Engine Ultimate mystery need help


New Member
Aug 21, 2005
Ok 5.0 tech gurus I need some serious help on my 93 5.0 AOD fox. First let me say I'm a very experienced with foxes having owned several with many different N/A and super charged combos all built and tuned myself. I'm only adding this so we can get passed the basics like did I check the fuel pressure or reset the computer. So here is the problem and the situation leading up to the issue. The car will start and run but its pig rich I don't mean slightly I mean black eye burning rich and my wideband is pegged at 10.0. Two weeks ago the car was running perfect, but I noticed a small fuel leak from the #5 injector lower o-ring. Instead of just swapping the o-ring i ordered a set of stock ebay injectors. ( i know bad idea). I installed the injectors and switched from my BBK AFPR back to a stock unit. When I started the car it was rough and the wideband was almost pegged LEAN. I though maybe a bad injector or regulator so I swapped in another set of stock injectors and back to my BBK regulator. This is when the rich AFR started with both sets of injectors and regulators. Below is a list of all the things I have tried with no change to the to super rich AFR. All changes below make no difference.

2 different stock MAFs
2 sets of o2 (autozone and motorcraft)
new ford TPS set at .97
new ford IAC
new coolant and air charge sensors
2 different TFI modules (dynamod and accel)
2 different coils ford and Accel
pulled codes only see a code for the missing smog pump
Pulled ECU no leaking or broken caps
replaced EVERY vacuum line
New Ron Francis injector harness
Checked and cleaned all grounds

Engine is stock save for 70MM TB, BBK FPR ,full exhaust, 3G alt and built AOD with a c3w computer
I feel like I have expended all possibilities with no solution If any one has ideas please let me know.
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Wasn't a pretty sight...and I've got big hands
SN Certified Technician
Mar 2, 2015
A bad iat sensor can cause this and doesn't set a code. Computer thinks it's below freezing temps so it goes rich....cold air would be denser = more fuel.
I had a bad BAP sensor cause a rich condition like this once. It didn't throw a code and there isn't a way to test this sensor so it was a gamble in replacing it. Mabey try unplugging the electric to this sensor as a part of testing? It will run with the sensor unplugged but will throw a CEL.