Anybody have experience with an AFR?

[old_man]

I have an AEM AFR wideband on a normally aspirated 4.7L stroker. . I was having problems passing emissions. I had it set to give me roughly 13.4 going down the highway. It read too high on the CO. I ended up having to adjust it to around 15.5 to get it to pass.

15.5 seems a bit too lean.

 

[sidewaysstarion]

I have an AEM AFR wideband on a normally aspirated 4.7L stroker. . I was having problems passing emissions. I had it set to give me roughly 13.4 going down the highway. It read too high on the CO. I ended up having to adjust it to around 15.5 to get it to pass.

15.5 seems a bit too lean.

You're going to want to run ~14.7 on cruise and closer to 13.5 on acceleration.

http://lmgtfy.com/?q=stoichiometric+ratio

 

[MoparManiac]

There's no "set in stone" rule that you HAVE to run 14.7 while cruising or EXACTLY 13.5 under acceleration. Those are guidelines.

Running 15.5 while cruising lightly (aka higher vacuum) is not a big deal. If the motor isn't running hot or bucking, I'd say leave it. Just means better emissions and fuel economy.

I'd actually be surprised if a stock 4.0 was at 14.7 while cruising.

 

[Boostwerks.com]

There's no "set in stone" rule that you HAVE to run 14.7 while cruising or EXACTLY 13.5 under acceleration. Those are guidelines.

Running 15.5 while cruising lightly (aka higher vacuum) is not a big deal. If the motor isn't running hot or bucking, I'd say leave it. Just means better emissions and fuel economy.

I'd actually be surprised if a stock 4.0 was at 14.7 while cruising.

Mine usually runs between 14.6-14.8 as indicated by an AEM UEGO.

I Personally wouldn't run leaner than 14.7 cruising, especially with the all iron motor. Narrow band O2's are incredibly sensitive to honing in on 14.7 for a reason. Anything leaner will just be pumping excess air into mix that doesn't burn. Depending on timing, this will only create more latent heat. You want to be richer in the 13-12's under load as the additional fuel will help cool the fuel/air mix to prevent pre-ignition.

Newer fuels tend to have up to 10% ethanol as well, which has an even "richer" stoich value. Because of this the corrected value is actually in the 14.1 range.

A newer more efficient all aluminum motor might benefit from running leaner, but I wouldn't put our tractor motor in that category.

I also have an EFI101 tuning cert if that matters. It was well worth the expense. Ben Strader knows his stuff :cheers:

 

[MoparManiac]

I agree with what you are saying, but if he's running 15.5 with no overheating, no bucking/surging, and no issues with tip-in, then what's the problem?

Sure, in theory 15.5 is way too lean, but in reality if the motor is fine with it, then who cares?

 

[Boostwerks.com]

I agree with what you are saying, but if he's running 15.5 with no overheating, no bucking/surging, and no issues with tip-in, then what's the problem?

Sure, in theory 15.5 is way too lean, but in reality if the motor is fine with it, then who cares?

Simply because a problem doesn't obviously show it self, doesn't mean that it isn't a problem.

Long term, it may not be fine. Running lean essentially reduces the safety buffer the engine has against pre-ignition, detonation, a bad tank of gas...etc. It may melt a plug, piston, or nothing. If your willing to risk it, that's really up to personal preference. If it were me, I'd be shooting for 14.7.

 

[old_man]

The funny thing is that the meter says I am running too lean, while the DOT emissions test says I am running on the rich side.

I'm old school. I am going to put a few highway miles on it and do a plug reading. It's crazy how few mechanics still read the plugs.

I noticed a steady drop in mileage and performance over the last year or two. It was running very rich. I had to drop the MAP supply voltage down to 4 volts to get it to pass emissions. The injectors were always too big but I never had to go below 4.6 volts before. It has been 12 years since I built the stroker and I don't remember exactly which injectors I put in but they were supposed to be from a Ford Mustang IIRC. I would like to find something that runs around 21 and try to get the injector pulse closer to what is optimal.

 

[DieselSJ]

I'd be shooting for 14.7.

