no power to fuel pump at fuse boxes, 96 vette

[colo. vette]

original onset gave thought of vapor lock. car was hard to start a few times, and died on the road.
multi meter tests show no power to either fuse for fuel pump. pump is newer, filter is newer. Do I need to replae the relay?

 

[BigJimZ16]

original onset gave thought of vapor lock. car was hard to start a few times, and died on the road.
multi meter tests show no power to either fuse for fuel pump. pump is newer, filter is newer. Do I need to replae the relay?

What you need to do is get a DVM and a schematic of the fuel pump system and trouble shoot down to the defective component. Throwinf "maybe" parts at a problem is the most expensive method of auto repair of any type!!

 

[colo. vette]

What you need to do is get a DVM and a schematic of the fuel pump system and trouble shoot down to the defective component. Throwinf "maybe" parts at a problem is the most expensive method of auto repair of any type!!

I cannot find power at the underhood fuse block #1. schematic refers me to power distribution cell 10. ?

 

[boomdriver]

Electrical is easy. Keep testing for power going backward thru the system until you find it.
Your fuel system is not so easy.......

it has a back-up system, that allows you to start the car in case of relay failure.....it just makes you crank on it until it builds 4 psi oil pressure. Thats what makes it hard to start when there is a relay failure. A FSM will describe all these details...in great detail.

Whats wrong with testing the fuel pump relay for power 'out' ? Thats kinda obvious at this point.

 

[boomdriver]

Yes, I see in the drawing how they took the links out (finally) and ran that back-up thru a fuse slot. That seems like the right thing to do for ease of access. Its still the same basic design with extra fuses and no hidden fusable links.

From what he says....I'd go with fuse 2 as well, but I'd test the oil press switch for power to one side...if none, back up and keep digging.

He can also jump the OP switch for diagnostic purposes ONLY.

 

[colo. vette]

have a red and a yellow, and a brown and white (? doesn't show in my schematic) at what I believe is the oil pressure sensor switch. red has power. I have power to fuse # 2(fuse block 1, underhood) but no power @ i/p fusebox # 14 (fp1) even when I jump red to yellow at the op switch. I have replaced the relay.
there is another sensor near the op switch with a single green wire, forget what it is

 

[boomdriver]

have a red and a yellow, and a brown and white (? doesn't show in my schematic) at what I believe is the oil pressure sensor switch. red has power. I have power to fuse # 2(fuse block 1, underhood) but no power @ i/p fusebox # 14 (fp1) even when I jump red to yellow at the op switch. I have replaced the relay.
there is another sensor near the op switch with a single green wire, forget what it is

Not sure you;re looking at the right switch....

Your oil pressure SENSOR has a single wire. It is mounted on a metal 1/4" plumbing "T" with the oil pressure SWITCH. They are next to each other.
Switch has 2 wires like the drawing indicates.; They are usually the same color as the drawings.

IF there IS power to one side of the OP Switch, car will start IF that circuit is not broken between the switch and the fuel pump. ( fuse? wire harness damage? ???? ) Engine must crank for several seconds to build oil pressure before the fuel pump gets any power. THIS is the tip-off that the fuel relay has failed. Hard starting when cold and fuel pressure is low or none.

That is the back-up circuit.

The primary circuit for the fuel pump comes directly from the fuel pump relay that gets its power from the ECM permissions, to run a 2 second prime then shut off. When you turn the key to ON the FP will only run for 2 seconds until the engine starts and runs on its own..so, do not think that you are going to turn the key on then go check for power...it won;t be there. The ECM only allows the relay to have power after the engine fires, when the dist sends an OK signal to the ECM telling it that the engine is running on its own and only then will the ECM allow constant power thru the fuel relay to energize the pump.

Get another pair of hands and YOU observe the DVM as the key is turned to ON....if there is NO power out of your new relay (assuming that there is power IN) then you either have a bad relay or the circuit is open before it gets to the relay, BUT...< big BUT, that is doesn't really matter because your "back-up" circuit is independent and WILL start the car thru the OP SWITCH, as long as it cranks for a few seconds and can build up 4 psi oil pressure to trip the OP switch. The fuel relay can be in Montana and this circuit will allow the engine to start.

Assuming the relay has no power out at ANY time.....go back and trace the system to the fuse box for that circuit, then back to the ECM if necessary. Follow thru.

Have you tested by leaving the fuel pressure gauge connected when you try to start the engine? or as you turn the key to ON ?

Understand the system. You need to get the color FSM drawings for the electrical for your yr model. The test/trouble trees are absolutely fool-proof...written by the people that designed the car and all of its systems. You can;t be a decent DIY Corvette guy without these 2 books. I learned more in 2 weeks with these books that the prior 20 years of being a Corvette owner and DIY guy with a good mechanical back ground.

 

[colo. vette]

ok, op sensor has a single green wire. op switch has a red wire, a yellow wire, and a brown and white wire.
if I jump the red and yellow wire, should that provide power to the pump where I could test for it?

Not sure you;re looking at the right switch....

Your oil pressure SENSOR has a single wire. It is mounted on a metal 1/4" plumbing "T" with the oil pressure SWITCH. They are next to each other.
Switch has 2 wires like the drawing indicates.; They are usually the same color as the drawings.

IF there IS power to one side of the OP Switch, car will start IF that circuit is not broken between the switch and the fuel pump. ( fuse? wire harness damage? ???? ) Engine must crank for several seconds to build oil pressure before the fuel pump gets any power. THIS is the tip-off that the fuel relay has failed. Hard starting when cold and fuel pressure is low or none.

