I've read through several threads here about an over-rich condition with some 460s. My '95 460 has me confused to say the least. The over-rich stumbling, bumbling idle showed up after pulling a cattle trailer on a few trips. After checking the "obvious", i.e. fuel pressure, fuel pressure regulator, EGR system, fuel filter, cap and rotor, wires, I've come up empty handed. The OBDI codes have varied but have not been constant. Heres' the twist: when I pop the emergency fuel pressure switch on the passenger kick panel the engine purrs like kitten. When I reset the switch it goes back to the over rich stumbling and roughness. This happens when the engine is warm or cold, front tank or rear tank, sunny or cloudy, etc. "Normally" when the emergency fuel switch is activated by a crash it would shut the fuel "off". This one will run as smooth as silk for about 2 minutes before it runs out of fuel.
Here's what's been replaced: fuel press regulator, fuel filter, cap and rotor.
Here's what has been individually disconnected to isolate the problem: MAF/MAP, TPS, IAC solenoid, O2 sensor.
Any and all suggestions are deeply appreciated.

 

When you ran codes did you do it with a jumper or a reader? Did you do a KOEO and a KOER test? Do you recall the codes you got? Sandy

 

Both, the jumper was intermittent and the reader mentioned emissions-type codes, with engine on and off.
Pop the emergency shut-off switch and it runs fine, no codes, no lights, "How comes iz it?"
Thank you for your timely response!

 

When you say you POP the inertia switch do you mean it has been activated and you are resetting it and then it runs good till it dies?

 

edited deactivated to activated above

 

No, I am 'manually' activating the switch to the "off" position to look for changes in the engine.
When I reset the switch to start the engine it runs poorly until I take a small screwdriver and pop it up.(Also replaced the inertia switch early on)
Thanks again!

 

After some looking at your issue, I think this article may be of help to you. You will see as you go through it, it contains some symptoms you mention. Hope this helps
EDIT: I would also hook up all the emission components you disconnected.
https://easyautodiagnostics.com/ford...-relay-tests-1

 

The engine should die within a few seconds of tripping the inertia switch.

You stated you checked the fuel pressure and regulator, could you provide more details? What was the fuel pressure at idle with the vacuum hose connected to the fuel pressure regulator? What was the pressure with the vacuum disconnected? Did the pressure rise when "goosing" the throttle, vacuum hose connected? How fast does the pressure drop after shutting off the engine? What is the pressure after 1 minute, 2 minutes, 5 minutes etc.?

 

Stumbling idle usually means overly lean not rich. Ignore the exhaust smell... if the cats have been removed it will smell rich even it's running lean.
Possible causes are low fuel pressure or EGR that isn't completely closing at idle.

 

Thank you for the link, I will try to go through it soon.
Everything I disconnected was reconnected one at a time separately to weed out issues. I've owned and maintained several Ford cars and trucks with carbs and F.I. over the years, this one has me scratching my noggin'. :-)

 

The two members that replied after me both know their stuff real well. I suggest you do what they offer.

 

I was trying to respond to the previous comments but am unable to answer to each one separately so here goes. I did the fuel pressure test off of the Schrader valve on the fuel lines, I "think" it was 40 psi at idle, it's been a few months, I replaced the regulator recently. I will run those tests gain soon and report back. I lean towards rich due to the black soot out the exhaust, the greatly decreased gas mileage, and that gassy smell; the cats are intact. The EGR checks out with vacuum. A failing fuel pump sounds interesting but both pumps work as normal, am trying to avoid a tank drop but it may be required.
What bothers me the most is that a simple change of the inertia switch position turns the beauty into a beast!
I deeply appreciate the replies and will follow up soon. Thanks!

 

Ok that definitely is rich and it also explains why tripping the inertia switch improves the way it runs. This suggests the fuel pressure is way way high, it should make 32-35psi at idle and increase towards 40psi every time the throttle is blipped or if vacuum is removed from the regulator. If that checks out the next likely cause is a bad MAP sensor, and third in line is the PCM itself. There could also be a wiring short or rodent damage so check for that too.

 

Check the fuel return line, probly plugged up causing higher than normal fuel pressure. With the fuel pumps not running and engine leans out withl fuel pressure drops is likely cause.

Rerun fuel pressure test and watch what happens when you "shut off" the fuel pumps.

Another possibility could be the MAP sensor is telling engine to run rich but not at the point to set codes. I did have this happen years ago, and what a PITA to find!

 

I will check that out, Thanks again!