Ford auto mechanic?

[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]

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.

[Ether]

Originally Posted by Al Skierkiewicz

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.

AIUI, the 8th digit of the VIN is either a "9" or a "W".

On my Vic it's a W. Anybody know what the differences are?

[JamesCH95]

Originally Posted by Ether

AIUI, the 8th digit of the VIN is either a "9" or a "W".

On my Vic it's a W. Anybody know what the differences are?

9 indicates a 'natural gas' burning CV, W indicates SFI (burns gasoline, 99%+ of CVs)

[Ether]

Originally Posted by Al Skierkiewicz

My guy is not a big fan of Stabil for cars BTW.

I've had excellent results using StaBil in small engines (chainsaw, go-kart, ATV, yard tractors, walk-behind brush mower, etc) but never used it before in a car.

What does he not like about StaBil in a car, and what does he recommend instead?

[JamesCH95]

Originally Posted by Ether

Anybody know how fuel pressure is regulated in this engine ?

It has a fuel pressure regulator. AND it has a fuel pressure sensor.
Rockauto.com lists both parts: Fuel Injection Pressure Regulator and Fuel Pressure sensor.

If the crash inertia switch were triggered the pump would not turn on at all.
See: http://troubleshootmyvehicle.com/for...rt-condition-2

Seeing as you seem fairly convinced it's a fueling issue I would recommend getting a voltmeter on the fuel pump or the fuel pump harness while the engine is started and then running. This will be most instructive and could indicate a bad fuel pump relay, relay fuse, fuel pump fuss, bad wiring, etc. Note: eye-balling fuses won't indicate if they're failed due to hairline cracking, which does happen. I believe this wiring may be accessed fairly easily in the trunk. I personally dislike using fuel pressure gauges in general because of the risk of leaking fuel.

There are a few other things to check on a car of that age that should take a total of 20 minutes:
-Check all vacuum lines (dry rotting, cracks, leaks)
-Clean the MAF (mass air flow) sensor (a dirty MAF is a sad MAF)
-Clean IAC (these like to get plugged with build-up from the PCV system)
-Check the air filter

FWIW my first car was a 2000 Crown Vic (police interceptor) and these days I maintain four cars and work on a couple race cars. While I'm no Ford engineer I have turned a wrench or two

[Ether]

Originally Posted by JamesCH95

Seeing as you seem fairly convinced it's a fueling issue I would recommend getting a voltmeter on the fuel pump or the fuel pump harness while the engine is started and then running. This will be most instructive and could indicate a bad fuel pump relay, relay fuse, fuel pump fuss, bad wiring, etc.

^This is an excellent idea.

Does anybody know where I can find a detailed electrical schematic?

I personally dislike using fuel pressure gauges in general because of the risk of leaking fuel.

ditto that. gasoline is scary stuff.

[JamesCH95]

Originally Posted by Ether

^This is an excellent idea.

Does anybody know where I can find a detailed electrical schematic?




ditto that. gasoline is scary stuff.

FSM (factory service manual) is your best bet. I like to get digital copies and have a laptop/tablet in the garage.

You could register with Autozone to get access to repair/service manuals, here.

There are, of course, numerous other sources.

IMO Haynes and similar are about useless except for listing torque specifications, so I do not think you should bother with one of those.

A google image search yields some interesting results, but nothing of great resolution...

[Ether]

Originally Posted by JamesCH95

You could register with Autozone to get access to repair/service manuals, here.

I couldn't find any electrical schematics for the fuel pump circuitry there. Maybe I'm looking in the wrong place.

[Ether]

Originally Posted by JamesCH95

FSM (factory service manual) is your best bet. I like to get digital copies

Is this the official service manual published by Ford?