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08 Expedition 5.4 L fuel pressure

I have a 08 Ford Expedition with a 5.4 L engine. Recently I changed all spark plugs and the fuel filter and now the engine is not running smooth. I had the fuel pressure checked and is 60 before start and 70 while idle. Is this normal? I should mention that the old spark plugs were bad and so was the fuel filter.

Is the check-engine light on? Did you use the OEM plugs or some other type?

No check engine light on and use the OEM plugs.

Check for vacuum leaks.
Make sure you didn’t upset some hose or connection when you did the plugs.

Don’t take this the wrong way, please

are you sure all the spark plugs are tight and down all the way? If the threads in the head are buggered up, the plug will seem tight, but it won’t be down all the way

On this application, you have to remove the coils. Are they all plugged in correctly? How did the boots look? The boots have a spring inside. If it’s corroded, you’ll get a misfire. It’s very common. Did you clean off all the old dielectric grease, and apply a dab of new . . . just a little

Sometimes, the coil itself will be corroded, where it attaches to that spring I mentioned

Removing the pcv hoses makes replacing plugs and coils easier. Did you put everything back correctly. I believe on these hoses, they have to audibly click when reinstalling

Thank for all the suggestions. I should have mentioned that the tune up was a result of intermittent problems while driving long trips. When accelerating uphill the engine would feel like is losing power and then I would hear a strange sound that dissappear as soon as I take my foot of the gas. This is a 4x4 truck and my impression is that the 4x4 tries to engage because is losing the vacuum, like I said it feels like the engine is losing power. If i would floor the gas pedal the engine will Rev up and get the power. It never happened in the city, always while going on long trips, up hill and intermitent. The only way to keep it working without making that horrible sound is to try and keep the gas pedal constant while uphil. I had the truck at the Ford dealer and they gave it a clean bill of health. They advised a tune up and try midgrate gas. So I think the fuel pressure might have something to do with my problems just do not know for sure what is supposed to be.


By chance, does this engine use those mile long spark plugs? You’ll remember them, if this is the case, because of the length, and the strange electrode design

Did you have a difficult time removing the plugs?

Was the coil boot black in color, as opposed to brown?

The fuel pressure spec for your engine is:

Key On Engine Off…35-45 PSI

Engine Running…62-69 PSI


db4690 no black color
Yesterday I had a friend check my work and he took all spark plug out and put them back checked all wires still running rough
Tester thanks for the specs, this means the fuel pressure might be too high since on running it goes over 70. Is the regulator in the fuel pump or somewhere else?


I’m not sure if I explained myself very well, earlier

By black in color, I meant this . . . are the rubber boots on the ignition coils black in color, as opposed to brown in color?

I didn’t actually ask if the plugs are black, which would have indicated a rich condition

Since you were apparently able to remove the plugs easily, I assume you have the brown coil boots and the plugs with the normal electrode design

You have a returnless fuel system, which means the regulator is part of the fuel pump module

These were regular spark plugs, initially the store gave me the long ones but I had to go and have them changed.
Based on what I have is it safe to say that I have to change the fuel pump?

In my opinion, the fuel pressure is within specs

According to my information, fuel pressure is supposed to be 35-70psi key on engine off

I’d be very hesitant to recommend a fuel pump replacement, especially because I don’t have the truck in front of me

I was doing more research and I will try and change the fuel pressure regulator. Can anyone give me an idea where this is located?

The fuel pressure regulator is part of the fuel module. It’s usually not available separately

Aka . . . drop the fuel tank and replace the fuel module, which consists of the pump, float, sender, fuel pressure regulator, etc.

You sure you want to go in that direction?

The pressure is 1-2psi over spec?
The gauge could be off by this much.
If the pressure were off enough to affect fuel metering (fuel trim) it would trigger the check engine light.

I agree with @circuitsmith

I’ve seen cases where low fuel pressure caused P0171

I’ve seen cases where high fuel pressure caused P0172

I’m doubting this is a fuel pressure problem. But no harm done – besides to your wallet – to replace the regulator. You might look inside the vacuum hose that attaches to the existing regulator. Before making the change in other words. If there’s any gasoline inside that hose the regulator is shot. But that would usually show up as a major fuel pressure problem, which you don’t seem to have. Your higher than spec readings could be an inaccurate fuel pressure gauge. In any event the feedback system your car’s computer uses, i.e. the O2 sensor feedback, will correct for a slightly high fuel pressure. It might show up as a “fuel trim” on a real time scan tool though. But it wouldn’t usually cause the symptom you are describing.

If this symptom only occurs when the engine is cold it could be a fuel pressure problem, but once the engine heats up and the O2 sensors come on line, I’d doubt a fuel pressure component to this.

I’m presuming you have no check engine light and no stored diagnostic codes.

If so, I have two guesses what’s causing your symptom.

  1. You’ve got some degraded insulation or connections in the wires/coil packs/ etc in the ignition system. As mentioned above. Not unusual for an 08. And changing the spark plugs caused enough movement in those parts to put it over the edge, and that is causing the symptom. You could either get a pro to hook up an ignition analyzer to your engine, or just replace all those parts and hope for the best.

  2. I used to get this symptom frequently when I changed the fuel filter on my late 70’s fuel injected Rabbit. In fact it happened almost every time. The engine would run much rougher after changing the fuel filter. Upon investigation, it was always caused by grit somehow getting into what is supposed to be the clean part (i.e. post filter) of the fuel system during the filter change. In other words, somehow the act of changing the filter can allow dirt and grit to get into the fuel line which exits the fuel filter and goes to the injectors. For the Rabbit, it wasn’t the injectors that clogged up, it was the fuel distributor. And giving that portion of the fuel system a good taking apart and cleaning solved the problem pronto. Let me ask you this: When you changed the fuel filter, before taking the hoses off the old filter, did you carefully clean off those areas of grit and debris?


I think you missed the part about this being a returnless system

Only 1 line going to the engine

No vacuum hose

Fuel pressure regulator is part of the fuel module

Interesting comment @db4690 … with that design how does the fuel system compensate for situations when the intake manifold pressure is lower; e.g. open throttle conditions. When the intake manifold vacuum is reduced, there’s less force pulling the gas through the injector, and less fuel injected for each pulse. That’s of course why there’s a vacuum line connected to the fuel pressure regulator in return-systems. So in returnless systems, just curious, does the fuel system measure the intake manifold pressure and compensate by longer injector pulses? Or does the fuel system in those situations increase the fuel pressure and keep the pulses the same duration?

There should be a fuel rail pressure sensor which monitors the line pressure. The PCM will adjust the injector pulse width based on what the pressure sensor is doing.

I can’t remember exactly when and which models Ford started using the FRP sensor on. My vague memory seems to recall the use starting around the 2000 model year.