6.9 has air in the fuel - Diesel Forum

oklahoma diesel · 11-15-2009, 02:50 PM

I have a 87 f-250 that keeps getting air in the fuel, I have replaiced the fuel pump and the line to the filter, and it keeps on air locking the injector pump. Can you help?

cdnsarguy · 11-15-2009, 07:24 PM

OK what did you use for the line to the filter.... a replacement metal line?? Under the cap nuts on that line and the one to the IP there are rubber seals.....did you replace them. (see my photo link)

Have you visited.... Ford diesel 6.9 7.3 IDI too much info to read in one day.... but check out the clear line test.

Also check the rubber hose from the steel line on the fram to the lift pump for holes. The steel line on the frame across to the FSValve is known to rust out too. Also check the fuel lines where they enter the fuel tanks for wet spots..... Have you acertained the problem is not broken off fuel pickups in the tank(s). What are the fuel level(s) in the tank selected must be above 1/4 full or you may suck air. Post back with results.....

mikeproeder · 11-16-2009, 02:25 AM

i have this same problem i have a 84 f250 6.9l

when my tanks get down to 1/4 tank i get air in my lines so i pulled out the rear tank and found out that the check valve in the fuel sending unit was no good and could suck air so i deleted it but im still sucking air down at 1/4 tank hopefully we can figure this out

Scoobywagon · 11-16-2009, 10:47 AM

As I've been fighting this problem in my own truck, I've found that the most common way for air to get into the fuel, at least on a 6.9 motor, is for the fuel return lines to crack. Start by replacing the main return line from injector #1 back to the fuel filter. You'll want 3/16 fuel line for that. Also, you'll want to replace the little hose clips with regular screw-down hose clamps. There is a kit you can buy that has all of this and more in it. Don't have the part # handy, but it runs about $80 or so at Napa. At least it does here. That kit includes fuel line, o-rings, injector caps and hose clips.

oklahoma diesel · 11-16-2009, 10:52 PM

The tank is half full, I put a clear hose between the lift pump and the filter housing and you can see the air go through the line. Any thoughts?

oklahoma diesel · 11-19-2009, 11:38 PM

I droped the tanks and it was like it should. I replaced the return lines with clear ones and when I tried to start it, and it still wont start. I replaced the lift pump, and still the same. When I let it sit to cool the starter you can see air come in the line between the lift pump, and the filter. The filter set up is off of my old 91. Any suggestions?

Njellison · 11-24-2009, 04:04 PM

Quote:

Originally Posted by oklahoma diesel

I droped the tanks and it was like it should. I replaced the return lines with clear ones and when I tried to start it, and it still wont start. I replaced the lift pump, and still the same. When I let it sit to cool the starter you can see air come in the line between the lift pump, and the filter. The filter set up is off of my old 91. Any suggestions?

You obviuosly have a leak somewhere. You say you can see the air come in between the lift pump and filter so I ASSUME you have a clear hose in line between the lift pump and filter and are seeing bubbles in the hose. Bubbles are being generated from somewhere below the point you see them so my guess is your leak is either before the lift pump or at the lift pump connection.

Rather than chase the air leak that is being enhanced by a vacuum lift pump pulling through all those hose connections, all that old rotted hose and possibly a leaking air sepertator, why don't you eliminate the problem and go with an electric lift pump that PUSHES fuel through most of your connections and eliminates most of the air sucking?

Yes it would be best to identify your air leak source, but you (and others, self included) could not find them all, so when all else fails, fix the air sucking design flaw and move on.

If you do this be sure and eliminate the stock lift pump from the picture, I think they make a stock lift pump plate for small block chevys that will work as a cover in place of your stock lift pump.

oklahoma diesel · 11-27-2009, 07:10 PM

Okay, i dont get as much air now that i have replaiced everything. My truck will not start with the starter i have tried 3 different starters that where new, and 2 new batteries new glow pluges and a new gp controller, and it wont start unless i pull start it, and after i get it started and warmed up it wont idle. And after it dies it still wont start with the engine being warm, any sugestions?

digimojo · 06-28-2010, 12:08 PM

I know this thread is old now, but I thought I'd relay my experience for others in the future who are searching for answers in this forum.

Having worked through this problem, I'm wondering if you have the original water separator that is down low way over left on the driver's side of the firewall. I had exactly the problem you describe. The lift pump generated good pressure (outlet) and vacuum (inlet) but it was just pumping air. Little or no flow of fuel at the fuel filter housing Shrader valve. Once I bypassed the original water separator with a 3/8" ID fuel hose, the problem disappeared, and I then had good flow of fuel at the Shrader valve. IIRC, there are many threads in this forum explaining why it's a good idea to remove these old water separators.