fische7 Posted September 8, 2013 Share Posted September 8, 2013 So... riddle me this... Anyone know why none of the wiring diagrams for the 1975-1979 20r yotas do not have the wiring information for the electric fuel pump???? I've tried old and new chiltons, p/u and car, autozone online(alldata)... and the results... nothing. So... the question persists... Does anyone have a fuel pump wiring diagram? If not, does anyone have any idea... How this fuel pump system works? Where the fuel relay is? How the oil sender unit is wired in? Where the oil sender unit is located? What are the colors of all these wires? How is the fuel pump resistor wired in? Why does it have the resistor? To slow down the pump? If it runs 100% of the time when the key is on, or is there some RPM/other shut-off switch? So as you could probably tell I am having a problem with my fuel pump. I am the recent recipient of a 1975 Chinook camper which came with a completely none operational fuel pump. I've been trying to diagnose if its an electrical problem or mechanical, but there is no information about the circuit. So far I have... Measured voltage at the fuel pump connector -- 0v one side and a very erratic reading on the other Put 12v directly to the pump -- nothing happened I just dropped the fuel tank last night, but it began to rain and I was unable to perform any more testing. Also it looks like there is a second external fuel pump 'T'ed into to the air vent with a plugged piece of rubber gas line on the other side of the device. Is this a normal set up to feed from a second fuel tank? I'm gonna do a write up about this fuel pump if I figure it out, otherwise I guess I'll write up whatever workaround I come up with. Quote Link to comment Share on other sites More sharing options...
zero Posted September 9, 2013 Share Posted September 9, 2013 So... riddle me this... Anyone know why none of the wiring diagrams for the 1975-1979 20r yotas do not have the wiring information for the electric fuel pump???? I've tried old and new chiltons, p/u and car, autozone online(alldata)... and the results... nothing. So... the question persists... Does anyone have a fuel pump wiring diagram? If not, does anyone have any idea... How this fuel pump system works? Where the fuel relay is? How the oil sender unit is wired in? Where the oil sender unit is located? What are the colors of all these wires? How is the fuel pump resistor wired in? Why does it have the resistor? To slow down the pump? If it runs 100% of the time when the key is on, or is there some RPM/other shut-off switch? So as you could probably tell I am having a problem with my fuel pump. I am the recent recipient of a 1975 Chinook camper which came with a completely none operational fuel pump. I've been trying to diagnose if its an electrical problem or mechanical, but there is no information about the circuit. So far I have... Measured voltage at the fuel pump connector -- 0v one side and a very erratic reading on the other Put 12v directly to the pump -- nothing happened I just dropped the fuel tank last night, but it began to rain and I was unable to perform any more testing. Also it looks like there is a second external fuel pump 'T'ed into to the air vent with a plugged piece of rubber gas line on the other side of the device. Is this a normal set up to feed from a second fuel tank? I'm gonna do a write up about this fuel pump if I figure it out, otherwise I guess I'll write up whatever workaround I come up with. I've got three Toyota manuals that clearly show the fuel pump wiring. One by Haynes and two published by Toyota. Toyota shows all the wiring in the Hilux book with a 20R engine and also has it in the 20R only book. Quote Link to comment Share on other sites More sharing options...
zero Posted September 9, 2013 Share Posted September 9, 2013 Here are some diagrams. The factory wiring diagram for the older trucks (70s up to 78) are in five or six separate sheets so it's not easy to scan paste together. Quote Link to comment Share on other sites More sharing options...
