Stalling

[patrickt]

Had you just recently changed out your battery you would have mentioned it, so this is not likely to be your problem. But I'll post it nonetheless because there may be some guys out there that are transitioning to AGM batteries and this is not something you read about on the forums.

I hadn't had to touch my idle in years and my FE idles nicely in the low 700's. A perfect "rumpety rump." A few weeks ago I put in a new Interstate MTZ-47/H5 battery. That battery is an AGM battery, as opposed to flooded, which brought about the need for an idle adjustment.

My engine actually stalled at a stoplight on its first run with the new battery because it was idling noticeably lower. Why would this happen? Because the internal resistance of an AGM battery can be as low as 2%. A flooded battery is usually up around 10-15%. This lower internal resistance means an increased battery voltage output along with a higher amperage draw while recharging. The higher amperage draw creates a higher load on the engine from the alternator, which reduces your idle, if you have a carb. If you happen to have an aluminum flywheel, balancer, water pump, pistons, valve train, etc. then the lighter your rotating mass the more you'll notice an increased drag at idle from the alternator. A small turn of the screw fixes the problem. So, that's your snippet of information on AGM batteries for today.