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914World.com _ 914World Garage _ Weak battery = erratic ignition??

Posted by: Mueller Jun 15 2005, 12:09 PM

History:

Kept getting an ignition related miss during idle and it was worse when I rev'd up the motor....

I started to think it was just due to my plugs being overly fouled from the too rich mixture while tuning the FI.

I cleaned the plugs, still had a miss, removed the HyFire CDI from the loop, still had a miss.....

During the entire time of trying to tune the motor, i had a 2 year old Optima battery in the car which had hardley any use on it, I also had my batter charger hooked up and turned onto 2amps and sometimes 15amps....still would get a miss

I had problems starting the car and cranked the battery charger to 50amps...car started right up and no ignition miss

Time to go get a new battery............

Posted by: lapuwali Jun 15 2005, 12:26 PM

Low battery voltage will cause all kinds of problems with EFI systems. Most ECUs have some sort of compensation to adjust injector timing based on actual battery voltage. A voltmeter hooked directly to the battery terminals is a great accessory when running EFI, esp. D-Jet, which does a pretty bad job of compensating for low voltage (tends to make the car run rich).

Posted by: airsix Jun 15 2005, 12:45 PM

Agreeing with James and adding that your tuning screen might even show the actual voltage seen by the ECU. My MIC3 does this - you can see the voltage live on screen. Mine goes nuts if it dips below 10v.

Mike, what are you using for crank possition signal? Watch the rpm on the tuning screen. Is it smooth and accurate or erratic? If it's erratic (noise, bad sensor, bad sensor adjustment) you'll have no end to your problems. BTDT. Switching from a home-brew dizzy sensor to the crank-mounted sensor cured those ills for me. My hair even grew back.

-Ben M.

Posted by: airsix Jun 15 2005, 12:57 PM

Followup: Maybe this is tied to your questions about plug gap. Low battery + wide plug gap = runs like crap?
Shoot, I'm starting to ryme. I'm reading too many Dr. Seuss beditme stories to my kids. ...If your Daddy's name is Dwight and he likes to look at birds at night, the gift for Dwight that might be right is a Bright Dwight Bird Flight Night Sight Light....

-Ben M.

Posted by: Air_Cooled_Nut Jun 15 2005, 02:07 PM

D-Jet does not compensate for low voltage which is why it's important to have a properly functioning charging system.