zero Posted September 9, 2013 Share Posted September 9, 2013 So... riddle me this... Anyone know why none of the wiring diagrams for the 1975-1979 20r yotas do not have the wiring information for the electric fuel pump???? Toyota certainly gives the diagrams in their manuals. Where the fuel relay is? Fuel pump relay is bolted to the steering column on the inside of the cab . How is the fuel pump resistor wired in? Resistor is under the hood on the right side near on the fenderwell. A real bad location and I've had to fix several that rusted out and went bad. A generic 2.2 ohm wire-round resistor available a most any auto parts store makes a good replacement. Why does it have the resistor? To slow down the pump? If it runs 100% of the time when the key is on, or is there some RPM/other shut-off switch? The fuel pump must operate well at 9 volts since that is the normal vehicle voltage when cranking. When the engine is running system voltage climbs to 13-14 volts. That's a big swing. I'm assuming the fuel pump is made to run at 9-12 volts for a long life and by adding that "dropping" resistor - it keeps voltage down in that range once the engine is running. Measured voltage at the fuel pump connector -- 0v one side and a very erratic reading on the other Put 12v directly to the pump -- nothing happened Did you also ground the pump? I takes a negative and a positive to make it work. Toyota did a poor job on wiring the 70s trucks. They are wired like GM did them back then. The electric fuel pump does NOT have a ground wire going to it. It relies on the fuel tank being grounded to the frame. So it only takes some rust to stop the pump from working. Quote Link to comment Share on other sites More sharing options...
zero Posted September 10, 2013 Share Posted September 10, 2013 Some more info including a resistor that went bad from road-salt and rust on a 1977 Chinook. Quote Link to comment Share on other sites More sharing options...
Maineah Posted September 10, 2013 Share Posted September 10, 2013 Something really funky with that wiring diagram it makes no sense. I see what they are doing with the resistor but that’s about it. The resistor is full voltage to the pump during crank and ballasted during run but the way it’s shown the pump would run with the key on at a lower voltage as long as there was no oil pressure but with oil pressure the relay would open and shut off the pump. I think there is a missing diode. Quote Link to comment Share on other sites More sharing options...
zero Posted September 10, 2013 Share Posted September 10, 2013 That's the Toyota factory diagram - not something I drew. I just added some annotations to indicate what is supposed to be going on (according to Toyota). When the key is turned to "start" position - there must be continuity between two terminals in the fuel pump relay marked "ST" and "PU." When this happens - power from the crank-circuit is fed to the fuel pump and makes it run. What exactly makes those contact close when cranking - I do not know for sure. Those contacts are normally "open" due to spring pressure. So the pull-in coil for the electromagnet needs to be energized to close those contacts. I do have a fuel pump relay sitting on my shop bench and it should be pretty easy to figure out. The relay only has one semi-conductor in it although the schematic shows a diode and a resistor in series. It has no markings (like a diode would) so I don't know if it's a diode or a small carbon resistor. Kind of hard to check in-place for resistance or continuity without some hard thinking. It's almost 11 PM and this is hurting my brain. Maybe it will be more evident tomorrow when my head is working better. Quote Link to comment Share on other sites More sharing options...
5Toyota Posted September 10, 2013 Share Posted September 10, 2013 they do use a resistor on the fual pump it was mounted under the hood on the left fender on some models ie the corona i had they all used it the relay is seperate and the oil pressure switch is in the curcuit also i have had 4 20rs with eletric pump in tank one for 15 years never did have any pump trouble every one had better then 200.000 on it. the resister is pretty large in size i mean left when looking at the raditer . good picture of that resister. that be it Quote Link to comment Share on other sites More sharing options...
5Toyota Posted September 10, 2013 Share Posted September 10, 2013 soory i posted with out first looking at the pictures they are right on as i live i a desert i never had rust issiews with any of the ones i had Quote Link to comment Share on other sites More sharing options...
fische7 Posted September 10, 2013 Author Share Posted September 10, 2013 You guys are my heroes!!! Thanks so much jdemaris for the pics, they are gonna help a bunch. Those useless Chilton's never have all/correct information. That is definitely the last one I will ever buy!! I'll be sure to post my progress over the next week or so. Quote Link to comment Share on other sites More sharing options...
