossible to balance in the middle. Wideband O2 sensors are different and emit a wider range of readings that don't suddenly flip from lean to rich or vice-versa.
(Edited to add this link which mostly matches my description– https://www.hondata.com/tech-closed-loop-oxygen-sensors) _________________ "Gundy" - '85 Westfalia
GoWesty 2300cc, Digijet |
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Steve M. Samba Member
Joined: July 30, 2013 Posts: 6798 Location: Fort Lauderdale, Fl.
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Posted: Fri Sep 24, 2021 8:53 pm Post subject: Re: 2.1 WBX RPM surging - Diagnosing with the new "WBX Emulator" |
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ohhorob wrote: |
Here's my basic understanding and would be happy to be corrected–
The lambda control of the fuel injection isn't chasing a perfect "goldilocks" (or stoichiometric) air-fuel combustion ratio. Instead, it's trying to swing between a narrow range rich and lean, either side of stoichiometric. I believe one main reason for this is to keep the chemistry in the catalytic converter functioning correctly. (I'm probably forgetting other reasons)
Quote: |
My O2 sensor was jumping from Lean to RICH constantly without stopping and it was doing it at all RPM ranges from Idle to 4000RPM. |
So that is what I expect. When I've monitored my Digijet controlled Fuel Injection while driving, the Air-Fuel Ratio and injector pulse width is swinging lean to rich and back again. I'll dig out an old capture file to see what the typical timing of that is.. something around a second or two from memory.
On regular cheap O2 sensors, they are very sensitive to that narrow band either side of stoichiometric and saturate their reading quickly and are (almost?) impossible to balance in the middle. Wideband O2 sensors are different and emit a wider range of readings that don't suddenly flip from lean to rich or vice-versa.
(Edited to add this link which mostly matches my description– https://www.hondata.com/tech-closed-loop-oxygen-sensors) |
Well that does sound very accurate for what it is doing.
The O2 sensor I put on was a Bosch and came from Van Cafe and had all the wires so not sure if that compares with a less expensive one where you need to modify the wiring to make work. _________________ This free advice is worth exactly what you paid for it.
There are seven days in a week. Someday is not one of them. |
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DanHoug Samba Member
Joined: December 05, 2016 Posts: 4715 Location: Bemidji, MN
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Posted: Sat Sep 25, 2021 6:00 am Post subject: Re: 2.1 WBX RPM surging - Diagnosing with the new "WBX Emulator" |
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here's a decent article on O2 sensor operation..
https://www.aa1car.com/library/o2sensor.htm
notice on the "Oxygen Sensor Switching Voltage" that at the 14.7:1 mix ratio the *slightest* change in A/F ratio will shoot the voltage high or low, no realistic middle ground. that's okay, the ECU trims the fuel back and forth like a Honey Badger-- it don't care. _________________ -dan
60% of what you find on the internet is wrong, including this post.
'87 Westy & '89 Westy both 2.1 4spd
Past projects can be found at--
www.thefixitworkshop.com |
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Yellow Rabbit Samba Member
Joined: August 31, 2005 Posts: 1145
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Posted: Sat Sep 25, 2021 7:19 am Post subject: Re: 2.1 WBX RPM surging - Diagnosing with the new "WBX Emulator" |
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Steve M. wrote: |
My TP WOT setting was not showing a response either when I put the pedal all the way to the floor just sitting there with the ignition on and the engine not running. The TP Idle Setting is working just fine. I'm not worried about the WOT right now because the only time I'm at full throttle was checking it out today.
Seems to me what ever is causing this could be the solution to my problem. |
Check your throttle cable adjustment. If it’s too loose the wide open switch won’t engage. |
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djkeev Samba Moderator
Joined: September 30, 2007 Posts: 32432 Location: Reading Pennsylvania
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Posted: Sat Sep 25, 2021 8:00 am Post subject: Re: 2.1 WBX RPM surging - Diagnosing with the new "WBX Emulator" |
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Yellow Rabbit wrote: |
Steve M. wrote: |
My TP WOT setting was not showing a response either when I put the pedal all the way to the floor just sitting there with the ignition on and the engine not running. The TP Idle Setting is working just fine. I'm not worried about the WOT right now because the only time I'm at full throttle was checking it out today.
