Hi I've recently brought a 2000 xj8 3.2, it drove great when I test drove it. But I realised on the way home that when you put you foot or if its under load that it has no power and there's no codes or management light on. It seems to idle fine and and works fine at low speeds but it struggles to go over 50 unless you're at part throttle. Has anyone else had a similar issue? Any help would be greatly appreciated.

 

If its a simple problem, sounds like a vacuum leak. Along with the regular vacuum lines, check the connection for the brake boost at the back bottom of the TB. Its a rigid plastic connector going into the side of the TB.
Another issue could be a bad TPS, which may be a bad pin connection. The replacements are gold plated.
Be sure to check the MAF and if your going to clean it, use a MAF only cleaner. Be sure your air box is clean and clear, to include the filter. Check the cam cover breather tube for any obstruction and clear it.

Here's a couple PDF's for the pin connections...

 

Thanks for the reply, I've checked the live data and the TPS seems to be working correctly, I've got a second hand MAF on the way as i got it for less than £20,the cam cover breather seems ok, But I will check the vacuum line thanks.

 

Check the fuel pressure as well, which should be around 3 bar.

 

Thanks its funny you should say that for some reason the last owners bypassed the fuel relay for some wierd reason.

 

If the PCM is registering 3 bar, but the pressure at the fuel rail is substantially lower, there is a restriction in the flow, which is usually a clogged fuel filter.

 

Thanks ill look at the weekend

 

The fuel pressure should be about 3 Bar with the engine not running, just the fuel pump activated and with the engine idling with the vacuum hose to the FPR disconnected. When the vacuum hose is connected and the engine idling, the fuel pressure should be about 2.6 Bar.

I would first replace the fuel filter. If clogged, it may still provide sufficient flow to provide good downstream pressure at low fuel demands but, at higher demands, it will cause downstream pressure drop.

 

Hi guys just a quick update it looks like its all good now after changing the fuel filter and forgetting to depressurise the fuel system it now seems all good