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2008-2013 Cadillac CTS General Discussion Discussion, Why so rich? in Cadillac CTS Second Generation Forum - 2008-2013; Just curious about why my commanded AFR is so rich? I'm used to seeing 14.7:1 (stoich) in other vehicles. Screenshot_20190408-152511.png ...
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    CaddyFred's Avatar
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    Why so rich?

    Just curious about why my commanded AFR is so rich? I'm used to seeing 14.7:1 (stoich) in other vehicles.

    Screenshot_20190408-152511.png Screenshot_20190408-152445.png

    I edited to add a second shot of some other parameters. Note that both were taken with engine hot, idling in driveway, which is why the coolant is so hot.

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    Joseph Upson is offline Cadillac Owners Enthusiast
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    Re: Why so rich?

    That's not rich, that's just a little below stoich and most certainly by design considering I read the same about 3 wks ago using the same program you appear to be using for the first time. It may be a form of pre power enrichment due to the nature of the fuel delivery system, or it may have something to do with other parameters. I did not check for it, but I'd expect to see closer to stoich during cruise speed. Rich is when you smell fumes and/or see black smoke bellowing from the exhaust tips and note a build up of smut around the exhaust tips extending to the bumper.

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    Re: Why so rich?

    Stoic is 14.7 so 14.0 is slightly rich though can dreop to 11-12 at max power. 15.5 is a good lean cruise (my 93 GTP had a "highway mode" of 15.7).

    Torque Pro is very handy but I look more at the fuel trims and O2 sensors.

    Interesting that the fuel pressure (4440 kpa/643 psi) is on the low ends of DIFI.

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    Joseph Upson is offline Cadillac Owners Enthusiast
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    Re: Why so rich?

    Without the actual air fuel ratio reading the commanded value can't be put into full context, as the commanded reading may be influenced by what the O2 sensor is seeing, as fuel management parts age and their performance changes. If the actual AFR reads the same as the commanded value then yes, it's a little below stoich, but if it's 14.7, then the commanded 14.08 may be what is necessary for that result at the sensor. OBD II is far more sophisticated than OBD I, but the principals are still the same. There were values in management tables in OBD I programming involving AFR that were more relative than literal as was explained by some of the programmers.

    Fuel pressure is normal as far as I can tell, my cold idle rail pressure from an old scan screen shot I just checked was 609 psi (4.2 MPa) and that was before the clogged fuel injectors were replaced, suggesting if I checked it now, the pressure would be a little lower at idle, although I recall having seen it below 600 psi before. Perhaps the baseline increased a little bit each year after 08, given there are 3 different yrs between us. Just kidding about that but anything is possible considering tune calibrations are VIN matched. I'm sure you're aware that the fuel pressure is variable based on demand.

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    Re: Why so rich?

    After reading this thread title, I was disappointed not to see pics of Kardashians.
    RedRover2018 likes this.

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    Re: Why so rich?

    Quote Originally Posted by Joseph Upson View Post
    That's not rich, that's just a little below stoich and most certainly by design considering I read the same about 3 wks ago using the same program you appear to be using for the first time. It may be a form of pre power enrichment due to the nature of the fuel delivery system, or it may have something to do with other parameters. I did not check for it, but I'd expect to see closer to stoich during cruise speed. Rich is when you smell fumes and/or see black smoke bellowing from the exhaust tips and note a build up of smut around the exhaust tips extending to the bumper.
    Technically any value less than stoich is "rich", any higher value is "lean". I am just a little surprised to see a commanded AFR of 14.1 at idle. I guess I'll have to do some data logging with Palmer ScanXL Pro since I can't seem to figure out how to play back Torque data logs in a line graph. I'm just curious about it. My previous Toyota project car never deviated from 14.7 in closed loop (AFR sensor controlled) and ~12:1 in open loop. I forget how many years I've been using Torque Pro. Less than Palmer but longer than Carista. Maybe 8 years?

