ArdWrknTrk Posted June 5, 2023 Share Posted June 5, 2023 Don't really have any pictures right now as the truck has been running fairly well. I have run into a couple issues where I have been unable to fill the tanks, sometimes the rear wont take gas, sometimes the front wont take gas, I've ordered new fill neck (87+) and will be replacing my hacked up ones. I also have a theory on why it will die on start sometimes. I'm using an aftermarket fuel pump on the frame rail. What I think is happening is the fuel in the lines between the pump and the tank is siphoning back into the tank, forcing the pump to have to work harder to get fuel to the carb and perhaps the bowl is running dry before the pump has a chance to fill it. I've noticed the die on start happens more with the rear tank which has a much longer fuel route. What I plan to do (at least temporarily) is add a relay and a momentary push button on the dash so that I can run the currently disconnected in tank pumps as a priming system to feed fuel to the main pump. I will likely also add an anti drainback valve to keep fuel in the line between the frame fuel pump and the carb. The pump prime will at least make the truck that much harder to steal lol. Fuel can never 'drain back' out of the float bowl. You just need to start your truck once a week. (or use the priming pump, I guess...?) Be aware that the '87 on fuel tanks have a different size collar in the fuel neck and the vent hose (now fill hose) is not quite the same. I'm sure it's something you can work out, but it's better to know ahead of time. Are you sure you don't have a cross return situation where one tank will fill the other? Ford instituted a retrofit of a pair of check valves to fix that. Gary probably has the TSB with part numbers. Link to comment Share on other sites More sharing options...
CRittaler Posted June 6, 2023 Author Share Posted June 6, 2023 Fuel can never 'drain back' out of the float bowl. You just need to start your truck once a week. (or use the priming pump, I guess...?) Be aware that the '87 on fuel tanks have a different size collar in the fuel neck and the vent hose (now fill hose) is not quite the same. I'm sure it's something you can work out, but it's better to know ahead of time. Are you sure you don't have a cross return situation where one tank will fill the other? Ford instituted a retrofit of a pair of check valves to fix that. Gary probably has the TSB with part numbers. There's a chance my floats are set too low and the bowl empties on high idle before the pump can pull fuel from the tank. I haven't cracked the top off the avs2 to check. I have a late model tank that I can use as well, I would just have to make the early sender work with the late tank. Starting it once a week doesn't make a difference, I was driving it daily and every start to go to work and then home it would highidle for a bit, then lean out and die. The priming system I was talking about would use the in tank pumps to feed the pump on the rail prior to starting the truck. It's not a cross return, I've double and triple checked the fuel line routing. I might also hook a multimeter to the pump power and see if it's losing power before it dies. Link to comment Share on other sites More sharing options...
ArdWrknTrk Posted June 6, 2023 Share Posted June 6, 2023 There's a chance my floats are set too low and the bowl empties on high idle before the pump can pull fuel from the tank. I haven't cracked the top off the avs2 to check. I have a late model tank that I can use as well, I would just have to make the early sender work with the late tank. Starting it once a week doesn't make a difference, I was driving it daily and every start to go to work and then home it would highidle for a bit, then lean out and die. The priming system I was talking about would use the in tank pumps to feed the pump on the rail prior to starting the truck. It's not a cross return, I've double and triple checked the fuel line routing. I might also hook a multimeter to the pump power and see if it's losing power before it dies. I have an AVS 650 that used to live on my truck (until the accelerator piston needed changing) There should be enough fuel in the bowls to idle for between a minute or two. (ask me how I know! 😉) The cross flow issue has nothing to do with how the lines are connected (just the switch valve) It is a documented issue and there is a 'factory' fix... I will try to look*** this up just to put it out there.... If you use a late model tank you need to modify the locating tabs, or the slots in the sender/pump cap to make the float hang in the correct position and the fuel nipples point the right way. I am running 85-86 senders in my '87 tanks. Because the one year wonder '87 with mechanical pickup/senders are completely unavailable NOS or aftermarket. I understood what you meant about the primer switch or button. Think about how much fun it is for me when I have to crank the engine over to pull fuel from the tank to the carb with just a mechanical pump.... 😁 If you think it may be losing power to the pump you might jump out the oil pressure sender and just watch the fuel pump relay close. These Hot Fuel systems changed a couple of times over the years. I need to do some digging If I want to address your specific issue. Link to comment Share on other sites More sharing options...
