Kennyt Posted September 29, 2016 Report Share Posted September 29, 2016 No voltage at fuel pump. Even removed the connector and tested bare wires. Still no voltage. Fuse #5 is good. Any suggestions? Quote Link to comment
Draker Posted September 29, 2016 Report Share Posted September 29, 2016 Check connector under passenger seat. I think it it's for the dome light timer. I left this unplugged once and the truck wouldn't start. Quote Link to comment
Draker Posted September 29, 2016 Report Share Posted September 29, 2016 It's been a bit since I've owned a 720 though.. you might just need to bust out a wiring diagram and get to work. Quote Link to comment
Kennyt Posted September 29, 2016 Author Report Share Posted September 29, 2016 I bypassed the fp relay and have voltage at the pump. Truck was switched on when tested. At what point does current flow to energize the pump? Quote Link to comment
datzenmike Posted September 29, 2016 Report Share Posted September 29, 2016 You just said you have voltage at the pump..... Do you mean normally? 1/ When ignition is turned on a timer begins to could down... maybe 20-30 seconds (I don't know could be 10 sec). 2/ If you don't start the vehicle the pump shuts off after counter times down. 3/ If you engage the starter the pump comes on and timer begins the count down all over, when key is released. 4/ If engine fails to start see 2/ 5/ If engine starts and the low oil pressure lamp and the charge lamp are both off (indicating a running engine) the fuel pump will continue to run until the ignition is shut off or the alternator is not charging or the oil pressure light comes on. Quote Link to comment
flatcat19 Posted September 29, 2016 Report Share Posted September 29, 2016 When you were testing did you have the key in the start position or in the on position? Quote Link to comment
Kennyt Posted September 29, 2016 Author Report Share Posted September 29, 2016 Key in the on position i have no voltage at the pump. Whenever the engine is turned over i can see about 10 volts and then nothing when engine is stopped. So the timer does not start and energize the pump for that short period. What / where / how is the timer start its function? Quote Link to comment
flatcat19 Posted September 29, 2016 Report Share Posted September 29, 2016 Have someone hold key in start position. Watch voltage. Quote Link to comment
Kennyt Posted September 29, 2016 Author Report Share Posted September 29, 2016 I did. Thats where i get approximately 10 volts Quote Link to comment
flatcat19 Posted September 29, 2016 Report Share Posted September 29, 2016 Do you have a way to test for fuel pressure. Pumps getting power. That's out of the equation... Quote Link to comment
Draker Posted September 29, 2016 Report Share Posted September 29, 2016 10 volts is correct if you factor in starter load. Quote Link to comment
Kennyt Posted September 29, 2016 Author Report Share Posted September 29, 2016 I do not hear the pump come on during the initial start up. Im thinking whatever energizes the pump during the initial startup is the issue. When it was running i could not hear the pump. I tested it directly to 12v and it works fine Quote Link to comment
flatcat19 Posted September 30, 2016 Report Share Posted September 30, 2016 If it's pumping gas... An electric pump is not always on. And they're never really that loud. What are you trying to diagnose? Quote Link to comment
Kennyt Posted September 30, 2016 Author Report Share Posted September 30, 2016 Its not pumping gas. I could hear it before during the initialization period. Then i did not hear it at all for a few months. Now no gas being pumped to carb. It makes a significant noise when testing. I have 3 pumps. They all make about the same amount of noise. I think it is the relay from an article I just read by axle addict Quote Link to comment
flatcat19 Posted September 30, 2016 Report Share Posted September 30, 2016 If you bypass the relay, does it start pumping gas? Quote Link to comment
