Fuel System Fuse

[Booker007]

Hello everybody,

Thank you for allowing me to join. Forgive me for jumping immediately in with a question but Im trying to fire this off before leaving for work. Im hoping to have some suggestions when I walk back in the door this evening,

The fuse for the fuel system continually blows. This is on my 1995 2.3L 4cyl 5spd manual standard cab Ranger. It may run beautifully for a week before it blows again. The fuel pump is new (i replaced it when trouble started a month ago, still doing same thing). So far the fuse only blows during initial turning of key during the 2 sec charge. It has not once blown during operation, only when starting.

This is in the fuse panel (power distribution box) located next to brake master cylinder.

Any suggestions?
Thank you.

 

[97RangerXLT]

You probably have a wire that is intermittently shorting to the frame. Check the wire harness from the power distribution block all text way to the fuel pump for bare spots that might contact metal or another bare wire.

AJ

Sent from my Samsung Galaxy Note 4 while sitting in my underwear

 

[hoosier1104]

^What he said. You have a short in your fuel pump circuit somewhere.

 

[enjr44]

I agree that you have a wire or something shorting to ground. The idea that it only happens before engine start and never after the engine is running is baffling.

Because nothing in the ignition switch goes to that wiring. You have power the the pump relay for two seconds when you go to run then the ECM removes the ground until engine hits 400 rpm. If you look at the wiring diagram it goes fuse, relay, inertia switch and then pump. If it was a wire I would think it would happen when going down the road from vibration or whatever, too.. And I would also think that once in a while it would start and then die immediately from lack of fuel pressure.

So I am going out on a limb and say there is an internal short in the fuel pump relay that only happens when the relay is being switched and only once in a while. And, if it gets closed without shorting, the contacts are passed the short and it doesn't happen. If it were me I'd change the relay (they are cheap) and inspect the wiring in that circuit.

This diagram isn't for your truck but they are pretty much all the same:
http://www.therangerstation.com/tec...les/Diagram_ElectronicEngControls2_3_1of3.JPG

 

[hoosier1104]

That makes sense. I would go relay and then the switch.

 

[Booker007]

Hey Guys

Thank you so much for the suggestions. I believe I will start with the relay. I had already done an inspection of the visible wiring. I didnt find anything suspicious although I did go through and clean up any grounding wires I found.
Gonna get out there and try once again to get it resolved before heading to work. At about $3.50 a pop I really dont want to continue to replace the fuse every few days.
Thank you again.
Cant tell you how much I appreciate these forums and the people who participate.
Will post reply after the outcome.

 

[sdsocalloco]

What is the fuse rating? 15amp? Electric fuel pumps, like fans, typically have their largest amp draw during start up. May be as simple as needing to step up the fuse amperage.

 

[Spott]

What is the fuse rating? 15amp? Electric fuel pumps, like fans, typically have their largest amp draw during start up. May be as simple as needing to step up the fuse amperage.

No. Never. Not even once.

Those fuses are there for a reason. They are calculated to fail before any other part of the circuit in order to protect everything else.

If you put in a larger fuse, it may not blow before something else fries. It may also mask electrical problems that can cause long-term damage.

If a fuse blows, it did its job, so replace it with the same size fuse. If it blows again, then you need to figure out why it blew, and fix the problem. Don't conceal a problem by putting in a larger fuse and bypassing your protection.

Although a large fuse might cost 3.50, that's a whole lot cheaper than fried electrical parts or engine fires.

 

[aspevacek]

How old is the pump? It is possible it is pulling to much juice when it goes to prime after the vehicle has sat. Is the rail holding pressure over night if you let the thing set for 12 hours or so or is it bleeding all the pressure off the fuel rail?

Has the vehicle been run under a quarter tank of gas on a regular basis? Because continuous operation at lower fuel levels will cause fuel pumps to start to die out from lack of cooling.

 

[sdsocalloco]

No. Never. Not even once.

Those fuses are there for a reason. They are calculated to fail before any other part of the circuit in order to protect everything else.

If you put in a larger fuse, it may not blow before something else fries. It may also mask electrical problems that can cause long-term damage.

If a fuse blows, it did its job, so replace it with the same size fuse. If it blows again, then you need to figure out why it blew, and fix the problem. Don't conceal a problem by putting in a larger fuse and bypassing your protection.

Although a large fuse might cost 3.50, that's a whole lot cheaper than fried electrical parts or engine fires.

I agree on the reason fuses are there. However, the older pump may have been going bad and pulling to many amps. When he replaced it, the newer one may require a different amp fuse. At least check the paperwork. If it tells you to run a 20amp fuse and you keep replacing it with a 15, you found your problem.

 

[Spott]

I agree on the reason fuses are there. However, the older pump may have been going bad and pulling to many amps. When he replaced it, the newer one may require a different amp fuse. At least check the paperwork. If it tells you to run a 20amp fuse and you keep replacing it with a 15, you found your problem.

