Morning chaps

Morning all.

As per the title really.

I need to do a compression test on my 2003 V6 X350, but I'm unsure which fuse, (or fuses) to remove in order to immobilise the fuel pump.

This website: http://www.jaghelp.com/2013/09/2005-xj-fuse-locati... lists three different fuses for the fuel pump. One in the engine bay fuse box, one in the interior fuse box, and one in the boot fuse box.

I'm very, very wary of messing around with electrics on anything with a CAN-BUS system, as I know only too well how sensitive they can be.

So, does anyone know which fuse, or fuses need to be removed without causing any further problems later on down the line?


In advance, many thanks

 

What I did so far in this case was unplugging the injectors and the ignition coil(s). That way it was ensured that only the systems were deactivated that I didn't want to be active.
And after measurement and re-connection any respective OBD errors would quickly disappear when the car found that all was back to work.

But I haven't done that on my Jaguar yet, too scared that the result tells me something I don't want to know at the moment

 

Thanks for that Aix,

I have, what with all rationale, appears to be a leaking cam cover / rocker cover gasket, (copious amounts of oil all over plug 6). I'm 90% certain that it's just the cam cover gasket, but I want to do a compression test just to be 100% sure before I go ordering a load more service parts.

I've no idea what sort of compression figures I should be looking for, dry or wet, so I'll just have to keep an eye out for a drop off on cylinder six when doing a dry test.

Coil pack are all unplugged anyway. I'll unplug the injectors as well, so long as the electrical connectors come off easy enough. I'm always worried about having a wrestle with those electrical connectors and ending up damaging them.

 

The 3.0L V6 is supposed to have a compression ratio of 10.5, so the compression pressure should be reaching 10 bar to still count as healthy for an older engine.
Pristine conditions should reach 12 bar with this ratio.

Personally I would consider the engine healthy if all cylinders are within a total range of approx. 0.5 bar and the average of them comes out above 10 bar. That's not new, but ok and no reason to rip anything apart.

Bigger differences in cylinder compressions will affect the smooth running negatively as cylinders will burn differently, thus creating a rougher run.
Lower absolute compression pressure will affect the cold start capability and in general cost some efficiency (i.e. fuel consumption). It may also cause higher oil consumption, because more blowby gas through the piston rings will of course also carry more oil mist through the crankcase ventilation system.

Good luck. When I tried this on my BMW 320i many years ago (just out of curiosity of course) I ended up ripping the whole engine apart, changing the piston rings and when all was open also all the bearing shells
That engine ranged between 6.5 and 9.8 bar at the time, with the same CR of 10.5.

 

LOL. Lets just hope that that does not happen in this case.

Having already removed the inlet manifold / plenum and the throttle body, I can confirm that both were very, very clean for an engine that has done nearly 100'000 miles. Hardly any sludge or oil gunk, and only a very small trace of, (what I assume is), carbon deposits on the throttle body. This, to me, is a good sign. The plugs looked nice and healthy as well, although for all I know they may have only been in the car for the last 500 miles.

I had both cleaned up with just a little bit of WD40 in around one hour.

Talking of WD40, have you ever wondered what, exactly, was wrong with WD1 through to WD39?

 

Fuses are listed in the owner's manual which you can download

from this forum. The Electrical guide also.

I have them on my desktop-very handy.

As far as I know ( from reading this forum for 10 years lol) there are

no problems pulling fuses etc. on this vehicle.

 

Thanks Meirion.