Seems to me what ever is causing this could be the solution to my problem. |
Check your throttle cable adjustment. If it’s too loose the wide open switch won’t engage. |
I know what Steve is saying, my driving habits are such that a Wide Open throttle is not a frequent occurrence.
Even on a long up hill pull, I'm not beating the engine for another horse.
I just go with the flow..... which is sometimes slow,
Dave _________________ Stop Dead Photo Links how to post photos
Ghia
http://www.thesamba.com/vw/forum/viewtopic.php?t=392473
Vanagon
http://www.thesamba.com/vw/forum/viewtopic.php?p=6315537#6315537
Beetle
https://www.thesamba.com/vw/forum/viewtopic.php?t=482968&highlight=74+super+vert |
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Steve M. Samba Member
Joined: July 30, 2013 Posts: 6798 Location: Fort Lauderdale, Fl.
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Posted: Sat Sep 25, 2021 8:23 am Post subject: Re: 2.1 WBX RPM surging - Diagnosing with the new "WBX Emulator" |
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Yellow Rabbit wrote: |
Steve M. wrote: |
My TP WOT setting was not showing a response either when I put the pedal all the way to the floor just sitting there with the ignition on and the engine not running. The TP Idle Setting is working just fine. I'm not worried about the WOT right now because the only time I'm at full throttle was checking it out today.
Seems to me what ever is causing this could be the solution to my problem. |
Check your throttle cable adjustment. If it’s too loose the wide open switch won’t engage. |
It's not loose 😁 _________________ This free advice is worth exactly what you paid for it.
There are seven days in a week. Someday is not one of them. |
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natejohn Samba Member
Joined: February 20, 2020 Posts: 57 Location: Vancouver, BC
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Posted: Sat Sep 25, 2021 8:37 am Post subject: Re: 2.1 WBX RPM surging - Diagnosing with the new "WBX Emulator" |
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ohhorob wrote: |
Here's my basic understanding and would be happy to be corrected–
The lambda control of the fuel injection isn't chasing a perfect "goldilocks" (or stoichiometric) air-fuel combustion ratio. Instead, it's trying to swing between a narrow range rich and lean, either side of stoichiometric. I believe one main reason for this is to keep the chemistry in the catalytic converter functioning correctly. (I'm probably forgetting other reasons) |
This sounds pretty correct to me. I work on LPG powered forklifts that will show the same "bounce" from rich to lean as they're running. _________________ 1990 Vanagon Westfalia |
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zoti Samba Member
Joined: December 26, 2007 Posts: 2039 Location: Plano, TX USA
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Posted: Sat Sep 25, 2021 9:22 am Post subject: Re: 2.1 WBX RPM surging - Diagnosing with the new "WBX Emulator" |
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I doubt the O2 is the reason for the surge.
Assuming no vacuum leaks, throttle body in good condition and everything adjusted correctly then it's probably the Idle control unit or valve. |
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DigiMatrix Samba Member
Joined: April 20, 2010 Posts: 449 Location: Up North Canada
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Posted: Sat Sep 25, 2021 10:26 am Post subject: Re: 2.1 WBX RPM surging - Diagnosing with the new "WBX Emulator" |
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Perfectly normal not to see Stoich. The swing from rich to lean is normal. The time spent at stoich passing from rich to lean is so short you don't always see it. If your idle throttle switch is working at idle I would be looking at idle contol module or ISV as mentioned above. I need to spend more time on the run/start fuel flag. It may be resetting in the code each loop, and because of that, not showing what I expected. My expectation was to show "start fuel" when starting and "run fuel" when running. It seems the flag is resetting. I will be fine tuning the adx file as more details are ironed out. I started sending out that flag to get the Hall sensor feedback. I tried to show some of the other bits of that flag at the same time, but as I said so may have unexpected results. _________________ _________________
'91 Syncro Westfalia
soon to be 2.5 liter stroker WBX 10:1 comp
Digifant ECU with knock sensor and custom
cylinder selective knock control by me |
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natejohn Samba Member
Joined: February 20, 2020 Posts: 57 Location: Vancouver, BC
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Posted: Sat Sep 25, 2021 10:46 am Post subject: Re: 2.1 WBX RPM surging - Diagnosing with the new "WBX Emulator" |