ArdWrknTrk Posted June 6, 2023 Share Posted June 6, 2023 I have an AVS 650 that used to live on my truck (until the accelerator piston needed changing) There should be enough fuel in the bowls to idle for between a minute or two. (ask me how I know! 😉) The cross flow issue has nothing to do with how the lines are connected (just the switch valve) It is a documented issue and there is a 'factory' fix... I will try to look*** this up just to put it out there.... If you use a late model tank you need to modify the locating tabs, or the slots in the sender/pump cap to make the float hang in the correct position and the fuel nipples point the right way. I am running 85-86 senders in my '87 tanks. Because the one year wonder '87 with mechanical pickup/senders are completely unavailable NOS or aftermarket. I understood what you meant about the primer switch or button. Think about how much fun it is for me when I have to crank the engine over to pull fuel from the tank to the carb with just a mechanical pump.... 😁 If you think it may be losing power to the pump you might jump out the oil pressure sender and just watch the fuel pump relay close. These Hot Fuel systems changed a couple of times over the years. I need to do some digging If I want to address your specific issue. I think you need to look at fuselink 'T' because the pumps should be running when cranking regardless of the oil pressure and inertia switch when the key is in the 'start' position. I can say with authority that your carb is not running out of fuel within seconds of starting. Link to comment Share on other sites More sharing options...
ArdWrknTrk Posted June 6, 2023 Share Posted June 6, 2023 I think you need to look at fuselink 'T' because the pumps should be running when cranking regardless of the oil pressure and inertia switch when the key is in the 'start' position. I can say with authority that your carb is not running out of fuel within seconds of starting. I have to admit I am wrong about the FDM cross flow TSB. That was for later generation trucks like mine with FDM's in the tanks. My apologies for trying to offer bad information! Link to comment Share on other sites More sharing options...
CRittaler Posted June 7, 2023 Author Share Posted June 7, 2023 I think you need to look at fuselink 'T' because the pumps should be running when cranking regardless of the oil pressure and inertia switch when the key is in the 'start' position. I can say with authority that your carb is not running out of fuel within seconds of starting. This is good info. I will check that link. It high idles for a few minutes before quitting. Sometimes it will restart right away, other times it will crank for 10 seconds or so and I'll have to pump the gas a few times to get it to catch. Link to comment Share on other sites More sharing options...
ArdWrknTrk Posted June 7, 2023 Share Posted June 7, 2023 This is good info. I will check that link. It high idles for a few minutes before quitting. Sometimes it will restart right away, other times it will crank for 10 seconds or so and I'll have to pump the gas a few times to get it to catch. Chris, You might want to look at the hot fuel documentation Gary has here on the site. https://www.garysgaragemahal.com/460-fuel-systems.html Consider this.. Minimum rated delivery for a 460 fuel pump is a gallon a minute. (See pg 37 of the TSB. Also note this TSB describes the cross flow problem I mentioned) A 3/8" fuel line has an internal volume of .73 fl oz per foot. So in round numbers if you flow one gallon a minute and there were 20' between tank and carb (.75 x 20=15 oz) 128oz/15 = 8ish 60sec /8 = 7.5 seconds for fuel to reach from tank to carb. That constant circulation of cool fuel from the tank is what keeps vapor lock from being able to occur (hence "Hot Fuel Handling") If your fuel pump is working, the only way I can fathom that your truck is running out of fuel is if the screen in the vapor separator/return bypass (the little 'T' fuel line fitting near the carb) is completely clogged. Part #s are: E3TZ 9N176B (blue dot, .040) E3TZ 9N176A (red dot, .060) EOTZ 9N176B (white dot, .090) obsolete I hope this helps! 🙂 Link to comment Share on other sites More sharing options...
