Hi everyone, i'm new here but have been on the fordification website as i also own a 1970 F250 with a 360. Been getting my feet wet in mechanics with it and now have a problem with my motorhome. Its a 1985 E350 with a 460. Don't know much more than that at the moment as i bought it second hand several years ago before i ever thought of trying my hand under the hood.

My problem: The engine starts fine, and if it's a cold start, will idle nicely for about 15 seconds or less, then bogs down and barely runs and eventually dies. If i can get going it runs a little rough but somewhat decent.

Had it to a mechanic who works on fords regularly and mine specifically since i bought it. He rebuilt the carb completely with new float and the truck still does the same thing. Not !

I took the air cleaner off today and started it up and checked some things Here's what i found. When i give it a significant throttle it would die when it came back down to idle. But if i held the choke mostly closed (rich) it would remain at idle pretty well. Also, there are two small vacuum lines that attach to the air cleaner when its on, one near the outside rim, the other incloser to the centre. When i plugged the one near the centre the engine died down and almost stalls.

Any help would be greatly appreciated. I'm starting to get familiar with my simple 1970 F250 but this 460 with more sensors etc on it is a little trickier.

 

Oops. Correction. The vacuum line on the outside edge is the one that when plugged affected the idle.

 

one other symptom is that i have a black mark on my driveway from the amount of carbon in the exhaust right now.

 

Any help would be appreciated?

 

Find out if you have an EGR valve. If it is leaking exhaust into the intake manifold, you will have a hard time keeping it running at idle. Remove and plug the vacuum line going to it to see if that helps. The inside of the valve carbons up a lot and that can let exhaust past it. jim

 

I think that i have that vacuum line plugged with a screw. No EGR. Is that possible? Will take a photo tonight and post. I need a diagram of the engine cause I'm not familiar with extra lines and stuff compared to my 70 f250

 

Ok. Had a look at a vacuum diagram. The line to egr is removed and plugged. Line to air bypass valve is rhe one when plugged that chokes the engine to a stall.

 

The bypass valve vents the smog pump. If the pressure from the smog pump isn't vented, it will stall the engine.

You need to get some diagrams for the smog and vacuum line routings. This is the one from my 88 E150. jim

 

So last night I took some pictures but haven't uploaded them from my home computer. I did reattach the EGR valve vacuum which didn't seem to change anything. I was just checking around with the engine running (roughly) and pulled a large vacuum hose off an attachment at the back of the valve cover on the passenger side and suddenly the engine roared to life with good rpm and sounded good. I took it out for a test run and it ran fine. Didn't die down at low rpms, idled fine at stops, BUT it ran really hot, almost overheated on the highway. Was ok at 50 km/hr and under.

So, as you can tell I don't know what i'm doing. I've decided to take it to a new mechanic. I explained to them the situation up to last night and suggested there is a vacuum/sensor/valve issue. I have ordered a shop manual for the truck and will spend this winter getting familiar with the engine. Any further help is appreciated though as I would love to troubleshoot the issue and narrow it down for the mechanic so they can spend less time looking.
Thanks

Lloyd