The entire exhaust system was replaced, going from 2.5" to 3" pipe. The muffler is a straight-through canister and there is no resonator. It has a definite exhaust note now, and makes more power until the brick wall is hit.

 

Here is a strech, but it might be worth checking. Some of the earlier FI systems had two fuel pumps, one in tank and one out side the tank, and two fuel filters. My son had an 86 Bronco, 5.0 liter, with the port injection. He was having the same problems you describe and we had gone through all the repairs you have described as well as replacing both fuel pumps, since we had low fuel pressure. A retired mechanic asked if we had replaced both fuel filters. After we located the second filter, and replaced it, all the problems went away.
The second filter was a screen type in a screw together pancake style housing. It was mounted above the transfer case mounting bracket on the driver side frame rail. You could not readily see it from below, you had to find it by feel. Didn't look like it had ever been changed.
I am not sure when Ford got away from the second filter, but it might be worth checking.
Hope this helps. Good luck.
Roger Carter

 

Two guesses, one based on some experience, the other "wild."

On my '88 F-150, the tank selector valve became restricted somehow. The symptoms were different than yours, but it DID cause fuel starvation--bad.

My truck wouldn't idle...or sometimes it would idle poorly, but would basically ONLY idle. It didn't want to rev above 1,500-2,000, but at an idle, it was smoother than when attempting to rev.

What finally tipped me to the starvation was the fact that, sitting in a parking lot trying to get it to run consistently enough to enter traffic, the temperature shot WAY up, to near "H" (or whatever it says). And this truck NEVER runs above the bottom quarter of the temp. gauge.

I was also having trouble switching tanks.

I put a new tank selector valve in and the truck ran great.

My other thought was--what about a bad Throttle Position Sensor? (I know it's not posting a code, and I have no answer for that, but IF) the sensor were bad, and you open the throttle, but the TPS wasn't registering the wider positions, I would think it would result in a "lean spike" and an misfiring, under load. But say the bottom portion of the TPS's "sweep" still works okay, so that it runs fine at lesser throttle demands.

Don't know if they fail "partially," or not--just a wild guess. If you had a "known good" TPS you could borrow, off a friend's truck, that might be a quick "parts hanging" diagnosis tool....

Just me guessing....

 

This van has two tanks with a low pressure pump in each. The rear tank pump has been replaced twice due to failure. The lines go to a selector valve, which is new (the old one sprang a leak about a year ago, and I found out they don't have an O-ring seal in the body that can be replaced -- just two plain plastic flanges). The line goes to the high pressure pump, which is also new. The line then goes to the canister fuel filter, which has been replaced twice. It then goes to the fuel manifold. There appear to be no other filters in line.

I checked the throttle position sensor by putting a voltmeter on it and moving it through it's full range of motion. The voltage starts out at the proper voltage at idle (about 0.9) and smoothly increases to full throttle. No erratic or abnormal response was seen at all. I suppose it could potentially behave differently with the engine hot, but I assume it's just a simple rheostat.

 

Another thing I am trying is installing an Innovate Motorsports LC-1 calibrated wideband programmable oxygen sensor with digital gauge. This will display the actual fuel/air ratio in real time. So if it's a fuel problem from any cause I should see it as a lean or rich mixture when the problem manifests itself. The device can also be programmed via laptop with a customized feedback curve to the computer so fuel/air ratios can be adjusted. In my case it may be compensating for another problem but at least I should be able to determine if it is a fuel problem or not. It still could be the computer is retarding the ignition drastically under heavy load.

BTW, does anybody know where the coolant temperature sensor for the computer is located on the 1989 460CI engine? It's difficult to see anything on a van so poking around to find something is near impossible.

 

A quick update on the '89 E-350 460CI:

I installed the LC-1 wideband oxygen sensor and took the van for a drive. When warm, it idles rich at about 13:1. It is a bit rough and uneven at idle too. Slightly off idle, it leans out (and smooths out) at approximately a stochiometric 14.7:1 ratio. Going down a level road, it runs very lean at 15.3:1. It runs smooth at this normal cruise. Somewhat lean is normal for cruise but it should go slightly rich (14.3:1 - 14.5:1) under heavy load for maximum power. When I go up a hill and give it lots of pedal, the power falls off and the ratio doesn't change appreciably. Since I've already checked the throttle position sensor, any ideas why it would continue to run lean under heavy load?

 

hi guy,s im a new user and want to say hi to all of u and think this site is great i also have a 460 but its on propane and was great but it to has lost power and i cant figer it out iv changed all filters gaped plugs at 30 cause it,s on propane but when i step on it it,s fine if i dont kick the 4 barrel in but soon as i do it just boggs down and want,s to backfire like it,s out of time. i dont know what,s wrong with it it,s in a 1978 ford f-350 and i have restored it from the ground up so i got lots of money tied up in it. i even got ride of the point,s and went electronic seem,s like it,s starving for propane but i just don,t know. im a farly good mechanic but no nothing about propane i sure could us some help with this problem if your up on this type of fuel. well thank,s for your time and have a good day. thank you ken. slick1

 

You might look at the fuel pressure regulator. If it is malfunctioning you could experience the problem you describe, lean at high load. Just another thought.
Roger Carter

 

Man, it makes me sick to read about all of your problems. Sick because I have been having all of the same problems on my '92 F-350. After replacing most everything I still get the EGR code. Light throttle is better. The more you put your foot into it, the louder it gets and the slower it goes. For a 460 you would think you would have all the power you want.

Anyway, if the '92 configuration is the same as yours, there are two sensors for the temperature. One sets next to the thermostat housing and the other sets about center of the intake manifold between the distributor and the throttle body, closer to the distributor. Your local parts place should get you each so you could match them up. I noticed some improvement in low end but no change on the pulling or higher speed power.

Best of luck. I really hope you can find the solution. I am even looking at a full rebuild/replacement to fix the problem. WYO92350

 

If you have the ability I would check the TPS with a graphing multimeter. This way you will be able to see if there are any glitches that a multimeter might not see. You said your fuel psi doesn't change at all when she looses power. I guess the best I could say is to someway rig up a secondary fuel supply like propane and when it acts up give her some fuel and see what happens. If it improves you know you have a fuel issue. You described the idle being rough and also said that you had excessive back psi. Was the same EGR valve on when you had the excessive back psi. Maybe the EGR valve is damaged, but I would think that would lean out the Idle if the valve is stuck open. Also Check all Grounds, Connectors, and wires for damage corosion etc...

I have worked on some vehicles at my diesel shop and was suprised to find that a loose Battery connection, slightly rubbed away insulation, or a connector pin that was slightly loose causing an intermittent loss of connection, was the cause of a Pandora's box of drivability issues.

 

ya thanks for the info my truck is on propane tho but i found the problem the power valve was turned just about all the way off i set that and presto more power than bc hydro lol i dont even have my second daries hooked up as it has all kinds of power running on two barrel setting hope this helps u some as 460 has all kinds of power so dont rebuild her yet might be something simpel sorry about the spelling ken

 

Power valve? Could you explain? I would love a simple fix.

 

No power valves on EFI motors, only on carbed engines.

 

what about the coil? I see you changed wires, cap, rotor but I didn't see that you replaced the coil...

 

we have an '88 F-350 1 ton dump,replaced everything but the cat. TPS,EGR,ignition control module,etc.
I'm scrapping the cat and going to replace it with some sort of tube/pipe/blank??? I was kind of hoping to find something on the internet before I "manufacture" something.