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Stutter at higher speeds


Active Member
July 3, 2018
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Year, Model & Trim Level
99 Explorer Sport
Starting having problems a few months ago started off when at a stop the rpms started to drop and raise and then I went to press on the gas it would not go and after a while it stalled. Started it back up and ran fine. Changed air filter. Cleaned maf. Throttle body. Iac. Changed spark plugs. And wires. It ran fine up until a few weeks ago it started to stutter. When pressing on the gas when getting above like 40 and when I let off the pedal it would go back to normal but if I would go full throttle it will go up to speed and sometimes the stutter would go away doing that but return shortly after. Pulled a code and had the o2 sensor bank 2 sensor 1. Changed that along with the coil pack. And the problem is still there but no code yet. I have a 99 Explorer sport v6 ohv

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And there will be sometimes where it won’t do it at all when going somewhere but on the way back it will do it or the other way around.

HAve you checked the fuel pump pressure? 65 psi plus at fuel rail. Had similar with my ST turned out to be a split in hose from fuel pump inside the tank.

I haven’t checked it yet that’s one of the things I’m gonna have to do. So with the car at idle the psi should be 65 at the fuel rail?

Thanks for the reply I will test it soon and will update

I checked the pressure at idle its 52 psi, and then afterwords I checked what it was when I turned it to the on position. went to 30 psi and jump all the way back down

So does this mean I need a new fuel pump?

The fuel pressure is low at 52 psi at idle.

You need to drop the tank and inspect all connections, that is pump to pressure relief valve and pressure relief valve to tank exit line. Splits in these hoses can be very difficult to see!

If you think the problem is the pump, it may be best to get a complete pump/hanger assembly as you may have a problem with the pressure relief valve. Which can't be purchased separately to my knowledge.

If you go complete hanger or pump only, replace the fuel filter and clean out the tank before installation.

I do notice sometime i hear the pump buzz when I turn the key on but most of the time it dosnt buzz

Every time you turn ignition on only, pump runs for 3 to 5 seconds to pressurise fuel line. Get someone to cycle ignition (not starting engine) and listen close to tank, you should hear pump each time ignition is "on".

Yeah that’s what I meant, whenever sitting in the drivers seat I can hear it when I turn the ignition on but now I only hear it every so often

Have you replaced the fuel pump filter yet??? A clogged filter will drop the pressure like a weak or dying fuel pump...I would change that if you haven't in 30 k miles or so first before I drop the tank and replace a possible good pump...