That is the back-up circuit.

The primary circuit for the fuel pump comes directly from the fuel pump relay that gets its power from the ECM permissions, to run a 2 second prime then shut off. When you turn the key to ON the FP will only run for 2 seconds until the engine starts and runs on its own..so, do not think that you are going to turn the key on then go check for power...it won;t be there. The ECM only allows the relay to have power after the engine fires, when the dist sends an OK signal to the ECM telling it that the engine is running on its own and only then will the ECM allow constant power thru the fuel relay to energize the pump.

Get another pair of hands and YOU observe the DVM as the key is turned to ON....if there is NO power out of your new relay (assuming that there is power IN) then you either have a bad relay or the circuit is open before it gets to the relay, BUT...< big BUT, that is doesn't really matter because your "back-up" circuit is independent and WILL start the car thru the OP SWITCH, as long as it cranks for a few seconds and can build up 4 psi oil pressure to trip the OP switch. The fuel relay can be in Montana and this circuit will allow the engine to start.

Assuming the relay has no power out at ANY time.....go back and trace the system to the fuse box for that circuit, then back to the ECM if necessary. Follow thru.

Have you tested by leaving the fuel pressure gauge connected when you try to start the engine? or as you turn the key to ON ?

Understand the system. You need to get the color FSM drawings for the electrical for your yr model. The test/trouble trees are absolutely fool-proof...written by the people that designed the car and all of its systems. You can;t be a decent DIY Corvette guy without these 2 books. I learned more in 2 weeks with these books that the prior 20 years of being a Corvette owner and DIY guy with a good mechanical back ground.

 

[boomdriver]

ok, op sensor has a single green wire. op switch has a red wire, a yellow wire, and a brown and white wire.
if I jump the red and yellow wire, should that provide power to the pump where I could test for it?

In the drawing that vetteoz provided there is no 3rd wire...so I am not going to make that call...The switches that I am familiar with are 2 wire and they can be jumped...same as the switch closing.

There is no real reason to do that if there is power to the red wire. The odds of having a defective op switch, relay at the same time are huge.....the op switch is back-up only....not designed to be the normal means of getting power to the pump.

If it were me, I'd be more interested in seeing if there is power at the red wire on the fuel relay when the key is turned to ON or RUN. If there IS, then do the same test at the yellow on the relay.the yellow should come ON for 2 seconds or longer if the car starts. THAT will tell you if there is a failed relay or primary fuel pump circuit.

If you had a FSM you could also do this the way the techs do at the ALCL by grounding the FP pin to grnd. I do not have your yr FSM so I cannot say what pin that would be. That makes the FP run for testing.

 

[colo. vette]

ok, I have power at fuel pump, by jumping at the op switch, pump doesn't run...replace it or is there a way to test it that I haven't thought of yet. ( or more, other, conditions that must be met to make the pump run?)

 

[colo. vette]

fixed!!

found a faulty connection from connector to pump in the fuel tank. looks as if it has overheated enough to melt the plastic of the connector a bit. cleaned it up, it now starts and runs..

My 73 stingray is a hell of a lot easier to work on!!

Thank you everyone for your kind assistance,..I will get bett as I become more familiar with this car...Thanks again

Don

 

[boomdriver]

Thats great !

This is a case of knowing the correct question as well as the answer...
it wasn't ever about "why don't I have power at the fuse or.." it was more of a question like "why doesn't the fuel pump run". if you had been fully aware that the system only activates for 2 seconds at key ON, and that there is a back-up circuit for the pump,. you would have gone right to the tank once you proved that the power circuits were healthy under the hood. There are only so many places where there can be a problem. Between the battery and the pump is just a handful of parts.

My best advice to you would be to invest in the FSM and get your C4 knowlege and SAVE a pile of money while you have that car. If you had the $100 set of books, you'd never have had to ask anyone here and wait several days for replys. As much as everybody wants to believe that they don;t need those books...I have never had anyone say that they regret buying them. They always save the owner time and most of all, MONEY. You just can't throw parts at C4s. They will eat the parts and wait for more. The FSM gives no doubt diagnosis and comfort in knowing that the parts that you DO have to buy will solve your problem. And trust me when I tell you that C4 parts cost as much today or more than they did when the car was new. Since 90% of the car is "corvette only" the mfg cost remains very high and with GM vendor contracts just recently expiring for the C4 parts line the aftermarket guys are just recently able to mfg many items now. Even so, there are still MANY items that will never be in aftermarket and are essentially dead and gone...so the rare salvage parts are priceless and hard to come by. The salvage guys know exactly what they can sell stuff for...LOTS. Someone will pay it. Since there is no new part available...its a sellers game. Thats where being accurate in diagnosis will pay you back for the cost of the books.

BTW...I'd seriously consider a new pump & tank gasket if there was overheating of an electrical connection in or near the tank. Thats serious business. That system is low amperage and low volts for a reason. If there is sufficient resistence to melt something,...that to me says poor connections, elevated resistence from a dying pump motor,. or direct shorting. ANY of those issues in a gasoline vapor enviroment could spell disaster. These pumps DO wear out and try to lock up and cause strange things to happen. If you can hear it run its dying. Avoid running the tank below 1/2 tank. These starve for fuel below 1/2 tank and the gas cools and lubes the pumps. Pumps that are run low on fuel more often will die sooner.

Good luck and enjoy !