I have a 1986 f350 4x4 460 auto. I was driving along then it just shut off and will not start. Had it cranked; but it just idles down and shut off. Tanks are full of fuel.
Any ideas on what it could be.
Thanks
TruckoffFord

 

Are you missing spark, or fuel?
Did it sputter to a stop or turn off suddenly like someone shut off the ignition?

Sounds to me like the DuraSparkII module has failed.

 

You've gotten advice from one of the best - Jim. Still, it would help us if you'd let us know more about your truck.

For instance, my assumption is that you have a stock truck and, IIRC, a stock '86 F350 w/a 460 has a carb, DS-II ignition, no computer, little if any emission controls, and a mechanical fuel pump. If that isn't correct, please advise since it would help diagnosis. And, if you don't know tell us that as well.

Edit - I've read on another thread that these trucks have electric fuel pumps in the tank. Is that true of yours?

 

Gary,
I have a mechanical fuel pump, but I've been told that most trucks like mine have the "Hot Fuel Handling" system in which a low pressure pump in each tank pushes fuel past a return orifice up atop the intake manifold.
I thought the mechanical fuel pump would be more common, but perhaps we don't see more posters inquiring about them because they fail so rarely.

I understand the HFH system is more often found in vehicles delivered to southern states due to vapor lock issues.

This system with the electric pumps has a number of failure modes.
Oil pressure switch, Inertia switch, Fuel pump relay, Selector valve, etc...

From the tone of TruckoffFord's post it sounds ignition related, but a little more information might help get him rolling again.

 

Jim - That's really why I asked for clarity. To me it sounds electrical due to the on/off nature. But, if there's a bunch of relays and pumps in the fuel system, then the fuel system is "electrical" and, therefore, suspect as well.

You may be right about the posts - no posts on 85/86 F350's with mechanical pumps doesn't mean they aren't there. Maybe it's because they adhere to the KISS theory and don't frequently fail.

 

OK alot of good questions! Lets see if I can answer all:
The truck is stock. I don't think it is electrical - it will start and run and run for a second or two on the first try. If I pour a little gas in the carb. it will start right up. Therefore I think the problem is in the fuel system.
I am not sure what can of fuel pump mechanical or electrical. I did not look- I was on my way to a job sight. I figured I just run down to NAPA and get a pump. If it is electrical there will be elect. wires to it right?
I don't know if there is any pumps in the tanks. I do have a selector between tanks and have had a problem switching between tanks. I was going to replace it too. I wasn't switching tanks at the time. My son-in-law was driving the truck, so I can't tell ya how it acted when it shut down. The truck is a spare and only get driven once in a while.
Thanks for you in put!
TruckoffFord

 

I hated it when mine would not start, we looked at fuel pumps, switches, ets, finally we just tried jumping the fuel cut-off switch under the passenger side dashboard and it ran!

 

Alright.
If you have a mechanical pump like mine you will see a bell shaped thing attached to the side of the timing case behind the water pump inlet.
From there a metal line will loop up and go directly to the carburetor inlet.

Here's a picture of mine on the stand where you can see the pump and the metal line.
http://www.flickr.com/photos/24183730@N03/2341395806/http://www.flickr.com/photos/24183730@N03/2341395806/ by http://www.flickr.com/people/24183730@N03/, on Flickr


If you have the Hot Fuel Handling option with electric pumps there will be a vapor separator (metal three way splitter) next to the coil bracket, before the carburetor and a return line going back to the tank.
If this is the case. the first thing you should do is try switching to the other tank.
Doing this will confirm or eliminate that one of the in-tank pump has failed or that one tank is empty

If you can hear the pump running it may be that the filter screen inside the vapor separator is clogged with debris.

Since it won't start we can assume the oil pressure switch is okay because the pumps should always run while the starter is cranking.

That would also eliminate the inertia switch that Glam_2 mentioned. (inside the cab, passenger side of the transmission hump) This has a reset button you can try depressing.

SO,
That leaves the tank selector relay or the switch itself keeping you switched to an empty tank.

"Subford" has made a clear diagram of the wiring.
Here is a link to that schematic...
https://www.ford-trucks.com/forums/a...6&d=1218602346


Hope this helps.

 

Just to be clear, the mechanical fuel pump in Jim's excellent picture & description above is the device on the lower RH side (except that the pump's arm is inside the engine) that looks similar to this:







Here is an edited copy of Jim's pic:

 

As always with a carbed engine there is the simple "eyeball" test. Take the air filter off. Start the truck and let it idle down and stall. IMMEDIATELY look into the throat of the carb and work the throttle my hand. You will see the accelerator pump squirt fuel into the throttle body if the carb is getting fuel. If you don't see a solid squirt, then start backtracking.

Check the ceramic/screen filter at the fuel inlet on the carb. Clean it. While you have the fuel line disconnected at the carb, stick the end of the fuel line in a jar or something and crank the truck to see if the pump is pushing gas. (PLEASE remove the coil wire before doing this so the truck won't start). Better yet, if you have a fuel pressure / Vacuum gauge, check to see how much pressure the pump is generating.

If you're getting fuel to the carb, check float levels. You may have a stuck float or something like that.

Check your fuel lines from the tank to the pump. You may have a crimp in the line. If you have an in tank pump, you'll have to check line pressure to see if it's working correctly.

If all that checks out, then you'll have to start looking at ignition issues.

 

if your truck is stock it will have the eletric fuel pumps. first thing to check is the inertia switch,this thing is supposed to stut the fuel pumps down if you get into an accident.it is located on the inside of the cab where the fire wall meets the trans tunnel,on the passenger side.if there is a white button showing ,press it down and it should reset it.

second, check the wires at the back where the oil presser switch. the engine has to be prodocing oil pressure, closing a switch and turning the fuel pumps on.this should be at the back of the intake manifold.

on thing to try to make sure your pumps are working is to take the wire off the "t" terminal on the starter solinoid and put it to a 12volt power.black wire on my truck. this wire turns the pumps on while you are cranking the the truck over before you getoil pressure.

next check for busted wires,i got my truck cheap because the truck would not start, one of the yellow wires the powers the fuel pumps was broken,( P.O. was pissed when i drove it out of his drive way , just by twisting 2 wires together) . good luck.

 

Thanks for the markup Chris! Not always true.
My truck is entirely stock and has the mechanical pump, as do many others.
The fact that it's as reliable as a hammer just means that you don't see many posting about problems with the system.

We already know for a fact that it's after the oil pressure and the inertia switch because it's not pumping with the key in 'Start'.

Take a look at the schematic I posted...

 

If you can hear the pumps kick on disconnect the line before the vapor separator and see if you have fuel being delivered that far.
If you do get fuel that far check both volume and pressure.
6-7 psi and a pint in under 10 seconds.

The screen in the separator is clogged.

 

Anafiel,
He has spark, say's the truck will fire if he puts gas down the throat of the carb.
But he doesn't have fuel delivered even while cranking.

If he has a mechanical pump- I KNOW they can take a long time to prime, or there could be a pinhole in the suction side of the line, or the pump could have failed.

If he has electric pumps- either the pump is fried or the selector is stuck on an empty tank because power while cranking comes directly from the 'I' terminal of the starter solenoid while cranking with this system.

 

Hahaha!! That's classic! Main reason I got my Bronco so cheap was because the TPS was bad.

PO thought the EEC was bad, I don't know why...he just thought so, and didn't want to have to buy a new one and have it installed.

Sounds like new thread material....