My '90 bronco II 2.9 efi is running really rich. so rich in fact that it runs ok for like 3 minutes and then will not go over 35 mph unless im going downhill. the fawker runs rough and spits nasty ass black dust and water out the tailpipe.
so far ive cleaned the air filter, cleaned the plugs, replaced the air charge temp sensor and map sensor. help me please and i promise to be a good boy for the rest of my life. any help at all. :(

plugged cat?? bad o2 sensor??..vacume leak on the intake??...thats about all I can think of..

Ignition module going bad? I know when mine when out it ran like crap and was burning so rich in made the cat glow orange

Ignition module going bad? I know when mine when out it ran like crap and was burning so rich in made the cat glow orange

I concur, the module is probably the most likely cause..

Been there, done that. O2 sensor 100%


And while you're getting your O2 sensor, pick up a code scanner. It could have saved you from throwing parts at the truck.


And don't forget to disconnect the battery after you replace sensors to clear the code in the computer, otherwise the code will stay put for 40 or so starts.

It's gotta be either a Coolant temp sensor or the fuel pressure Regulator. I would lean towards the temp sensor. It's the two wire one for the puter, not the single wire one. Good luck

map sensor...
they go bad and it gets rich real quick.lots of black smoke.

sorry-i just read again and saw you did that already.

Ok, since you're getting everybody telling to something different, it's really no help at all. So I'll try to make it easier on you.

Pick up a scanner for about $30 at a parts store.
Warm the truck up, then take the key on,engine off codes and the engine running codes.

This is just by memory, so bear with me.

If all runs well until it's warm, that normally points towards a sensor. The computer doesn't begin acknowledging the sensors until warm for the most part.

Ignition modules normally don't just weird out in my experience. They'll either go out for good, or completely shut down when they get hot. You can pull the TFI off the back of the distributor and get it checked for free at Autozone.

If you get an 11 code, then your computer is saying that all the emissions related sensors are OK.

If the Coolant Temp Sensor goes out, you'll get a code for just that. A bad CTS will cause some crappy running.
Same for the MAP.

A bad O2 sensor will store a 41 (O2 reading lean;does not switch), or a 42(O2 reading rich;does not switch)

There's also a possibility that the Throttle Position Sensor is acting wacky, which will effect the timing and fuel mixture.

If you have a fuel pressure gauge, hook it up to eliminate the fuel pressure regulator. You should have around 35-40psi with the key on, engine off. Another way to check is to turn the key on, then pull the vacuum hose off the back of the FPR. If fuel runs out, it's bad.

You can check vacuum leaks around the intake by spraying carb cleaner around the mating surfaces of the upper and lower intake manifold. If you hear a change in idle rpm, then you have a leak.


I was mistaken in my first response by saying 100% O2 sensor. In MY Experience with 2.9's, what you described sounds more like an O2 than another sensor, but they're all a possibility.

What it boils down to: Pick up a code scanner and tell us what codes it's sending, cause there's no conclusive answer with the symptoms you've given us.