Hi guys, I'm in the process cleaning the intake manifold throttle body etc on my 1995 xjr.

my question is should I replace the top breather hose on the tappet covers with an open breather? and block off the breather from the intake and throttle body to stop oil from entering and clogging up the system? is there need for some oil to come into that section or can it run dry?

thanks in advance for any light on the situation

 

Hi Michael,

Here's what the AJ16 Engine Management System Dealer Training Manual has to say about the breather system, which it calls the "Crankcase Emission Control" system:

"The crankcase emission control arrangement is similar to the 1994 AJ6 arrangement. Crankcase vapour is collected from the camshaft cover. At part throttle, the gases are fed into the intake manifold through a coolant heated restrictor. During full load operation, the gases are fed into the engine through both the coolant heated restrictor and air intake elbow connection.

"The necessary crankcase vacuum is balanced by the part throttle restrictor and the full throttle orifice in the inlet elbow. The restrictor and orifice sizes have been carefully chosen to control the crankcase vacuum, which in turn reduces the amount of breather gases entering the manifold. This ensures that idle speed remains unaffected.

"The part throttle restrictor is coolant heated to prevent icing during cold weather operation."

So would engine performance be effected if you simply disconnect the hose from the cam cover port and allow it to breathe freely? I don't know. The fact that the manual refers to "The necessary crankcase vacuum..." would be worth further study. Would the oil and contaminants in the crankcase gases make a mess in your engine compartment? Probably, unless you attached a breather filter, and it would no doubt have to be cleaned from time to time.

If you remove the hose from the intake air elbow and coolant heated restrictor, you would definitely have to block both ports airtight to prevent air that is un-metered by the Mass Air Flow Sensor (MAFS) from entering the intake and causing idle and running issues.

Sorry I can't give you a definitive answer, but I hope this info is helpful.

Cheers,

Don

 

thanks for the response Don, much appreciated, the way it reads makes it sound like a crucial part on the idle especially of the engine. the plan would be to attach a breather filter, my main reason is trying to avoid oil getting into the intake (assuming it is ok for the intake to be "oil free" my other possible option is an oil catch can i suppose, allowing the oil to be seperated from the air required to create the correct vacuum i suppose, some more reading etc will be needed.

also side note, try not to ever damage the crank case breather hose, as it has set me back around $250 to replace.

 

I'm not sure where you picked one up for that price but they are only $31.79 at Rock Auto.
PCV Valve / Crankcase Ventilation Hose

1997 JAGUAR XJ6 4.0L L6 :
Emission : PCV Valve / Crankcase Ventilation Hose Price $31.79
ÜRO PARTS Part # NBC3937BB
Crankcase Breather Hose
Cover to adapter 3 Outlet

 

Jag made a modification to the breather hose setup as they were getting a lot of issues with oil entering the air intake elbow and eventually fouling things up.

Their solution was to cut the breather hose and put in an oil separator. The separator then has two output connections. One to the elbow as normal and another at the bottom of the separator that sends any scavenged oil back to the sump via a connection made on the oil dipstick tube.

Here is the TSB
17-11 Throttle Difficult to Open on Cold Engine.pdf

 

From the days of the now defunct XJR/6.com forum I recall a couple guys rigging up a catch can type separator. I can't remember the details but apparently it's 'doable' with a little imagination.

XJRengineer might see this thread and chime in. He might have some input.

Cheers
DD

 

Doug, great minds and all that!! See my post just above yours

 

Just a slight correction as the XJR/6 uses NBD7748AA. Still only about $30 from Rock Auto, though.

Not sure about the n/a cars but on the supercharged cars this hose is a real bitch to contended with. Stock up on Band-aids

Cheers
DD

 

That looks promising.

Jag also had an X300-specific breather modification/tech bulletin. Later, though, I think they retracted it because it wasn't working as planned.... some of the members with dealer background might chime in on that.....which is why some guys rigged up their own version.

Cheers
DD

 

This is not an uncommon "issue" on a lot of cars, and many folks end up rigging up catch can solutions. I put quotes aroud issue because in many cases it turned out to be a minor if even inconsequential issue around oil consumption, etc. once the catch can was in place and they could evaluate how much oil was being ingested into the intake.

Now in a few cases, the oil loss and intake contamination was not trivial, but that really indicated a problem.

