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A/F ratio not changing with increased fuel pressure?

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#1
fw87

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I have a new issue where increasing fuel pressure is not changing air fuel ratio. I have gone from 50-54 psi with no noticeable change in AFR. Logging with AIM data system. Things I have checked/done:

 

Moved fuel pressure sensor under hood from regulator to under hood (between factory quick connects)

Installed new fuel pump

Injectors were cleaned at beginning of season and have 50hrs on them

No exhaust leaks

 

Fuel pressure stays perfect the entire session with no dips. Voltage is good and constant

 

Any ideas?



#2
Tom Sager

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No change when comparing data from the same day and with similar weather same day? You're comparing multiple laps from each on-track session? 


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#3
steveracer

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Calibrated your AFR sensor lately?


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#4
Mark

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Which wideband system are you using and how are you sending the afr data to the AiM? Can you post a screenshot of rpm, fuel pressure, and afr traces overlaid from laps selected from multiple sessions? 


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#5
DrDomm

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I would suggest looking at the AFR guage, and not rely on the AiM data.  My (old) system does not accurately log the AFR.


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#6
Jim Drago

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I have a new issue where increasing fuel pressure is not changing air fuel ratio. I have gone from 50-54 psi with no noticeable change in AFR. Logging with AIM data system. Things I have checked/done:
 
Moved fuel pressure sensor under hood from regulator to under hood (between factory quick connects)
Installed new fuel pump
Injectors were cleaned at beginning of season and have 50hrs on them
No exhaust leaks
 

 
Any ideas?


I assume this is a 99? 50-54 psi? Your regulator is in the front? Is it one of the old Wheeler regulators?

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#7
steveracer

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I would suggest looking at the AFR guage, and not rely on the AiM data.  My (old) system does not accurately log the AFR.

 

I've noticed this with my TraqMate also. Logged AFR not the same as what the display showed in the video.


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#8
Steve Scheifler

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I've noticed this with my TraqMate also. Logged AFR not the same as what the display showed in the video.


Then the data logger probably hasn’t been configured correctly for that particular wideband, or the gauge is not correctly calibrated for the sensor. Or, if the logger data seems very erratic it may simply need better filtering & damping settings.

Keep in mind that both the logger and the dash gauge are simply voltmeters, and if correctly configured and functional both will read the same, even if that reading is wrong for some reason. Any decent wideband should include exact specs for volts to AFR (and/or Lambda), and some have multiple settings or can be set to a custom output using a PC. Any decent data logger provides the option to define a curve for a standard 0-5v input to translate that to AFR (or temp, or oil pressure, or whatever). So if you set the logger up per the specs for the wideband and it reads significantly different than the gauge that came with the sensor, then you would be well advised to figure out which is correct.
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#9
steveracer

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Then the data logger probably hasn’t been configured correctly for that particular wideband, or the gauge is not correctly calibrated for the sensor. Or, if the logger data seems very erratic it may simply need better filtering & damping settings.

Keep in mind that both the logger and the dash gauge are simply voltmeters, and if correctly configured and functional both will read the same, even if that reading is wrong for some reason. Any decent wideband should include exact specs for volts to AFR (and/or Lambda), and some have multiple settings or can be set to a custom output using a PC. Any decent data logger provides the option to define a curve for a standard 0-5v input to translate that to AFR (or temp, or oil pressure, or whatever). So if you set the logger up per the specs for the wideband and it reads significantly different than the gauge that came with the sensor, then you would be well advised to figure out which is correct.

 

Yes, functionally intelligent adult here. Set it up per specs.

Just haven't taken the time to figure out how to adjust for the difference yet. Seems like it will be tiringly tedious to me.

I was just sharing that my experience matched DrDomm


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#10
Steve Scheifler

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Yes, functionally intelligent adult here. Set it up per specs.
Just haven't taken the time to figure out how to adjust for the difference yet. Seems like it will be tiringly tedious to me.
I was just sharing that my experience matched DrDomm


I get it, and it was the fact of a second person with the same issue that prompted me to point out the basics since no one else had.
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#11
Tom Hampton

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Yes, functionally intelligent adult here. Set it up per specs.


Alleged adult, sir. I believe the accusation to be on very weak ground.
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#12
steveracer

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Alleged adult, sir. I believe the accusation to be on very weak ground.

