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#1
ChrisA

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Anybody logged voltage? I installed an AiM MXL2 system recently, only got out with it last fall. When viewing data, how do you determine what is erratic and what is not? Also, the voltage the system is indicating is at least .5v higher than what I read at the battery (& cut-off switch) with my Fluke DDM. The Fluke is an older, lower end model and needs to be replaced, because the LCD screen has been damaged. So, possibly the multi-meter is reading off a little  :noidea: . The MXL2 is showing peaks of 15.5v. Testing in the paddock the paddock the Fluke was showing 13.x-14.7v at Batt., which would be correct range according to specs.

 

Reviewing the data I have, the voltage range stays consistent from start to finish of a session. Also, the traces are relatively similar from lap to lap. I had to reset the upper alarm to 15.5v and low at 12.7v (I think) to keep it from staying on while on track. So my first concern is, is it over charging (assuming data is correct). If the MXL2 is reading high, is there a way to calibrate the unit? If not, I can live with the alarm adjustment. Second, concern was, is this alternator ON too much and robbing me Hp? Or, does this look like normal behavior? The upward spikes would seem appropriate to me, since they follow RPM drops from upshifts, but should this trace be so aggressive?

 

Here's a not very clean lap rpm/volt trace.

Volt/RPM data

 


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#2
JJ Servis

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Here's what mine looks like from my last race (Mid Ohio, Mid October).  Seems to me there is something going on there, but i'm far from an expert so i won't speculate further than that.

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#3
Tom Sager

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One man's opinion.....

 

If you look at your traces, it appears that your voltage is throttle sensitive, it dips with the acceleration trace.  Shouldn't be that way IMO.  When it's healthy on an NB, voltage is very flat regardless of speed or throttle.  My '01 had a similar issue but with much greater dips in voltage.  Can't recall if voltage regulator function in a '99 is in the ECU or the alternator.  Someone else here will know.   You could have an alternator issue or weak grounds or flaky kill switch or some other wiring weakness.  15.5 volts is very high.  Should be high 14's and pretty flat IMO.  Good news is you've got plenty of voltage to run the car.

 

Others here will know more. 


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#4
ChrisA

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I'm not sure the 15.5v is correct, as my multi-meter reads between 0.3-0.6v lower (in paddock) than the AiM unit. So one of these is reading incorrectly. I would expect to see voltage spikes after an up-shift, as we're seeing, because the demand on the coils suddenly drops with RPM. But, I would have thought the trace would have been dampen more than I see. And yes, on the '99-05 the ECU regulates the Alt.


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#5
RWP80000

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Below is the Thumbnail from the VIR Runoffs SM Race in Oct 2019 in a 99 MY vehicle.  I believe it is similar to the previous Thumbnails. 
 
Looking at the set of all three different Thumbnails, the averages were;
Lap Min voltage 14..0 volts
Lap Max voltage 15.0 volts
Full Lap voltage 14.7 volts
 
First, It should be noted that the trace appearances can be deceiving due to differences in each chart's voltage scale. The other variable that may be affecting what each data logger see's for the signal may be a function of how the logger is connected to the vehicles electrical system.  On our car, the AIM system is on its own independent circuit with the Ground "reference" tied directly to the Battery negative post and the Power coming off the Disconnect switch which is also traces directly back to the battery Positive post. All Data logger systems are on their own independent fused circuits controlled by the Master shut off along with a toggle switch in the Dash panel.
 
Looking at the three lowest voltage points during our "full lap" plot shows that they occurred at both lower RPM and Vehicle Speeds (don't know why speed would be a factor).  Chris's voltage does seem to be higher in general to the other two but I have no clue if this has to due with how his Data Logger is tied in to the Vehicle's electrical system or if his Alternator is putting out a higher voltage or if his the ECU's regulation strategy is a factor.
 
While I do not think there is enough difference here to be concerned about, I would first try swapping out the Alternator and then the ECU to see if either of these show a measureable difference. If neither of these make any difference I would then look to how the Data Logger Power and Ground circuits are wired.
 
99 SM VIR 1020 AIM Ext Volts
 
Rich Powers


#6
Tom Sager

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Below is the Thumbnail from the VIR Runoffs SM Race in Oct 2019 in a 99 MY vehicle.  I believe it is similar to the previous Thumbnails. 
 
Looking at the set of all three different Thumbnails, the averages were;
Lap Min voltage 14..0 volts
Lap Max voltage 15.0 volts
Full Lap voltage 14.7 volts
 
First, It should be noted that the trace appearances can be deceiving due to differences in each chart's voltage scale. The other variable that may be affecting what each data logger see's for the signal may be a function of how the logger is connected to the vehicles electrical system.  On our car, the AIM system is on its own independent circuit with the Ground "reference" tied directly to the Battery negative post and the Power coming off the Disconnect switch which is also traces directly back to the battery Positive post. All Data logger systems are on their own independent fused circuits controlled by the Master shut off along with a toggle switch in the Dash panel.
 
