Ford auto mechanic?

[Ether]

OK CD I need some help.

2001 Ford Crown Vic 4.6L V8

symptoms:

turn ignition key to "ON": I can hear fuel pump run for roughly 2 seconds

turn key to "START": engine starts immediately, runs fine for about 1 or 2 seconds, but then starts misfiring and stumbling and dies after about 3 to 5 seconds.

The above is repeatable. Happens every time.

There's a half a tank of fresh gas in the tank.

Since it was so easy to do, I installed a new fuel filter, but that didn't help.

Any help you can offer would be greatly appreciated.


Some questions:

1) I understand there's an inertia switch to shut off the fuel pump in case of rear-impact collision, and sometimes these switches go bad. But since I can hear the fuel pump when I turn the key to "ON", and since the engine starts fine, I assume this switch is not the problem?

2) How does the engine computer regulate fuel pressure in this vehicle? Does it read a fuel pressure sensor and pulse-width-modulate the fuel pump voltage accordingly? If that sensor fails, does it typically fail to a "high pressure reading" state that would cause the engine computer to leave the fuel pump off? Where is that sensor located on this vehicle and how difficult is it to replace?

3) If I can get my hands on a scan tool that can access live data, is there a PID for the above-mentioned fuel pressure sensor?

[sanddrag]

That engine is Coil-on-plug and aluminum heads right? I'd check to make sure none of the coils have burned up and also that you haven't blown a spark plug out of the head. I've seen both happen on a 2002 F-150 with the 4.6.

How many miles on it?

Crankshaft or camshaft position sensor could be a possibility as well. Do you get a check engine light while cranking?

I'd check/clean the Idle Air Control as well.

[Ether]

128000 miles. It's still a pup. Last year it ran like a champ. Then sat unused over the winter (but I put StaBil in the tank, and started and ran it for half an hour every week, and charged the battery once a month).

The engine starts every time, and idles smoothly, quietly, and at the correct speed every time. So I'm pretty sure it's not an ignition problem. And for sure no plugs blown out.

My working hypothesis is that the fuel pump runs only during the brief period for a couple of seconds after the key is turned from OFF to ON. Just enough to pressurize the system so the engine starts and idles for a couple of seconds. Then the pump doesn't run any more, and that's why it starts misfiring and stalls out.

Anybody have any insight into questions 1 2 3 ?

[Mike dennis]

Once it starts idling have you tried maintaining a higher engine speed to see if it still dies? If that suddenly makes it maintain speed then you might just have a massive air intake leak.

Edit: I looked around a little and it appears that this is a fairly common issue on this car, they recommend checking the idle air control valve. then the fuel pump.

[Ether]

Hi Mike,

Cannot achieve/maintain higher speed with a higher throttle setting.

If it had a massive air intake leak, would it idle smoothly, quietly, and at the correct speed (as it does) ?

The idle air control valve controls the engine idle speed.

The engine idles smoothly, quietly, and at the correct speed. Symptoms do not appear consistent with a faulty idle air control valve.

[Mike dennis]

if it is only idling smoothly for a second or two then yes it can still do that, but if you get more than four or five seconds before it starts dropping then it probably won't be the issue.

[Ether]

Cannot achieve/maintain higher speed with a higher throttle setting.

If the IAC were causing the problem, shouldn't I be able to press the throttle and hold engine speed at a higher value?

[Ether]

Anybody know how fuel pressure is regulated in this engine ?

[Simspi182]

Usually pressure is not modulated at all. The fuel pump is full on while a regulator regulates to the pressure (which is usually unchanging). This leads me to believe that it's not the fuel pump. The thing that would be change fuel to the engine is fuel injectors that are controlled by the ECU (engine Control Unit). If you're looking for data output from that, an OBD2 sensor is something that mechanics use to diagnose the car. Hope this helps

[Al Skierkiewicz]

Ether,
With a car of your age, it is possible that the filter bag around the fuel pump is clogged or that the fuel pump is just weak. Most of the injected vehicles pump a rather high pressure to assist with the injection. A mechanic will likely do a fuel pressure delivery test to see if the pressure is reaching spec. According to one site your pressure should be in the 35 psi range. Many vehicles regulate the pressure by sensing pressure and turning the pump on or off. Some simply bypass the fuel back to the tank. It is common to only hear the pump during the first few seconds until everything is pressurized. At that point the pump is still running, it is just not making a lot of noise as it is running against pressure. The inertia switch seems to be a one time only device which would work or not. The fuel pressure is the first place to look but be very careful. Pressurized fuel rails is the most often cause of engine compartment fire. Follow the instructions carefully. You do not mention that your dash lights are indicating a problem so if that is the case, then a code might not be displayed on a monitor device. There is always the possibility that the wiring has gone bad with all of the salt and corrosion under the car in northern climes.
My pump makes more noise in the winter than summer.

[Ether]

Originally Posted by Simspi182

The fuel pump is full on while a regulator regulates to the pressure

See attachment. Is there a Ford mechanic or engineer out there in CD-land who can confirm the statement in the attachment?

This leads me to believe that it's not the fuel pump.

