GM Volt Forum banner

1 - 20 of 28 Posts

·
Registered
Joined
·
3,396 Posts
Discussion Starter #1
I just had my first EMM since I've been using my OBD to monitor things.

I was under the impression that EMM simply switched to gas mode to get things running, and otherwise normal operation, despite having battery left over. And that any unused power from the engine spinning the generator would go into the battery (provided not full)

Well, in checking the OBD values, it is literally just wasting gas. 0 electricity was generated and stored.
The battery SOC did not increase despite the engine running for ~12 minutes.
In fact, it actually went down faster than if I had just been idling.
Used about 450-500Wh in the 12-13 minutes. (Normal idle draw is that much in an hour)

So the engine is not only wasting gas, it's not even generating the electricity used to run the extra components it needs..

I was parked while running it, but for those who do it while driving, does your battery still get used as you drive? or is it actually using the gas energy to move?

I would hope FMM works like a forced hold mode, as expected, no?

Seems like a missed opportunity for efficiency with EMM to not capture at least some of that energy.
And I'm pretty sure most people would be under the impression that it is doing that, like I was.
 

·
Moderator
Joined
·
8,680 Posts
What exactly are you watching with OBDII? What was the car's SoC when EMM hit? What was the car doing at the time (driving? parked? HVAC settings?)

My experience has been that just like any other time the engine starts cold, MG A is pulling 6-12 kW from the engine during EMM while the engine runs at 1400 rom (it starts in a part throttle warm up period and 6 kW - after which it pulls 12 kW.) I'm not sure why you didn't see that.
 

·
Registered
Joined
·
3,396 Posts
Discussion Starter #3
Parked, completely idle. No HVAC or anything.

Starting SOC 66.27%
ending SOC 63.53%

I would've thought at minimum it would maintain the starting SOC point. But nope.

I think I had torque set to log, I'll analyze it in the morning. But the SOC number says it all, zero gain of electricity from that gas.
 

·
Moderator
Joined
·
8,680 Posts
Parked, completely idle. No HVAC or anything.

Starting SOC 66.27%
ending SOC 63.53%

I would've thought at minimum it would maintain the starting SOC point. But nope.

I think I had torque set to log, I'll analyze it in the morning. But the SOC number says it all, zero gain of electricity from that gas.
Huh. If I had seen that, I would have drawn similar conclusions, but it does not match my past experience, and I have trouble believing this is a feature GM would change for newer cars. The Volt never runs at idle except for momentary transitions (and it would take the engine longer to warm up at idle.)
 

·
Registered
Joined
·
79 Posts
I've only hit EMM once, and it did the same thing according to Torque Pro (MyGreenVolt app doesn't work with my adaptor for some reason, but torque does). SOC went down. Odly enough the info display on the DIC did show about 12kw positive (the green/yellow lines below speed) it looked like it would in mountain mode, but HV Amps was in a state of DISCHARGE not charge, and SOC went down about 6% according to OBDII data.

So what I'm going to do from now on is every 5 weeks or so I'll run it in hold mode for my trip to work and see if it won't hit EMM next time this way if I'm going to have to burn gas I atleast want it to be for something...
 

·
Registered
Joined
·
3,396 Posts
Discussion Starter #6
Torque wasn't set to log, unfortunately.

Good to see I'm not crazy and at least one other has noticed the same thing.
Seems really stupid to just waste gas. If you're going to run, at least use the generator to top up the battery to get the most of it.

Guess I'll start using hold mode as well when it gets near the six weeks no-gas point.
I might let it run once more and do a full torque log (make sure it's set up properly this time :)), just for the data analyst side of me.
(Assuming I get there once more before winter.. might not be until spring)
 

·
Registered
Joined
·
347 Posts
Not to get too far off topic here, but can I ask what adapters everyone is using? I seem to remember there being some OBD issues in years past? Is that specific to a certain model year or type of adapter? I purchased one of the inexpensive adapters and have the Free Torque app for troubleshooting purposes only. I've been very cautious to leave it plugged in indefinitely. This is also the first I've seen of the MyGreenVolt app as well.

Thanks.
 

·
Registered
Joined
·
3,396 Posts
Discussion Starter #8
I have an ELM327 bluetooth one from China from quite a few years back. I would hope it's genuine, as it cost like $50 back then, compared to the $5-10 you can get one for today.
I don't leave it in 24/7, only when I'm actually measuring, usually just a few minutes at a time. No issues to date.
 

