Help with A/F Ratios ???

[Wells]

I have a lm-1 wideband and dsmlink ..

I had it pretty well perfectly set from 4500 (when my turbo hits full boost) to 7500 at 11.7 A/F ratio ..


The next night I went out, the temp was a little warmer, and started to tune when I had to take away more fuel to get it back to 11.7 ... It was a little rich.


I got it back to 11.7 most of the way, then all of a sudden it dropped back down to 11.0, which is rich ... So I decided to ask before I took away even more fuel to get it back to 11.7.


Why is the a/f ratio getting more rich all of a sudden? The wideband is maybe a month old, and seems to be working correctly.

Any ideas?

 

[daren_p]

Refer to this log that a user posted (DSMLINK logger). Watch how the timing and A/F follow eachother. Not saying I am right, or I am the best tuner out there, but I was experiancing similar curves on my previous car and I always a assumed A/F was affected by timing. (or vice versa but I don't see how A/F could affect timing).

That log really doen't show us much. That air/fuel ratio is just an estimate in DSMLink & not a WB reading. You also have to look at where his fuel sliders are, they lean out in the upper rpms, at the same time as the air/fuel ratio est. increases.

 

[Wells]

Ok ... I replaced the pcv valve and then did another boost leak test ..

I pushed the throttle plate and the sound didn't change .. So I don't think it's the throttle body seals anymore ..

I couldn't really hear the leak behind the tb after I replaced the pcv valve, but there is a lot of air rushing out of the crank case vent ... I pulled up the dip stick and there was air coming out of that, and the same with the oil cap ..

I'm not sure what is normal, but there doesn't seam to be leaks from my intercooler piping .. so if it's not a boost leak then i don't know why I have to drag my fuel sliders so far down to get it out of the 10's (A/F ratio) ..

 

[daren_p]

Ok ... I replaced the pcv valve and then did another boost leak test ..

I pushed the throttle plate and the sound didn't change .. So I don't think it's the throttle body seals anymore ..

I couldn't really hear the leak behind the tb after I replaced the pcv valve, but there is a lot of air rushing out of the crank case vent ... I pulled up the dip stick and there was air coming out of that, and the same with the oil cap ..

I'm not sure what is normal, but there doesn't seam to be leaks from my intercooler piping .. so if it's not a boost leak then i don't know why I have to drag my fuel sliders so far down to get it out of the 10's (A/F ratio) ..

Since there is air coming out of your crank case vent, I would think you would want to do a leak down test to see if your valve seals are shot (someone with more experience in this area, chime in). Did you spray down everything with soapy water including all vacuum lines, injectors, pipes, ic core, bov etc? Please refer to my post 3 up about your tuning, what are your lo & mid LTFT? what are your global & deadtime settings? This can account for why your rpm sliders are set way too low. Like I said I think its best if you start over, somethings not right you are pulling WAY to much fuel & timing. If you want more help we need to know the info that I've asked in above posts.

 

[GVR4592]

yes believe it or not it will drop your A/F ratio by how much? i dont know...but a 10 degree temp variation is good enough. also you said night and day temp change from 98 to 55 degrees....then yes it will definitly drop a point or even more. those temperature changes are drastic in my opinion. your best bet is to have two setting, night and day.

That's not correct. The maf sensor determines the actual mass of the air(which requires the temperature to be known), and the ecu adjusts fueling accordingly. The only time A/F should change with air temperature is when temps are too cold to maintain a stable A/F ratio. 55 degrees is not that cold. A/F ratio in the high load area's on a completely stock car is around 9.7:1, if it went a full point richer the engine would not run very well, if at all.

Pulling timing will change your air/fuel ratio, care to explain that .

Ignition timing can effect A/F ratio indirectly. If you advance ignition timing "generally" that will produce more torque. More torque requires more fuel. A/F ratio is affected.


My advice is find out why air is coming out of the valvecover vent, it's not supposed to do that. A leakdown test is the next logical step. Fix ALL of the boost leaks no matter how small they are. Get a real fuel pressure regulator, and see where that gets you. All of that might not solve the problem, but it's kind of pointless to tune a car that isn't 100% mechanically sound. Good luck.