If the new pump draws more current, then you would technically need to use larger wiring in that circuit as well, to be safe.

OEM equivalent replacements will draw the same (or possibly less) current than originals. If you put in a non-equivalent part, you are responsible for either making the necessary changes or accepting the resultant problems. It doesn't sound like he installed a larger pump designed for a different vehicle.

Circuits are designed with a certain amount of "safety margin" already. A circuit that's calculated to draw 10A momentary maximum might be protected with a 15A fuse and 25A wiring, so that it doesn't blow too easily, and the fuse blows first before the wiring is at risk. A slight variation in part performance should not significantly affect that safety margin.

 

[Booker007]

Resolved!

Hey Everybody...

Can't thank you all enough for the responses. I was able to pick up a new relay on the way to work the other evening. No problems since! Yay!

I despise taking my truck to the shop. Not because of them but because I know there is a solution and that a little investigative work combined with testing and the process of elimination will more than likely reveal the cause.

Without you all I've no doubt my efforts would have been an exercise in futility.

Because of my inane curiosity I can't resist the urge to carefully cut open the old relay and check it out. I'll post a pic if I find anything.

Thanks again very much.

 

[hoosier1104]

Was there corrosion on the old relay when you pulled it out? That could show a bigger problem that caused the original problem. I speak from experience.

 

[1997ranger]

I'm currently having almost the same problem. It's a 1997 Ranger 2.3l 5 speed. Truck will start fine and run for about 5 seconds before blowing the 20A fuel system fuse under the hood. I've replaced the fuse a couple times now and the same thing happens. After it blows I'll cycle the key off and on again but no sound from the fuel pump priming and no fuel pressure at the rail. I'm kind of at a loss of what to do now. I tested the fuel pump relay by connecting it to a 12v source and measuring it with my multimeter and it checks out. Checked the inertia switch and reset it but it didn't make a difference. I'm unsure of how to jump it, because every source I read online only talks about two wires, one going into the inertia switch and one going out towards the fuel pump. However, mine has three wires, and I don't know which ones are which.


Also, I tested the connector going into the inertia switch and it's getting about 6.5 volts for power with the key on. Does that seem normal?


Thanks

 

[enjr44]

I'm currently having almost the same problem. It's a 1997 Ranger 2.3l 5 speed. Truck will start fine and run for about 5 seconds before blowing the 20A fuel system fuse under the hood. I've replaced the fuse a couple times now and the same thing happens. After it blows I'll cycle the key off and on again but no sound from the fuel pump priming and no fuel pressure at the rail. I'm kind of at a loss of what to do now. I tested the fuel pump relay by connecting it to a 12v source and measuring it with my multimeter and it checks out. Checked the inertia switch and reset it but it didn't make a difference. I'm unsure of how to jump it, because every source I read online only talks about two wires, one going into the inertia switch and one going out towards the fuel pump. However, mine has three wires, and I don't know which ones are which.


Also, I tested the connector going into the inertia switch and it's getting about 6.5 volts for power with the key on. Does that seem normal?


Thanks

You have the same problem, overloaded circuit (bad wire(ing), bad relay, bad pump).

Looked at the diagram in the earlier post http://www.therangerstation.com/tec...les/Diagram_ElectronicEngControls2_3_1of3.JPG

I don't know how the 97 is physically wired; but, you see there are three electrical connections to the inertia switch. One to the pump, one to the relay, and one to the ECU (from the relay). The relay closes when the ECU applies the ground. The fuel pump relay gets 12 volts from the fuse. When closed (by the ECU relay), the 12v DC goes to inertia stitch and the ECU. The 12 volts to the ECU is so the ECU can monitor the relay status (knows when the relay is closed and pump is on). The diagram is not for your model year truck. So the monitoring wire on yours may very well come out of the inertia switch since it is closer to the ECU, rather than the relay which is all the way over on the other side of the truck. In any case, on my 2002, you get 12v DC on one wire for 2 or 3 seconds. It then drops to some low voltage (can't remember for sure, think about 5 volts). I was told that is from the ECU and is normal. The other (the third??) wire goes to the fuel pump and will also (if connected to the inertia sw) have 12v DC for the first 2 seconds. If disconnected 0v DC.

The reason for just the first 2 seconds is so the computer knows the relay will close. It then turns the pump off until the engine hits 400 rpm. Safety feature so pump is off if engine is not running.

In your case, my first guess is that the pump is drawing too much current at start up and blows the fuse. If you apply power to a DC motor, it has a high current draw until it is up and spinning. If it does not start spinning/running immediately the high draw may/can/will exceed the fuse's limit. So if the truck starts and keeps running sometimes the pump is spinning up sometimes and sometimes not.

Your symptoms tell me (my guess) )that you have normal fuel pressure when you shut the truck off. When you start it you have enough system pressure to get running before low fuel pressure shuts it back down (are you sure it runs for 20 seconds??).