My 2000 XKR has suddenly lost at least 300 HP. It starts and idles fine, there are no OBDII codes. The fuel trims look near zero. When punched it runs quitely up until 4000 rpm and then some harsh sounds are heard under the hood (detonation?).

When the problem surfaced the car went from fine to sluggish, back to fine two or three times in a couple miles and then stayed very sluggish.

The fuel pressure is around 37 psi at idle and during attempts at hard accelleration. RPM will increase to 4000 rpm but with no pulling ability.

In trying to find the issue I replaced the knock sensors, the Air Mass Flow sensor, and the supercharger coupler. Blowing smoke into the intake shows no escaping air/vacuum leaks. I removed both fuel pumps and they appear to pump well outside the vehicle.

I did try pulling the fuel pump relays and it will idle with only one (either) installed.
I do hear the fans more than I remember and at one point I noticed that the exhaust on one tail pipe appeared hotter than the other. I also replaced 4 spark plugs so far and none appeared really clean like water was in the cylinder.

I will install two new pumps tomorrow but guessing is getting expensive.

Any sugestions from you experts?

 

A couple more points: I replaced the engine about 12,000 miles ago with a rebuilt unit. The supercharger has 100,000 miles on it and I've found maybe 4 tablespoons of oil in the air tube. I've been told the oil is likely due to clogged screen in the valve covers. I'll be cleaning them soon as well as doing a compression check.

 

Have the exhaust backpressure checked, w. a pressure gauge installed in the o2 sensor bung it will be easy to rule in or out if the catalyst is melted/plugged.

 

It does feel like a restricted exhaust. Thanks for the O2 hole suggestion!
Does anyone know a resonable supplier for the front cats?

 

You mention fuel pressure at around 37psi at idle. I don't know how you are measuring that, but if with OBDII reader, then it MAY be low, but, the more important question is, what is the fuel pressure when driving and pushing the accelerator pedal all the way down. I had a very similar problem on my 2004 XK8, ran fine unless I opened it up, then stumbled, slowed down...fuel pressure would drop from 55-60 down to 10 psi or so when wide open. Now, I say your 37 psi MAY be low because I am not sure if the early models actually should run at 55-60 psi, but I believe they should. Regardless, check pressure at WOT. Now, if it turns out your pressure drops, you may have a bad pump, or clogged fuel filter.

 

Thanks for your reply. The fuel pump pressure was measured with a gauge and a long hose so it could be read while going down the road. The pressure was steady. The new pumps arrive today so I'll send an update after I install them.

 

Steve mentioned the fuel filter........was that checked / replaced??

Sometimes its the easist and cheapest things that are overlooked......just sayin.

Hope you can get to the bottom of this and we can help

Good luck

 

I had the exact same symptoms with a Mercedes- it was perfect All of the sudden right before a long trip it would only go about 40mph. Floored or not, 40mph was the top speed.

Occasionally it would go a little faster but felt like it was being held back by a giant force field. The cat was clogged by a honeycomb turned sideways. As Anders said, a post cat pressure test is inexpensive and will identify or rule out that as an issue.

 

Well I just installed two new fuel pumps and I had already installed a new filter last week. There was some small improvement but the engine still lacks any ability to pull hard. I will check out the exhaust next. Thanks!

 

Try Nameless Performance The 400 cell are roughly emissions equivalent to stock and flow better. The 200 cell will improve performance and should still pass emissions, thought by less margin. Their products are high quality, a perfect fit and far cheaper than OEM.

 

Just heard back from the muffler shop and there is no restrictions in the exhaust.

 

I have to ask...are you definitely punching the throttle in DRIVE?

In this car the RPMs are electronically limited in PARK and NEUTRAL...this is normal.

 

If punched at about 30mph the RPM will increase to 4000 but there is no real increase in speed. It used to slam you into your seat. The muffler shop really did not pull anything so I'm not sure how they claimed all was well with it.

 

Without a gauge in the pre cat o2 sensor there is NO way to tell if exhaust/cat is clogged.
If the exhaust is indeed free flowing, another thing that could drastically reduce power w/o codes is knock sensors retarding timing from bad sensors or engine noises which can be interpreted as ignition knock, oh bad fuel could cause the same thing.

 

I had a knock sensor fail soon after replacing the motor and I replaced the second knock sensor last week so both knock sensors are new. I found it is easy to identify these by connecting a new one and just hanging it in the air. Perhaps my 5 month old one already failed so I'll try that again. Thanks again for all your suggestions. The fuel has been replaced since I just removed the tank so we can eliminate that. I'm pretty sure a bad injector or coil would throw a missfire code.

 

To give you an idea on how much power loss I am seeing, just driving up my ramps was not easy.

 

Have you checked your plugs? It may also be related to bad coils, all hard to say without hearing/seeing what happens.

Could you record it on video, so that you can see the rpm (and acceleration) and also hear the engine? This might help us in identifying the issue.

But it isn’t good to do wots now of course, so keep that to a minimum.

 

The only thing I can think of....

Symptoms

Idles OK, no codes, lucky to get 50mph on full throttle........ Your MAF has packed up!!!

 

Would be a much better fit then coils, but he said in his 1st post he changed the MAF

 

E-brake stuck on? S/C belt slipping? Can a s/c break and not compress anymore? If engine related, wouldn't it throw a code?