Electrical gurus, I need your help!
My friend just finished a 1961 Ford Wagon (Pictures coming) and is using a Holley computer to control the stack injection. The problem we have is that the computer needs to see 12v to operate and often especially after the car sits for a week at a time or the blower motor is on when you turn on the key, it will drop just below that threshold (11.99V). The starter will spin the engine just fine, but there will be no spark or fuel...
The battery is in the rear of the car (14 ft to the starter) and is a new battery. Car runs and drives properly and charges at 13.8-14.1v. Getting the jump box out and starting the car after sitting at the car show is not an option.
Any tricks to keep/maintain the 12V?
Thanks, Patrick
Put in a DC - DC converter to feed the computer, that way you can give it a steady, regulated voltage regardless of the actual system voltage.
A 12v DC-to-DC power supply is what you need here, something that will bump up the output voltage by taking more current on the input.
That seems like a colossally stupid design feature for an aftermarket car ECU though, and I'd have to wonder what else in the design was done that badly.
I had a similar issue on my boat. Starter motor kicked in and its load dropped voltage to as low as 6v. Computer wasnt a big fan of that. I cleaned up the connections and got rid of excess wire and it helped. Id suggest putting a meter on the batter and seeing just how how its dropping when starting.
Is the electrical system being fed from the lug on the starter? If so, pulling power directly from the battery might fix the situation.
How big is your battery cable? 14 feet is a hike.
But for an easy battery maintainer, Harbor Freight sells a cheap, low-watt solar charger that you could set in the rear window and run to the battery. Link
codrus (Forum Supporter) said:
A 12v DC-to-DC power supply is what you need here, something that will bump up the output voltage by taking more current on the input.
That seems like a colossally stupid design feature for an aftermarket car ECU though, and I'd have to wonder what else in the design was done that badly.
Any ECU. OEM's design to about 6v, so that you can deal with very cold temps- so when getting that DC to DC converter, make sure the input range goes low enough (probalby 8 for this car). Nothing worse to have a car not start than to have the voltage drop just as you are starting to inject fuel. Get a partial fire, and it shuts down.
thought this was going to be about the 12v Cummins. I have nothing to contribute
You'd want to contact Holley's support. The ECU should be able to handle voltage drops resulting from the starter or the like. Does the ECU lose communication with your laptop or tuning device when the voltage goes below 12 volts?
I'd get a different computer. It sounds like it was poorly engineered, in this way that you CAN see.
The computer is fed directly from the battery. The starting (spinning of the starter) doesnt seem to affect it.
For example: Last Saturday, we went to the Caffeine and Octane and when we went to leave - Randy turned on the car and then hesitated to start the car while he adjusted his seat or something and the Heat /AC blower was on high. When he did go to crank the car, the starter would spin the engine easily - but no spark or fuel. I measured the voltage at the battery and it read 11.86v. We touched a set of jumper cables to the battery and it fired right off.
I was almost thinking of some sort of capacitor or the like to hold 12v + on the Holley computer. I'll have to look into the converters mentioned.
Thanbks for all the help. This is really bugging us.
Patrick
In reply to pbkelley :
What happens if the alternator dies and you have to limp somewhere? Most automotive grade electronics are good to 9v, the rest are good further down than that. It sounds like the hardware engineers designed in no fault tolerance.
I suspect it's a hardware fault in the ECU - you'd have to try to intentionally make one cut out at 10 mV under the 12 volt spec. Or possibly some sort of stray battery voltage correction table that is doing weird things under 12 volts.
I was 100 miles from home, leaving an autocross when I noticed my wipers were very slow. Dead alternator.
I can personally verify that at least one 2001 Miata will keep running with less than 5 volts left from the battery. Pulled into the driveway right at dusk.
A battery in good condition shouldn't drop below 12 volts in just a couple weeks. I'd make sure it and the charging system are okay, and check all wire connections. Also, maybe run a larger wire to the ECU to make sure voltage drop is minimized.
Some cars have multiple ignition circuits. Certain circuits will cut out when cranking - the HVAC blower, for example - to make sure the starter has maximum juice. Any chance the ECU is wired in to one of these? Seems unlikely when it will start with extra power.
How about a bad ground? The battery might be supplying enough voltage, but if you have a crap ground on the ECU it may not be able to use it.
In reply to Keith Tanner :
Ford's ignition circuit was run-only, true, but if this were the case then it would never start at all, no matter the battery voltage.
IIRC, the ignition resistor wire was connected directly to the ignition switch in that era, so you couldn't really get 12V from a run circuit without getting really fancy, anyway.