My working hypothesis is that the fuel pump itself is good (because I can hear it turn on for a couple of seconds before I crank the engine... and the car always starts), but it is not being turned on once the car starts (and thus the engine gets starved for fuel, starts misfiring, and stalls).

I am looking for possible ways that a DIY-er like me can test that hypothesis.

My central problem is that I am unfamiliar with the design of this engine so it makes it difficult to draw conclusions from the data I already have. For example, consider question #1 in my original post. Can I rule out the inertia switch as a possible culprit because I can hear the fuel pump running before I crank the engine? In other words, is the circuit of the inertia switch such that if the switch were indeed tripped or faulty I would not hear the fuel pump come on under those conditions?

[Ether]

Hi Al,

Thanks for jumping in here.

This car spent its entire life in North Carolina and Florida until a couple of years ago when my mother stopped driving and gave the car to us. My daughters flew down to Florida and drove it back up here. I asked them to keep all their gas receipts, which they did. I was quite surprised (and pleased) to see that it got over 26 mpg on that road trip.

So being from the south, there's no rust and very little underbody or engine compartment corrosion.

If the pump is strong enough to supply the necessary flow and pressure to start the car and idle it smoothly for a few seconds, it's not clear to me why it wouldn't be able to keep the car idling.

So my working hypothesis is that the fuel pump itself is fine, but it's not being controlled properly once the engine is started.

In my previous post I attached a screenshot from the Chilton manual for this engine, indicating that fuel rail pressure is regulated by the engine control computer adjusting fuel pump speed (I assume by pulse-width-modulating the supply voltage).

That's why I asked question #3 in the original post. Does the engine computer for this engine have a parameter ID (PID) for the fuel rail pressure sensor? If so, I can borrow a scan tool and see what the fuel rail pressure sensor is doing.

[Al Skierkiewicz]

My guy says the fuel pressure test is the telling diagnostic at this point. He asks if you depress the accelerator after it starts, will it continue to run? If you can keep it at 1500 to 2000 RPM then it points to something in the idle circuit. There is a pipe/hose that runs from the intake to the throttle body that feeds the MAS air flow sensor. That could be clogged or cracked or the sensor is defective. There is also a flap in the throttle body that supplies idle air that may have become dirty or stuck. It is able to be cleaned but it may take someone holding the throttle open while you use some carb cleaner on a brush to clean the plate and pivot. Don't spray into the throttle body. You may also have a IAC valve that is not working.
There is a wire that runs from the fuel pump relay on the front driver's side of the engine compartment across the front of the radiator and back into the passenger side of the car to the computer. This wire sometimes breaks,frays, goes intermittent.
Of course, if the pressure doesn't stay up during start and run, then it points to the fuel pump.

[Ether]

Originally Posted by Al Skierkiewicz

if you depress the accelerator after it starts, will it continue to run?

Here's the test sequence and results:

1) Turn key from OFF to ON and pause:
    can hear fuel pump run for about 2 seconds and then stop

2) Rotate key from ON to START:
    Engine starts immediately and idles smoothly, quietly, at correct speed

3) Before misfiring begins, press accelerator:
    Engine bogs down and stalls.

My working hypothesis is that the fuel pump itself is fine, but it's not being controlled properly once the engine is started. A fuel pressure test would only confirm what I am already pretty certain is true. It wouldn't help me find the cause. If I had an appropriate fuel pressure gauge and all the proper fittings I'd probably test it just to be sure... but in the meanwhile I'm exploring if there are other simpler things I can check -- things which might be interfering with the proper operation of the fuel pump once the engine has started.

I visited three auto parts stores and two auto shops this morning. There appears to be much confusion concerning fuel pump operation and fuel pressure regulation on this engine for this model year.

On the one hand:

Chilton's says there is no pressure regulator: The PCM (Powertrain Control Module aka engine computer) controls the speed of the fuel pump to regulate to the desired fuel pressure. To do that, I would assume the PCM would need a fuel rail pressure sensor, and sure enough Autozone's website shows a drawing of the top of the engine with a Fuel Rail Pressure Sensor (FRPS).

On the other hand:

None of the auto parts stores (including the afore-mentioned Autozone!) could find a FRPS listed for this engine. They all said the engine uses a FPR (Fuel Pressure Regulator). The auto shops I visited thought the engine has a pressure regulator. One even gave me a quote to replace it.

There is a large hard plastic cowling covering the top of the engine, hiding from view the area I would otherwise simply look at to resolve this question, and it is securely fastened with a weird fastener whose removal process I have yet to figure out.

Later today I will take a photo and post it here, maybe someone has seen something like it.

[Al Skierkiewicz]

Ether,
My guy also said there is a fuel rail regulator rather than direct control of the fuel pump. Again the fuel pressure test would show if that was at fault as well. I have been told that more often than not, the pump gives up all at once. Since the engine bogs down and quits with either the pedal depressed or simply idling, we can rule out idle circuit troubles I think. Still points to fuel pressure/delivery. My guy is not a big fan of Stabil for cars BTW.
The MAS airflow still could be an issue and in some cars, you can disconnect it to get the engine running and some you can't. Be warned that there are two numbers for the same engine in that line. When you order parts you need to know that number or the VIN number to get the right parts.