fords4life Posted May 14, 2018 Share Posted May 14, 2018 Hi all, had a no start on the '86 this morning. I can hear the fuel pump come on, but it is running continuously and not building enough pressure to shut off like it normally does before I start the truck. I let it run and checked for fuel at the schrader valve on the fuel rail, and I have fuel, it just doesn't seem to be building enough pressure and isn't firing. I didn't have time to check for spark, but with the pump not shutting off, I'm guessing I have a fuel issue of some kind. Thoughts? Link to comment Share on other sites More sharing options...
Gary Lewis Posted May 14, 2018 Share Posted May 14, 2018 According to the EVTM you should have an in-tank low pressure pump and a frame-mounted high pressure pump. Do you know which one is running? If the low pressure pump isn't running then the high pressure pump won't have any fuel to pump and can't bring the pressure up. Do you have dual tanks? If so, can you switch to the other tank to see if that in-tank pump will work? Link to comment Share on other sites More sharing options...
fords4life Posted May 14, 2018 Author Share Posted May 14, 2018 According to the EVTM you should have an in-tank low pressure pump and a frame-mounted high pressure pump. Do you know which one is running? If the low pressure pump isn't running then the high pressure pump won't have any fuel to pump and can't bring the pressure up. Do you have dual tanks? If so, can you switch to the other tank to see if that in-tank pump will work? I was in my work clothes so I didn't climb underneath, but the sound was in the typical spot under the drivers side frame rail where the high pressure pump sits. I tried switching back and forth between tanks with no change. There was fuel at the rail(used my knife to push on the schrader valve and got fuel immediately), it just doesn't appear to be enough pressure. Just to confirm, truck turns over just fine, no starter issues, just won't fire. Link to comment Share on other sites More sharing options...
Gary Lewis Posted May 14, 2018 Share Posted May 14, 2018 I was in my work clothes so I didn't climb underneath, but the sound was in the typical spot under the drivers side frame rail where the high pressure pump sits. I tried switching back and forth between tanks with no change. There was fuel at the rail(used my knife to push on the schrader valve and got fuel immediately), it just doesn't appear to be enough pressure. Just to confirm, truck turns over just fine, no starter issues, just won't fire. I would think that any pressure would eventually get the engine to kick over. Maybe not run, but hit intermittently. And while that might point to an ignition or electrical problem, the fact that the pump doesn't stop running like it usually does says it really is related to fuel. And the first test I'd suggest is to put a gauge on the schrader valve. Is there any chance you are out of gas? Do you see any signs of leaks? If the pressure is low then it would seem like the high-pressure pump is the problem. However, you said that switching back and forth between tanks didn't make a difference, and that may indicate a problem with the 6-port valve. It determines which in-tank pump is supposed to run as well as where the fuel to the high-pressure pump comes from and where the return from the regulator goes. So a problem with the valve could starve the high pressure pump of fuel, causing low pressure at the rail. And the 6-port valves are known to have problems - I just bypassed the one on Big Blue as it sprang a leak, but NumberDummy says they were a problem from the day they came out. You can get a kit at the parts store to repair fuel lines, and you could use it to bypass the 6-port valve. But you have to cut the lines and graft in a line from the kit. That means you won't have the other tank available unless you repair what you cut out. And, since the gauge circuit goes through the 6-port valve you will have to wire around it, leave the valve but not have it being used, or do w/o a gauge. Perhaps there's another kit that has the right connectors to let you just bypass the valve w/o any cutting? Maybe Bill knows? Link to comment Share on other sites More sharing options...
