A/F question

[DieselNuts]

I posted this in the Time Slip Bar and Posi brought up something I would like to discuss. I got a baseline dynojet reading yesterday and this is the result:

I am stock with the exception of 1chamber flows welded into stock piping. The A/F was read through the tailpipe and not through a wide ban. Posi pointed out that I am running lean and need to get more fuel. My question is, When reading A/F from the tailpipe and not the bung, will it read more lean?

 

[thelpb]

Last time I was on a dyno, the tailpipe sniffer read a full point leaner than my on board wideband. Based on what you described it sounds like you still have the stock 4 cat midpipe which will play havoc with a sniffer. You're ok.

The A/F chart shows you're between 12 and 13 at the tailpipe, so your actual pre-cat A/F is probably between 11 and 12.

 

[DieselNuts]

Yes, I do have the stock 4 cat midpipe. Thanks for the reassurance. Posi had me worried for a min. lol

 

[BIGV]

Those tail pipe sniffers will have you driving your car like an old lady until you get a tune. Thats what happened to me the dyno shop kept stopping me saying I am way to lean. Turns out my af was aroudn 11-12 there sniffer was f'd up reading like 15. I have a wideband now.

 

[xenodragon]

11.5 a/f reading from the bung vs 13.3 a/f from a sniffer for me....

 

[Jomo1994z71]

I posted this in the Time Slip Bar and Posi brought up something I would like to discuss. I got a baseline dynojet reading yesterday and this is the result:

I am stock with the exception of 1chamber flows welded into stock piping. The A/F was read through the tailpipe and not through a wide ban. Posi pointed out that I am running lean and need to get more fuel. My question is, When reading A/F from the tailpipe and not the bung, will it read more lean?

Correct me if I'm wrong but it looks pretty good, very close to mine

 

[IronTerp]

A properly calibrated and maintained tail pipe A/F analyzer will read from .4 to .5 leaner than a bung reading. In the above graph, you're reading about 12.5 tailpipe, which is about 12.0 actual, IF the sniffer is functioning acurately.