Evening all,

I picked a XKR up a few months back as my new weekly commute, LPG converted and 140K Miles its very much a work on progress and i'm slowly improving its overall condition.

So far i've done about 1200 miles over the last 6 weeks and on LPG am getting an equivalent 41MPG (18MPG factored to 41MPG with the difference in prive between the two) which i'm not considering too bad for my 200 mile round commute of fast A roads (50-70) and motorways (70-90) however i'm thinking theres a bit more to come considering the below with the engine probably having to constantly draw through the supercharger bypass valve at all engine speeds.

Now onto my query, the car's definitely not making the power it should be making, a seat of the pants guess puts it somewhere around 200bhp. OBD fault diagnosis has shown a faulty ignition coil causing a slight misfire, moving the coil to a different cylinder transferred the fault and a new coil has cleared the fault. My only remaining logged fault is a P1647 and i'm awaiting a upstream lambda sensor to clear that. The car feels underpowered on both LPG and Petrol, a compression test has indicated no concerns which got me thinking about the supercharger.

The intake vacuum function on my Torque OBD app is showing a vacuum across all engine speeds from around 5inHg at idle to around 30inHg at WOT under hard acceleration. It appears the supercharger is not delivering a positive boost. I've confirmed this as accurate using an analogue boost gauge connected to the supercharger to charge cooler casing where the fuel pressure regulator gets its signal.

Starting the car I can see that the supercharger bypass valve is drawn open by the engines vacuum, disconnecting the vacuum line to the bypass valve to keep it closed (and plugging the line) gives no difference in boost/vacuum readings. Removing the supercharger to charge cooler casing and starting the car confirms drive to the supercharger scrolls.

When I originally bought the car, there was a small LPG leak so I replaced all of the LPG hosing, this involved removal of the Supercharger and charge coolers to access the LPG injectors underneath, all gaskets were faced with Silcoset prior to fitting and there was no obvious difference in performance before and after action so i don't believe i'm loosing the superchargers output through boost leaks alone.

Supercharger belt configuration is correct so its being driven positively, belt tension is good.

So, possible causes?

I'm assuming the supercharger bypass valve is positively closed by the spring action of the actuator and then the building of positive charge of the supercharger. Is this a common failure point?

Is the supercharger prone to complete loss of boost generation through lobe wear etc? The supercharger is not overly noisy, it has the occasional knock at idle but doesn't sound like a bag of bricks, although the rotors show wear to the leasing edge of the lobes and carbon deposits, theres no significant/catastrophic damage from FOD ingestion etc.

If supercharger replacement is the likely solution, looking to second hand units, is there a fundamental difference between the X100 Gen IV Eaton M112 and the later X150 Gen V Eaton M112s? Are they interchangeable, adaptable, driven at different ratios etc.

Suggestions/Advice greatly accepted.

Regards, Pete

 

Bypass valves can leak, but there can also be leaks in the piping to it. At idle (warm engine) you should have more like 16" (give or take) of vacuum (assuming 30 is absolute vacuum), so if you have 5 now, there is definitely a leak.

Best guess for the boost side is that the vacuum valve isn't working, so it stays open.

The P1647 pending on the build year it could ether be a fuel pump issue or a O2 issue. Here is some more info:
https://www.jaguarforums.com/forum/x...nfusion-57005/

I would fix the P1647 and the vacuum part (so check bypass valve unit/piping to find the leak), and then check the boost side again.

 

In case it's an O2, drive it as little as possible till fixed as it will be runnig rich (to save the engine) so damaging the catconv.