fords4life Posted May 14, 2018 Author Share Posted May 14, 2018 I would think that any pressure would eventually get the engine to kick over. Maybe not run, but hit intermittently. And while that might point to an ignition or electrical problem, the fact that the pump doesn't stop running like it usually does says it really is related to fuel. And the first test I'd suggest is to put a gauge on the schrader valve. Is there any chance you are out of gas? Do you see any signs of leaks? If the pressure is low then it would seem like the high-pressure pump is the problem. However, you said that switching back and forth between tanks didn't make a difference, and that may indicate a problem with the 6-port valve. It determines which in-tank pump is supposed to run as well as where the fuel to the high-pressure pump comes from and where the return from the regulator goes. So a problem with the valve could starve the high pressure pump of fuel, causing low pressure at the rail. And the 6-port valves are known to have problems - I just bypassed the one on Big Blue as it sprang a leak, but NumberDummy says they were a problem from the day they came out. You can get a kit at the parts store to repair fuel lines, and you could use it to bypass the 6-port valve. But you have to cut the lines and graft in a line from the kit. That means you won't have the other tank available unless you repair what you cut out. And, since the gauge circuit goes through the 6-port valve you will have to wire around it, leave the valve but not have it being used, or do w/o a gauge. Perhaps there's another kit that has the right connectors to let you just bypass the valve w/o any cutting? Maybe Bill knows? So....had to run home for a few minutes and truck fired right up. Fuel pump turned on with key in run position and shutoff a few seconds later just like always.....I'm stumped....This is going to be a fun one to figure out I'm sure. Link to comment Share on other sites More sharing options...
Gary Lewis Posted May 14, 2018 Share Posted May 14, 2018 So....had to run home for a few minutes and truck fired right up. Fuel pump turned on with key in run position and shutoff a few seconds later just like always.....I'm stumped....This is going to be a fun one to figure out I'm sure. I hate intermittent problems. They are so hard to find. Anyway, glad it ran for you. Link to comment Share on other sites More sharing options...
85lebaront2 Posted May 14, 2018 Share Posted May 14, 2018 I would think that any pressure would eventually get the engine to kick over. Maybe not run, but hit intermittently. And while that might point to an ignition or electrical problem, the fact that the pump doesn't stop running like it usually does says it really is related to fuel. And the first test I'd suggest is to put a gauge on the schrader valve. Is there any chance you are out of gas? Do you see any signs of leaks? If the pressure is low then it would seem like the high-pressure pump is the problem. However, you said that switching back and forth between tanks didn't make a difference, and that may indicate a problem with the 6-port valve. It determines which in-tank pump is supposed to run as well as where the fuel to the high-pressure pump comes from and where the return from the regulator goes. So a problem with the valve could starve the high pressure pump of fuel, causing low pressure at the rail. And the 6-port valves are known to have problems - I just bypassed the one on Big Blue as it sprang a leak, but NumberDummy says they were a problem from the day they came out. You can get a kit at the parts store to repair fuel lines, and you could use it to bypass the 6-port valve. But you have to cut the lines and graft in a line from the kit. That means you won't have the other tank available unless you repair what you cut out. And, since the gauge circuit goes through the 6-port valve you will have to wire around it, leave the valve but not have it being used, or do w/o a gauge. Perhaps there's another kit that has the right connectors to let you just bypass the valve w/o any cutting? Maybe Bill knows? Gary, the 6 port tank selector on the EFI is not the motor operated beast on the hot fuel handling package 460. It is a combination reservoir and tank selector and on the 1986 models has a filter in it. The fuel tank selector switch (page 104 of the 1986 EVTM) shows it as being the only thing common to both in-tank pumps. The relay and inertia switch are in the circuit before the switch and would also affect the high pressure pump. Link to comment Share on other sites More sharing options...
vjsimone Posted May 19, 2018 Share Posted May 19, 2018 The fuel pumps running continuously when the engine is not under power, is a fairly common sign of a corruption in the ECA/Computer. Link to comment Share on other sites More sharing options...
Gary Lewis Posted May 19, 2018 Share Posted May 19, 2018 The fuel pumps running continuously when the engine is not under power, is a fairly common sign of a corruption in the ECA/Computer. Vinny - Is that intermittent? He's had it happen and then go away. And, what causes it? Just a bad ECA? Link to comment Share on other sites More sharing options...
85lebaront2 Posted May 19, 2018 Share Posted May 19, 2018 Vinny - Is that intermittent? He's had it happen and then go away. And, what causes it? Just a bad ECA? Gary, ECA and FPR along with the inertia switch will affect all the pumps, Other than the actual connector plugs on the tanks, the tank selector switch is the only electrical item in the circuit that does not affect the high pressure pump, even the ground, G701, is the same. Link to comment Share on other sites More sharing options...
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