Issues with AFR

88GriggsGT

Member
Feb 19, 2021
6
2
13
40
Thousand Oaks
Hello all, new to this community, but not new to Mustangs. Im hoping you can help with an issue I'm having. I recently installed an AEM AFR gauge and it is reading lean. When I start the car it will read 14.7 for a short while, and then steadily climb until it goes full lean. It pretty much stays full lean until I go WOT, at which point it will go down to about 13.5. I haven't pulled past 4500 because i don't want to damage anything.

The car has a 331 NA and it runs great. The only reason I installed the gauge was to see if my new long tube headers and high flow cats changed the tune. My prior exhaust was shorties and off road x pipe. The car has new o2 sensors and spark plugs, and I can't find any vacuum leaks. I pulled the codes and got a 33 and 84.

Im wondering if the gauge is faulty as I got it used from my brother. If it was actually lean, wouldn't it throw a code?

Thanks, Ian
 
  • Sponsors(?)


90sickfox

Wasn't a pretty sight...and I've got big hands
SN Certified Technician
Mar 2, 2015
5,863
4,950
203
43
Get a cheap fuel ratio gauge from the parts store and hook to one of your o2 sensors. It could be the gauge, the sensor, really running lean,, or an air leak. The el cheapo gauge will show stoich, lean and rich.

If it's running lean enough to peg the WB the manifolds should be almost red hot. You could take a thermal gun and record the readings at each exhaust runner. If one is way hotter than the others it could point you in the right direction.

Where are your o2 sensors mounted in the long tubes ? It shouldn't cause the tune to change much if at all. Long tubes can put the sensors too far from the engine causing bad readings ( pegging lean still wouldn't be expected ). Some long tubes used to only have the sensors in one tube instead of at the collector. That only gives the reading for that one cylinder.

Also, did you do a free air calibration on the WB ?

View: https://youtu.be/-u57_BfU_bU
 

KRUISR

5 Year Member
Apr 16, 2015
924
351
83
51
Also, did you do a free air calibration on the WB ?
If not do it.

I have dual widebands (Innovate DLG-1) as well. My car would idle lean (15-17) and then be at stoich once I moved and 12-13 at WOT. I have an Anderson PMS plugged in for monitoring as I learn where I need to adjust and recently added a little fuel at idle. Now idles at stoich, is smoother and it doesn't stink sitting int drivers seat when idling in the garage. Wideband (that is calibrated) is the best tool in understanding if your car is running right.
 

88GriggsGT

Member
Feb 19, 2021
6
2
13
40
Thousand Oaks
Thanks for the replies. The o2 sensors for the computer are located in the collector of each header. The o2 for the wideband is located in the x-pipe between the collector and cat on the driver side. I don't hear or see any exhaust leaks at the heads or between the header and x.

The headers are ceramic coated, so it may hard to tell, but I dont any signs of excessive heat. I also checked primaries with a thermal gun and didn't see any temps greater than 180 with the car idling.

I will perform a fresh air calibration on the gauge tomorrow when I get home.

Thanks, Ian
 

96pushrod

I think they're a little easier to get off
May 15, 2018
975
589
103
29
Savannah
A new aem really shouldn’t NEED a free air calibration, but it won’t hurt.

What did you tune the car with? If it’s something like a quarterhorse you can look at the narrowband voltage to give you a sanity check. If it’s full lean on the wideband, it would be under .7v on the narrowband. If it’s not, then something is going on with the wideband. Even if you don’t have a quarterhorse you can still tap into the signal voltage on the narrowband with a multimeter.

If it goes full lean and then comes back under wot, that usually means the wideband is functioning. I’ll usually pull one out and cover it with a gas saturated rag to see if it’ll change its reading, since they usually show full lean once the sensor is/has gone out.
 

KRUISR

5 Year Member
Apr 16, 2015
924
351
83
51
Don't forget O2s and wideband sensors need to get hot to work right. Being that far down the exhaust, it may not be getting enough heat.

I have shorties and the O2s are 4-6" down from the collectors and my widebands are installed right near the bend where the exhaust flattens out.
 

junkyardwarrior

Active Member
Jan 10, 2011
349
87
48
also look for exhaust leaks, even tiny ones will cause a lean reading. Feedback EFI system has to be sealed up.
 

88GriggsGT

Member
Feb 19, 2021
6
2
13
40
Thousand Oaks
So it looks like my older aem wideband does not have the ability to perform a fresh air calibration, but I did try a new o2 sensor and it was still lean.. i also tried a cheaper narrow band afr gauge and it was pegged lean.

I leaning towards a vacuum leak so I'll perform a smoke test this week
 
  • Like
Reactions: 1 user

88GriggsGT

Member
Feb 19, 2021
6
2
13
40
Thousand Oaks
Performed a smoke test and found a significant air leak between the intake manifold and the canister that goes to the fuel tank. Now it runs better but is still lean.

At idle it's s pegged lean, part throttle cruise it bounces between 16.5 and 18, and WOT it drops to just below 15. I did the smoke test at the vacuum tree and can't find any other obvious air leaks, eventually the smoke comes out the filter.

I'll probably bring it back to a tuner, but I'd like to eliminate any other obvious issues. You guys have any other ideas?