CRittaler Posted June 8, 2023 Author Share Posted June 8, 2023 Chris, You might want to look at the hot fuel documentation Gary has here on the site. https://www.garysgaragemahal.com/460-fuel-systems.html Consider this.. Minimum rated delivery for a 460 fuel pump is a gallon a minute. (See pg 37 of the TSB. Also note this TSB describes the cross flow problem I mentioned) A 3/8" fuel line has an internal volume of .73 fl oz per foot. So in round numbers if you flow one gallon a minute and there were 20' between tank and carb (.75 x 20=15 oz) 128oz/15 = 8ish 60sec /8 = 7.5 seconds for fuel to reach from tank to carb. That constant circulation of cool fuel from the tank is what keeps vapor lock from being able to occur (hence "Hot Fuel Handling") If your fuel pump is working, the only way I can fathom that your truck is running out of fuel is if the screen in the vapor separator/return bypass (the little 'T' fuel line fitting near the carb) is completely clogged. Part #s are: E3TZ 9N176B (blue dot, .040) E3TZ 9N176A (red dot, .060) EOTZ 9N176B (white dot, .090) obsolete I hope this helps! 🙂 I'm going to try and dig into it soon. What I think it's happening is the fuel in the lines between the tank and carb is draining back to the tank, leaving only what remains in the float bowl. I suspect, but have not confirmed, that the frame mounted fuel pump is struggling to reprime before the float bowls empty. It could even be only the fuel between the tanks and the pump that drains back. I haven't had a chance to look at the truck yet though to investigate. The fuel system on this truck was hacked up long before I got it. It doesn't have the big 6 Port fuel selectors, but 2 3 Port ones. I installed a relay to switch the sending units, PO had a toggle on the dash. Link to comment Share on other sites More sharing options...
ArdWrknTrk Posted June 8, 2023 Share Posted June 8, 2023 I'm going to try and dig into it soon. What I think it's happening is the fuel in the lines between the tank and carb is draining back to the tank, leaving only what remains in the float bowl. I suspect, but have not confirmed, that the frame mounted fuel pump is struggling to reprime before the float bowls empty. It could even be only the fuel between the tanks and the pump that drains back. I haven't had a chance to look at the truck yet though to investigate. The fuel system on this truck was hacked up long before I got it. It doesn't have the big 6 Port fuel selectors, but 2 3 Port ones. I installed a relay to switch the sending units, PO had a toggle on the dash. But the fuel pumps in the tanks are still there, right? And if they are, fuel should reach the carb in under eight seconds, with an additional quart every 15 seconds. If that's working there's no way you're running out of fuel. If you could sketch up how you have wired your relay and two 3 port valves I'd be interested to see that. The six port Pollak valve with wiring pigtail is only ~$75- 80 on eBay last I checked. Then you could get rid of the switch, "extra" pump and relay. Go back to how the system is supposed to operate. Link to comment Share on other sites More sharing options...
CRittaler Posted June 8, 2023 Author Share Posted June 8, 2023 But the fuel pumps in the tanks are still there, right? And if they are, fuel should reach the carb in under eight seconds, with an additional quart every 15 seconds. If that's working there's no way you're running out of fuel. If you could sketch up how you have wired your relay and two 3 port valves I'd be interested to see that. The six port Pollak valve with wiring pigtail is only ~$75- 80 on eBay last I checked. Then you could get rid of the switch, "extra" pump and relay. Go back to how the system is supposed to operate. The in thank pumps are there, but they are not connected and I don't know if they work. The on frame pump is pulling fuel through them. I will try to sketch something up on the current system. Link to comment Share on other sites More sharing options...
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