Question about cold start knock, battery

[steve99]

Originally Posted by radroach

My car struggled somewhat to start this morning in 31*F weather with a low battery. A couple seconds after cold start the engine did a quick stumble which I could hear and feel and guess it was knock. Note I could hear it knock clearly. Everything else after was ok, car drove really strong all day in the cold temps.

Question is, could the low battery induce a knock situation on a cold start?

Well at 31F the ECU is adding a crapload of fuel to get the engine lit up..
via increasing the cranking pulse widths (yep the tables are for E85 but same deal on petrol just smaller pulsewidths but it still increases heaps at low temps) and then the maf scale offset (kind of like an electronic choke).


and the ignition timing gets retared to -15 degrees until the high rev cold start sequence is completed.


so you do get the odd stumble or pop occasionally in cold weather even on petrol. especially if you try to drive off while the warmup sequence is active


just let the ecu do its thing until the high rev sequence is complete , if you monitoring ignition timing you will see the ignition timing go from -15 to about +12 once the sequence is complete about 90 seconds or so.

[phrosty]

What Steve said. When I cold start in ~20F weather, there are usually at least one or two pops.

[gravitylover]

Originally Posted by Tcoat

I have followed these starting and battery issues closely (just ask @Ultramaroon ) and it is interesting that about 8 out of 10 people with premature battery failure or problems starting have BRZs. We see the occasional FRS with issues but they are very rare. Considering there are about 10 times the number of FRSs to BRZs out there that is a very telling number. Now the question that raises is, why? There is something different between the two that is causing either a parasitic draw when shut off or preventing the battery from charging properly when running. I have no theory as to what that is though. It will be interesting to see as the 86 gets closer to the same equipment as the BRZs if the frequency of battery issues increases.

Just a thought... Does the FRS have the alarm light that flashes on the dashboard all the time when the doors are closed?

[geezerbrzeezer]

Originally Posted by humfrz

The short answer is NO. However, the lights will eventually go off ...... when the battery runs out of electrons.....


humfrz

Ha ha, and where the hell is the 'No Thanks' button.

[Tcoat]

Originally Posted by gravitylover

Just a thought... Does the FRS have the alarm light that flashes on the dashboard all the time when the doors are closed?

Yep. It just means the immobiliser is on. Of course it looks like an armed alarm to so we have that going for us.

[humfrz]

Originally Posted by geezerbrzeezer

Ha ha, and where the hell is the 'No Thanks' button.

....... "you talken to me" ....??

Well, ya never know what people know and don't know ......

When my father was in his mid 90s, his eyesight was failing badly.

I bought him a "atomic", talking watch.

He was very appreciative.

About a year later, he mentioned his watch quit running, although he had set in the window sill from time to time.

I ask him if he had replaced the battery.

He said "no, I thought you said it was an "atomic" watch.


humfrz

[radroach]

Originally Posted by Tcoat

and it is interesting that about 8 out of 10 people with premature battery failure or problems starting have BRZs. We see the occasional FRS with issues but they are very rare. Considering there are about 10 times the number of FRSs to BRZs out there that is a very telling number. Now the question that raises is, why? There is something different between the two that is causing either a parasitic draw when shut off or preventing the battery from charging properly when running. I have no theory as to what that is though. It will be interesting to see as the 86 gets closer to the same equipment as the BRZs if the frequency of battery issues increases.

I'd like to check some things out with a multimeter then, maybe the lights. I've had a couple dome light failures in the last year. A halogen and an LED.

Maybe the BRZ '13-'16 front lights being a little too much of a power draw on cold start. I wonder what their draw is running in any mode (headlight, brights, boomerang, and the adjusting motors)

[Tcoat]

Originally Posted by radroach

I'd like to check some things out with a multimeter then, maybe the lights. I've had a couple dome light failures in the last year. A halogen and an LED.

Maybe the BRZ '13-'16 front lights being a little too much of a power draw on cold start. I wonder what their draw is running in any mode (headlight, brights, boomerang, and the adjusting motors)

Be interesting if somebody validated my theory.

[Spartarus]

Originally Posted by steve99

and the ignition timing gets retared to -15 degrees until the high rev cold start sequence is completed.


so you do get the odd stumble or pop occasionally in cold weather even on petrol. especially if you try to drive off while the warmup sequence is active

Back when I had the car, before I started tuning it, I used to be able to interrupt / cancel the cold start sequence mid-cycle by applying load.

Timing and idle speed would immediately kick back to normal, and not return to cold start values. Didn't work every time, never bothered to narrow down the exact conditions that would do it.

[Ultramaroon]

Originally Posted by Spartarus

Back when I had the car, before I started tuning it, I used to be able to interrupt / cancel the cold start sequence mid-cycle by applying load.

Timing and idle speed would immediately kick back to normal, and not return to cold start values. Didn't work every time, never bothered to narrow down the exact conditions that would do it.

Cancels every time as soon as I start moving.

[Hoahao]

Originally Posted by Tcoat

Classic signs of a battery on the decline. You should never have to boost a battery. Eventually it just won't work at all and then you will be stuck.



I left my trunk open for 16 hours once and had no battery issues. Mine cranks the same at -20 as it does in the middle of summer.
I have followed these starting and battery issues closely (just ask @Ultramaroon ) and it is interesting that about 8 out of 10 people with premature battery failure or problems starting have BRZs. We see the occasional FRS with issues but they are very rare. Considering there are about 10 times the number of FRSs to BRZs out there that is a very telling number. Now the question that raises is, why? There is something different between the two that is causing either a parasitic draw when shut off or preventing the battery from charging properly when running. I have no theory as to what that is though. It will be interesting to see as the 86 gets closer to the same equipment as the BRZs if the frequency of battery issues increases.

I posted here a while ago about a battery problem. I have a Monogram with the running lights and heated seats. I suspect that my battery does not get quite as much juice when running, especially if you just do short trips like I usually do.

I'm still on the OEM battery and proactively gave it a 7 hour trickle charge about 2 weeks ago with the start of cold weather. I've taken a couple of longer trips lately and have tried the old "turn on the overhead light light and then start the car" trick to see if it dims. No dim, but in cold weather, like 10 degrees F it takes an extra crank to kick the engine in.