    Quote Originally Posted by Padgett View Post
    Stoic is 14.7 so 14.0 is slightly rich though can dreop to 11-12 at max power. 15.5 is a good lean cruise (my 93 GTP had a "highway mode" of 15.7).

    Torque Pro is very handy but I look more at the fuel trims and O2 sensors.

    Interesting that the fuel pressure (4440 kpa/643 psi) is on the low ends of DIFI.
    Leaner than stoich increases NOx emmisions. That's why you don't see new cars running 15.7:1.

    Quote Originally Posted by Joseph Upson View Post
    Without the actual air fuel ratio reading the commanded value can't be put into full context, as the commanded reading may be influenced by what the O2 sensor is seeing, as fuel management parts age and their performance changes. If the actual AFR reads the same as the commanded value then yes, it's a little below stoich, but if it's 14.7, then the commanded 14.08 may be what is necessary for that result at the sensor. OBD II is far more sophisticated than OBD I, but the principals are still the same. There were values in management tables in OBD I programming involving AFR that were more relative than literal as was explained by some of the programmers.

    Fuel pressure is normal as far as I can tell, my cold idle rail pressure from an old scan screen shot I just checked was 609 psi (4.2 MPa) and that was before the clogged fuel injectors were replaced, suggesting if I checked it now, the pressure would be a little lower at idle, although I recall having seen it below 600 psi before. Perhaps the baseline increased a little bit each year after 08, given there are 3 different yrs between us. Just kidding about that but anything is possible considering tune calibrations are VIN matched. I'm sure you're aware that the fuel pressure is variable based on demand.
    Possibly but I would expect the PCM to compensate with increased injector pulse width rather than commanding a richer AFR to achieve stoich. However, although I know how Denso does it I don't know about Bosch. FWIW I grabbed another screenshot at the same time that showed 560psi rail pressure. I assume that the pressure fluctuates with the mechanical high-pressure pump.

    Quote Originally Posted by Long View Post
    After reading this thread title, I was disappointed not to see pics of Kardashians.
    Really? I'd be disappointed to see pics of the Kartrashians.

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    Re: Why so rich?

    ...and the answer is... E10. 14.08 is stoich for E10. Now it makes sense. Thanks Google.

    Does anyone know if HPTuners can do the same diagnostics as a tech2? If so I might get it instead.

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    Re: Why so rich?

    We shoulda thunk of that.

    BTW you can set Torque Pro to save run parameters as a .csv and Excel (or good clones) can make any chart/graph you want from that. Look in
    /torqupro/triplogs/(id number)/triplog.csv. .See here for how to set up logging.

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    Re: Why so rich?

    Quote Originally Posted by Long View Post
    After reading this thread title, I was disappointed not to see pics of Kardashians.
    Here you go....you asked for it!!

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    Re: Why so rich?

    Quote Originally Posted by CaddyFred View Post
    ...and the answer is... E10. 14.08 is stoich for E10. Now it makes sense. Thanks Google.

    Does anyone know if HPTuners can do the same diagnostics as a tech2? If so I might get it instead.
    That also suggests the PCM worked backwards using the O2 sensor readings to arrive at what the commanded value should be, otherwise it would have been 14.7:1 because non E85 models do not have ethanol sensors. Yes technically 14.08 is rich, but without an engine code there's no need to second guess the PCM and as suspected, that translates into the desired AFR. The in tank fuel pump runs at a steady pressure but the high pressure pump delivers variable pressure, no need to run 2000 psi at idle, not to mention the injectors probably wouldn't be able to deliver a small enough quantity of fuel to maintain idle at that pressure.

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    Lifespeed is offline Cadillac Owners Enthusiast
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    Re: Why so rich?