·
Moderator
Joined
·
8,680 Posts
Not to get too far off topic here, but can I ask what adapters everyone is using? I seem to remember there being some OBD issues in years past? Is that specific to a certain model year or type of adapter? I purchased one of the inexpensive adapters and have the Free Torque app only troubleshooting purposes. I've been very cautious to leave it pulled in indefinitely. This is also the first I've seen of the MyGreenVolt app as well.

Thanks.
The ScanGauge II that a number of Prius drivers use is known to cause issues. We've had a couple reports of BT OBDII adapters creating issues, but they were not a recognizable brand AFAIK.

The safest approach is the most expensive one - DashDAQ. Drew Technologies licenses info from GM, so presumably they know all about the bus capacity and loading. It also has all the PIDs sorted out. But it's not cheap, and it doesn't let you use your smartphone/tablet (has it's own 5"? touchscreen.)
 

·
Registered
Joined
·
142 Posts
I've only hit EMM once, and it did the same thing according to Torque Pro (MyGreenVolt app doesn't work with my adaptor for some reason, but torque does).
I am the developer of MyGreenVolt app and would need your debug log. Just start the app and try to connect to your OBD adapter. After 30s go to the setting tab and click "Email debug log". You can review the log and add any details you want before sending the email.

I received a log couple of days ago showing a weak connection. The initialization is ok but the adapter returns "Searching...Unable to connect" to all the commands past the initialization. May be a timing problem with a slow adapter. Might be yours :)

Fredo
 

·
Registered
Joined
·
3,396 Posts
Discussion Starter #11 (Edited)
Well, I wasted another cup of gas - for SCIENCE! (lol)

Confirmed my earlier findings again. There is zero benefit to doing EMM while parked, except to preserve your voltstats, I guess.

Starting SOC (raw): 64.31%
Ending SOC (raw): 60.39%
Estimated energy used from battery: 0.67kWh
Estimated energy used from battery (console display): 3.7kWh - 3.0kWh = 0.7kWh (agrees with above)
Expected energy used from battery: 0, or negative.
Fuel used (est from console): 0.25L (same as every EMM so far)

Idle power use: 0.422kW
Duration: 14 minutes
Expected battery energy use if engine entirely decoupled (i.e. normal idle use for being parked for 14 mins): 0.1kWh
Net energy use: 0.6kWh

Graphing the MGA inst. power over time, it appears that everything starts up as expected for the initial warm up period.
For the first minute or so, MGA is generating around 6-7kW
SOC actually climbs one unit to 64.7%, and then MGA generation drops to level out and SOC starts to fall again.
For about one minute, MGA is generating exactly enough power to sustain SOC level. Net inst. power is 0.
Then for the remaining 12 minutes, MGA averages a power USE of about 2kW, when one would reasonably expect it to continue the mode it was just in - generate enough power to maintain current SOC.

So to sum it up:
Net gas used: 0.25L
Net battery used: 0.6 kWh

Contrary to what you'd expect, that perhaps that 0.6kWh would be negative.


My theory - GM programmed some sort of 'engine assist' mode here, in order to use less fuel to do EMM. The electric motor helps the ICE spin so that it's really just using the absolute minimum amount of gas. Something that wouldn't normally be enough to keep it idle on its own, but with added help from the motor allows it to do so without stalling.

In that sense it is truly a waste of gas (and battery power), but you did minimize the overall gas used.
 

·
Moderator
Joined
·
8,680 Posts
MG B (the big drive motor linked to the wheels) shouldn't be doing anything at all while you're parked. I assume you meant to be referring to MG A, the 55kW motor that's linked to the engine a lot of the time.

I'm still surprised by your results, but I've only had a few EMMs, and never had one where I stayed parked, o I don't have any data to the contrary.

One way around what you're seeing would be to run the battery most of the way down, and then engage Mountain Mode after you accept EMM or in its place. We know that will use the gasoline to charge the battery so you'll get benefit from it. On older Volts it would still read those out as electric miles as long as you didn't run the battery all the way down; I think newer Volts are smarter about that...
 

·
Registered
Joined
·
3,396 Posts
Discussion Starter #13
Yes, sorry. Meant MGA. MGB read 0 the entire time, as expected.

