unknown location of air in the fuel system

[keefer]

ok, so i havnt found much on fuel problems in the forum so im making a new thread.
heres the problem. my truck is periodically dying when i drive down the road. im definitly getting air in the fuel system somewhere because i can immediatley bleed a ton of air out of the bleeder on the fuel filter base. so far i have
-replaced the fuel pump with no luck
-bypassed the fuel filter to see if the leak is in the fuel filter base (dont worry i have another filter, cav style canister filter/fuel heater). no luck there either

I can bleed the air out usually and run it for a few miles before its sucking air again. anybody know

-how to properly bleed a cav style filter? it has one screw on the top that looks like its for bleeding and i tried it with some air coming out but doesnt seem to be nearly enough to purge the system
-places to look for leaks?
-how to tell if its the injection pump thats bad?

any help would be appreciated. this is my dailey driver. dont want to take the motorcycle 140 miles round trip each day. especially if it rains

 

[doghead]

Drop your fuel tank and inspect the fuel pickup. Might be rusted through where it goes into the tank. While you have the tank down, pull the sender unit and inspect inside also.

Also, then you can pressure test your fuel lines.

 

[keefer]

thanks doghead, ill try that. can you give me some more info on the pressure testing? ill definitly take a look at that sending unit before i shell out big bucks for an injection pump.
you know anything about cav filters? i looked all over for a technical manual and cant find anything. it looks like this http://cgi.ebay.com/ebaymotors/Cool...QQcmdZViewItemQQhashZitem2a1149256eQQitemZ180
678632814QQptZMotorsQ5fCarQ5fTruckQ5fPartsQ5fAccessories

the only difference is that mine has two extra fuel fittings that i suppose is for marine applications where you would run two engines off of one filter.

 

[Warthog]

Have you checked the rubber hose that connects the frame fuel line to the mechanical pump? if the passenger side motor mount is bad, the engine drops slightly and the hose rubs on the crossmember.

 

[emmado22]

replace every single bit of rubber hose in the engine compartment. It's all 20+ years old. It may fix this and avoid some future problems.

 

[keefer]

ok now i believe that it is the filter base. can anyone tell me how to bleed a spin on or canister style filter? i would love to just use my secondary canister filter but i cant bleed it. i have found no information on this on the internet anywhere but all these people are talking about converting them! i know the air has to bleed out somewhere. this is starting to get frustrating. i can see fuel leaking out somewhere near the water in fuel sensor but i cant tell if its coming from the sensor itself. why does everyone keep saying to replace the filter base? why would you do that if the problem is typicaly the sensor? somebody please help!

 

[Westech]

you can not buy just the sensor that is why you need to replace the whole base.

 

[southdave]

here you go BTW water in fuel and heater on fm100 system is a direct fit

 

[timntrucks]

same thing my blaxer does. just dies off.. starts right back up.. first start of the day is hard.. takes a couple minutes for it to idle right

 

[keefer]

ok, so heres my update. in addition to the parts replaced at the top. i have
-replaced every bit of fuel line under the hood.
-fixed a screwed up seal on my cav filter
-bypassed the stock fuel filter with the cav filter
-cut a hole in the bed and inspected the sending unit. everything looks good. no rotting. even the rubber lines look fine but it think ill replace them anyway since im there.


there appears to be no problems at all! im still getting air in the filter. anyone have anymore suggestions?

 

[albersondh]

Something to look at, proly isnt the problem, I have only seen it once and it was on an EBFL with a DB2 FIP. Check to see if there is a restriction in return fuel. The hose that loops to the hard line out of the top of the IP. The pumps advance piston works in a balance between housing pressure and vane pump pressure. A restriction to return fuel (out of the hose coming from the top of the FIP) will raise housing pressure and advance inj timing. In the worst case, it will start for 3-5 seconds, then just die. I imagine a slight restiction would allow running for a while untill enough return fuel back pressure is built up, translating to housing pump pressure, then advancing to the point that the engine stalls. Just to prove this, nect time its ideling, kink the outlet hose on the FIP, it will stall.

 

[TedG]

I had a similar issue with a hmmwv. The return fuel line had blockage and when I clear it out, the engine ran perfectly.

 

[keefer]

was that a metal line or rubber one? were you getting air in the system from that?

 

[albersondh]

Its return and the pump is checked (valve on cap, on top of pump = outlet/return fuel check valve) so air into the return side wont get back into the pump, but should be avoided, if air is getting in so is crap, and flowing to the tank. The return/outlet check valve on the IP cap is placed at the highest point on the IP, the pump is self bleeding in this way, air will rise and make its way out the ruturn check valve. The outlet from the IP feeds the hose that loops to the hard line, which is retrun from the pump and inector nozzels.