MAP Sensor - Method for removal

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Lordgaz
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MAP Sensor - Method for removal

Postby Lordgaz » Mon Jul 16, 2018 2:46 pm

Hi All
I have recently become a Jaguar owner - XJR X350 2005 - and found this forum to be well stocked with answers...

I have had an engine management light come on relating to the MAP sensor. This appears feindishly difficult to access, and wondered if anyone has the correct procedure to remove this sensor - (I would not want to start dismantling things if there was a simple access tip -)

Many thanks in advance.
Gareth
XJR S/C X350 - 2004

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Re: MAP Sensor - Method for removal

Postby J44EAG » Tue Jul 17, 2018 1:40 am

It is located below the throttle body on the elbow leading to the supercharger. I`d advise removing the throttle body once you have removed the inlet trunking and the expansion plenum and its various Jubilee clips. A spring drive 8mm socket driver is most useful as often the Jubilee clip worm drive tightener is often in the most awkward of positions.

Before starting the job, buy a new throttle body crush gasket and also some decent 1/8" ID vac/suction hose. Nether are expensive even from a main dealer. The throttle body is Torx bolt x 4 to the elbow. It isn`t difficult to remove those four bolts and lift off the throttle body. You will find it filthy so plenty of lint free rag, inspection gloves and spray carb cleaner. The underside of the throttle and the throat venturi are notorious for gathering crank case breather gung. Get that throttle spotlessly clean. Remove the old crush gasket and dis-guard. Clean up the mating surfaces. Fit a new crush gasket on re-assembly.

Once the throttle is off the elbow, the fun begins. The elbow will be full of breather gunge which may be seriously solid and may well have built up over the end of the MAP sensor. The sensor is mounted to the rear of the elbow and is secured as I remember by a couple of small cross head screws or perhaps small Torx bolts. The seal is just an O-ring which can be cleaned and re-used. Undo the screws and pull the sensor out. Carb cleaner cleaning may well sort your problem. The issue is the amount of gunge which blocks the sensor and fills up a "trench" in the elbow. Stuff the elbow with a rag and get that gunge cleaned out from around the sensor entry, the hole in the elbow, from the "trench" and from the accessible lower part and radius of the elbow. If you have a compressor, this is useful to blow out the gunge detritus. Wear protective goggles to stop the crap getting in your eyes. Expect a black face also! Once all is clean, refit the MAP sensor and fit a new throttle body gasket.

I strongly advise fitting new 1/8" vac and pressure hoses. You need about 28" of it either genuine from a main dealer for about £9 a length or from Halfords which is cheaper and in my opinion a much better and thicker walled alternative. The used lengths of rubber 1/8" ID hose breaks up after about 70k miles and needs replacement at each 70K mile interval. The length of new hose gets cut into two suitable lengths. One hose goes from the cow-horn manifold on top of the supercharger on the near side of the manifold, around and under the throttle body (perhaps easiest changed whilst the throttle is off the elbow) and links to the supercharger by-pass actuator) This is a pressure hose and pressure from the cow-horn manifold blows the by-pass flap closed under acceleration. A rotted hose will cause ELM illumination and poor performance.

The second 1/8"ID hose is vacuum which comes into operation at idle or low inlet manifold partial depression situations such as descending a hill with a closed throttle. Just like the cow-horn pressure manifold produces pressure which works on one side of the by-pass actuator, there is an elbow vac stub pipe on the side (can`t remember whether near side or off side) which also links to the by-pass actuator. That vac pipe also rots falls to bits.

So what you are dealing with is a suck and blow situation which self balances under high load with charger producing pressure or at idle when high vac situations occcur ie going down a hill with closed throttle. The vac side induces a partial vacuum which acts on the vac side of the actuator capsule and opens the by-pass valve to relieve excess charger pressure when it is not needed. So if either or both of those little pipes rot and fall to bits, that really upsets the balance of things leading to ELM illumination, fault codes and poor drivability. The job is easy whilst you attend to the MAP sensor, elbow and throttle body clean up but it is a real pig if the throttle body is still on the car.

I suspect that you will not have a sensor fault issue. Its far more likely to just be clogged with grunge. So a fiver for a throttle body gasket, £9 for some 1/8" ID pipe and another fiver for some carb cleaner. A £20 total spend will probably get you out of trouble. Allow about three hours for the job.

Hope that helps.

See also some of my 350R posts on the engine section for further info on keeping these cars going well....unfortunately none of this essential work is done at service time or is on the usual servicing schedules. Although essential maintenance, dealers can and will charge heavily to repair what is essentially fairly easy work.

Mike K
X350 Co-ordinator

2004 XJR

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Re: MAP Sensor - Method for removal

Postby J44EAG » Tue Jul 17, 2018 12:27 pm

Some images here of the XJR 4.2R elbow showing the mounting point for the MAP sensor, the "trench" and the vac take off stub pipe for the 1/8" ID vac pipe. The MAP sensor fits on the back of the elbow. The throttle body mount on the top of the elbow is clearly seen. A metal crush gasket (must be renewed) sits between the throttle body and the elbow. All needs a good clean up to clean metal before re-assembly.
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See how you get on.

