A LITTLE HELP WITH MY 1986 6.9 air in the fuel system

[HSkinner]

I recently purchased an 86 super cab 4x4 with about 140k on the clock. It had been sitting in the Arizona sun for 3 years but started right up after charging the batteries. I replaced the tires and drove it 150 miles back home and got around 7 mpg on the way home. I noticed it would smoke a little up the hills and occasionally would get a little warm. It felt like it was missing a little but I got it home. The next day I saw that the plastic caps on the top of the injectors looping the fuel system were leaking on a couple so I replaced all of them, the orings and the fuel line. It took me awhile too get it started after that. The schrader valve on the side of the fuel filter would have air in it after cranking it. I loosened the filter and got fuel to the top of the filter. It started but ran rough so I cracked all of the injector caps insuring that all the air was out of the system and it began to run better but after a few minutes of running I would hit the Schrader valve again and there would be air again. this happened multiple times although the truck continued to run. The truck was blowing a lot of grey smoke this whole time. If I'm getting air in the fuel filter is this not an indication of a crack in the fuel system somewhere behind the fuel pump? Also, is this a manual pump or an electric fuel pump? While driving it I could not get it to switch from the front tank to the back tank also. Is it a common problem to get air in the system? Can the valves be adjusted to try and eliminate they grey smoke? Thanks

 

[franklin2]

If the fuel system is original, it has a mechanical pump mounted down low on the pass side front of the engine. But a lot of people add electric pumps, so you will have to follow the fuel lines all the way back to see if it's all original or not.

While you are tracing the fuel lines, look at their condition. You are correct, you must be getting air in from somewhere, possibly you will find a wet spot somewhere that would indicate a leak.

You could also look at the fuel lines at the switching valve, take the lines loose, splice them together and just use one tank to see if the problem goes away. Since your valve doesn't work anyway, this would be a good way to eliminate it as the problem.

 

[franklin2]

P.S. Also make sure the air separator on the firewall is bypassed. I am not sure when they quit using those things, but they had a lot of trouble with them and most people just bypass them. They do tend to leak air also when the truck is turned off..

 

[gandalf]

P.S. Also make sure the air separator on the firewall is bypassed. I am not sure when they quit using those things, but they had a lot of trouble with them and most people just bypass them. They do tend to leak air also when the truck is turned off..

He meant to say the water separator. It filters out any water which may come through your system, supposedly. It's located, as I recall, on the driver's side inner fender wall, near the hood hinge. It has a pull ring on the top. It's designed to separate out any water, and drain it when you pull the ring. It is infamous for two things: 1) not working well, 2) allowing air into your fuel line. The problem is that when you pull the ring, it usually doesn't close properly, and allows a steady flow of air in. Most people are more worried about air in fuel than they are about water in fuel. Many people have eliminated that water separator from their system, simply spliced a line around it.

I'm not sure which years have this separator, but I know my '86 did. I think Ford discontinued it shortly after than.

 

[HSkinner]

would this water separator have anything to do with the poor gas mileage? Thx for the help thus far. What kind of mileage should I expect?

 

[Lithgow]

Mid teen mpgs. Some can get closer to 20, or over, but this is usually with a lot of tweaking the timing, gear ratios, etc. 7 mpg not so great! When you get your problem fixed it should get much better.

 

[OLDBULL8]

Can the valves be adjusted to try and eliminate they grey smoke? Thanks

There is no adjustment for the valves. With an engine that old and setting that long, I would give it an "Auto-RX" treatment, it'll do wonders for it. Take a new fuel filter, fill it with ATF, run the engine for about 5 minutes and let it set overnite or longer if you can, this helps to disolve any varnish/gunk in the IP, if some ATF gets to the injectors, that's great, it helps clean them also. Probably will increase your MPG.
If you don't have a new fuel filter, just empty the old, dump the fuel out then fill it with ATF, but only fill it thru the outside small holes, the ATF has to go thru the filter that way./

 

[HSkinner]

I've spent the last few hours reading everything I can about air intrusion and I think I will just replace all the obvious fuel lines tomorrow. I will do the ATF in the filter after I figure out the air intrusion. Will an e40d bolt up to the 6.9? I really like this truck but I need another gear...

 

[79jasper]

The loop fuel line at the mechanical pump is a common leak spot.
Fuel hose is cheap, replace all rubber areas.

Look into fuel line olives also.
Your fuel heater, and restriction sensor.

Sent from my USCC-C6721 using Tapatalk

 

[franklin2]

He meant to say the water separator.

Thanks for fixing that goof.

 

[chris142]

Is that loop necessary? Mines ocasionally sucking air. Maybe once in 20 starts. Can I just run a straight piece of hose there? If that hose was bad would it be leaking fuel? Mines dry?

 

[theguruat12]

Just replace all of the old fuel line, and the olive seals at the filter header and injector pump.

The FSV might be clogged with old pieces of the in-tank fuel pickups too, drill out the rivets, open it up, and take a look. You might get lucky and it works fine after being cleaned out!

Speaking of the in-tank pickups, how full are your fuel tanks? It's possible you're just too low because the pickups rotted off and thus you're sucking air IN the tank.

Nice to see another AZ member, I'm from Tucson, in Albuquerque for school. We have a cabin in Alpine, so I drive through Show Low sometimes, never seen Snowflake in person though.

 

[chris142]

I just found another leaking cap! How do I pm a seller here to git the better quality ones?

 

[79jasper]

Pm Typ4. Just go to new message and type what you need.
The loop isn't completely needed. Only need enough room for engine flex.

Air molecules are smaller than fuel molecules. So while air can come in, most of the time fuel won't come out.

Sent from my USCC-C6721 using Tapatalk

 

[chris142]

What's the fsv?