My previous two Jaguars were XJ8s so this new XJR brings with it an element I am not familiar with; the supercharger.

I have my suspicions that it's just not working anymore. Either that or I've gotten so adjusted to driving a SC car that it feels normal now. I don't "think" I hear the pronounced whine like I used to, and it is fast but I don't think it's "supercharger fast".

I don't know the anatomy of the supercharger, yet, but it basically consists of three parts that I can see, a central part where the pulley shaft goes in and a manifold bank on each side. The central part feels hot after driving, the two outer parts are warm but I can lay my hand on it and it doesn't burn. Does that sound right? If I rev the engine with my head near the supercharger I don't really hear it do anything. As I let the revs drop back down I hear a squeaking sound where the shaft goes in from the pulley. It's not much and you'd have to be listening for it to hear it, but that's the only sound I detected.

Is it possible for the supercharger to fail and give no real evidence other than reduced power?

 

There are several possibilities. A boost gauge will answer your questions. Tap into the manifold pressure side of the fuel regulator. If you are not getting boost, your bypass valve or control piping might be fouled up.

A quiet SC is probably a good sign, although I suppose there is a small possibility you broke the coupling. An XJR without the SC would be noticeably less power than a NA , I would guess.

 

There is a "boost" gauge on my Ultragauge app. It did nothing when hooked to my XJ8, but on the XJR it fluctuates between -4 and -10 (from what little bit I have observed it). I don't know how to interpret that gauge so I have not paid much attention to it.

Is that gauge useful and if so how do I interpret the data? There is also a MAP sensor gauge that fluctuates now. It too was inactive on the XJ8. I have not really paid attention to it either though.

 

I drove mine up the street with the supercharger drive belt removed. It was remarkably slow. Think 4 cylinder Camry. Or take the standard V8, remove the VVT, and drop the compression ratio - that kind of slow.

 

Secondary fuel pump maybe? I'm not sure if that would affect the whine at all, but I remember reading somewhere that the secondary pump that kicks in under high throttle sometimes fails. This leads to normal driveability under low throttle, but power loss at high throttle since the one pump can't dump fuel in quickly enough. Hopefully someone with more experience can chime in here.

Or you could manually test each pump by feeding it power and listening, and eliminate that as a cause?

 

You don't listen, or touch, or "feel" a supercharger to tell whether it is working or not. The supercharger is a device that generates a considerable increase in power that is very, very hard to miss. We're talking about a 28% power increase over the normally aspirated AJV8 engine, which in the case of the X308 it means an 80HP shot in the arm, as it goes from 290HP to 370HP and this difference is impossible to miss.

My first question would be how long have you own this XJR and has it ever felt more powerful than your previous XJ8's? I owned an XJ8 before I got my XJR and I can tell you that the XJR felt like a total dragster by comparison, you simply cannot miss it.

Unless you have previously felt significant more power and now it has dropped, it sure appears like you may have bought this XJR with a bad supercharger. Under normal circumstances, if you de-select the track control (center console, top) and you, then, floor the gas pedal, the rear wheels will spin making a lot of smoke while you stay in place going nowhere. You can't do that with a normally aspirated XJ8 and this shows the immense torque that an XJR can apply to the rear wheels.

Yes, you can install a boost gauge, but all that gauge can do is to read boost, i.e. manifold pressure. This means vacuum at idle or coasting and positive pressure from the S/C upon acceleration; if you read some 12-15 PSI it means that the S/C is working fine, but not necessarily that it is boosting engine power because other functions may be out, such as tuning (too much fuel) or even the ignition may be at fault, etc.

So, first thing, find a way to read boost from the correct vacuum line/point to assess the S/C capacity to build up enough positive pressure in the manifold. BTW, I'm one of the very only souls who have experienced a bad S/C on an XJR, but not for lack of power, but rather because of intense noise and ready to kick the bucket. NOT cheap!

Cheers

 

OK, so it fluctuates from -4 to -10, meaning that the reading is staying within the vacuum segment and with no positive pressure readings (i.e. boost). Is -4 the highest it goes? Does it read -4 upon WOT? If this is the case, then boost is certainly NOT happening and need to find what's keeping the boost from rising, which may not necessarily be the S/C itself, as I previously had stated. It'll be interesting to have the XJR shop manual with a troubleshooting chart. It may well be a fairly simple procedure. Unfortunately, I don't have this manual.

Cheers,

 

I'd make sure the fuel pumps are working properly as nilanium said; as it really makes a difference. Make sure the fuses and relays are good; then there is a procedure documented (at least on the X100 forum) how to jump each pump manually to ensure they are working. I had my final fuel pump crap out about 2 months after buying my XKR; I was running on just one. Replacing the leads and pumps and the car was quite a bit faster.

Also, make sure your intercooler water pump is working properly; it helps deal with heat soak that can slow the car too. Turn the key to on but don't start it; it should be running. You'll hear it; it's above the alternator and below the airbox. Mine failed a few weeks ago on my XKR and replacing it meant a noticeable difference when the car heated up. It was quick while cold but suffered textbook heat soak when warmed up and given the stick a few times.

Generally a quiet supercharger is a happy and working one. Clunking can mean issues like a coupler (very common) that links the input shaft on the snout to the gearset for the rotor pack; or worn rear rotor needle bearing packs; or even worn rotor pack bearings. If it's quiet, it's not likely those things. My XJR is off since it was worn rotor pack bearings; and you can't get them off, put in new bearings, and put them back together and time them at home.

