Fuel Pressure/Leak Down Test?

Rearanger · Feb 24, 2015

Still looking into possible cause of dropping mpg from my other thread. I thought I'd see if there were any external fuel leaks in the system as oil analysis showed no fuel in oil. Yes, I could just run the engine and crawl underneath and roll around, but I referenced the FSM and found how to perform the tests.

Both tests (fuel pressure and fuel pressure leak down) do not specify to start the vehicle or do key on. Instead the manual says to - "Access the Output Test Mode". This is a mode activated by a scan tool which runs the fuel pump for about 8 seconds. Not sure why the tests are performed this way. Don't know why just a key on would not activate the pump, unless the run position activates a relay and key on does not start pump.

Any techs out there who can clue me in?

RonD · Feb 24, 2015

Ford computer only runs(powers) the fuel pump for 2 seconds when key is turned on, fuel pump won't come on again until engine starts, OR you turn the key off and then on again.
It is a safety "thing", in case of a break in the fuel system, if engine stalls(no fuel) then pump would shut off, instead of continuing to pump gas out the break/leak.

Check fuel pressure with engine running, 2003 should be 65-70psi.
Leave gauge connected and shut off engine, pressure should hold between 55-65psi.
Slow drop means a leak.

A Leak down test is to test if a cylinder in the engine is losing more pressure than it should.
You remove the spark plug and put that cylinders piston at Top Dead Center(TDC) Power stroke(both valves closed).
You screw in an air pressure line to spark plug hole.
There is an air pressure gauge on this air line.
You pressurize the air line with a Known air pressure, like 100PSI
If the air gauge reads 90PSI, then you have a 10PSI Leak Down, or 10% leak down.
That was a Dry test

You then remove the air line and add a teaspoon of oil to cylinder, rotate crank a few times and then retest, this is a wet test.
Pressure will come up, by how much tells you if rings or valves are leaking the most.
If retest showed no improvement the valves are leaking
If retest shows a big jump up in pressure then rings are leaking the most

Rearanger · Feb 25, 2015

Ron, I was referring to fuel pressure leak down. Spec says system should hold within 5 psi of max for 1 minute.

Still trying to figure out why Ford says to use Output Test Mode and not just doing an engine on/engine off procedure.

RonD · Feb 25, 2015

Because it is easier to do in a shop.
Running the engine means exhaust so you have to hook up the hose to pull exhaust out of the shop, not a big deal but also not needed if you are just doing a fuel pressure test

Rearanger · Feb 25, 2015

RonD said:
Ford computer only runs(powers) the fuel pump for 2 seconds when key is turned on, fuel pump won't come on again until engine starts, OR you turn the key off and then on again.

Well that explains the 30psi I got at initial key on.

JP02XLT · Feb 25, 2015

I still get 75 psi with just key on for FP, (I have modified my regulator for an increase in pressure for the SC) and I have a gauge in the cabin, so I monitor it all the time. I still get a full amount of FP even in the short 2-3 second Key on, not cranking nor yet to start.

Are you seeing a lower than spec'd FP? and have you checked it cold & up to temp?

JP02XLT

RonD · Feb 25, 2015

Rearanger said:
Well that explains the 30psi I got at initial key on.

Maybe if you JUST changed the fuel filter it would be 30PSI at first turn of key.

You have an issue with fuel pressure if that's the way it tests.

On the 2003 there are 3 places fuel pressure can be lost without smelling gas.
The Check Valve on the fuel pump, it is a one-way valve that prevents pressure from being lost when pump is off.
MPG won't go down with this issue

The Pulse Damper on the fuel rail, this stabilizes rail pressure as injectors open and close, this causes pressure waves in the rail, Damper absorbs the waves.
It has a Vacuum line attached, remove it and check it for fuel or fuel smell, if fuel is in there replace Damper.
MPG will go down with this type of leak.

