Background: This car was "down" from mid-November of last year until two weeks ago, when the transmission was finally rebuilt. As soon as I picked it up I filled it up (it was down to about 1/4 of a tank). The transmission now behaves as expected. It's starts and idles fine.

The issue is this. While driving the other day, it began to feel a bit sluggish at about 50 MPH.. I put my foot down to the floor (slowly, I didn't want kickdown to activate), and the engine produced no more power than it did when I just had a touch of throttle going. The engine didn't sound like it was even trying. No coughing, sputtering or anything like that. It just acted as if I hadn't pressed down on the pedal. Puzzled, I backed off the throttle and cruised along while I thought about this. I then put my foot into it again about a minute later and the engine responded normally.

The next day I went thru the same thing. Foot down, no increase in power, gave it a minute, foot down again and engine responded as expected. When it responded normally I put my foot into it quickly and kickdown activated as it should.

My first thought was a fuel delivery issue, but I can't think of why it would fix itself.

Thoughts?

Thanks
John 1987 XJ-S V12
75000 miles

 

Lucas or Marellli ignition?

How recently have you changed the fuel filter?

Have you ever renenwed the B bank fuel pressure regulator?

 

Hi Greg,

Should have anticipated that first question. Lucas.

Fuel filter is about 6 or 7 years old.

I removed the A bank regulator several years ago. No ill effects. I thought I'd replaced the B bank regulator, but I can't find a record of doing so, so probably not.

Fuel pump and filter were replaced in 2017, also cleaned out fuel sump and sump screen. I'm about to open up the sump and see if it needs cleaning.

Thanks,

John
1987 XJ-S V12
75,000 miles

 

Just de-pressured the fuel system and removed the fuel filter. Maybe fuel filters are supposed to work like this, but when I tried draining the filter by turning the left side down (see photo) fuel just trickled out. When I turned it the other way (right side down) fuel poured out. If the filter was directional I would have thought that would have been stamped on the filter, but there is no indication of flow direction.

I did measure the pump voltage before draining, checked it at ilde and 2500 RPM, voltage never dropped below 13.5 volts.

Made an error in my post before, filter and pump were replaced in 2015.

Thanks,

John
1987 XJ-S

 

For sure replace the filter, say I.

 

The fuel filter is definitely directional, mine only had that indication on a cellophane wrapper that was on the filter.

 

Thanks all. New fuel filter did the trick.

John