Gary Lewis Posted November 22, 2020 Share Posted November 22, 2020 Howdy, I'm RenoHuskerDu's son, tomorrow I will rip out the water separator and replace it with some fuel line. We'll see if that fixes the problem, and keep you updated. Welcome! Glad you joined. Maybe you can sort out the old man. Seriously though, how 'bout going to the New Members Start Here folder, read the guidelines, and then introduce yourself. We ask people to do that to ensure they've had a chance to see our guidelines as we hold people to them and wouldn't want you to get surprised. Link to comment Share on other sites More sharing options...
RenoHuskerDu Posted November 22, 2020 Author Share Posted November 22, 2020 Welcome! Glad you joined. Maybe you can sort out the old man. Seriously though, how 'bout going to the New Members Start Here folder, read the guidelines, and then introduce yourself. We ask people to do that to ensure they've had a chance to see our guidelines as we hold people to them and wouldn't want you to get surprised. He will do that. Thanks. On the 6.9 today we found the water separator already bypassed. Currently we're installing a section of transparent 3/8" RC fuel line as a debugging tool, looking for bubbles. One thing escapes me. If air gets in the fuel return line, and all that fuel is just on its way to getting dumped back in the tank, then how does that cause air to get into the fuel fed into the IP? I must be missing something. Link to comment Share on other sites More sharing options...
Ford F834 Posted November 24, 2020 Share Posted November 24, 2020 He will do that. Thanks. On the 6.9 today we found the water separator already bypassed. Currently we're installing a section of transparent 3/8" RC fuel line as a debugging tool, looking for bubbles. One thing escapes me. If air gets in the fuel return line, and all that fuel is just on its way to getting dumped back in the tank, then how does that cause air to get into the fuel fed into the IP? I must be missing something. In my experience, air intrusion on the inlet side of the IP comes with rough running and power surging. Intrusion on the return side doesn’t really affect how it runs but can make it a bear to start. The air does not have to make it back to the IP, it just needs to enter the injector which prevents it from firing. Usually this happens around the O-rings in the plastic caps, or old return lines that are cracking or not tight on the cap barbs. If your truck has a return hose coming from the fuel filter head to the return line system, cap it off and delete it. It’s not necessary and is another infamous point for air to get in. Its’s a high point and drain back to the tank sucks air in if it’s not perfectly tight. Link to comment Share on other sites More sharing options...
RenoHuskerDu Posted November 24, 2020 Author Share Posted November 24, 2020 In my experience, air intrusion on the inlet side of the IP comes with rough running and power surging. Intrusion on the return side doesn’t really affect how it runs but can make it a bear to start. The air does not have to make it back to the IP, it just needs to enter the injector which prevents it from firing. Usually this happens around the O-rings in the plastic caps, or old return lines that are cracking or not tight on the cap barbs. If your truck has a return hose coming from the fuel filter head to the return line system, cap it off and delete it. It’s not necessary and is another infamous point for air to get in. Its’s a high point and drain back to the tank sucks air in if it’s not perfectly tight. Is this the superfluous return line you mention? All my return lines look pretty new. The PO was a heavy diesel mechanic and he had the IP rebuilt, looks like the lines were new. Link to comment Share on other sites More sharing options...
Ford F834 Posted November 25, 2020 Share Posted November 25, 2020 Is this the superfluous return line you mention? All my return lines look pretty new. The PO was a heavy diesel mechanic and he had the IP rebuilt, looks like the lines were new. Yes, that looks like the one i capped off on mine. It may or may not be an issue for you, but it is a problem spot like the old water separators. The return lines do look brand new, but a twisted or badly installed O-ring can still cause you grief. If everything else looks to be in order, you might need to go back and pull the caps to double check the install. It’s highly advisable to use Viton o-rings, and install them with petroleum jelly so they don’t roll when you push the caps on. It’s not that hard to nick or cut one. They are affordable enough it might be a good idea to have a new set on hand: https://www.ebay.com/itm/Set-of-18-Ford-6-9-7-3-IDI-Fuel-Injector-Return-Cap-Viton-O-Rings-E6TZ-9229-AA-/192517074499 Link to comment Share on other sites More sharing options...
