pope91rs

Hey guys, I have recently gottern my carbed 6.0 project up and running. It's a 93 toyota x-cab, carbed 6.0, comp cam used not shure of specs, 317 heads milled 35 thous, home built headers and a street 750 hp. I have a lm1 wideband that is reading lean at idle and part throttle around 20 to 26 afr. I tried a new o2 sensor no change. If I adjust my idle mixture out more than 3/4 of a turn exhaust gets very rich to the point it will burn your eyes with almost no change on the afr. With the idle mixture at about 1/2 turn it idles well but still a little rich judging by exaust smell. Header tubes are pretty long o2 sensor is about at the end of the trans pan which is a 4l80. Any ideas of why it seems rich even though wideband is saying lean. At wot above 3500 afr gets to about 13.1.

Pop N Wood

iTrader: (1)

Exhaust leak?

ZONES89RS

iTrader: (25)

Possible reset the initial setting out of the exhaust?

3pedals

iTrader: (3)

If the cam is big enough to make the engine lope, it will always read lean on the O2 even though it will smell rich on the tail pipe.
When the engine lopes, it is miss firing, and unburned oxygen is flowing out into the exhaust - the O2 sensor see's this and reads lean even though you have the idle mix screws out far enough to get it to idle nice.
Running lots of initial timing helps ALOT

ZONES89RS

iTrader: (25)

Mine smells rich, but it is 14.7ish at idle.

bad67ls

iTrader: (2)

same here. mid to high 14 at idle and its stinky.

pope91rs

Thanks guys for the info, I do have a little exhaust leak. I have slip fit collectors that I just did about 1/2 inch stitch welds on. I thought this may be some of my afr problem. I'm not shure of my cam specs bought the cam used and lost the info on it. At about 800 rpm it has a pretty good loap. If anyone else has any opinions please chime in.

89sierra

have you tried hooking a vacuum gauge up. i am pretty sure you can tell if its lean or rich at idle with a vacuum gauge depending on how the indicator moves.

speedtigger

iTrader: (16)

The way I would describe it is that the overlap of a larger camshaft means that there is a period of time when the intake valve and the exhaust valves are open at the same time. This allows the fresh intake charge of air & fuel to pass straight from the intake tract into the exhaust. This is where the un-burned fuel comes from in the exhaust of an engine with a long duration camshaft. As the engine rpm increases, it diminishes this pumping inefficiency and that is why the engine smooths out as the RPMs increase on an engine with a high performance or racing camshaft.

pope91rs

I have hooked up a vacuum gauge I have about 14" at idle, idles well wideband reads very lean I'm thinking its exhaust leaks.