Go Back  Miata Turbo Forum - Boost cars, acquire cats. > Performance & Tuning > ECUs and Tuning > MEGAsquirt
Reload this Page >

Battery voltage affecting idle AFR and fuel problem

MEGAsquirt A place to collectively sort out this megasquirt gizmo
Sponsored by:
Sponsored by:

Battery voltage affecting idle AFR and fuel problem

 
Old 03-29-2019, 01:41 PM
  #1  
Junior Member
Thread Starter
 
Join Date: Sep 2017
Location: Baltimore; States
Posts: 119
Total Cats: -35
Default Battery voltage affecting idle AFR and fuel problem

Summary of the datalog if you do not wish to review it for yourself.

Start car, either cold or warm same thing happens in this order every time:
Battery voltage: 11.7-8 to 12.00 (Via datalog as well as tunerstudio dash)
TPS: 0%

Car's running idling with 0% throttle input and...

Then as it's trying to warm up you begin to notice that EGO correction is adding fuel to compensate a very lean AFR that otherwise would be right on point if the battery voltage was at normal running power. EGO is using it's entire 10% authority to help bring the AFR down from what would otherwise be so lean it would stall the car if left like that long enough.

So I give it some gas at about 61.5 seconds into the log:
TPS: 1 to 2.4% throttle blip (just to give the alternator a jump up I suppose =S?)

then bam, interior lighting glows brighter, tunerstudio on the laptop starts to read out Battery Voltage 15.5 to 15.3.
AFR then comes to normal idle target. And you notice that EGO drops immediately from 109.2%+ fuel compensation to 99.9% aka no EGO correction.

If you do open the log to view, don't mind the fact that after battery voltage is 15.3, ego eventually starts pulling fuel. Because that just means that I need to make changes to my VE Fuel table. Which doesn't make much sense to do at this moment with this problem occurring. Because if it's a battery voltage correction issue for the injectors or ECU, the whole fuel table might have to be modified to fit good again.

So what do you guys think the problem is?? Is this a easy thing to fix or a common problem? Who else has dealt with this before??
I'm thinking it could have something to do with my settings but don't know which to mess with to fix. I haven't seen any menus though that would lead me to feel they are specific to being the reason behind this.


My log and tune is uploaded

ECU: Megasquirt 2 PNP 94-95 1.8l
Injectors: FlowForce 640cc's
Fuel pump: OEM
Fuel filter: replaced 7k miles ago

Injector dead-time/pwm settings I copied from https://goflowforce.com/instructions - Scroll down to Dead Times and what not, to see for yourself the information regarding these if needed.

This is a screen shot image of my current settings in MegaSquirt.
Attached Files

Last edited by NASSEX; 03-29-2019 at 02:20 PM.
NASSEX is offline  
Old 03-29-2019, 02:27 PM
  #2  
Design Engineer
iTrader: (1)
 
DNMakinson's Avatar
 
Join Date: Jan 2013
Location: Seneca, SC
Posts: 3,512
Total Cats: 468
Default

You should be able to find a curve that corrects dead time against voltage. Do that. Then when voltage is low, which causes the inj to open more slowly, there will an adjustment that gives a longer electrical pulse to compensate.

EDIT; Yeah, what you posted. MS3 gives a curve, rather than a single value. Whether those voltages are typical for your model car, I don’t know.
DNMakinson is offline  
Old 03-29-2019, 02:58 PM
  #3  
Junior Member
Thread Starter
 
Join Date: Sep 2017
Location: Baltimore; States
Posts: 119
Total Cats: -35
Default

Originally Posted by DNMakinson View Post
You should be able to find a curve that corrects dead time against voltage. Do that. Then when voltage is low, which causes the inj to open more slowly, there will an adjustment that gives a longer electrical pulse to compensate.

EDIT; Yeah, what you posted. MS3 gives a curve, rather than a single value. Whether those voltages are typical for your model car, I donít know.
Yes! That was exactly what I was searching for, and hoping to be the way to fix it but I don't think MS2 has that same menu feature that's on MS3. I tried doing searches on Tuner Studio and all I could find was the "Dwell Battery Adjustment" chart graph. Which I don't think is related because in the TS description for it, it mentions inductive coils. I think that feature is for ignition, not injectors.
If there was a chart like that for injectors in MS2... That would be perfect!

