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Canuck Tech
Canuck Tech, Auto Service Technician
Category: Car
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Experience:  Red Seal Journeyman Technician, 20 Years experience
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E350: 1988 E350/460/auto/FI. My problem is that the truck dies

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1988 E350/460/auto/FI. My problem is that the truck dies unexpectedly on deceleration only. It will travel at most about 20 miles, die, then after an hour or so start back up and go the distance again. I have thoroughly checked all fuel systems up to and including the fuel pump relay and everything is good. I replaced both the engine control module and the pickup module(in the dist.). Still have the problem. Last time it quit, in the drive way, idling, I checked and had excellent spark. WTF! is wrong?

The Auxiliary air valve controls the air needed for idle. Betcha it's sticky. I would probably toss one at it, and clean up any carbon while the valve is out. It is right under the throttle body. Also, check the throttle plates and shaft for wear. If the shaft is worn and the plates don't close correctly, there will be an erratic idle. Bulletin number 95-7-11 talks about the symptoms you describe, and looks at some other issues like exhaust restriction. The no-start is a bit puzzling, but the bulletin addresses it.


These guys want some cash to look at the bulletin, but maybe you can find it somewhere else on the net

Customer: replied 4 years ago.

Is your description, "Auxiliary air valve", the same as 'Idle Control Valve'? Sits just in front of the throttle body and attached to the intake manifold. 2 wires attached. Must be the same.

I'll check the shaft and plates, as you suggested.

The exhaust system has been recently replaced, so that couldn't be it.

One point .... would the 'Throttle Position Sensor' or the 'MAP Sensor' share fault in the problem I'm having?

Anything else you might throw at me?

Thank you for your reply.

Idle air control and auxiliary air are the same. A TPS will usually give a hesitation on the way to open throttle, but it is a possibility. Relatively inexpensive. MAP will usually give a more consistent driveabilty, rough running, but again, possible.Let keep the conversation going - I love automotive victories, and I'd like to see you beat this one!
Customer: replied 4 years ago.

I'm heading down to get a new Idle Air Control Valve this morning. I'll let you know how that goes. The shaft and plates are tight. I think I'll leave the TPS for now. Other than this current problem, the truck runs awesome! It still runs awesome, until the second it dies! Thanks again for your reply. I'll be in touch later today.

Sounds good. Best. Canuck
Customer: replied 4 years ago.

Well, I had high hopes, but that didn't work. After installing the new idle air control it started right up, ran for about 20 seconds, then died. It started up after that and ran about 10 seconds and died. Now, nothing. I went back out about 4-5 minutes later and it did the same, started, died. I have good spark. Just seems to keep starving for fuel. Can't figure it out. Both fuel pumps check out good, lots of delivery. Why does the high pressure pump only run for 15-20 seconds? I know this is normal but it makes no sense. I'm at my wits end. Nothing is working here! Any other ideas??


Customer: replied 4 years ago.

okay, a little update.....I found an item that resembles a tire valve on the passenger side fuel rack. I'm assuming this is for checking the fuel pressure(?). There's nothing there, no fuel, nothing, even with the key on or while trying to start, nothing. I also noticed an item resembling a vacuum pot on the driver's side fuel rack........fuel pressure regulator. No wires to it, just a vacuum line directly to intake manifold vacuum. Could this be the problem?? Could this little regulator prevent fuel from flowing if it is defective?

Customer: replied 4 years ago.

Another update......... I was reading on the Ford Enthusiasts forum about a guy who had already replaced everything I have replaced, same problem. Turned out to be the MAP sensor. Apparently they regulate fuel flow through varying signals based on manifold vacuum. What the hell, might as well replace that too! I wouldn't mind doing all this if the truck needed it, but it has always run like a bat outta hell for me. This is one of my work trucks, my workhorse, to be exact. I pull my 12K lbs trailer full of tools to my jobs with it. I live in the mountains in Central Cal and do almost all my driving up and down around here. One hell of a powerful truck, but not when it won't pop! I'll get a MAP and get back. Thanks again.



Sounds like a plan. Thanks for your patience. Canuck
Customer: replied 4 years ago.

I give up. Nothing works, still dead in the water. No fuel in the lines to the injectors. I have no more money to spend on this right now. Thank you for your help.

Man... I'll do some more research tomorrow - so, it seems like the fuel pump is stopping according to you last post. I'll repost tomorrow. Canuck

Customer: replied 4 years ago.

The pumps work, both of them. Something is stopping the fuel. The injectors have power. I don't get it. Okay, thanks Canuck!

Longshot - take the fuel filler caps off... a tank venting issue??? Tank is going into a vacuum, stopping fuel flow... Long shot...
The regulator won't prevent fuel from flowing... Have you replaced the pump. and the fuel pump relay? There is another relay in the system called the EEC power relay that controls power to the fuel pump relay. If it has good spark, this means the pick up in the distributer is working, so we are looking at fuel pump circuitry - control from the ecm, and then the high current side for the pump
Customer: replied 4 years ago.

