EFI Question

[Tom Lins]

Could someone explain to me why an exhaust leak could affect the reading of a O2 sensor?
I cannot picture how a leak out of a pressurized pipe could make a difference in the AFR reading inside the pipe.
Or am I not understanding something here.

--
Tom Lins
St Augustine, FL
77 GM Rear Twin, Dry Bath, 455, FI-Tech EFI, Aluminum Radiator Quad-Bag Suspension Solar Panel
Manuals on DVD
GMC Dealer Training Tapes
http://www.bdub.net/tomlins/

 

[Larry Davick]

I'm no expert but I expect that the pressurized pipe is really filled with pulses of exhaust gas pressure interspersed with pulses of vacuum. The
vacuum (less than ambient pressure) draws in outside air.

--
Larry Davick
A Mystery Machine
1976(ish) Palm Beach
Fremont, Ca
Howell EFI + EBL + Electronic Dizzy

 

[Matt Colie]

> Could someone explain to me why an exhaust leak could affect the reading of a O2 sensor?
> I cannot picture how a leak out of a pressurized pipe could make a difference in the AFR reading inside the pipe.
> Or am I not understanding something here.

> I'm no expert but I expect that the pressurized pipe is really filled with pulses of exhaust gas pressure interspersed with pulses of vacuum. The
> vacuum (less than ambient pressure) draws in outside air.

This is exactly the correct answer and it is why when running a closed loop engine in a laboratory setting, we still needed an absolutely tight
exhaust system.
Yes, even a little leak can matter.

Matt - the refugee from DynoLand
--
Matt & Mary Colie - '73 Glacier 23 - Members GMCMI, GMCGL, GMCES
Electronically Controlled Quiet Engine Cooling Fan
OE Rear Drum Brakes with Applied Control Arms
SE Michigan - Twixt A2 and Detroit

 

[Jim Hupy]

I agree. Even reversion of gasses or reverberations in sonic pulses in the
gas stream can affect the O2 sensor. Placement of it upstream or downstream
is also critical, but nowhere near as critical as an exhaust leak.
2 stroke exhaust design is almost as critical, particularly on
expansion chamber type exhausts. Pipe shapes, twists and turns, even
welding slag, pipe diameter and length also have an effect.
Jim Hupy
Salem, Oregon

On Tue, Oct 29, 2019, 1:14 PM Matt Colie via Gmclist <

> > Could someone explain to me why an exhaust leak could affect the reading
> of a O2 sensor?
> > I cannot picture how a leak out of a pressurized pipe could make a
> difference in the AFR reading inside the pipe.
> > Or am I not understanding something here.
>

> > I'm no expert but I expect that the pressurized pipe is really filled
> with pulses of exhaust gas pressure interspersed with pulses of vacuum. The
> > vacuum (less than ambient pressure) draws in outside air.
>
> This is exactly the correct answer and it is why when running a closed
> loop engine in a laboratory setting, we still needed an absolutely tight
> exhaust system.
> Yes, even a little leak can matter.
>
> Matt - the refugee from DynoLand
> --
> Matt & Mary Colie - '73 Glacier 23 - Members GMCMI, GMCGL, GMCES
> Electronically Controlled Quiet Engine Cooling Fan
> OE Rear Drum Brakes with Applied Control Arms
> SE Michigan - Twixt A2 and Detroit
>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
>

 

[jim kanomata1]

Asperaton, when moving air has lower pressure than stagnant air.
I see it in our air filter side all the time.

On Tue, Oct 29, 2019 at 1:36 PM James Hupy via Gmclist <

> I agree. Even reversion of gasses or reverberations in sonic pulses in the
> gas stream can affect the O2 sensor. Placement of it upstream or downstream
> is also critical, but nowhere near as critical as an exhaust leak.
> 2 stroke exhaust design is almost as critical, particularly on
> expansion chamber type exhausts. Pipe shapes, twists and turns, even
> welding slag, pipe diameter and length also have an effect.
> Jim Hupy
> Salem, Oregon
>
> On Tue, Oct 29, 2019, 1:14 PM Matt Colie via Gmclist <

>

> > > Could someone explain to me why an exhaust leak could affect the
> reading
> > of a O2 sensor?
> > > I cannot picture how a leak out of a pressurized pipe could make a
> > difference in the AFR reading inside the pipe.
> > > Or am I not understanding something here.
> >

