engine looses power at 3000 rpm

[typeop24]

I have a 97 expedition with a 4.6.In 1st gear the engine will pull without any problems.In 2nd gear it starts to have a drop off right around 3100 rpm.if you give it more gas it will stumblue through to about 3600 and then seem to pick up power like normal.While crusing on the highway in OD and then making a pass the truck will down shift and when it hits about 3100 the tack will sweep past 3100-3200-3300 with loss of power fall down a little and try again to climb in rpm.With the foot hard on the gass it will break through the rpm at about 3600-3700 and seem to come to regular power and keep pullin till 6000.Crusing at high speed without the OD on and gettin to about 3200 while staying on the gas the power falls off.I replaced the plugs .wires.and even tried to swap out the coil packs.Same problem before and after tuneup.The service engine light has not come on at all,and does not show any codes.Been to 3 ford dealers and they could not tell me what is causing the problem and some of them have told me not to worry.I am a good mechanic when it comes to cars.and been fightinng with this problem for a while.any help would be helpfull.Thanks Mark

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[Krewat]

Did you check the fuel pressure while it does this?

[typeop24]

when the dealer test drove it .it did not show the engine lean on the computer.

[LxMan1]

Cloggged cats?

[typeop24]

I checked the fuel pressure today.31 psi with the engine at idle.40 psi with the vacume pulled off the fuel pressure valve.engine off 40 psi after 5 minutes.any ford guys in the hartford area.thanks mark

[Krewat]

Originally Posted by typeop24

I checked the fuel pressure today.31 psi with the engine at idle.40 psi with the vacume pulled off the fuel pressure valve.engine off 40 psi after 5 minutes.any ford guys in the hartford area.thanks mark

Pretty good, but I was really asking if you checked the fuel pressure while it's doing this "no power at 3000RPM" thing

[typeop24]

i need to get a longer hose so that i can drive it an see what is giong on.

[1958]

I forget what it's called but on the 01s there is a valve under the intake that opens
around 3000 rpms to blend the intake pulses. you may check to see if it applies to yours.

Take Care
Bill F

[pronstar]

Check your MAF with a scan gauge that can check its barometric-pressure function.

[LxMan1]

I believe that only the V-6 and 4V Cobra/Mark VIII/Navagator engines have the split port intakes.

[Krewat]

Originally Posted by LxMan1

I believe that only the V-6 and 4V Cobra/Mark VIII/Navagator engines have the split port intakes.

Uh, what he said.

And 3-valve 5.4's and V10's.

And the 3-valve 4.6L Mustang.

[1958]

I found the valve I was thinking of it's the Intake Manifold Tuning valve.
According to the 97 to 02 Haynes it's in the V6 & V8s and it opens above
3000 rpms to blend the intake pulses for a better air/fuel intake charge.

It may not apply to the OPs problem but the RPM range is about right.

Take Care
Bill F

[Krewat]

Originally Posted by 1958

I found the valve I was thinking of it's the Intake Manifold Tuning valve.
According to the 97 to 02 Haynes it's in the V6 & V8s and it opens above
3000 rpms to blend the intake pulses for a better air/fuel intake charge.

It may not apply to the OPs problem but the RPM range is about right.

Take Care
Bill F

This is actually the first time I've heard of it, but you're right, it does exist...

And it seems to be the right RPM range too...

Something to look at.

[LxMan1]

Where is it Krewat, in the fat bottom section of the intake where the lifter valley would be on a OHV engine?