I've checked the fuel pumps, both work fine, it seems. I downloaded four pages of pump/relay tests and all checks out good. I'm going out there this morning to check again just to make sure they're still working. I'll try the cap thing too, cover the bases. There is a sediment canister just before the high pressure pump under the cab. I've had the cap off many times and every time I do it's full of fuel and the tank pump delivers a very good amount to that point. Changed the filter. The high pressure pump runs for about 15-20 seconds when the key is turned on, which is normal. The truck has died several times while I'm out in it. I wiggle wires trying to get something that's working to not work but everything keeps working! That's the problem.

Is it possible for the fuel pump relay to 'over heat' and stop doing it's job momentarily?

I need to re-approach the situation with a clear head because I am about to try dynamite! Haha!

One thing though ..... the first time this problem occured I was able to keep the truck going by constantly pumping the pedal. The truck ran very badly for a ways, cleared up, then when I came to a stop sign, died. It does appear it's starving for fuel, just can't find the source.

Where is this EEC POWER RELAY??? The fuel pump relay is mounted on the pass. fender well w/ another relay under a black plastic cover. Can't recall what the other relay is but I went through the test procedures and both are working good.

I'll go check the pumps again. I'll leave the dynamite in the barn for now. I keep it in a box with a noose, in case things get tough.

One way or another this is gonna get solved!

Good morning Dan. It is possible for the relay to crap out when hot. I'll work on getting a location for you for the EEC relay.
Customer: replied 4 years ago.

Thanks Canuck. Have a great day. I'll be out checking over stuff again.



Not sure if you've seen this or not...

An in-line reservoir has been included in the fuel system. Under normal operating conditions, valving in the in-line reservoir allows the high-pressure pump and engine to be supplied with fuel directly from the tank while return flow is routed directly back to the tank. When the pick-up tube is exposed to air, the high pressure pump draws fuel from the reservoir.

When the pick-up is again submerged, normal operation resumes.

There are two types of reservoirs single function and dual function. The dual function reservoir is used with dual tank vehicles. A dual function reservoir combines the function of the reservoir with the function of a mechanically actuated selector

Vehicles with dual tanks have three electric fuel pumps. Two low pressure in-tank fuel
pumps, located in both the front and rear tanks, pump fuel into a reservoir.
A high pressure in-line fuel pump then takes the fuel from the reservoir to the
fuel injectors. This system can draw fuel from either the front or rear fuel
tank unit. With the ignition switch in START or RUN, current flows through a fuse link to the fuel pump relay. The dual function reservoir replaces the six port selector valve
on fuel injected dual tank vehicles. The dual function reservoir switches the
tank from which the engine draws fuel mechanically, instead of electrically.

The dual function reservoir operates as follows: Fuel pressure created by the selected in-tank fuel pump exerts force on a 3 inch fluorosilicon diaphragm which is in turn connected to a T-bar and two shafts. This force moves the valve shaft,
simultaneously opening and closing supply and return ports. When the alternate
fuel tank is selected, pressure is exerted on the opposite side of the diaphragm,
moving the valve shafts to open the alternate fuel tank ports.

What a complicated system!!!

The EEC relay is under the right hand side of the dash board.


This dual function reservoir has me concerned... gotta be honest - I've never had the pleasure(!!!) of dealing with one of these dual function reservoirs in person.


Would you like me to put the question back out to other experts?

Customer: replied 4 years ago.

Actually, the EEC relay on this model is the other relay next to the fuel pump relay on the pass. side fender well. I went back through my papers and discovered it. That's all good, been checked many times including again this morning.


Things I've done;

1) Replaced the fuel filter

2)Replaced the ECM (mounted to the outside of the distributor)

3)Replaced the magnetic pick-up coil (inside the bottom of the distributor)

4)Replaced the Air Idle Control (mounted on the intake manifold just in front of the throttle body)

5)Replaced the MAP sensor

6)Checked the relay circuits (all good)


This morning;

I discovered, by pulling fuel lines and checking flow, that the high pressure fuel pump sometimes works, sometimes doesn't. I'll get a real good flow for several tests, then nothing, even though there is power to it.

Can the high pressure pump, on its own, work intermittently?

Is there some other reason, other than the relay, that would intermittently prevent it from working? The relay is good. I check it every time I try something new. Not knowing the nature of the pump itself, I am unsure how to proceed. Most electric pumps I've worked with over the years will either work or not work, nothing in between.

Whatcha think?



Customer: replied 4 years ago.

This is a single tank vehicle so no complication there. I have checked the reservoir and get a good flow from the tank pump. I appreciate that you considered that aspect. Thank you.



Customer: replied 4 years ago.

"I love automotive victories, and I'd like to see you beat this one!" your words. Sorry Charlie, you're stuck with this one until one of us gives up. One way or another, hopefully, we both learn a new trick or two, huh?


