Wierd AF at Idle
 

I've got an LM-1 in one of my exhaust manifolds. It gives me great results at everything but idle where I have to run very rich for it to idle well (11.5 - 12).

The exhuast is dry all the way back to the tail pipe, where a little bit of water is introduced. The cam is similar to an HP500EFI cam. I get a tad of moisture through the O2 bung but not much.

I am wondering if this is the moisture playing tricks on the sensor or if it's actually running that rich at idle (it won't even idle at 14:1).

Well is this a stock 500hp efi calibration? If so, thats normal. Otherwise, its tough to get a totally accurate af at idle, in a collector, but its probably quite close with a new sensor.

Thanks,
Dustin

No, it's a carbed 502. 800cfm Holley, four corner idle

Water is not good for the o2 sensor more because of thermal shock.

Water found there may be showing you that reversion is playing havoc on your A/F ratio. Atmospheric air can be pulled in easily and thus your sensor shows this too because it 'just reads air.'

SO, you may have a different ratio than what it's showing you.

This fools many people.

Tric is to mount the sensor as far back as possible and if that doesn't work bump idle speed just a touch and read A/F then. If that doesn't work, your out of luck for idle A/F ratio's.

Innovate states they like to see 02 atleast 18" further back from exhaust to atmosphere opening.

BTW" larger cams usually need richer A/F to maintain smoothness. Increased base timing too.

Then thats very standard for stock jetting. Mercury had them 11.5-12:0 across the entire rpm range. Chances are, your reading pretty accurate. Because it's in a collector, you'll get pulsations, to be truly accurate, it needs a constantly velocity.

Talked to Inovate and they said there's almost no circumstance where the sensor will read richer than actual. Almost all error modes obviously including excess air and reversion will show up as a lean condition.

SO maybe that's just what it needs. I'm not a carb guy. worked with FI for the last 20 years and never seen an engine that needed that much fuel at idle, but I guess it needs what it needs. Just don't like the thought of washing down the cylinders, and fouling sparkplugs when I need to idle for extended periods (which happens a lot)

We'll I've seen them certainly read rich in some conditions when they weren't, but I doubt thats your issue. The 500hp carb is rich everywhere, it can be leaned up on all 4 corners. Think about this, we can install a SC on that motor, install factory carb, and it still runs 11:1 @ WOT!!! So start by taking 2-4 jet sizes out of the front, then work your way through it. The factory jets are staggered.