Yes, unless you're Ari_c, just pop it into hold or mountain when your EMM message pops up, not much point to letting it run on its own.
 

·
Registered
Joined
·
2,867 Posts
I've had 21 EMMs so far. Isn't the point to use less gas? Also, temperature effects EMMs. I should have created a graph with amount of gas used in an EMM compared to OAT. I have found the colder it is, the more gas that is used. In the warmer months, it is usually right at 0.03303 gallons. However, the EMMs that I have had in February or March can go as high as 0.057 gallons. This is in my garage where it almost never really drops below freezing. Could be a bit more for a Volt really exposed to the elements.

I believe the EMM is measuring for a specific engine coolant temperature. That's probably why it sometimes counts backwards near the end of the EMM.

Also, the amount of gas used in an EMM is right about 1/2 cup. So not very much to be concerned about as far as being wasteful.
 

·
Registered
Joined
·
803 Posts
Yes, unless you're Ari_c, just pop it into hold or mountain when your EMM message pops up, not much point to letting it run on its own.
I was getting EMM warnings yesterday. In an attempt to avoid "useless" running, I let the charge drop until the engine came on, drove at least 5 miles on city streets with in sustain mode (enough to get lots of engine heat help for the climate control) then shut off normally in my garage. Today, it insisted on running a full EMM sequence anyway.

The mystery deepens ...
 

·
Registered
Joined
·
3,396 Posts
Discussion Starter #16
Hmm... Perhaps it didn't hold temp high enough/long enough?
I found during summer, EMM took like 4 minutes
Yet this past one took 14 (it's much colder now).
When mine pops up next I'll try putting it in hold right at that moment and drive a freeway run. Or anticipate it coming up and do the day before.
Or maybe use mountain mode to charge battery from empty. Would force sustained engine run and get it hot real quick.
 

·
Registered
Joined
·
3,396 Posts
Discussion Starter #17
Had another thought, if you use hold or MM to use the engine and get it good and warm, try pulling over and turning off and on. Say yes to EMM (if it asks). Perhaps it will start, detect engine is above temp threshold and complete in a few seconds?
 

·
Registered
Joined
·
3,396 Posts
Discussion Starter #18 (Edited)
So, didn't get a chance to do a long-ish drive before EMM time, decided to log it while driving this time.

Before the engine died completely (sigh), it was working the exact same way.
It only generates electricity during the initial warm-up period, and then it seems the car basically just drives in electric mode, with the gas engine still running. It appears that it tries to hold the net generation at zero, such that the engine is basically running unloaded (it does not appear declutched from the engine though - while it is ~0, it is not 0. It fluctuates very slightly +/- 0). Most of the work is electric and the result is a net reduction in SOC and gasoline. After a while of running at 0kW, MGA switches to running at 3-4kW (note that is 3-4kW consumed, not generated)

It is not like a hold mode, I think it acts more like an ERDTT in that it just runs on its own in the background, regardless of what you're doing while driving.
I'll have to log an ERDTT to see if this is indeed the case for that.

If this is the case, it's basically just extended ERDTT mode to bring the oil up to a higher temp and hold it there for a certain time.
So in older models (v1.0), it would essentially be hold, as my understanding is ERDTT essentially does a full switchover to gas.
While in 13+ (v1.1, v1.2) it is a milder process and does not do a full switchover, is basically just a long idle.
 

·
Registered
Joined
·
3,396 Posts
Discussion Starter #19
Additional findings this time around
1) ERDTT does not count towards EMM clock
2) ERDTBT does not count towards EMM clock, despite running in full gas mode and getting nicely warmed up
3) EMM while driving does not work like ERDTT while driving.
3b) ERDTT runs at a constant RPM and varies generation from 1-7kW. If conditions are favourable to do so, will hook into two motor mode.
3b) EMM starts out like ERDTT and my previous observations, a minute or two of generation at ~6kW and then essentially 0 load the rest of the time. Engine did appear to join in two motor mode once or twice on my drive, but very briefly.
4) EMM does not obey 'disable engine while plugged in'. Warning for garaged remote-starters. (Only applies after the 24h grace period, when it force starts)
 

·
Senior Member
Joined
·
1,027 Posts
It may be an "exercise mode" where the motor is providing a resistive load rather than charging to put the engine under stress.

Generators and especially diesels need to run under moderate to heavy load to prevent gunk and wet stacking.
 
1 - 20 of 28 Posts
Top