> > > I'm no expert but I expect that the pressurized pipe is really filled
> > with pulses of exhaust gas pressure interspersed with pulses of vacuum.
> The
> > > vacuum (less than ambient pressure) draws in outside air.
> >
> > This is exactly the correct answer and it is why when running a closed
> > loop engine in a laboratory setting, we still needed an absolutely tight
> > exhaust system.
> > Yes, even a little leak can matter.
> >
> > Matt - the refugee from DynoLand
> > --
> > Matt & Mary Colie - '73 Glacier 23 - Members GMCMI, GMCGL, GMCES
> > Electronically Controlled Quiet Engine Cooling Fan
> > OE Rear Drum Brakes with Applied Control Arms
> > SE Michigan - Twixt A2 and Detroit
> >
> > _______________________________________________
> > GMCnet mailing list
> > Unsubscribe or Change List Options:
> > http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
> >
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
>

--
Jim Kanomata
Applied/GMC, Newark,CA
jimk
http://www.appliedgmcrvparts.com
1-800-752-7502

 

[john r. lebetski]

Because the flow in the tube is more like "- - -- " in the left bank and " -- - - " in the right bank. The low pressure gaps are pretty big where
two consecutive cylinders fire on the opposite bank in the 18436572. This can ingest outside air into the leak. False high O2 tells computer to add
fuel.
--
John Lebetski
Woodstock, IL
77 Eleganza II

 

[Jim Hupy]

This might get into reaction time for O2 sensor response to rapid
pulsations of different concentrations of air/fuel. I have not got a clue
how rapidly the sensor can read changes like we are discussing. But, I bet
Matt can shed some light on it.
I do know from 1st hand experience that when the system is in closed
loop, that very tiny changes, like a misfiring plug or an injector that
sprays odd patterns occasionally due to foreign stuff in the fuel stream,
will cause fluctuations in rpm. So, is the computer playing catch-up with
erratic information from sensors? I dunno.
Jim Hupy
Salem, Oregon

On Tue, Oct 29, 2019, 4:11 PM John R. Lebetski via Gmclist <

> Because the flow in the tube is more like "- - -- " in the left bank and
> " -- - - " in the right bank. The low pressure gaps are pretty big where
> two consecutive cylinders fire on the opposite bank in the 18436572. This
> can ingest outside air into the leak. False high O2 tells computer to add
> fuel.
> --
> John Lebetski
> Woodstock, IL
> 77 Eleganza II
>
>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
>

 

[Matt Colie]

> This might get into reaction time for O2 sensor response to rapid pulsations of different concentrations of air/fuel. I have not got a clue how
> rapidly the sensor can read changes like we are discussing. But, I bet Matt can shed some light on it.
>
> I do know from 1st hand experience that when the system is in closed loop, that very tiny changes, like a misfiring plug or an injector that
> sprays odd patterns occasionally due to foreign stuff in the fuel stream, will cause fluctuations in rpm. So, is the computer playing catch-up with
> erratic information from sensors? I dunno.
> Jim Hupy
> Salem, Oregon

Jim is very right (not any big surprise here), his experience is well founded.

Ready, Long story follows.....
The reaction time of O2 sensors is fast enough that back in the 80s, we were doing a development program for the 302. The OE was having a hard time
getting the power that they though should be there without other problems. We did a two fold distribution study. This was a study of first mixture
and then charge pressure (just after the intake closes). We could see the variations in mixture by cylinder, but even flow matched injectors could
not fix it. This lead to the charge pressure study. Because the intake is a dynamic system, it is also crankshaft speed dependent. We looked at the
maps we developed and then went back to watching the O2 signals. Things didn't make sense until we built "stereo EGO" exhaust. Then we used high
speed analysis instruments to watch both banks individually. Whoa, we could isolate the individual cylinders! This was not a passcar production ECU,
so we were able to adjust the cycle time of injectors by cylinder and then pull up to WOT and configure the individual timing to match. All this from
the output of the "stock" (no special part number) O2 sensors. We were able to map and modify the controls to the individual cylinders and not just
let the poor ones rule.

