Fuel System Troubleshooting

[shr3dd3r 09]

My 2000 Ranger 5.0L is losing fuel pressure randomly while driving, and sometimes while idling. The truck will "stumble" or lose power a bit but usually catches itself and continues to run smooth. However, occasionally it will die altogether, but it will start right back up after cycling the power.

I replaced the fuel filter and that did not help at all. I picked up a pressure gauge and drove around with it attached to the schrader valve on the fuel rail. when the truck stumbles and loses power the fuel pressure drops down to 20 psi for a split second and then bounces right back up to where it should be. It usually hangs around 57psi except for when I have trouble.

It happens independent from engine load. I have floored it to recreate the problem but it seems like it randomly happens.

What should I check next? Seems like fuel pump, regulator, or wiring? Any tests I should do to determine what the problem is really?

I need help ASAP! This truck is my daily driver and I can't afford to get stranded. This problem needs to be solved quickly.

Thanks.

 

[BPiston]

When my 94 ranger was doing the same thing, (fuel pressure dropping to about 20 PSI), I discovered that the fuel pump in the tank was intermittent. My truck had two fuel pumps. One in the tank and another one on the frame on the driver side. I replaced both pumps and the fuel pump relay. Problem solved.

 

[shr3dd3r 09]

Well I would like to know if it actually is the fuel pump or just a loose connection that is shorting out intermittently. My fuel pump and pressure regulator are both inside the tank, so I'd have to remove the whole tank to get to it. I just want to make sure I know what the problem is before I do that. If I spend $250.00 on a fuel pump and it turns out that wasn't the problem, then my money is wasted. Any tests I can do to pinpoint the problem?

 

[Tominator]

Try a volt meter on the fuel pump circuit.

Are you using the Ranger fuel system, wiring, etc?

 

[doorgunner]

Don't start replacing stuff (been there/emptied my wallet).

Does the truck act-up when the engine is warm or cold?

Take your TIME--Watch the pressure gauge--start the engine/warm up to operating temperature....

then begin moving/wiggling EACH fuse.....

then begin moving wiggling each relay/fuel shut-off switch----slightly thumping on them also....

then move wiggle each wiring connector & wiring bundle (including battery wiring)....(I had one connector with a pin that was corroded/green causing an injector harness problem for example)

(It could take 1 or 2 hours to go thru everything including the chassis wiring to the fuel tank )

A wire can break INSIDE the colored insulation/a relay can be defective intermittently/a wire can be loose in the ignition connector under the dash/etc. and it will still look O.K......

Then start investigating f.p. regulator/pumps/etc.

 

[RonD]

Does the truck have a PATS system, anti-theft?

Those have been known to act up and cut voltage to fuel pump, but usually you would get a dash light during that incident.


I would get to the inertia switch, behind the kick panel and check out it's connections, make sure there is no corrosion.
Then put a volt meter on the pink/black wire(goes to fuel pump) and watch to see if voltage drops when engine stumbles.
If it does then move volt meter to the green/black wire(from fuel pump relay)
See if you get the same voltage drop when engine stumbles, if not, replace inertia switch.
If voltage does drop then move to fuel relay to test voltage.....
You should be able to feel the relay click, if PCM is cutting power momentarily to the pump.

If voltage doesn't drop when engine stumbles then check ground for in tank fuel pump.

Yes, it could be the fuel pump is failing, if voltage is stable at the pump and engine still stumbles.

 

[Earl43P]

The fuel pump relay coil is grounded by the PCM, Pin 80, LB/OG wire.

Fuel Pump relay performance is actually MONITORED by the PCM, Pin 40, DG/YE wire.

I strongly suspect that if your fuel pump relay power was getting interrupted, you'd have a Check Engine light and a code telling you so.

It probably isn't the Inertia Switch, because there is a Fuel Reset Switch Indicator light in your dash that comes on if the Inertia Switch gets tripped. Obviously, that is not what's happening, but there have been issues where the Inertia switch contacts intermittently open but does not close the "Inertia Switch tripped" contacts (which give you that dash light).

So, you might try replacing your fuel pump relay (relay #5, under the hood) with one just like it (swap with Horn, Foglights, etc.). No sense buying one when you have others just like it in there. I don't expect that to fix it though.

Since you are willing to try things, try connecting a voltmeter to your Inertia Switch wire (PK/BK one is output to pump). To do this easily, just take off the Inertia Switch connector, jumper DG/YE and PK/BK together. Use spade terminals and a length of wire to do that securely. Strip some insulation off the jumper to connect the voltmeter red lead to and connect the black lead to bare metal ground. Alligator clips on the meter leads makes that easy.

