QuestionQUESTION: need clear picture of power to activate fuel pump have cked. all fuses and relays but don't understand power flow, last connector before tank shows switched power to one wire but that dead ends there grnd the sending unit wire it shows working but no power to the other two wires. Does the system energize then switch to a run circuit ? Help
ANSWER: Hi Joseph,
Tell me the year/make/model/body style of the vehicle, please. Do you not hear the pump run for even 1 second when a helper turns the key to the 'run' position? That is the normal way it goes, and then it starts to run again when you turn the key to the start position; and then if the engine idles it maintains the pump action. If the engine won't idle then the pump won't run again until you repeat the above actions.
I can tell you what the various wires are supposed to show when you tell me about the specific vehicle that you are dealing with.
Roland
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QUESTION: Thanks Roland it is a 95 voyager no operation from the pump, then the pump ran three times then nothing, ran 12v jumper to pump pig tail and could not get it to run again but still do not understand power feed.
ANSWER: Hi Joseph,
The black wire is a ground for both the pump and the fuel level sensor signal wires. It goes to a large ground at the kick panel to the left of the driver's left shin.
The dark blue wire is the fuel level sensor so ignore that one.
The dark blue/black is the 12V power wire for the pump. It goes thru a 4-pin plug and then to a 16-pin plug at the left side of the instrument panel and then to to fuel pump relay's pin 22. That relay power the pump and the fuel injectors. It is activated for about 1 second when you turn the key to run position. Then it is activated again when you start cranking it over and remains activated so long as the starter motor is turning and finally will stay activeated if the engine starts and idles. Otherwise it 'opens' if there is a no start. And then it repeats the cycle until the engine starts and idles. So don't be surprised to have it run for a second and then die, etc. That circuit is meant to only power the pump continuously during cranking and actually running of the engine. It cuts out as a safety feature in the event that there is a situation where the engine dies in an accident and you would not want the fuel pump to continue merrily along it way. You can pull the fuel pump relay and jump a wire from the front pin socket to the rear pin socket and that will power up the fuel pump/injector circuit for test purposes. But don't drive around with it that way for safety reasons.
The relay closes only if there are signals coming from the crank and cam rotational sensors to the engine control module. Have you checked for fault codes using the ignition key? "On-off-on-off-on and leave on" doing that in 5 seconds or less elapsed time. Then watch the check engine light to see it begin to flash, pause. flash, etc. Count the flashes before each pause. Then repeat to be sure of an accurate set of flash counts. Tell me the counts and we'll go from there. You problem may have nothing to do with the pump.
Roland
PS Thanks for the nomination/rating. You can do it again if you so choose. Thank you
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QUESTION: Very helpful
1St no codes showing my wires are as follows Grn/Blk stripe no 1 second pulse but becomes live as soon i crank it. blu, blk,and pink/brn stripe
the pump should run if power is applied to the pump directly should it not?
thanks again Joseph
Answerhi Joseph,
The 1 second pulse may be too short to 'catch' but as long as the green/black shows 12V while cranking that is normal and so the pump should also run. If you want to do a direct jump to test the pump then do what I suggested at the fuel pump relay socket.
Is the problem that you can't get it to start? Any relevant history? What is the size (L) of the engine?. The main cause of no start with no codes is when the egr valve get stuck slightly ajar which leans out the mixture too much. You can spray some WD-40 on the stem where it enters the body of the valve and then move the stem back and forth to loosen up the action.
Roland
