Power cuts out at 4K

My 87TC is losing power at 4K, just as it passes 10psi of boost, it then falls on it's face, not really a miss just no power. It runs fine as long as you stay below 4K.

It has fairly fresh Motorcraft tune up parts.

I tried a few known good parts but this didn't fix the problem, Coil, PIP, and TFI.

I also checked the Intercooler hoses, all are good.

I replaced the Fuel pressure reg about 6 months ago when I had the tank down to replace the little rubber line that had split on the fuel pump, did not replace the pump and no idea of it's history.

So, I put a gauge on the fuel rail today and it shows 29psi idle, hot. 37psi with the FPR hose unhooked. Driving the car with the gauge taped to the window shows that the fuel pressure goes up to 45psi until the boost come in around 10psi at 4k and the pressure then drops to 27-29psi and then it loses power.

The rest pressure is holding at about 25psi for the last 2 hours.

Do I need to do any further tests or go ahead and replace the pump? Could the Fuel regulator be bad and cause this?

Thanks

Fuel pressure should rise one psi for each psi of boost. If I read your post correctly, that is not happening?? Can you clarify?

It does rise 1 to 1 until about 10psi or 4K, after that the pressure fall off to around 27 or 29psi and of course the power falls flat, I can ease off the throttle and it's fine again. Basically, WOT is where my problems occur.

Pump is failing or filter is clogged.

Is there any point in considering the stock replacement FPR could be bad at this point? I don't smell gas from it and the line is dry.

I figured it was probably the pump

Pump failing, fuel filter plugged, or filter sock on the pump clogged.

Before dropping the tank, Cceck to be sure there arent any splits in the vac/pressure line to the FPR that open under boost thus lowering the pressure signal to the FPR.

The fuel filter is good, no vacuum leaks around FPR or any where else.

I did a fuel pump volume test and have nearly a quart in 30-40 seconds. Tested in front of fuel filter. I was expecting a more forceful stream to be honest, looked more like a cow pissing on a flat rock.

You guys ever seen a pump carry good pressure at idle and pass a volume test but still not work correctly when the car is under WOT? Just Curious...

Dr. Phil. Are you saying your car does not make 10 psi until 4000 rpm? It should make 10psi before that.

If you keep the boost under 10 psi, can you get the rpms above 4K?

Have you taken the IC hoses off and bent, folded and mutilated them looking for cracks and leaks?

To clarify, at around 10psi it begins acting up. I guess 10psi and 4K was just the gear I was in at the time and trying to read the fuel gauge taped to the window too. Yes, it will run under light throttle all the way to redline.

Yes checked all hoses vacuum included, found one small crack on one rubber end at the vacuum tree, still no change.

I bought pump, strainer, filter, I'm out of ideas. How long to do a pump replacement? It is on empty, luckily.

Any additional or increase in noises when the power cuts out.