I got an email today from JaguarForums wishing me a happy birthday. If someone could tell me how to do this, I'd consider it a great birthday if I'm able to get my Jag purring once again.

My underfloor cats were restricted and replaced them the other day but, although much better now, backpressure still seems to build up after warming up. So, I'm assuming some of the innards from the underfloor cats must have broken free and clogged the resonators and/or rear mufflers.

I was able to remove the rear mufflers and I have the resonators unclamped and the pipes separated. The resonators are free from any connection points but I'm struggling a bit to snake the pipe by the shock spring, axle, a-frame, etc.

I just backed the car onto ramps to attack this issue. I don't have a lift.

My question is: Does anybody have any suggestions on how to remove these resonators?

Do I need to take the car off the ramps and jack it up instead so the rear wheels can sag a bit? Do I need to unbolt something that would allow the rear pipe section to be pulled free from the car. I'd like to avoid cutting the pipes.

Thanks for any suggestions.

 

So, I tried jacking up the rear wheels, hoping they'd sag enough to manipulate the rear pipe of the resonators around the suspension, etc. Unfortunately, the scissor jack doesn't go high enough.

However, it appears the resonators are not the problem. Since I was unable to fully remove them, I just looked through the opening with a flashlight and didn't see anything which would restrict exhaust flow. So, I replaced the resonators and went for a test drive with just the mufflers removed (I couldn't look through them w/ the bends in the pipe).

At first, it drove great...quick, responsive, proper shift points, nice acceleration, etc. After reaching normal temp, it still drove well...until I started climbing a pretty steep incline and pressed the pedal trying to kick down a gear. Then, it showed the same symptoms as before replacing the underfloor cats - surging, hesitation, loss of power esp at higher speeds and, if I mashed the pedal to the floor, it's almost like it cuts out for a sec but doesn't actually stall.

I pulled in the driveway and, while still at normal temp, undid the clamps to the resonators and let them rest on the ground while I revved the car in neutral. At higher RPM's, it still surged. I'm assuming that means the resonators and mufflers are not the problem.

I got my infrared thermometer and traced the exhaust from engine block to the rear of resonators. Temps still appeared normal on the cat/downpipe but right before the clamp in front of the underfloor cats, on the single pipe, the temp was significantly higher than in front or behind it.

So, I'm wondering if I have a restriction in that pipe. Are these pipes double-walled and known to collapse?

Any ideas? Suggestions? Diagnostic tips?

It's really frustrating because the car runs great until it doesn't, which I thought was due to the excessive backpressure from the clogged underfloor cats which, after diagnosing myself with temp gun, vacuum gauge and by removing the O2 sensors, were also identified as being restricted by an exhaust shop doing a flow test on the system. However, the underfloor cats are flowing freely now and, although there's improvement, the problem still exists.

 

I'm possibly being far too simplistic but it sounds like when you really load the engine it doesn't pull. Can't be fuel starvation could it?

Mike

 

Mike, thanks for the reply. Yeah, I think you might be on to something with suggesting possible fuel starvation when under load.

I've dropped the different sections of the exhaust and test drove it with the sections removed. Problem was still there when climbing hill and/or at higher RPM's. So, that seems to rule out excessive exhaust back-pressure.

I don't see any signs of voltage leak and spark plugs look good.

I'm thinking fuel. But...is it a failing fuel pump, fuel pressure regulator, or faulty fuel injector?

Unfortunately, there doesn't seem to be an easy way to check fuel pressure on a '95 XJ6, as there's no schrader valve on the fuel rail and it looks tricky to unplug the fuel injectors individually.

Anybody have any suggestions on how best to systematically diagnose?

What's the best way to read fuel pressure on the X300's? Is there a typical place where people like to tap into the fuel line?

Open to any advice/suggestions....

Thank you.

 

I have no idea about testing flow etc. apart from checking the fuel filter isn't clogged (cheap to replace) but I had a problem where the engine ran well and freely up to 3,500 rpm after which it flatlined and misbehaved. It wouldn't rev any higher, didn't pull well. Using a scanner I could see that everything just flatlined after 3,500 rpm.

It was the crank position sensor that caused this which was nice as they are cheap and easy to fit. That said I suspect your problem may be different.

 

82WingNut
"if I mashed the pedal to the floor, it's almost like it cuts out for a sec but doesn't actually stall"


That is exactly the symptom that made me change my fuel pump and it cured my problem.

 

That does sound more likely. Pity it's hard work changing the fuel pump.

 

Thanks for the replies/suggestions. I ordered a new fuel pump and it has arrived. I'd planned to install today but discovered new info while driving yesterday that I thought might be more indicative of a sensor issue.
So, I posted a new thread this am, "Power loss/surging under load when warm - Erratic RPMs on scanner but steady Tach," in hopes that the new info might lend to diagnosis. I'm just hoping someone will say, "Oh...it's your CKP sensor...just replace it," as I'm really not looking forward to swapping out the fuel pump. Might not be so bad if I had a lift, but trying to crawl around under there.....Argggg!