Customer was introducing a new and more capable ECU. When we passed the reports along, BOOM. We were in the middle of an unexpected (but very
profitable) amazing development program. This was before internet, we tried to Modem the days data to their group. In a month, we had the first ISDN
line I had seen installed to pass the days data to them in almost real time.

Matt
--
Matt & Mary Colie - '73 Glacier 23 - Members GMCMI, GMCGL, GMCES
Electronically Controlled Quiet Engine Cooling Fan
OE Rear Drum Brakes with Applied Control Arms
SE Michigan - Twixt A2 and Detroit

 

[Tom Lins]

> I agree. Even reversion of gasses or reverberations in sonic pulses in the
> gas stream can affect the O2 sensor. Placement of it upstream or downstream
> is also critical, but nowhere near as critical as an exhaust leak.
> 2 stroke exhaust design is almost as critical, particularly on
> expansion chamber type exhausts. Pipe shapes, twists and turns, even
> welding slag, pipe diameter and length also have an effect.
> Jim Hupy
> Salem, Oregon
>
> On Tue, Oct 29, 2019, 1:14 PM Matt Colie via Gmclist <

>

> >> Could someone explain to me why an exhaust leak could affect the reading
> > of a O2 sensor?
> >> I cannot picture how a leak out of a pressurized pipe could make a
> > difference in the AFR reading inside the pipe.
> >> Or am I not understanding something here.
> >

> >> I'm no expert but I expect that the pressurized pipe is really filled
> > with pulses of exhaust gas pressure interspersed with pulses of vacuum. The
> >> vacuum (less than ambient pressure) draws in outside air.
> >
> > This is exactly the correct answer and it is why when running a closed
> > loop engine in a laboratory setting, we still needed an absolutely tight
> > exhaust system.
> > Yes, even a little leak can matter.
> >
> > Matt - the refugee from DynoLand
> > --
> > Matt & Mary Colie - '73 Glacier 23 - Members GMCMI, GMCGL, GMCES
> > Electronically Controlled Quiet Engine Cooling Fan
> > OE Rear Drum Brakes with Applied Control Arms
> > SE Michigan - Twixt A2 and Detroit
> >
> > _______________________________________________
> > GMCnet mailing list
> > Unsubscribe or Change List Options:
> > http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
> >
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org

Thank you all that replied, I think I remember some of this from college

Makes sense Thank you all
--
Tom Lins
St Augustine, FL
77 GM Rear Twin, Dry Bath, 455, FI-Tech EFI, Aluminum Radiator Quad-Bag Suspension Solar Panel
Manuals on DVD
GMC Dealer Training Tapes
http://www.bdub.net/tomlins/

 

[chris tyler]

Slightly off topic but related:

Given the above discussion about pulses, are 02 sensors/gauges useful as a tuning aid on two stroke engines, or would EGT be more useful?
--
76 Glenbrook

 

[Matt Colie]

> Slightly off topic but related:
>
> Given the above discussion about pulses, are 02 sensors/gauges useful as a tuning aid on two stroke engines, or would EGT be more useful?

Chris,

I hope you are ready...... EGO - Exhaust Gas O2 UEGO - Wide Band EGO HEGO - Heated EGO

There have been attempts to use EGOs and/or UEGO on some 2 stroke engines. They have been used in development, but in a real world application, there
are some big issues. 2 Stroke exhaust temperatures are lower. They are hot enough to light an EGO at load, but they are not reliable to do so.
There is (with some special exceptions) more lubricating oil residual in that exhaust. Lubricating oil must contain (even the modern ashless oils)
some of the "metallic" antiwear additives. These will foul the chemical process that makes the EGO work. It is very difficult to tell when a sensor
is failing, because they don't "go out". From a calibration stand point, they just get slow. So, if you were to use it for initial calibration, you
might get by. But, you would have to do this with the understanding that the sensor life may not be very long.

If the electrical system can support it, I HEGO might get you by the slow heat up time.

Is that a help? I can try again if there is a not understood point.

Matt - the engine lab refugee
--
Matt & Mary Colie - '73 Glacier 23 - Members GMCMI, GMCGL, GMCES
Electronically Controlled Quiet Engine Cooling Fan
OE Rear Drum Brakes with Applied Control Arms
SE Michigan - Twixt A2 and Detroit