Tom Jackowski Jr.

hey all, I've searched for this issue among the forums and haven't seen anything that seems the same. I have a 1992 XJ with a 4.0 that has 285k miles. Engine runs pretty well, but sometimes it will suddenly lose power. The engine does not stall, but seems to bog down and make a popping noise from under the hood. If I floor it, it hops out of the bog and drives fine. I have tried adjusting the kick-down cable, have new spark plugs, and ran seafoam through it. It doesn't happen always but often enough to be annoying. I have only had this car for a few months, but the previous owner (gf's father) says that he's had it looked at by several shops and they can't find the issue. Any suggestions where to start?

also, fuel pump is relatively new I believe so I don't think it's a fuel pressure issue. Especially since flooring it seems to fix it. O2 sensor and TPS are also new.

Tom Jackowski Jr.

I have a new fuel filter laying around that I can try to replace. Anyone have any other thoughts?

tjwalker

You absolutely have to test your fuel pressure. Even though you have a relatively new fuel pump installed, they can and do fail ALL THE TIME.

So as you already have a fuel filter, install it. It's a 20 minute job on your vintage as the filter is right along the frame rail. A clogged filter can impede proper fuel pressure to the fuel rail and injectors.

If that new filter doesn't help, then get a fuel pressure gauge. They can often be rented inexpensively from local parts stores; call around for availability.For your 92, you need 31 psi to power your 4.0 properly. Then disconnect the vacuum line leading to the fuel pressure regulator under the hood and the pressure should jump to approximately 39 psi.

And I'd also suggest finishing your tuneup. Get some quality plug wires, distributor cap and rotor installed. The importance of tuneup hardware cannot be overstated.

You are effectively starting over here. Who knows what the previous shops did. Assume NOTHING. Use a testing based strategy to get to root cause.

Start there. Good luck and keep us updated!

Tom Jackowski Jr.

Tom Jackowski Jr.

Update: I replaced the exhaust manifold and the O2 sensor a week ago and I haven't had the loss of power issue again yet. Hopefully it is now fixed. My header had some pretty decent cracks in it and the O2 sensor that was in there was a bosch, so I replaced it with an NTK.