Looking at the three lowest voltage points during our "full lap" plot shows that they occurred at both lower RPM and Vehicle Speeds (don't know why speed would be a factor).  Chris's voltage does seem to be higher in general to the other two but I have no clue if this has to due with how his Data Logger is tied in to the Vehicle's electrical system or if his Alternator is putting out a higher voltage or if his the ECU's regulation strategy is a factor.
 
While I do not think there is enough difference here to be concerned about, I would first try swapping out the Alternator and then the ECU to see if either of these show a measureable difference. If neither of these make any difference I would then look to how the Data Logger Power and Ground circuits are wired.
 
 
 
Rich Powers

 

Interesting and the source of the data is certainly a variable.  Looking back at some data from my '00, the voltage is nearly as flat as a pancake throughout entire track session ranging 14.2-14.4 volts.   I think that data was coming off the ECU but not certain.  Don't own the car any longer.  My '01 is equally flat but reading more like 14.9 volts using the same logger.  In the '01 I started to see peaks and valleys at one point and ultimately it developed a problem which was not solved by the alternator alone. 


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#7
Mark

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AiM has had some different approaches to measuring the voltage via the internal logger power input channel over the various generations of data logger circuit boards. If in doubt it is best to measure voltage using a analog input channel and ignore the internal voltage channel. I doubt this is the case here as what I've seen in the past with earlier (MXG/MXS/MXL2) iterations of AiM hardware is voltage that is always reported as 12.5-13v peak (IIRC) regardless of the alternator output and rpm. This has led to lots of alternator swapping for no reason in a couple of cases :). I'd change the alternator out and look hard at all the grounds and the kill switch as a start.

 

 

 


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#8
ChrisA

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AiM has had some different approaches to measuring the voltage via the internal logger power input channel over the various generations of data logger circuit boards. If in doubt it is best to measure voltage using a analog input channel and ignore the internal voltage channel. I doubt this is the case here as what I've seen in the past with earlier (MXG/MXS/MXL2) iterations of AiM hardware is voltage that is always reported as 12.5-13v peak (IIRC) regardless of the alternator output and rpm. This has led to lots of alternator swapping for no reason in a couple of cases :). I'd change the alternator out and look hard at all the grounds and the kill switch as a start.

 

Mark, for what it's worth, the voltage I read at the power connection to the MXL2 is less than what the dash says by 3 tenths, this is without the engine running. So it seems to be the way the dash "sees" the power internally. Looking at my notes, I see that my battery is 7.5 yrs old, so I'm going to replace it first. While it has been maintained on a BatteryMinder, it's nearing the end of its' life expectancy anyway. Then I'll look at Alt & ECU.


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#9
ChrisA

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I found this thread https://forum.miata....ad.php?t=622491 on the Miata Forum, kind-of interesting discussion on the charging circuits route through the OE gauge pod. I removed my gauge pod when I installed the MXL2. I'm wondering if the breaking of this circuit is causing the Alt. to charge at all times and preventing the ECU from managing the cycles, thus causing the more aggressive voltage log? Does that thread appear correct and this circuit should be re-established? Rich & Tom, was the OE gauge cluster retained or deleted from your set up?


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#10
38bfast

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there is different voltage drops in the car. You will get a different reading at the fuse box, battery and alternator. 


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#11
Tom Sager

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I found this thread https://forum.miata....ad.php?t=622491 on the Miata Forum, kind-of interesting discussion on the charging circuits route through the OE gauge pod. I removed my gauge pod when I installed the MXL2. I'm wondering if the breaking of this circuit is causing the Alt. to charge at all times and preventing the ECU from managing the cycles, thus causing the more aggressive voltage log? Does that thread appear correct and this circuit should be re-established? Rich & Tom, was the OE gauge cluster retained or deleted from your set up?

Gauge cluster removed from both of the cars mentioned.


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#12
RWP80000

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I found this thread https://forum.miata....ad.php?t=622491 on the Miata Forum, kind-of interesting discussion on the charging circuits route through the OE gauge pod. I removed my gauge pod when I installed the MXL2. I'm wondering if the breaking of this circuit is causing the Alt. to charge at all times and preventing the ECU from managing the cycles, thus causing the more aggressive voltage log? Does that thread appear correct and this circuit should be re-established? Rich & Tom, was the OE gauge cluster retained or deleted from your set up?

 

Chris, OE Gage Cluster is removed from our car as well.

 

Rich Powers



#13
Alberto

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Does your fuel pressure or AFR change with the change in voltage?


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#14
Steve Scheifler

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Shouldn’t if your fuel pressure regulator is working.
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#15
Alberto

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Shouldn’t if your fuel pressure regulator is working.

 

I've seen one NA 1.8 where the alternator was not regulating properly generating as much as 18 volts at full throttle result in a richer fuel mixture to the point where the engine was stumbling.  Hence my question.  It was an odd situation.


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#16
Steve Scheifler

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I’d be suspicious of the fuel pressure regulator while also fixing the charging situation that will eat batteries, particularly the type we typically use.
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#17
Tom Hampton

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Shouldn’t if your fuel pressure regulator is working.

 

Depending on the output stage of the ECU for the injector pulse...its entirely plausible that an unregulated V+ could lengthen the injector pulse width.


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