Cranking with weak battery

[dyermullet]

Xfi 2.0 If my battery is low car will crank but check engine light will blink and car won't start. I have to put a battery charger on the car just on 10 amps then car will start when I crank it. This is very annoying. Factory computer would have started under these same conditions.
I have a holley hp from cruz but have not installed it. Does the holley have the same trouble with low battery voltage?

 

[dynoman]

You're probably dropping below 10v or less during cranking and modern ECU's usually need to meet a minimum voltage to operate properly . This is done to protect circuits . Sounds like you need a new battery and check the charging system . Make sure you're getting + 13.5 v from the alternator to the battery .

 

[dyermullet]

Yes that is exactly what is happening.

My question is will the holley have the same trouble?

 

[dynoman]

Probably with a low voltage . New ECU's are more "finicky" than the old school stuff . If you have low voltage to operate the ECU the current goes up and new ECU's are not as robust as old stuff and so protection is built into the circuitry .

 

[Turbo6inKY]

Yes that is exactly what is happening.

My question is will the holley have the same trouble?

Yes.
I take issue with your characterization of this situation as "trouble" on the feet of the ECM. You're trying to start a car with a dead battery. That's bad for the battery and the electronics, and if it starts it becomes bad for the alternator. Don't do that.

Here's the deal, electrical components consume watts to operate. Watts are delivered as a function of voltage and amperage. If the voltage goes down, the amperage to supply the necessary wattage goes up. Amps are what generate heat in a conductor as the current flows through it. It's what blows fuses. The conductor melts

Trying to start a car at 10v instead of 13.5 results in a larger current draw (35%!) to power all these things, which starts cooking stuff. Specific example: If your fuel pump needs 100watts to operate at a level sufficient to pressurize the rail and let the car idle, it'll pull 7.4 amps at 13.5V. But at 10V? The draw becomes 10 amps.

Translate that to modern ECMs that have overcurrent protection, and they just won't work below a certain voltage. All those electronics packed into that box cannot run at those kinds of current levels without melting stuff, so they're designed not to.

So don't do that.

Get a new battery and put it on a tender when you're not driving the car.

 

[dynoman]

Yes.
I take issue with your characterization of this situation as "trouble" on the feet of the ECM. You're trying to start a car with a dead battery. That's bad for the battery and the electronics, and if it starts it becomes bad for the alternator. Don't do that.

Here's the deal, electrical components consume watts to operate. Watts are delivered as a function of voltage and amperage. If the voltage goes down, the amperage to supply the necessary wattage goes up. Amps are what generate heat in a conductor as the current flows through it. It's what blows fuses. The conductor melts

Trying to start a car at 10v instead of 13.5 results in a larger current draw (35%!) to power all these things, which starts cooking stuff. Specific example: If your fuel pump needs 100watts to operate at a level sufficient to pressurize the rail and let the car idle, it'll pull 7.4 amps at 13.5V. But at 10V? The draw becomes 10 amps.

Translate that to modern ECMs that have overcurrent protection, and they just won't work below a certain voltage. All those electronics packed into that box cannot run at those kinds of current levels without melting stuff, so they're designed not to.

So don't do that.

Get a new battery and put it on a tender when you're not driving the car.

Thanks for doing the long version of why low voltage is bad !! lol

 

[Mr.Spool]

Xfi 2.0 If my battery is low car will crank but check engine light will blink and car won't start. I have to put a battery charger on the car just on 10 amps then car will start when I crank it. This is very annoying. Factory computer would have started under these same conditions.
I have a holley hp from cruz but have not installed it. Does the holley have the same trouble with low battery voltage?

Charge your battery or get a new one

 

[dyermullet]

Bump has anyone experienced this with a holley hp?

 

[Chuck Leeper]

Have you checked batt volts while cranking?
Have you checked alt performance once the car is running?
Before you condemn the batt, do a volt drop test on both sides of the batt.
A bad ground will cause this when there's no issue with the batt.

As for the Holley systems and 10V... I've installed a few but have not had the issue. The Holley forum has this come up. I know the Sniper will go nutz at 10V or less. Might do a search there.
I have tested stock ecm/injs at <10v. Injectors worked.

 

[dyermullet]

As for the Holley systems and 10V... I've installed a few but have not had the issue. The Holley forum has this come up. Might do a search there.
I have tested stock ecm/injs at <10v. Injectors worked.

Thanks that is what I am asking about. (While I appreciate the effort in the writeups on electricity that's not the question I am trying to answer). I like everything about the xfi over the stock ecm except for this issue. It is very frustrating when this happens havin to run two or three extension cords to get a charger to the car just so I can get it started.

I am looking at more of the issue someone left head lights, on dome light whatever. Go camping and then car won't start when you ready to go home etc.

I will try searching the holley message board .
How about any of the other computers do they also have this problem megasquirt based ones?

Thanks everyone.

 

[Turbo6inKY]

Bump has anyone experienced this with a holley hp?

Is the Holley HP a modern ECM with over current protection? Yes, it is.

Thanks that is what I am asking about. (While I appreciate the effort in the writeups on electricity that's not the question I am trying to answer). I like everything about the xfi over the stock ecm except for this issue. It is very frustrating when this happens havin to run two or three extension cords to get a charger to the car just so I can get it started.

I am looking at more of the issue someone left head lights, on dome light whatever. Go camping and then car won't start when you ready to go home etc.

I will try searching the holley message board .
How about any of the other computers do they also have this problem megasquirt based ones?

Thanks everyone.

If the car is regularly dead when you go out to start it, then you should have a tender on the battery when the car is not operating, or disconnect it entirely while it sits. Even on the stock ECM, you should not start it with the battery that low. The stock ECM does not have over current protection, which means you're eventually gonna melt stuff if you keep doing this to it.

The Megasquirt based units have fuses on the board for severe situations, and they will not fire the injectors if the battery is below ~10.2 volts.