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DigiMatrix wrote: |
Perfectly normal not to see Stoich. The swing from rich to lean is normal. The time spent at stoich passing from rich to lean is so short you don't always see it. If your idle throttle switch is working at idle I would be looking at idle contol module or ISV as mentioned above. I need to spend more time on the run/start fuel flag. It may be resetting in the code each loop, and because of that, not showing what I expected. My expectation was to show "start fuel" when starting and "run fuel" when running. It seems the flag is resetting. I will be fine tuning the adx file as more details are ironed out. I started sending out that flag to get the Hall sensor feedback. I tried to show some of the other bits of that flag at the same time, but as I said so may have unexpected results. |
Have you created any sort of baseline map of what a proper running engine should be showing? Some specs to shoot for? _________________ 1990 Vanagon Westfalia |
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DigiMatrix Samba Member
Joined: April 20, 2010 Posts: 449 Location: Up North Canada
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Posted: Sat Sep 25, 2021 1:08 pm Post subject: Re: 2.1 WBX RPM surging - Diagnosing with the new "WBX Emulator" |
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I haven't created any baseline, but I have recorded my engine warming up, transitioning from open to closed loop and showing the proportioal and integral gain adjusting for the feedback from the O2 sensor. In my case, I have the Marco Mansi injectors and 1.25:1 ratio rockers, so the adjustment is quite a bit. I haven't compared to anything else because no one else had these until recently. _________________ _________________
'91 Syncro Westfalia
soon to be 2.5 liter stroker WBX 10:1 comp
Digifant ECU with knock sensor and custom
cylinder selective knock control by me |
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zoti Samba Member
Joined: December 26, 2007 Posts: 2039 Location: Plano, TX USA
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Posted: Sat Sep 25, 2021 9:31 pm Post subject: Re: 2.1 WBX RPM surging - Diagnosing with the new "WBX Emulator" |
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Did you try disconnecting the ISV? |
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Steve M. Samba Member
Joined: July 30, 2013 Posts: 6798 Location: Fort Lauderdale, Fl.
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Posted: Sun Sep 26, 2021 4:03 am Post subject: Re: 2.1 WBX RPM surging - Diagnosing with the new "WBX Emulator" |
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zoti wrote: |
I doubt the O2 is the reason for the surge.
Assuming no vacuum leaks, throttle body in good condition and everything adjusted correctly then it's probably the Idle control unit or valve. |
I don't think it is either. Just seeing it for the first time on the Emulator going Lean/Rich was a new thing for me. The explanations given here validate it is operating as it should.
I am interested in why the "Fuel" is showing it flipping "Start/Run" after the engine is running. _________________ This free advice is worth exactly what you paid for it.
There are seven days in a week. Someday is not one of them. |
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DigiMatrix Samba Member
Joined: April 20, 2010 Posts: 449 Location: Up North Canada
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Posted: Sun Sep 26, 2021 7:37 am Post subject: Re: 2.1 WBX RPM surging - Diagnosing with the new "WBX Emulator" |
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Steve M. wrote: |
I am interested in why the "Fuel" is showing it flipping "Start/Run" after the engine is running. |
I'll spend time using my simulator program to understand that flag more completely and I will post the results here. _________________ _________________
'91 Syncro Westfalia
soon to be 2.5 liter stroker WBX 10:1 comp
Digifant ECU with knock sensor and custom
cylinder selective knock control by me |
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DigiMatrix Samba Member
Joined: April 20, 2010 Posts: 449 Location: Up North Canada
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Posted: Sun Sep 26, 2021 7:37 am Post subject: Re: 2.1 WBX RPM surging - Diagnosing with the new "WBX Emulator" |
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Steve M. wrote: |
I am interested in why the "Fuel" is showing it flipping "Start/Run" after the engine is running. |
I'll spend time using my simulator program to understand that flag more completely and I will post the results here. _________________ _________________
'91 Syncro Westfalia
soon to be 2.5 liter stroker WBX 10:1 comp
Digifant ECU with knock sensor and custom
cylinder selective knock control by me |
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