    Quote Originally Posted by CaddyFred View Post
    Technically any value less than stoich is "rich", any higher value is "lean". I am just a little surprised to see a commanded AFR of 14.1 at idle. I guess I'll have to do some data logging with Palmer ScanXL Pro since I can't seem to figure out how to play back Torque data logs in a line graph. I'm just curious about it. My previous Toyota project car never deviated from 14.7 in closed loop (AFR sensor controlled) and ~12:1 in open loop. I forget how many years I've been using Torque Pro. Less than Palmer but longer than Carista. Maybe 8 years?
    Your Toyota probably had the old design oxygen sensor which switches when it crosses stoich. It has no ability to measure AFR, just when it is above or below 14.7.

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    Re: Why so rich?

    Quote Originally Posted by Padgett View Post
    We shoulda thunk of that.

    BTW you can set Torque Pro to save run parameters as a .csv and Excel (or good clones) can make any chart/graph you want from that. Look in
    /torqupro/triplogs/(id number)/triplog.csv. .See here for how to set up logging.
    I've done some logging but ahd hoped that Torque could play it back the way scanxl does. I'll try graphing it in Excel, thanks.

    Quote Originally Posted by HurstGN View Post
    Here you go....you asked for it!!
    You just had to do it...

    Quote Originally Posted by Joseph Upson View Post
    That also suggests the PCM worked backwards using the O2 sensor readings to arrive at what the commanded value should be, otherwise it would have been 14.7:1 because non E85 models do not have ethanol sensors. Yes technically 14.08 is rich, but without an engine code there's no need to second guess the PCM and as suspected, that translates into the desired AFR. The in tank fuel pump runs at a steady pressure but the high pressure pump delivers variable pressure, no need to run 2000 psi at idle, not to mention the injectors probably wouldn't be able to deliver a small enough quantity of fuel to maintain idle at that pressure.
    After reading a little about HPtuners tuning it appears that the commanded AFR is more informational than instructive. The actual AFR can and does differ greatly depending on the myriad other parameters that actually determine the final AFR. I was simply surprised to see a value other than the 14.7 I expected. I do agree that 14.1 isn't very rich but if the engine ran 0.6:1 richer than stoich all the time it would negatively affect mpg.

    Quote Originally Posted by Lifespeed View Post
    Your Toyota probably had the old design oxygen sensor which switches when it crosses stoich. It has no ability to measure AFR, just when it is above or below 14.7.
    Nah. It had Denso and Bosch widebands pre-cat and a Denso narrow-band sensor post-cat. The Denso WB informed the ECU and the Bosch WB informed my AFR gauge. I could log the Denso sensors with ScanXL but could only read them in lambda. I installed the AFR gauge for instant AFR monitoring and I 'read' AFR much more fluently than lambda. Maybe I should have mentioned that the AFR did deviate from 14.7 in CL but only by 0.2 rich/lean. Clearly the ECU was trying to maintain stoich. The AFR went to ~12.5 when my Split Second Enricher (SSE) sensed boost and ~11.0 when the ECU calculated enough load to enter open loop (OL).

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    Re: Why so rich?

    Not sure about your car but mine are in a closed loop mode called PE (Power Enrichment) when the PLA (throttle) exceeds about 50% AFR drops to 11-12 and the advance drops back a bit.

    ps just checked my AFR and at warm idle is sitting at 14.7 per the OBD.

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    Re: Why so rich?

    With my Toyota it would run in closed loop (AFR sensor feedback based fuel delivery @stoich) until the ecu calculated sufficiently high engine load and then it went into open loop (lookup table based fuel delivery @ ~12:1). I don't know exactly how my CTS' Bosch PCM does it but imagine it is very similar.

    I looked but didn't see an available actual AFR parameter in Torque which is why I logged the commanded AFR instead. I'll look again.

    BTW, something I just realized last night is that the reason my AFR gauge read 14.7 instead of the actual 14.1 when running E10 is because it was calibrated that way. AFR sensors don't read AFR, only oxygen content. So lambda 1.0 (stoich) is 14.7:1 with pure gas, 14.1 with E10 and 9.8 with E85.

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    Re: Why so rich?

    Why you get about a third lower mpg with E-85.

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