Maineah Posted September 10, 2013 Share Posted September 10, 2013 That's the Toyota factory diagram - not something I drew. I just added some annotations to indicate what is supposed to be going on (according to Toyota). When the key is turned to "start" position - there must be continuity between two terminals in the fuel pump relay marked "ST" and "PU." When this happens - power from the crank-circuit is fed to the fuel pump and makes it run. What exactly makes those contact close when cranking - I do not know for sure. Those contacts are normally "open" due to spring pressure. So the pull-in coil for the electromagnet needs to be energized to close those contacts. I do have a fuel pump relay sitting on my shop bench and it should be pretty easy to figure out. The relay only has one semi-conductor in it although the schematic shows a diode and a resistor in series. It has no markings (like a diode would) so I don't know if it's a diode or a small carbon resistor. Kind of hard to check in-place for resistance or continuity without some hard thinking. It's almost 11 PM and this is hurting my brain. Maybe it will be more evident tomorrow when my head is working better. I know it's not your diagram but here is what I think the signal to the relay coil comes from the start signal not the ign signal. So when the key is turned to start full voltage is applied the pump. Once the key is released or there is oil pressure the coil collapses and swings over to the ign side through the resistor. The way it is drawn as soon as the engine has oil pressure the relay will shut down because the coil has no ground once there is oil pressure. The diode in the relay is a spike suppressor it has no other purpose and the diode on the oil light is to keep it from being back feed from the relay coil. Quote Link to comment Share on other sites More sharing options...
zero Posted September 10, 2013 Share Posted September 10, 2013 The diagram in my British Haynes-Strasman makes more sense and is better then what is in the Toyota factory service manual "wiring" book. So much for factory manuals. As a note to the original poster here. The Haynes books in Great Britain are a heck of a lot better then the ones being sold here in the USA. Note - this diagram is showing the circuit when there is no oil pressure and the contacts are open for the "fuel pump run" circuit. Quote Link to comment Share on other sites More sharing options...
Donnie Posted September 10, 2013 Share Posted September 10, 2013 You had one question that was not answered: yes, when the pump is running there is a pop off valve in the hose between the pump & the gauge sender in jde's photo #5....it is the small white device in the center of the black hose.. this keeps the pressure at the desired level for a carburetor system while the pump is running.......Donnie Quote Link to comment Share on other sites More sharing options...
Donnie Posted September 10, 2013 Share Posted September 10, 2013 My error, it is in another illustration, properly called a relief valve....These pumps often get lazy from lack of activity...Years back I recall a truck, maybe A '75, had sat for a couple of years, not sure of the year where the pump refused to run with 12 volts supplied to it on the bench....As I recall, I removed it from the tank assy, removed the sock, soaked it in a hog pan with a couple of gallons of KEROSENE---don't use gas, for an hour or so, connected voltage to it. tapped it a couple of times & it started running,,,,I left it run until I felt it was going to be ok, cleaned the sock. connected it all back together & let it pump kerosene for a while while, while blocking the outlet to flush & clean the relief valve, put it back in the tank & all was well............ NOTE: this all happened years ago when we had pure gas & alcohol was not in the fuel then..NOW , I'm not sure what an inactive pump would look like, or if this would work... I am just relating a story of how I repaired A problem.........Donnie Quote Link to comment Share on other sites More sharing options...
zero Posted September 10, 2013 Share Posted September 10, 2013 Donnie -thanks for the info on the Mercedes Hanamog for sale near me (kind of). I get a kick out of seeing them but cannot imagine trying to drive one on a USA highway. They use a tiny British diesel engine and front wheel drive. Since the engine is a British BMC - I'm not sure what part of those things have anything to do with Mercedes. It has the same size diesel as the Volkswagen Rabbits used to have! Pretty small. I already have one foreign RV that is miserable to find parts for. A Winnebago Phasar built on a French Renault Chassis. Also front wheel drive but if it was diesel, it would be a 2.2 turbo. Not a 1.6 non-turbo like that Hanamog has. http://ithaca.craigslist.org/pts/4051826783.html Quote Link to comment Share on other sites More sharing options...
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