Checking things related to heat and fuel delivery is where I'd start.

 

As Mark suggested Remove the supercharger belt and drive around the block. You will know right away.

 

Good morning. Massive thanks for all of the feedback.

A few weeks ago I did the fuel pump test and discovered the secondary pump was not working. I replaced both fuel pumps and noticed a difference in performance. I will re-test the pumps today to insure that one of the new ones has not failed. My main symptom before was a long cold start (secondary pump was not priming). The cold start is fine now so I feel confident the secondary pump is still fine, but I guess the primary could have failed. I will have a finite amount of diagnostic time as I have to put new brakes on my sister-in-law's Lexus. Fun day off, huh?

Yes, the XJR is night-and-day difference from my XJ8. It is not just faster, it is massively faster. Also, based on what you guys are saying there is no way the supercharger is NOT working. The car is still very fast, at least as fast as was the XJ8. It is definitely not in 4 cylinder Camry territory. I guess I just feel I've perceived a reduction in power since I bought the car two months ago. The fuel trims are pretty good so I feel the air/fuel mixture is probably not a problem. I just posted this question as a whim after I drove home from work last night. There may not BE a problem I may just need to go out and drive it like a race car for a while and restore my confidence in it's power. Ask Ross (Spark), sometimes I am overly sensitive to a potential problem because I like fixing problems so much! lol

I don't have a great deal of faith in the Ultragauge boost readings, but I will pay more attention to them for a few days and see what I can learn.

I know I've heard the intercooler before when I first turned the ignition, I originally thought there was something wrong with my alternator until someone on here explained what that noise was. I have not noticed if that noise still occurs though. I will test that today, too. If I don't hear it then I can investigate that as a possible issue.

 

After driving put you hand on the intercoolers. If theyfeel hot like the rediator something is wrong.

 

I just got back from a very spirited 15-20 mile drive. The intercoolers (outer two pieces that say "supercharged" on them) are warm but I can put my hand flat on either of them and leave it there.

I guess it could have been an anomaly or maybe I was just tired from working and my perceptions were off. Add that to my desire to better understand the supercharger and perhaps I thought there was a problem.

When I walked back in the door a few minutes ago I said to my wife "I'm almost surprised it's not illegal for a car to be that much fun." I did a 4 mph to 75 mph on an uphill on-ramp to the interstate; took maybe 5-7 seconds. I did the same on a downhill on-ramp and I felt like I was on a roller coaster. I had an adrenaline rush by the time I merged with traffic (doing 85 by that point). The car revs very smooth and strong all the way to it's almost 6,000 RPM shift point so I'm not going to bother pulling fuel pump relays for testing. It had plenty of high RPM juice.

I changed the supercharger fluid about two months ago so I wanted to check the fluid level just to be sure. When I first bought the car the supercharger would rattle a little for the first few minutes after the car was started and it made noise most of the time, but not much noise. After the fluid change it has gotten progressively quieter and in fact makes no noise on start-up anymore and no noises while driving. I removed the fill plug with the car at a very slight rear-down angle (my driveway). Before I got the plug all the way out a little fluid began streaming down so I immediately re-tightened the plug. So, it's not low on fluid.

 

So I wonder where the Ultragauge gets a boost measurement since there is no boost sensor AFAIK!

 

I wonder if it's measuring intake vacuum?

The other option would be that Jaguar have their own use for that particular OBD2 channel, and it's not related to boost at all

 

Most likely.
I also have a transmission temperature on my Torque, but it is just a duplicate engine oil temperature.

 

Does anyone know what the secondary IAT should read?

Maybe at idle, or while driving in relation to the IAT what should the IAT2 look like?

 

I think its using the MAP sensor on the bulkhead, which is after the throttle body, but before the supercharger, so wont read boost.

I think, far more likely than an internal failure of the supercharger, is a problem with the supercharger bypass valve not closing when required.

 

IAT2 is just another temp sensor and rarely fails. The SC (or IC if you prefer) pump fails, though. IAT2 can then help flag the fault.

IDS/SDD can read IAT2 as can various other tools (on the STR at least).

 

Yes, I have read multiple scanners. It seems the vehicle they are working on reads the IAT2 for a few minutes. Will stabilize around 345F while backroad driving, then spike and go off charts.

The aux. pump is running (can feel it) not sure if it is actually pumping but will check. My guess is the intercoolers are not getting fluid to chill them. This causes the IAT2 to go off charts, air is thin which causes the rich condition and bad MPG.

Everything else seems to check out ok. MAF may be different but by watching numbers doesn't look to be off. Secondary O2 is a bit all over and will be replaced but it is a symptom of another problem.

So I still don't know this. I'm assuming since the engine temp stabilizes around 200 and the coolant should help manage the charge coolers the number should be around the same.
I'm in the middle of replacing parts so I cannot scan mine. Any help is appreciated.

 

Aux pump - or IC pump? Mine has both but the IC one is what matters here.

At idle the SC is doing nothing so IAT2 should be whatever you think the air temp should be bearing in mind it's wandered down some piping whose temp depends on what you've done with the car so far. Obviously (!) cold engine IAT2 should be about the same as IAT.