MyBlueC5

I made a post about having problems with my car running too rich... black smoke, loads up, etc, etc...

One question:

Is is possible to have good air/fuel ratio numbers but yet still be too rich?

I thought that if your a/f ratio was correct, it couldn't be too rich or lean.

Thanks,

Mark

SBNova

The Air/Fuel ratio is a direct numeric value of rich/lean. If the A/F ratio is *normal* then you arent too rich or lean. The exception is that every engine likes a slightly different ratio. Temperature, humidity and elevation all play a role in this as well. Stoich is said to be 14.7:1 which is reasonably good for a cruise ratio, but under wide open throttle it needs to be richer, like in the 12-13;1 ratio. Some cars will idle at or near 14.7, some need to be richer- like high 13's/low 14's. You can attain higher mileage in the 15:1's but you need to be careful of running too lean. I hope this helps.

XTwinTurbo

It also depends on when you are measuring A/F ratio compared to when you are noticing the overly rich condition. For example, you're Vette can have perfect air-fuel ratio at idle or during conservative driving because the O2's are monitoring the a/f ratio. As soon as you go WOT or step on the gas, the motor can go rich because the Vette now ignores the O2's and uses a computer map for fueling. The opposite fueling problems are possible if your O2's are bad.

In other words, are you measuring A/F ratios and seeing the fuel problems under the same conditions? That shouldn't be happening and the black smoke may be symptoms of another problem.

PUREC4

I have the same problem 'rich',taking this a step further. On a recent dyno pull. starting at 2400 rpms air fuel was at 16.8. By 3000rpm air fuel was now 12.1, 3500@11.7, 4100@11.7, 4800@11.4, 5300@10.1
and killing HP. Peak hp came in at 4200@ 257.4 then drop to 215.1 by 5300 rpm. As you can see I was very disappointed in the hp curve considering, the mod's done. Torque was ok at 390 ftlbs. Where would you look? Thanks

Timmy!

I would look to the fuel mapping on that one. The Power Enrichment tables need to be dropped down some from 3500 on.

65Z01

If you have a custom chip look to mapping; if not, for WOT richness, look to:
-fuel injectors too large
-fuel pressure too high
-faulty fuel injector

For part throttle richness, look to:
-faulty coolant temp sensor
-faulty O2 sensor
-air leak

Mo_Bandy

Under normal operatin conditions as the O2 sensors cycle back and forth th ECM will try to keep the AFR as close to 14.7 -14.1 as possible.

Like the above post, when you go WOT generally about 60% throttle or more the ECM reverts to the MAF /MAP and then looks at the fuel maps and enrichment tables.

If you have put larger injectors on the car, in most cases the ECM will compensate probably up t about 1.5 times... then you would see issues in your idle ( black smoke) or if you have bumpped up your fuel pressure with an adjustable fuel pressure regulate this could have the same effect even the combination of the two. This could also translate to the wide open throttle as well in a normally aspirated L98 or LT1 you wouldn't need to go more than 30 pound injectors... I only run 36's on my S/C LT1...

Hopefully this helps... another thought , is if you have done any recent modifications to the car you may want to go back get a baseline and change things one at a time...

Mo