I've got a 95 with a 5.0. My question is what can cause it to burn rich?

-If I understand correctly, the MAF reads the amound of air coming in and also its density. This tells the computer how to adjust fuel.
-Oxygen sensor, reads the exhaust and tells the computer how to adjust ratio.
-Air charge temp sensor play any part here?
-What else could cause it to burn rich? I checked the timing (with spout removed) and its at 10 deg. The idle seems pretty good. I say pretty good because it has a slight miss once in a while. I'm trying to figure out why my bronco wont pass emissions. Its failing the low rpm test. I cleaned the IAC, but am thinking about replacing it since its been on the vehicle for about 100k. I checked for vaccuum leak and found none (All lines are new anyway, but I had a buddy hook up a machine to engine that fills everything with smoke so you can find any leaks). Adj fuel press reg is set for 40psi. Any ideas? Could the MAF be bad? The 02 was replaced about 40k ago. I was thinking of pulling it out and wiping it down.

 

Why the adjustable fuel pressure regulator? Have you checked it with a gauge to make sure its accurate? Are there any codes being set? Truck might have one of those "super chip" thing to "add" power causing it to run rich. Those area few things off the top of my head.

 

Thanks for the reply,

I have an adj fuel reg because several people recommended that I get one. I had the engine rebuilt, added edlebrock heads and intake, and changed the cam. I did have a custome performance chip made. I will be pulling that out before I take it to emissions again. Just curious if there is anything else I should try. I cleaned the IAC and it didnt really make a diff for the idle. The idle misses every now and then. I fig I"m just going to relplace the IAC anyway. I'm hesitant to replace the o2 since I did so about 40k ago. If I cant get this bronco to pass emissions I might have to let it go. I've had nothing but issues with the vehicle. I spent about 5 grand on the engine to up the performance and cant feel much of a diff over stock power. I cant even break traction in soft sand with 31 in tires. Biggest waste of money. Now it wont pass emissions (keep in mind it barely passed emissions the first time I tested it with new motor, so it is possible to pass with all the mods). I was better off with the 150k mile engine in it before because it had pretty much the same power, passed emissions with flying colors and I had 5 grand more in my account.

 

As for the codes, most of the time the test wont complete because it cant hold the rpm steady during the koer. If you step on the gas pedal and quickly let go the engine will die most of the time. Other times it will drop the rpm to about 300, almost die and then come back to the normal rpm range.

 

Then you will need to pull the Codes from the KOEO test and correct the issues causing those Codes to be stored THEN move on to the KOER test. If the computer cannot maintain idle there is a reason for it. Find it. Fix it. Until then, you will be chasing a ghost and throwing time and money at a problem you can't solve.

The "rich" condition can be triggered by innumerable things including vacuum leaks. Yes, I know that's a counter-intuitive idea but when you take into account that the computer COMPENSATES for the additional air in the mix, it will actually throw the ratio off the other way... towards rich.

EVERY sensor plays a role in controlling the system. However, trying to guess which one is the culprit will leave you frustrated and penniless.