I have a recently purchased 1975 F-250 Ranger Camper Special with a (I believe) 390 engine. While driving it back to Texas from California, I noticed a problem with stalling.

This typically only happened after I had it up to highway speeds and kept cruising for 30+ minutes. Upon pulling off the highway and coming to a stop the engine would stall. I mean, instead of idling at a stop sign, it would stall. When I started the car, it would start right up and idle. But, once I got it rolling and stopped again, there was possibility of stalling. I found myself braking with one foot and revving the engine a bit with the other, which would prevent the stalling. Around the city, this stalling problem doesn't happen.

Perhaps unrelated, when I had the truck up to highway speeds and cruised for 30+ minutes (similar precursor to the stalling) the engine would backfire if I let off the gas. Since I was driving at night, I could see the backfire was coming out the exhaust. The idle in this case was also rather rough sounding.

And then yesterday, when I came to a stop sign at the bottom of a hill, I experienced a similar type stall. Pulled up to the stop sign and the engine stalled. I had a hard time restarting on that hill (kept on stalling out).

All three of these seem to me to be related. I'm thinking that there must be a carburetor problem at the root cause. Is that probable?

The bloke who sold it too me mentioned something about the floats (and gave me a container of them), but since I've never worked with a carb before it was in one ear and out the other.

 

Actually, I'd be more suspect of the advance mechanism in the distributor sticking. You may want to just pop the cap off, and see if the rotor move freeley. You should be able to turn it clockwise about 15*, and have it spring back smoothly. Also, the vacuum advance should move freely when vacuum is applied to the diaphragm, and release to it's original position when the vacuum is removed.

 

Ford_Six, thanks for the suggestion. I've just gotten around to looking at the distributor.

The truck is stalling now a lot more often than it was. Yesterday I drove about 3 miles to the store and it stalled at almost every stop light on the way home after getting off the highway. When I got back home it stalled as I pulled in, and I couldn't restart immediately. Gave it about 2-3 minutes and then it started without dying. One clue here is that the "Fuel Economy" light does come on every time it stalls out. It seems that the stalling is predicated by getting the vehicle up to highway speed. On the way there I used surface streets and no stalling. On the way home, stalling only after being on the highway.

I looked at the distributor, but I'm pretty sure the previous owner replaced it with an electronic distributor setup. I remember he told me about the lack of points in the distributor. Anyway, there's no free rotation at all on the rotor. It's firm. Would that be a function of the electronic distributor, or should there still be the 15deg. rotation you mentioned? If so, what would you suggest I do?

TIA.

 

Following up my own message.
My instincts are telling me that the stalling problem is because the engine is becoming starved for fuel. My instincts here are less than perfect though. The reason why I think this is that if I pump the gas just right and rev the engine I can occasionally thwart the imminent stall. Also the "Fuel Economy" light comes on suggesting something fuel related. Could it be that some part of the carburetor is sticking after running the engine at full throttle, like the throttle mechanism or the floats?

I'd think that if the distributor advance mechanism were at fault, especially given that I can't even advance the rotor at all on a cold engine, then I'd see the problem manifesting itself in other circumstances too. Only stalling is after highway speeds / full throttle and then coming to a complete stop. Although there was one instance where it stalled when I came to a stop at the bottom of a steep hill, without having had the truck on the highway previously.

Could it be the floats need replacing or adjustment?

 

All the fuel economy light is is a vacuum switch- when the engine vacuum gets low, say if you mash the gas, the light will come on. It was kinda like an "honor system" means of increasing economy.
Those trucks came from the factory with an electronic distributor. The rotor should turn, as the timing isn't controlled by a computer. I still really suspect the dizzy. If you want, you can give a shot at rebuilding the carb, but I don't think that will fix the problem. If it was running excessively lean, as you say, it would backfire out of the carb, and have no power on the highway or at higher engine speeds.

 

Check out the grounds on the engine and the one in the dissy.
I think you have a ground problem AND a fuel delivery problem .

 

I'm still trying to isolate this problem. Trucky's been sitting, and it wants to play.

I'm now thinking vacuum leak somewhere. Here's what I've done:
Tested the vacuum advance, and it holds vacuum, so does the hose going from carburetor to advance. Also tested hose going from rear of carb to PCV valve, and that also holds vacuum. Replaced PCV valve.

Perhaps it was there before, but I now have discovered a very loud whine coming from the vicinity of the carburetor. The whining noise is not there when I cold start the engine, only after it's run at full throttle. There does seem to be a correlation between stalling and the whine. I'm thinking that the whine is caused by a vacuum leak at the carburetor ... is that sensible? I took a hose I had lying around, put it to my ear and poked the other end around the carb. Noise seems to be isolated to the bottom rear, near where the hose attaches from PCV valve.
Perhaps one of the gaskets between carb and throttle body needs replacing?

Before noticing the whine, I took a closer look at the carburetor, and tightened down bolts holding it to throttle body (rear right was only one that took tightening). There don't appear to be any other vacuum hoses coming off the carb. I'm not sure how to identify the carb positively, but appears to be a Holley.

Also, there is a three-way hose connector that comes off the engine near the PCV valve and goes to the brake vacuum booster, some unknown item on the firewall (?), and a third hose that connects into a metal line that I didn't trace. Noticed a bolt in that three-way connector plugging off what may have once been a fourth hose. I'm wondering if that may have gone to EGR valve. I can't seem to locate EGR valve, but might be looking for the wrong thing. I thought it would be at the base of the carb and have a vacuum hose coming in? Is it possible EGR valve has been removed?

Any help appreciated.

Thanks.

 

If there is a whining noise coming from the carb, I would pull it and the spacer off, check the spacer for cracks, and replace the gaskets. I had these gaskets fail on me before. Most auto parts stores call them carb base gaskets, or carb to plate gaskets.

 

Is it sucking the pvc line shut, causing an over rich mixture? Is the fuel pump up to snuff? Could it be trying to vapor lock after being at highway speeds? My 460 will do this on hot days. It needs a high volume pump.
Jimmy

 

lxman1, How would I test for these things (sucking PCV line shut, vapor lock after being at highway speeds)?

I'm going to replace the carb base gaskets and see what that does for it.

Cheers.

 

Finally ...
I got the carb off, and pulled the base gaskets. The gasket between spacer and throttle body was clearly a bit worn. I tracked down matching replacements and put them in. Used Permatex #2 to seal the gaskets. Cinched down the retaining nuts.

That seems to have fixed the stalling issue. I took her out on the road and tried all the ways I knew how to stall her out, and she didn't succumb.

However, the whining noise is still coming from the carburetor. It's more like a high pitched whistle than a whine perhaps. Clearly I misdiagnosed where the sound was coming from, and lucked into the solution to my stalling problem. Maybe I should leave well enough alone, but the noise concerns me. Only starts after the engine has warmed up. Inside the cab, I can hear it just barely. With the hood up and the air cleaner off the noise is LOUD. Definitely coming from the carb. Hard for me to isolate it though. I torqued down the retaining nuts as tight as I could. I'm fairly confident that the whistle is not due to a vacuum leak now. What could it be though?

A couple of other questions too, please:

- How do I identify the carburetor. I believe it to be a Holley, and the only
identifying marks I could find were:
D4TE 9510 ASA
LIST 6830
What's confusing is there's a Motorcraft tag on the carburetor too. Reads:
D4TE-ASA 4116

- There are two metal lines coming off the right side of the carb and going into the crankcase below the PCV valve. What are these? When I removed the carb, they came out, but that seemed to be what was supposed to happen. I just want to be sure I didn't break them.

Cheers,