Do me a favor, please Canuck, ask around the shop if the high pressure pump is capable of intermittently working, other than the normal 10-20 seconds when the system is energized?? Thanks






I just wanted to give you the option, Dan! Research, research... Todd

Customer: replied 4 years ago.

Misery loves company! haha! I turned a wrench or two in the past. Had my own mobile repair business ... construction equip. and trucks. Took care of a couple fleets, including small trucks and cars. Been a long time ago, things have changed dramatically since then. That's why I'm lost on this one. Used to be that a problem like this would be a piece of cake, not any more. Nowadays it's not only frustrating for a professional, such as yourself, it's also expensive for me! Dang!

Just want to say THANK YOU for sticking with it Todd. That's how we learn.



Just retrieved some more info from the archives... gotta blow the dust off it, and have a read... No problem... If there is anything I have it is tenacity... sanity??? maybe another story!

From what I can see, that high pressure pump should run all of the time... 30-40 psi, engine running, 35-45 psi key on, engine off. I have yet to find a wiring diagram the the duel pump system, but from what I am seeing, if there is a power or ground interruption, the low pressure and the high pressure pumps should all stop running at the same time... Yet another long shot, but have you tried bypassing the inertia switch?

I'm not sure how I missed your earlier post about it being a single tank...

I worked on a dual pump system in a Volvo years ago, and the high pressure pump was making a heck of a racket... It turned out the low pressure pump inside the tank was bad, and the high pressure pump had to work like crazy to draw fuel through the in-tank pump. I'm assuming that there is no abnormal noise at this point from the high pressure pump. I have seen fuel pumps fail when they get hot. Getting high tech here, we could run an ammeter in series with the high pressure pump, and monitor it as the pump gets warmer. Most multimeters have a 10 amp ammeter scale.

So, if I understand correctly, we have no fuel pressure when the engine stops. That leaves us with the computer opening the circuit on the fuel pump relay, the inertia switch... or either pump, or wiring. When the engine stalls, the pumps will turn off because the ECM doesn't see an RPM signal. No RPM signal, no power through the fuel pump relay.It would be possible to bypass the fuel pump relay, and the inertia switch to rule them out as possibilities

Canuck Tech and 3 other Car Specialists are ready to help you
Customer: replied 4 years ago.

When the truck stalls there is power everywhere, the key is still on.


The high pressure pump gets excellent pressure when it runs. I tried a hot wire to the pump. The power comes back out the ground side????


I'm thinking intermittent open circuit in the pump itself, but I'm not convinced because the truck will die in the driveway, I pull the line at the pump and it gives fuel. The ignition circuits stay energized.


I suppose that replacing the pump will reduce by one the number of problems possible. I'll do that and get back to you. If you come up with anything about the pump working intermittently, as opposed to all the time or not at all, let me know.


Thank you for the diagram.



Hey Dan,

You make a reference to seeing power out both sides of the pump... this sort of makes sense... if the ground circuit is open, you will see power out both sides of the pump... power is supplied to the pump, it goes through one of the brushes of the pump, through the armature of the pump, through the other brush, and to ground. But if the ground circuit is open, you will indeed see power on the ground wire... I have seen intermittant pumps

Customer: replied 4 years ago.

Well, you've seen another. I replaced it and all seems well, so far. And, with all that other stuff I replaced it's even running better! Whoo Hoo! Idled in the driveway for a good 30 minutes, no problemo. See there, stick with it, never say die. Above all, Canuck, a little lesson I learned many years ago ....... never, ever think you know it all or even most of it. Be willing to accept that things can sometimes be different than you, or I, think they should be. You did good. Thank you so much for just hanging in there. That's something. I'll close out the case and give you top marks. Hope you make something on the deal, it cost me plenty! haha! it out!

Hi Dan - well, this is great news! The trick with this internet car repair is that I need to have a person on the other end that can check some items... and that is you! You did an awesome job!


I run into all kinds of people in this business. I didn't want to give up, but I needed to give you the option. Thanks for sticking with me, and for the nice bonus - very much appreciated! Best, Todd

Customer: replied 4 years ago.

You're welcome Todd. Hope you have an awesome weekend.



May you have a great weekend as well, Dan. Regards, Todd

Customer: replied 4 years ago.

Hey Todd,

Don't know if you'll get this. I was finally able to take a trip to the 'local' dump (about thirty miles down the hill and across the valley) with a load of job debris and the truck is running awesome, just like it used too! I have a bunch of good used parts for sale! haha! Just a side note: the OEM (Motorcraft) fuel pump was $503.00!!! The BestTest BE2000 fuel pump was $85! Take a guess which one I got. Excellent fit. Got me on the road again and puts out 70-90 psi.



Excellent! To quote Mr. T - I love it when a plan comes together! Thanks for the update - I am very happy that you got it beat! Todd