 

Chronologically speaking, I are adultish.... :P


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#13
fw87

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here is a data trace of what im experiencing. this was run in the same session, pulled into pits and dropped fuel pressure ~1.8 psi. oddly enough the car ran richer with reduced fuel pressure??? makes no sense

 

regulator is mounted in trunk, fuel pressure sensor is under the hood

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#14
Steve Scheifler

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I’m not experienced with AIM’s software but what I see from the graphs is exactly what I expect from you lowering fuel pressure. What I don’t understand is your choice of data points (blue & red triangle markers) to generate the grid on the right. What matters are the long relatively flat stretches between shifts, and the last one is higher (leaner) than the early ones. Your markers are at shift points, showing extreme lean when you lift then very briefly fat after the shift (the equivalent of an accelerator pump in an old carb), both of which are completely normal.
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#15
Steve Scheifler

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In the right data grid what are the 3rd & 4th columns (white arrow and LCC)? They don’t seem to correlate to particular points or averages but I gather that’s what you are looking at.

You might also want to re-scale the graphs for better resolution in the relevant ranges.
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#16
Tom Sager

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Yes very tough to discern much change in the fuel pressure and A/F traces given those scales. Also you might view those with along with water temp and RPM rather than speed.  A change in water temp will have some impact.  A less than 2 PSI change won't result in a big swing in a '99.  A few tenths maybe in A/F ratio when comparing several laps. 


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#17
Steve Scheifler

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OK, I took another look and realized I misinterpreted how the before & after adjustment are represented. The full horizontal length being one lap and the six selected laps overlaid, of course, stupid of me not taking the time to understand. I saw the first “straight” richer than the next two and jumped to confusion. But everything else I said stands, I think. The data point markers look like automatically selected max/min which have zero relevance to an AFR curve. The scaling is so compressed that even if there is the expected change in AFR it would be difficult to discern. Heck, at that scale the line width alone covers a significant range. And I still don’t grasp the meaning of those last two columns. Someone please educate me.
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#18
Steve Scheifler

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And I must say, IMO the use of colors really sucks. Time and velocity at least display each lap in its assigned color, though I’m baffled as to why three of them are the same, but why the heck are fuel pressure and AFR mono-color?? That’s where my own confusion started and makes it impossible to make any sense at all out of the graphs even if re-scaled.
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#19
Mark

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Check the per lap color option in RS2 analysis so that you can differentiate the channel values for each lap and zoom in to a lap segment where you are accelerating in the range of 6500 - 6800 rpm and 100% throttle. 

 

Mark


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#20
RWP80000

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OK, I took another look and realized I misinterpreted how the before & after adjustment are represented. The full horizontal length being one lap and the six selected laps overlaid, of course, stupid of me not taking the time to understand. I saw the first “straight” richer than the next two and jumped to confusion. But everything else I said stands, I think. The data point markers look like automatically selected max/min which have zero relevance to an AFR curve. The scaling is so compressed that even if there is the expected change in AFR it would be difficult to discern. Heck, at that scale the line width alone covers a significant range. And I still don’t grasp the meaning of those last two columns. Someone please educate me.

 

Steve, 

In the AIM software the Blue "down" triangle and Red "up" triangle represent that Laps lowest and highest recorded values during the Lap.  The "right pointing" plain triangle represents the "average" value for the data in the Lap.  The round colored dot  and the adjacent numerical value represents the value in that lap where the cursor is located which is at about the 320 foot mark.  With this information it is not necessary to guess what numbers the lines are showing and if this were in AIM software you would be able to move that cursor to any point of interest that you wished to see the numerical values without having to guess.

 

As described, and reading the numbers for Fuel Pressure and A/F ratio, the Pressure starts out at around 55 psi for the first 3 laps and then the next three it is around 52 something. Next the A/F ratio for those three higher pressure laps averages about 12.62 while for the next three laps at lower pressure, averages 12.40.  So, it does show that in fact the pressure was decreased and the net affect was that the A/F ratio did get richer by about 1/4 ratio.

 

So at this point the question is do you believe the data and try lowering the pressure in hopes of seeing the A/F get richer? Don't count on it, but what you may need to think about is what else might have been going on.  How long did you take to make the change?  Did you shut the car off while making the change?  How hot was the car running before and after the change.  

While you were making your change appropriately with the regulator adjustment, the ECU may have been countering your change in response to other factors.  I doubt that there was a sudden drop in barometric pressure going on so I tend to lean to the under hood sensor environment conditions that could be working against you. I have found over the years that the ECU curve tends to overly lean the calibration as you go up in altitude and that when going from a lower altitude to higher I have to increase the fuel pressure regulator rather than decrease it as expected.  Also, I much prefer using the Lambda scale as it reports the mixture balance as being plus or minus to 1 with less (0.9) being 10% rich or 1.05 being 5% lean.  When using A/F you need to know what the Stoic value actually is for the fuel you are running in order to know what A/F ration you want to target. If you are running expensive race fuel, you can find that on their web site but what are your chances of getting from the local gas station or even for fuel pumped at the track if it is not a known vendor.

 

Rich Powers






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