RenoHuskerDu Posted November 25, 2020 Author Share Posted November 25, 2020 Yes, that looks like the one i capped off on mine. It may or may not be an issue for you, but it is a problem spot like the old water separators. The return lines do look brand new, but a twisted or badly installed O-ring can still cause you grief. If everything else looks to be in order, you might need to go back and pull the caps to double check the install. It’s highly advisable to use Viton o-rings, and install them with petroleum jelly so they don’t roll when you push the caps on. It’s not that hard to nick or cut one. They are affordable enough it might be a good idea to have a new set on hand: https://www.ebay.com/itm/Set-of-18-Ford-6-9-7-3-IDI-Fuel-Injector-Return-Cap-Viton-O-Rings-E6TZ-9229-AA-/192517074499 Done deal on the O-rings, thank you. I cannot quite fathom why that top return line is there at all. That line feeds fuel into the IP. And yes if it were to leak that would let fuel leak back down to the tank. I'll close it off. I'm going out to check that out on our 7.3 Bricky tomorrow also. It's always a moderately long crank start. Link to comment Share on other sites More sharing options...
RenoHuskerDu Posted November 28, 2020 Author Share Posted November 28, 2020 He will do that. Thanks. On the 6.9 today we found the water separator already bypassed. Currently we're installing a section of transparent 3/8" RC fuel line as a debugging tool, looking for bubbles. One thing escapes me. If air gets in the fuel return line, and all that fuel is just on its way to getting dumped back in the tank, then how does that cause air to get into the fuel fed into the IP? I must be missing something. Quick update on progress. A new FSS did not fix the problem but the old one was clearly dying. Still acts like air in fuel lines. Spitting some air out of cracked injector fittings on long crank sputtery no start. Checked the evil water separator and found it already bypassed. Decided to insert a section of clear hose there as a debugging method. But on attempt, one of those rubber hoses cracked in two. Ah hah. Found that replacement fuel pump at NAPA is only $35, so bought and installed that today. Decided to abandon the whole fuel line loop up to upper driver firewall, and cross over with new tubing at the frame rail under driver seat. Will update later today with results. Had to take a break to work on a 7.3 SD and update its tunes. Link to comment Share on other sites More sharing options...
Gary Lewis Posted November 28, 2020 Share Posted November 28, 2020 Quick update on progress. A new FSS did not fix the problem but the old one was clearly dying. Still acts like air in fuel lines. Spitting some air out of cracked injector fittings on long crank sputtery no start. Checked the evil water separator and found it already bypassed. Decided to insert a section of clear hose there as a debugging method. But on attempt, one of those rubber hoses cracked in two. Ah hah. Found that replacement fuel pump at NAPA is only $35, so bought and installed that today. Decided to abandon the whole fuel line loop up to upper driver firewall, and cross over with new tubing at the frame rail under driver seat. Will update later today with results. Had to take a break to work on a 7.3 SD and update its tunes. Good luck! Link to comment Share on other sites More sharing options...
RenoHuskerDu Posted January 2, 2021 Author Share Posted January 2, 2021 Good luck! We'd somehow bent the arm on the FSS when we installed it. Or it came bent. We're not sure, because #2 son took it apart and didn't take pictures or check for goolagtube videos first. Truth be told, there's not much IDI knowledge out there anymore. But anyway, that little arm that holds the valve open was bent and not holding the fuel valve open enough. Enough to start a little and sputter, but not run. Link to comment Share on other sites More sharing options...
Garys New Test Name Posted January 2, 2021 Share Posted January 2, 2021 We'd somehow bent the arm on the FSS when we installed it. Or it came bent. We're not sure, because #2 son took it apart and didn't take pictures or check for goolagtube videos first. Truth be told, there's not much IDI knowledge out there anymore. But anyway, that little arm that holds the valve open was bent and not holding the fuel valve open enough. Enough to start a little and sputter, but not run. Glad you found that! It can be really, REALLY frustrating when you have all new parts and it still won't run. Link to comment Share on other sites More sharing options...
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