Then, while watching the voltmeter, turn the key to Run. You should see voltage for 2 sec. With the engine running, you should see voltage all the time. I have zero faith in this test because it could still be a bad pump and show bad voltage, misleading you.

Or, (what I would do) simply install that jumper in place of the inertia switch and drive it around for a while. If it quits stuttering, replace the Inertia Switch.

Here's one of many articles on testing for fuel pump voltage drop:
http://www.underhoodservice.com/issue/article.aspx?contentid=104797

If you do replace the pump, most guys remove or prop up the bed to do that. Dropping the tank is the hard way because the lines go in at the top.

Lastly, the PCM grounds the fuel pump relay coil as a result of seeing the PIP signal from the Crank Sensor (engine running). I'd look at that wiring for chafes and breaks before I spent $250 on a pump.

 

[shr3dd3r 09]

Don't start replacing stuff (been there/emptied my wallet).

Does the truck act-up when the engine is warm or cold?

Take your TIME--Watch the pressure gauge--start the engine/warm up to operating temperature....

then begin moving/wiggling EACH fuse.....

then begin moving wiggling each relay/fuel shut-off switch----slightly thumping on them also....

then move wiggle each wiring connector & wiring bundle (including battery wiring)....(I had one connector with a pin that was corroded/green causing an injector harness problem for example)

(It could take 1 or 2 hours to go thru everything including the chassis wiring to the fuel tank )

A wire can break INSIDE the colored insulation/a relay can be defective intermittently/a wire can be loose in the ignition connector under the dash/etc. and it will still look O.K......

Then start investigating f.p. regulator/pumps/etc.

It actso up randomly both warm and cold. I have the pressure gauge on it still. So far I have let it run while jiggling the battery cables, all the fuses, and I tapped on the inertia switch. Nothing happend. But then it did it again once I had stopped checking out of the blue. Must be something else. Guess I'll check the wiring under the truck next.

 

[shr3dd3r 09]

I shorted the inertia switch and it still stutters. Inertia switch is good. I hooked a voltmeter to the pk/bk wire which sends power to the fuel pump, and every time the fuel pressure drops and the truck stutters the voltage remains constant at 13.75V. So, I am thinking the fuel pump itself may be bad or the wires leading directly to it are damaged somehow.

Are there anymore regulators or switches under the truck downstream from the inertia switch that I should check before trying to remove the pump?

 

[Earl43P]

Last item is the connection at the top of the tank.
Pack that with dielectric grease.

 

[shr3dd3r 09]

Last item is the connection at the top of the tank.
Pack that with dielectric grease.

I unplugged the connector on top of the tank and noticed some of the pins had some corrosion on them. I had some MAF cleaner handy so I sprayed that on there and got all the corrosion off. Waiting for it to dry before I plug it back in and fire it up.

Dielectric grease would work nicely to seal it up good, but I don't have any at the moment. If the problem was corrosion the MAF cleaner should have fixed it and I 'll get some grease later. Somehow I doubt it was that simple...

 

[Andy D]

Vaseline or grease will work.

 

[shr3dd3r 09]

So I swapped out the fuel pump. No change. My fuel pressure still drops randomly and the truck dies every so often in the middle of driving. I've checked the fuses, inertia switch, and the voltage to the fuel pump when the pressure drops remains constant. This suggests the pump is always getting power yet the pressure still is not staying up all the time.

The fuel pressure also stays steady for several minutes after I shut it off, suggesting that the pressure regulator is good. The problem does seem to happen slightly more often when the truck is warm. I guess I'll check the voltage at the pump connector itself. Perhaps there is some resistance between the inertia switch and the pump. On the bright side at least I have a brand new fuel pump instead of a 13 year old one.

 

[shr3dd3r 09]

Where is the fuel pump grounded? I have wiring diagrams for my model year but it's not very specific about where all the chassis/engine bay grounds are. If it's a bad ground, the pump could be getting too hot and shorting out.

 

[shr3dd3r 09]

I just started the truck and let it run for a while, and I got under it and started jiggling wires and connectors. Nothing recreated the problem. However, it stalled out yet again only this time while idling. After it died, however, I could hear the fuel pump still running. So it must not be the pump or the wiring going to it, unless it is just losing power long enough to stall and then continues pumping. What else would cause it to stall out like this?