AFR


ALEX-CY

Active Member
Joined
Mar 17, 2009
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790
what is the air fuel ratio on stock b18cr at idle. mine is between 20-1 and 23-1. if I rev up the engine go to normal (14-1 and 15-1) . the idle speed is ok
I use p73 ecu
 
It should sit at 14.7-1, is this very lean idle on a hot restart by any chance?
 
It should sit at 14.7-1, is this very lean idle on a hot restart by any chance?
Agreed. it is safe to run slightly leaner at idle (maby 15.5 AFR) But you generally want it to be as close to 14.7 as possible. 20 AFR is would give me a scare if I saw that on my car.
I have seen older and dirty AFR sensors give leaner readings until more air passes over them when the throttle is opened. I've also seen AFR sensors welded in too far away from the exhaust stream to read right. I always like to have two sensors pre-cat; one wide and one narrow to have a comparison.
What kinda of AFR set up do you have? Whats the info man? You running a stock O2 sensor for the P73? In theory, the ECU should add fuel until it achieves 14.7:1 AFR. If it doesn't, it will set a code for running too lean, etc... You can also look at the short and long term fuel trim to see how your ECU is reacting when its at idle.
20:1 AFR is going to make your valves very hot with that lean burn. But it doesn't take much fuel to idle our engine- so it is possible.
 
I wouldnt be too concerned with running an engine low/mid 15s in light throttle situations tbh. No real heat being generated and youll be saving abit of fuel.
Id not to worried about damage from lean idling either tbh for the same reason.
Clearly not right that it idles so lean though.

Your not on an open downpipe are you? Or a bad exhaust leak?
 
I wouldnt be too concerned with running an engine low/mid 15s in light throttle situations tbh. No real heat being generated and youll be saving abit of fuel.
Id not to worried about damage from lean idling either tbh for the same reason.
Clearly not right that it idles so lean though.

Your not on an open downpipe are you? Or a bad exhaust leak?
I don't have any exhaust leak(it is stock) with out a cat. I don't understand what you mean open downpipe
 
An open downpipe is basically your exhaust ends at the manifold or downpipe, so no catback. You clearly have a catback its not air being introduced into the exhaust and fooling your sensor.
This 20-1. Is it there when you come to stop after driving or just on a restart with the engine warm?
 
If its only on a warm restart and it goes after a short drive ive noticed the same issue with alot of these cars.
Im not 100% on the cause but i think the fuel gets hot sat in the fuel rail and its vaporising before it gets the chance to be combusted by the engine. I could be wrong but thats my only theory so far.
 
If its only on a warm restart and it goes after a short drive ive noticed the same issue with alot of these cars.
Im not 100% on the cause but i think the fuel gets hot sat in the fuel rail and its vaporising before it gets the chance to be combusted by the engine. I could be wrong but thats my only theory so far.
I too have seen this and agree with what jesse888 says. It is something you can clean up with a tunable ECU I believe.
 
I too have seen this and agree with what jesse888 says. It is something you can clean up with a tunable ECU I believe.

I have tried afew different thingd within hondata to fix it but what i really need is a post start vs coolant temp fuel compensation table. Something hondata doesnt have, it only has a generic post start adjustment so any adjustments made to that table will effect the cold start aswell as hot.
 
so it looks like is something normal. I will borrow my mec air fuel ratio meter next week and I will check the car on all conditions when aim driving.
what do you think is the best ecu for tuning. is worth to tune a stock engine with some bolt ons?
 
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I have tried afew different thingd within hondata to fix it but what i really need is a post start vs coolant temp fuel compensation table. Something hondata doesnt have, it only has a generic post start adjustment so any adjustments made to that table will effect the cold start aswell as hot.
Me as well. I love Hondatas interface and ease of tuning- but after a while of using it I began to see the benefits of a true stand alone, where you could tune the finer details like post start vs coolant temp.
Its worth it if you want the most out of your bolt ons and IF there is a good tuner near by. Seen many cars wreaked by bad tunes. The factory ECU does fine most of the time with 'over the counter' performance mods.
Maybe just an Oxygen sensor tho?
 
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