300E Now Running Rich
 

Well, I went through an intermittent no idle situation. I ended up replacing the airflow position sensor and the idle has been fine ever since. That was about a month and about three tanks of fuel ago.

I filled up day before yesterday and fuel mileage was SERIOUSLY off. This morning I ran my fingers in the tailpipe right after shutting it off and it is solid black soot.

I guess I'm headed for the manuals. In the meantime I will get out my other car.

Bummer!

Have you checked the duty cycle at all?

Larry,

Have you checked the duty cycle on the X11? Maybe its throwing a fault telling you that one of the sensors is had it? Maybe O2 sensor?

How "off" is it? I agree with checking duty cycle first.

I just discovered the sooty tailpipe this morning before walking inside for work. I haven't had a chance to so much as get it home and raise the hood yet. I will check trouble codes at both places and go from there. I have a duty cycle meter and an LED code reader that I made.

It's hotter'n hell right now, and I plan on flying in the morning, so I'll park it and get to it in a few days.

Thanks for the comments & suggestions. I'll probably be back for more in a few days. I might mess with it early Sunday morning before it gets hot. Very easily could be the O2 sensor sense it hasn't been touched since it left Germany 25 years ago.

O2 sensor would be my first bet, take note of the duty cycle before and after it warms up, it should go into O2 sensor control. Either way, replacing that old O2 sensor can't hurt as they're typical maintenance items anyways. If you do decide to, you can save a good amount of money by splicing in a mid-90s Bosch O2 sensor, IIRC just the wires have to be swapped/crossed over. A search on here should reveal what model/year Mustang works.

Also FWIW my O2 sensor didn't throw any codes when it crapped out (maybe not hitting the code threshold?). Lambda was off though.

Duty cycle should be solid 70% with engine idling cold, open loop. Then it should start fluctuating at around 50% when the engine goes into closed loop.

As far as the O2 sensor, it's really cheap if you splice in a '90 Mustang GT O2 sensor Bosch part# 13953 (available at ANY parts store) for around $40, as opposed to the factory sensor @ $100.

If that's not the problem, probe the EHA with your volt meter. Specifically pay attention to the voltage when you rev the engine above 3000rpm. The EHA can seriously affect mileage (like 15mpg bad) if it goes bad in a certain way.

Yeh I would bet O2 sensor Larry. Definitely start there. At your mileage it's well beyond time and even if it's not that, it's probably going from rich to lean very slowly and affecting your power and fuel economy to some extent.

It won't throw a code since all it checks for is voltage.