Fuel injectors, if an injector gets grit in it, it can't close all the way, this will cause a pressure loss when pump is off.
All the Injectors get 12volts when key is on, computer Grounds each injector to open it, if one of these Ground wires is shorted to metal that one injector could be opening causing loss of pressure.
MPG will go down with this type of leak.

Cycle your key on, count to 3 then turn key off
Repeat 3 or 4 times, pressure should be above 60psi now, normally this would hold for a few months

Rearanger · Feb 26, 2015

JP02XLT said:
Are you seeing a lower than spec'd FP? and have you checked it cold & up to temp?

No, with engine running FP is to spec. Can't remember if engine hot or not. If FP was significantly higher that might explain rich LTFT.

Rearanger · Feb 26, 2015

RonD said:
The Check Valve on the fuel pump..MPG won't go down with this issue

Yes, for now not too concerned if FP leaks backs through through pump, I'm on a lower mpg hunt.

The Pulse Damper on the fuel rail

Already checked, it's dry.

Fuel injectors

That was why I did an oil analysis, but the analysis came back with no fuel in oil. I'm still on to the dirty injector route in trying to explain rich LTFT with idle %s in -7 to -8. Started to improve with Lucas gas additive (usually don't believe in them), but yesterday those numbers went back up.

Cycle your key on, count to 3 then turn key off. Repeat 3 or 4 times, pressure should be above 60psi now, normally this would hold for a few months

Pressure did not hold when I used, engine running/then off, to test FP leak down. It did not dive to zero, but it did drop, >5psi I'll have to do the test again as I did not time the pressure drop or record it. I just did the oil analysis from the drop I saw, and that, added to LTFT led me to injectors.

stmitch · Feb 26, 2015

I don't recall from your previous thread, what's the status of your O2 sensors? How are you determining your fuel trims?

I'd definitely keep running the Lucas injector cleaner through it if you've never done anything like that before. It's the best thing I've found (other than e85) for keeping the fuel system functioning at it's best. All of my vehicles get it periodically, and it's the first thing I reach for if I ever see any misfire codes.

Rearanger · Feb 26, 2015

stmitch said:
I don't recall from your previous thread, what's the status of your O2 sensors? How are you determining your fuel trims?

I have one of those dash mount scan gauges. O2s seem to be switching between .45v, but it's hard to tell without graphing software. As well the O2s were replaced no more than year or two ago. The scan gauges are OK but they switch so fast that it's hard to keep track of. I had to slow down the data display from one second to two second.

I just received my OBDII connector with graphing software and will try it as soon as the weather gets better. Very cold here in NC and this morning about 4-5 inches of snow.

Of course none of these readings are near enough to set a code and most people would not notice. I just keep tracking MPGs very regularly.

My 92 Mitsubishi 3.0 V6 with 175k has always gotten from 19-21 mpg - no slow decline as I have recorded on this Ford. Quality shows.

JP02XLT · Feb 26, 2015

I would check your FP again, if its low you get a very poor spray pattern, which also shows up as poor performance and your stepping deeper in the accelerator to compensate.

You should see the normal FP on the initial hit of the key, not taking 2-3 cycles to get to full pressure in the rail, that is a sign of the pressure regulator failing in the tank

JP02XLT

Rearanger · Mar 3, 2015

Update:

I filled up yesterday and got the best mileage in 7 tank fills at 19.24 mpg, an improvement of about 1.4 mpg over last two tanks.

This was with one tank of Lucas fuel treatment. I added another bottle for this tank. My OBD-II graphing software is installed but waiting for better weather.

The way my scan gauge is showing LTFT, Bank1 is the (bigger) culprit, so I don't think FP is the problem although I'm going to test once more. With the graphing software I'll get a better view of all the fuel trim inputs.

Also looking to install digital water temp gauge to verify coolant temp. I'll be replacing the stock gauge sender. This temp gauge is rated at .01 degrees accuracy. So I'll see how the ECT sensor compares.

Fuel Pressure/Leak Down Test?

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