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Ford Fuel
Pressure Regulators by Randy Dillman LTS
North
How do components get
their name? When I first heard a fellow employee utter “I think it has a bad
MAP sensor” I pictured a CRT equipped Riveria giving the wrong directions to
travelling salesman. Hey, I had a broom in my hand what did I know? Twelve
years later I can see why many technicians still don’t fully understand the
device called a fuel pressure regulator. Sounds like it changes fuel pressure
under varying engine loads, right? Wrong! Its purpose is much different. I’d
like to change the name from fuel pressure regulator to constant differential
device if I had the opportunity. Let me explain.
If you were a
computer in control of a vehicle’s engine control system, would you want some
clown adding or subtracting fuel pressure to the injectors? I wouldn’t. It
stands to reason that if you opened the injector for three milliseconds at a
fuel pressure of 45 psi versus 25 psi delivery rates would be drastically
effected and so would air-fuel ratios. But wait, isn’t that what the regulator
does? Don’t we check regulator operation by removing the vacuum hose and
watching the pressure increase? When the engine is under a heavy load, meaning
vacuum is low, isn’t fuel pressure increased thus changing the delivery rates?
Nope! Time to change the name.
The regulator is in
charge of maintaining a constant differential pressure drop across the injector
so that the computer can count on the fact that three milliseconds provides the
same amount of fuel regardless of the engine load. You see, most forget the
vacuum inside the intake is the other half of the picture. You have pressure in
the injector inlet and vacuum at the outlet. These forces must work in tandem
to maintain this balance that the computer counts on. High vacuum means we need
less pressure and visa versa. It’s simple once you think about it. So let’s fix
a lot of cars with this new thinking.
When a tech hangs a
gauge on a fuel-injected car and starts his analysis, does he/she know what
they should be reading? Most don’t’,
and that’s a fundamental flaw. It goes up and down with engine load, great! But
is the regulator maintaining the correct constant differential drop?
For example I want to use the Ford 39 psi system, which is used on most the
their port fuel vehicles except a few, e.x. 2.3 HSC, 4.9, 3.0/3.2 SHO. The rest
of the engine families use the most overlooked regulated pressure in history
IMHO.
This 39 psi system,
or should I write 39 psi above atmospheric pressure system,
has a common flaw of regulator failures. Let’s look at two examples I did
recently.
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The first picture
is taken at idle on a ’92 Explorer 4.0L and 109 rounds on the odo. The
complaint is a MIL only. Stored code is a 173 - system rich. The only thing
I’ve done is hook-up the NGS and the pressure gauge. |
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Thirty seconds
later, while I’m just grabbing the digital camera, boom! You knew that was
coming, right? |
Next case is a ’94 E250 with 160 rounds and a 5.8L idling in the bay
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Idle Fuel Pressure No MIL or
driveability complaint. It’s my sister’s van and we were doing brakes and a
tie rod. Since she uses it as a taxi for her kids and is rarely ever parked I
decided to check things over. Yep, it’s broke
too! You do know what they should read, right? |
Stay tuned
for part 2!