datzenmike Posted September 30, 2016 Report Share Posted September 30, 2016 OK go to the fuse box and pull the #5 and #6 fuse and replace them. It's easier and more reliable that testing or simply looking at them. Got power on both ???? No power on the #6 or no power on the #5 is a problem with the ignition switch Yes there is power. keep going.... Go to the fuel pump relay (above) it's up above the pass side kick panel just forward of the door. Remove it with the wire harness is probably the easiest thing. Ignition ON test the BLUE wire for power, test the White wire for power. No power on one or both. The problem is between the relay and the fuse box Yes power on both wires. Make a jumper and with the relay unplugged, join the BLUE wire to theWHITE/BLACK wire on the connector. When ignition is turned ON you should hear the fuel pump. It will stay ON as long as the ignition is ON. No pump does not come on... pump has failed. * Yes pump comes on..... fuel pump relay has failed ** 1 Quote Link to comment
datzenmike Posted September 30, 2016 Report Share Posted September 30, 2016 No Pump * Check the BLACK wire is grounded. Fix ground Check that there is power on the other wire. (probably BLACK/RED) No power the wire between tank and pump is bad or corroded. Fix. If good ground and power and no pump the pump is certainly bad. Fuel pump relay. ** Check the BLACK wire is at ground. This is about as far as you can go. If timer still does not come on with ignition switch take relay apart and look for burnt or damaged components. Fix or replace. Quote Link to comment
Kennyt Posted September 30, 2016 Author Report Share Posted September 30, 2016 Will do it tomorrow. I do know that i can short the white tonthe white/black on the relay connector and get a full 12v. I took pump off to test independently. Thanks. Ill be back with the results tomorrow Quote Link to comment
Z-train Posted September 30, 2016 Report Share Posted September 30, 2016 Take the cover off the relay. There is a solder joint that has come apart. Quote Link to comment
flatcat19 Posted September 30, 2016 Report Share Posted September 30, 2016 No Pump * Check the BLACK wire is grounded. Fix ground Check that there is power on the other wire. (probably BLACK/RED) No power the wire between tank and pump is bad or corroded. Fix. If good ground and power and no pump the pump is certainly bad. Fuel pump relay. ** Check the BLACK wire is at ground. This is about as far as you can go. If timer still does not come on with ignition switch take relay apart and look for burnt or damaged components. Fix or replace. Good flow charting. 1 Quote Link to comment
datzenmike Posted September 30, 2016 Report Share Posted September 30, 2016 Will do it tomorrow. I do know that i can short the white tonthe white/black on the relay connector and get a full 12v. I took pump off to test independently. Thanks. Ill be back with the results tomorrow Of course you'll get the full 12 volts, you've already checked the BLUE wire for it. Jumping the BLUE to the WHITE/BLACK sends 12 volts to the pump. As Z train said it's likely the relay, but expensive... and a waste of time and money is it's a blown fuse. Eliminate everything else and what's left has to be the problem. 1 Quote Link to comment
Kennyt Posted September 30, 2016 Author Report Share Posted September 30, 2016 Went to junkyard and got another relay. I can hear the relay click when switched on however the pump does not come on for a few seconds. It will however start now and the pump will run with engine running. Just curious as to why pump will not come on momentarily when switched on initially. Maybe another bad or inconsistent relay? I have a new one on order just to verify. Thoughts? 1 Quote Link to comment
flatcat19 Posted September 30, 2016 Report Share Posted September 30, 2016 It is not supposed to get power when on. That'd why I asked about available voltage in the start position. Most cars only provide a second or two of power to the fuel pump when key is initially turned on to help prime the pump before command from the car running kicks in. 1 Quote Link to comment
Z-train Posted October 1, 2016 Report Share Posted October 1, 2016 Don't throw the old one out.It's about 5 minute fix for it. 1 Quote Link to comment
Kennyt Posted October 1, 2016 Author Report Share Posted October 1, 2016 I looked at solder joints with magnifying glass. I do not see any cracks or anything bad. I think i will resolder the 2 connections andd see if it helps. I tried it today also and could hear it click when i turned switch to start and turned over the engine. Still wondering about the timer thingy. 1 Quote Link to comment
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