Anybody experience this before?

On a side question, is the alternator generally supposed to start powering things up the moment the car is started? To me, it seems like there is a mechanical or electrical switch that opens either with throttle/rpm input or maybe with enough random time of letting it idle, where it just stays 12v or a tad bit less to immediate ramp to 15.3+. It does that the moment the alternator "turns on...". It's a noticeable event when it happens. All interior/exterior lighting increases at that moment. But it's like there's a switch designed somewhere to prevent the power from going straight from the alternator to the battery unless some kind of requirement is met. Which I assume is TPS > 0%. /me shruggs
Nonetheless, that doesn't have anything to do with the fact that the VE Fuel values to injectors are so far off based on voltage.
NASSEX is offline  
Old 03-29-2019, 03:40 PM
  #4  
Junior Member
Thread Starter
 
Join Date: Sep 2017
Location: Baltimore; States
Posts: 119
Total Cats: -35
Default

....Or wait 15.2-15.3 volts is not normal is it? Even with headlights, running lights, signals and everything off.

Yeah actually that battery voltage is actually not correct. Pretty sure I have a bad voltage regulator at the alternator. Not surprised, that thing was a ticking time bomb anyway. Fully covered in oil gunk since the day I bought the car.

But it still wouldn't fix this problem with the VE fuel being so far off between given ranges of battery voltage if I'm not mistaken. That has something to do with megasquirt/tunerstudio. Could it be the Dwell Battery Adjustment setting?

Any ideas or suggestions

... Bueller? ............ ..

Last edited by NASSEX; 03-29-2019 at 07:28 PM.
NASSEX is offline  
Old 03-30-2019, 09:24 AM
  #5  
Senior Member
 
Join Date: Mar 2014
Location: Jacksonville, FL
Posts: 1,199
Total Cats: 145
Default

All the cars I ever owned, when the engine is running and no large loads, the charging voltage is 14.2-14.5
15.5 sounds way too high, I suspect a bad voltage regulator.
borka is offline  
Old 03-30-2019, 12:10 PM
  #6  
Junior Member
Thread Starter
 
Join Date: Sep 2017
Location: Baltimore; States
Posts: 119
Total Cats: -35
Default

Yeah i definitely need a new alternator... Aside from that tho i think i might've found the solution to my main or secondary problem. I'm ganna make a post about it when i am home and not on my phone so i can add in some images. I think to fix it the battery correction value needs adjustment along with replacing the alternator. And i should be all good if not close enough to continue tunung VE MAP.
NASSEX is offline  
Old 03-30-2019, 05:55 PM
  #7  
Elite Member
iTrader: (1)
 
Join Date: Apr 2014
Location: SF Bay Area, CA
Posts: 2,473
Total Cats: 267
Default

I think those of us who are stuck on ms2 need to use the big end of the voltage correction curve since we only get a single value.
sonofthehill is offline  
Old 04-03-2019, 12:08 AM
  #8  
Junior Member
Thread Starter
 
Join Date: Sep 2017
Location: Baltimore; States
Posts: 119
Total Cats: -35
Default

Originally Posted by sonofthehill View Post
I think those of us who are stuck on ms2 need to use the big end of the voltage correction curve since we only get a single value.
Thank you that's good advice. You probably saved me a lot of time
NASSEX is offline  
 
Related Topics
Thread
Thread Starter
Forum
Replies
Last Post
Braineack
General Miata Chat
60
04-29-2011 05:39 PM
apariah
General Miata Chat
8
08-10-2009 03:14 AM
ctxspy
MEGAsquirt
33
04-27-2009 08:56 PM
AlexO35
ECUs and Tuning
5
03-28-2009 12:13 AM
emilio700
MEGAsquirt
17
07-15-2008 04:24 PM


Thread Tools
Search this Thread
Quick Reply: Battery voltage affecting idle AFR and fuel problem


Archive - Advertising - Cookie Policy - Privacy Statement - Terms of Service

© 2019 MH Sub I, LLC dba Internet Brands

We are a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for us to earn fees by linking to Amazon.com and affiliated sites.