Mike
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2004 XJR

Lordgaz
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Re: MAP Sensor - Method for removal

Postby Lordgaz » Tue Jul 17, 2018 1:50 pm

Hi Mike

Thank you very much for your superb and detailed replies. To be honest, I have put the car into an indie Jag specialist as of yesterday, however I have forwarded all of the information you have supplied in the reply to the man looking at the car. As the specialist also caters for Merc and BMW, I am not sure how many opportunities he has had in the past to access this sensor. I agreed yesterday to allow the swapping of the sensor for a new one (car has 108k on the clock so may as well), but hopefully the other points raised in your reply will also be attended to.
Previously I have owned some S55 V8 Mercedes, and got my hands well and truly dirty dismantling and fixing (including the valve block of the gearbox and overhauling the airmatic system and valve block) - But this was after gleaning a lot of information from the MB Forums - I am so glad you have an in depth knowledge of the XJR - I am sure my confidence to approach future issues will be boosted knowing you can be consulted. Happy to be a member of this forum. Many thanks. Gareth
XJR S/C X350 - 2004

Lordgaz
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Re: MAP Sensor - Method for removal

Postby Lordgaz » Tue Jul 17, 2018 9:25 pm

Hi Mike
I received a call from my garage this afternoon advising work had stopped due to 5 pointed anti tamper tamper torx bolts for which he had no tool - The mechanic hopefully has sourced the relevant tools for tomorrow - Is this something you were aware of on the Jags, (looking at the torx on one of your photos, it seems to be 6 pointed)

Cheers
Gareth
XJR S/C X350 - 2004

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Re: MAP Sensor - Method for removal

Postby J44EAG » Wed Jul 18, 2018 2:55 am

Ordinary Torx heads as I recall. They wazzed straight out on the throttle body. Recessed pipped Torx driver fittings are easy enough to get hold of. Halfords have quite a nice set in their tool department.

The pics of the elbow above are in fact from an earlier 4 litre XKR rather than from the 4.2 XJR/XKR of 2002.5>. Slight differences but nothing to be concerned about. The pics show some porting and polishing mods I carried out for friend prior to opening up the elbow and charger cross sectional area by about 25% and reducing some of the volumetric strangulation from which a standard car suffers. Well worth a day with a die grinder and some cutting burrs.

Mike
X350 Co-ordinator

2004 XJR

Lordgaz
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Joined: Mon Jul 16, 2018 2:36 pm

Re: MAP Sensor - Method for removal

Postby Lordgaz » Wed Jul 18, 2018 9:19 am

Thank you for the reply.
The mechanic encountered 5 point (Torx TS) bolts somewhere on the route to the MAP sensor - not 100% sure he was talking about the actual sensor bolts come to think of it - I googled "5 point torx Jaguar" and it seems some parts are indeed held with 5 point anti tamper torx TS https://www.jaguarforum.com/archive/ind ... 47504.html

I will find out more today no doubt.
XJR S/C X350 - 2004

Lordgaz
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Re: MAP Sensor - Method for removal

Postby Lordgaz » Wed Jul 18, 2018 1:37 pm

Aggh - now I hear the torx bolts holding the MAP sensor are damaged / unable to be released - And with such little space to work, the mechanic is not having much fun - They said they can try and break it off to remove the plastic lugs under the bolts on the sensor and then remove the bolts easier, or talk of removing the supercharger, which I obviously would want to avoid.
Currently the mechanic is trying to remove some of the black plastic bulk head trim to try and get a better access to the sensor - Not sure if that is a solution or not
XJR S/C X350 - 2004

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Re: MAP Sensor - Method for removal

Postby J44EAG » Wed Jul 18, 2018 3:01 pm

Avoid removing the charger as it is a pig of a job. See my posts on the subject in the engine section. However, that said, the valley hose can be changed at that point. Its well worth doing. The hose bulges and splits just below the NS front end of the charger drive pulley. Access is impossible unless the charger comes off. Easier to change the charger oil whilst it is off the car. Getting the four bolts out which secure the elbow to the charge is NOT easy. Neither is removing two 8mm hex head bolts to the EGR valve. One thing leads to another with this area of maintenance and none of it is easy. I had to put this job out to the trade having got started with it but my rageing sciatica in my right leg and two collapsed back discs caused back and leg muscles to spasm so I had to knock the jb on the head and admit defeat. Its probably the worst area on the 4.2R and its not for the faint hearted or inexperienced.

As regards the MAP sensor bolts, what you are suggesting is feasible although rather brutal. Very much a last ditch stand measure. However if needs must.....

If the charger has to come off, expect your techi guy to be near tears at the end of the job. That is no exaggeration!T he whole saga is to be found in this link. Its not a funny story .viewtopic.php?f=281&t=10231

Best of luck.

Mike
X350 Co-ordinator

2004 XJR

Lordgaz
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Joined: Mon Jul 16, 2018 2:36 pm

Re: MAP Sensor - Method for removal

Postby Lordgaz » Wed Jul 18, 2018 5:43 pm

Thanks Mike -
Yes, I had previously read your woes with a cold sweat - and the various other posts on the net about such a job -
Awaiting the next call from the garage (probably tomorrow)
XJR S/C X350 - 2004


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