What do you like for AFR at full load? And what do you like for timing? Assuming 4.0 with 214 degree cam (at 050) and 9:1 with head work?

 

[Boostwerks.com]

The funny thing is that the meter says I am running too lean, while the DOT emissions test says I am running on the rich side.

I'm old school. I am going to put a few highway miles on it and do a plug reading. It's crazy how few mechanics still read the plugs.

I noticed a steady drop in mileage and performance over the last year or two. It was running very rich. I had to drop the MAP supply voltage down to 4 volts to get it to pass emissions. The injectors were always too big but I never had to go below 4.6 volts before. It has been 12 years since I built the stroker and I don't remember exactly which injectors I put in but they were supposed to be from a Ford Mustang IIRC. I would like to find something that runs around 21 and try to get the injector pulse closer to what is optimal.

There are a lot of factors at play though. Timing being the other major player. Reading the plugs is by far the best way to see what's going on in there. Unfortunately, to get a good reading you need to get the engine under load and then shut it off before it has a chance to wipe the reading off the plugs. There should be a fairly obviously line about halfway up the ground strap which is the best indicator of timing. If the line is low, it may need more timing (advanced) and timing pulled if it's too high.

Have you done a compression test? Condition of the cat? You shouldn't have to go leaner than 14.7 to pass, which leads me to think that something else may be up.

What do you like for AFR at full load? And what do you like for timing? Assuming 4.0 with 214 degree cam (at 050) and 9:1 with head work?

It really depends on the specific engine. As a rule of thumb, most N/A engines should be in the 13's under load. Timing should be dialed in as I had described above. The values are going to be different for every engine due to the variables involved. Obviously the safest and easiest way to do this is spend some time on a dyno. Tune fuel first, then timing, then fuel again.

 

[hexdmy]

I have an AEM AFR wideband on a normally aspirated 4.7L stroker. . I was having problems passing emissions. I had it set to give me roughly 13.4 going down the highway. It read too high on the CO. I ended up having to adjust it to around 15.5 to get it to pass.

15.5 seems a bit too lean.

You did not specify in your post if you are running a factory or aftermarket ECU, assuming you're running a factory ECU it should be running in close loop unless you're nearly at full throttle in which case it would taper into a power enrichment mode. And the ECU does not hold the engine at exactly Lambda 1 instead it is constantly switching back-and-forth crossing lambda 1 by a few percent rich then lean as this is the nature of the O2 sensor feedback control loop.

 

[old_man]

You are right about it bouncing around, but going down the highway at 75, it seems to run around 15.3 or so. It just bothers me that the meter says one thing and the DOT test station says another.

I am running a stock Renix ECU. To get it out of the 10s, I had to drop the supply voltage on the MAP to 4.0 volts. Once I dialed the mixture, I started getting more power.

I am boring a throttle body tonight, so before I spend a ton of time on the numbers, I want to get the new setup on and fired up.

 

[streetpirate]

IIRC a 14.7 ratio SHOULD be optimum for emissions. Its the most efficient ratio, and I think that running leaner than that will raise the NOx?

leaner than that in cruse is fine as long as it reacts quickly when the vacuum drops while accelerating. 14.7 is good for light acceleration but you want it to transition to 13.5-13.8 under full throttle and 0 vac.

 

[Dr. Dyno]

Under WOT you'd need the AFR to be somewhere around 12.5-13.2 (0.85-0.90 lambda).
An AFR of 14.7-15.4 (1.00-1.05 lambda) is the desirable range for light throttle cruise, and an AFR of 14.0-14.7 (0.95-1.00 lambda) is where you need to be for light throttle acceleration.
________________________

1992 Jeep Cherokee Laredo - 4.6L Stroker - AX15
202rwhp @ 4700rpm, 258rwtq @ 3400rpm

 

[old_man]

From what I can tell, I had a bad temp sensor that goes to the ecu. Sometimes it would be open loop, others it would be closed, with little rhyme or reason.

 

[NorCalChris]

Do you have a way to monitor egts? Im curious as to what they are while at cruise with that AFR.

 

[old_man]

I don't have a way at the moment, but being a test engineer, I have been thinking of throwing some high temp thermocouples at it.