6.9-250 Posted October 9 Share Posted October 9 I was driving home one day and the truck started to stumble. I have experienced this before when I had some injector line seals leaking. I knew it was a fuel supply/air leak issue. So I switched it back to the front tank and the issue cleared up. The gauges don't work below half so I keep track of the mileage. It should not have been empty. I filled it up with 50 liters. From the research it should be 75 liter tank. Drove around some more and maybe 10km into the full tank and it died totally. I checked the Schrader valve at the filter and low pressure there. I switched back to the front tank and got pressure back after some cranking. Runs good on the front. My problem appears to be isolated to the rear tank. Just wondering if anyone has any thoughts before I dig into this. There must be a strainer on the pickup..plugging? In another post someone mentioned a rubber line back there somewhere - possibly failed? I want to put a new sending unit assembly in but i did not come across any good options for Canada. I was going to install an aftermarket fuel sending unit from amazon, I just need to find the tank depth first. Thanks! Link to comment Share on other sites More sharing options...
Gary Lewis Posted October 9 Share Posted October 9 In the olden days people that were having problems pulling fuel would put air pressure to the fuel line coming out of the tank and blow the "sock" off the pickup arm. Or maybe blow the crud off the tank. But your fuel lines may be Nylon the whole way and it won't be that easy to find a spot to do that. I'm not familiar with the diesel fuel system, but I know that in 85 they'd gone to the Nylon lines for the gassers and there's no rubber hoses involved. Getting to the rear tank is tough. I doubt you can get the sending unit out w/o dropping the tank or raising the bed. And if you've not had the bolts loose on the bed recently that can be a major project. So I'd drop the tank, but that is very hard to do if there's any fuel in it as the fuel sloshes. The best way I've seen is with a piece of plywood under the tank and a floor jack under that. Link to comment Share on other sites More sharing options...
6.9-250 Posted Thursday at 03:55 AM Author Share Posted Thursday at 03:55 AM Thanks Gary, I see it online sometimes and I may do it myself, cut an access hole from the top. I'm not overly interested in dropping the tank or lifting the bed, lol. Yes, I believe the lines are that nylon type. Link to comment Share on other sites More sharing options...
viven44 Posted Thursday at 04:20 AM Share Posted Thursday at 04:20 AM Don’t know about diesels.. Is this a mechanical fuel pump ? I would definitely suspect the fuel selector and ensure it is letting the pump pull/push fuel in the rear tank setting Link to comment Share on other sites More sharing options...
6.9-250 Posted Thursday at 04:26 AM Author Share Posted Thursday at 04:26 AM Yes, mechanical pump. I am not fully aware of how that fuel selector works but I sort of ruled that out based on full flow when set to front. If the selector didn't move to the rear, it would just stay stuck on the front and be fine. If it isn't switching all the way though, shouldn't it still pull some front fuel? The problem still seems isolated to the rear tank... Link to comment Share on other sites More sharing options...
viven44 Posted Thursday at 12:58 PM Share Posted Thursday at 12:58 PM 8 hours ago, 6.9-250 said: Yes, mechanical pump. I am not fully aware of how that fuel selector works but I sort of ruled that out based on full flow when set to front. If the selector didn't move to the rear, it would just stay stuck on the front and be fine. If it isn't switching all the way though, shouldn't it still pull some front fuel? The problem still seems isolated to the rear tank... Yes you have a good point... i'm thinking from the perspective of electric fuel pumps... Jim runs mechanical pump with fuel selector so he would know more, but I don't know if the selector can be stuck in a position in between tanks.... It would be good to run some sanity tests such as trying to pump out fuel from rear tank using a cheap pump like below or a hand pump. If it can't pump out fuel you can definitely isolate to strainer being clogged. Amazon.com: Universal Electric Fuel Pump Kit 12v 3-6 PSI Low Pressure with Fuel Filter 6.56 FT 5/16" ID Fuel Line Replacement For Carburetor Lawn Mower Gas Diesel Fuel Transfer Pump : Everything Else Link to comment Share on other sites More sharing options...
Gary Lewis Posted Thursday at 01:21 PM Share Posted Thursday at 01:21 PM The selector valve can easily get stuck in between. They are notorious for returning fuel to the wrong tank. Someone on here took his valve off and either took it apart or otherwise got it unstuck by applying power and some solvent. Don't remember who that was but perhaps a search would turn up how he did it. 1 Link to comment Share on other sites More sharing options...
ArdWrknTrk Posted Sunday at 11:07 PM Share Posted Sunday at 11:07 PM I once had my dashboard switch to bad, but thankfully haven't had any trouble with the switching valve itself. I've never heard of the valve bypassing to the wrong tank, though I have seen where electric in-tank pumps have a failed check valve. Ford has a TSB about this and used to have a add on check valve kit that got spliced into the nylon line. (I don't think anything like that applies to diesels) You might check to see if polarity reverses at the valves harness connector, and if it does, try carefully blowing back into the tank Link to comment Share on other sites More sharing options...
Gary Lewis Posted Monday at 03:07 AM Share Posted Monday at 03:07 AM Ask Ray/@Ray Cecil or Brandon/@Bruno2 about the valve returning fuel to the wrong tank. I think it was Ray, but one of them came to the shop getting horrible gas mileage. He was filling the front tank 'cause the back tank was "bad" and the front tank was running out quickly. Turned out the back tank was almost full. IIRC we pulled the return line off the rear tank and plugged it. Problem solved. Link to comment Share on other sites More sharing options...
ArdWrknTrk Posted Monday at 06:04 AM Share Posted Monday at 06:04 AM Are either of them using a mechanical pump??? I thought Brandon has a 351 and Ray a 302? With the 3 port valve you are reliant on the pump building pressure to hold the check valve off its seat, allowing fuel to return to whichever tank is pumping. If the spring gets rusty or the seat has garbage the return stays open and you start filling the other tank. The 6 port valve is a linear shuttle. While I suppose a seal can fail there's no way for my truck to be 'between' A&B on either the supply or return ports. Link to comment Share on other sites More sharing options...
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