 

thanks for all the feedback guys, I have already ordered the hose, (genuine - that should give idea to the ridicules price and the fact that I'm in Australia)

the oil consumption isn't my worry, it is more the idea of oil going threw the intake and sooting things up, I did notice that shifts at higher rpm a bit of a smoke puff out the exhaust I am assuming this is because of a push of oil through the inlet manifold?

The idea of an after market catch-can is probably the way, although the amount of rigging up may prove to be more trouble than it is worth.

 

Honestly rigging a catch can is a doddle. You can buy the Jaguar oil separator for about $18US. You then cut your existing hose, tie in the separator and run a small hose from the bottom to a can or whatever catchment device you like. You could even buy a used dipstick tube that has been modified (or modify your own) and then the liquid oil would just return to the sump.

The problem is not about oil consumption, rather that oil finds it's way into the intake and eventually coats and then hardens on the throttle disc causing all sorts of problems with idle and drivability.

Here is a pic of the separator I just bought, I added arrows to show where each hose goes.

 

Doug,

The mod for the X300 was exactly the same as for the 95 & 96 XJS. The problem is that the separator can break but it's cheap to replace.

 

I did a lot of those modifications on customer cars way back when. Interestingly enough, though, my own two cars do not have it. One thing I remember from the mod is the tendency of the separator to ......separate, causing idle and running issues. It good to see it is available separately. I don't recall it working as well as intended. We still did a lot of t/body cleanings regardless of the use of the separator or not.

 

Mark,

Yes exactly, my separator did indeed separate in two If Jag had just designed the two halves to screw together it would never have had that problem.

I think it really does help maintain the cleanliness of the throttle body for a bit longer but ultimately the discs will get gunked up, especially if the car is not driven often

 

Again thanks for the advice guys, I am still currently waiting for all my ordered parts to arrive, but will have a look for that separator.

Also just to clarify, from what i have read it is not a good idea to just block off the hose inlet going to the intake and add a breather filter to the crank case? if this is done the idle would play havoc?

 

Michael,

The thing that gives me pause about plugging the intake breather hose inlet and installing a breather filter at the cam cover is this statement from the manual that I quoted previously:

"The necessary crankcase vacuum is balanced by the part throttle restrictor and the full throttle orifice in the inlet elbow. The restrictor and orifice sizes have been carefully chosen to control the crankcase vacuum, which in turn reduces the amount of breather gases entering the manifold. This ensures that idle speed remains unaffected."

With a simple breather filter, pressures might develop in the crankcase that could affect engine performance. Why is crankcase vacuum desirable? Here's some information I found via google. It's obviously oriented toward race engines, but it seems to be just as applicable to a Jag saloon engine, especially the last paragraph:

"What is the advantage to using a large amount of crankcase vacuum in a race engine?

HORSEPOWER; WHAT ELSE?

And it is the cheapest HP you can buy. If you can achieve a crankcase vacuum level of at least 8 inches HG, you will very likely realize an immediate power gain of at least 15 HP.

If you run a dry sump system with a three stage pump (one pressure stage, two scavenge stages), in most cases you cannot achieve a sufficient level (8 "HG) of crankcase vacuum to achieve that power gain. The extra cost of a four stage pump will net you around 15 HP in most cases. At NRC, it costs less than $100 for that extra stage. How can you beat that price for an extra 15 HP?


HOW IT WORKS

The reduced pressure ("vacuum") in the crankcase is generated by having a substantial excess of scavenging capacity with respect to the engine's oil flow rate. The "vacuum" increases the pressure differential across the ring package, producing an improved ring seal. The improved ring seal allows the use of a low-tension (reduced friction) ring package, yielding a power increase as well. Further, the reduced crankcase pressure dramatically reduces windage losses at high RPM."


The above is from this link:

http://nutterracingengines.com/racing_oil_pumps/crankcase_vacuum_facts.html


Cheers,


Don

 

Thanks Don B, your response has been extremely informative, Looks like it is worth keeping the system original from what i can read and understand.

And regular cleaning of the throttle body, rather than messing around with the system to avoid what in reality is probably not that much oil and just me being overly worried about the loss of any possible power etc with oil residue build up.

 

So I decided to clean the throttle body on my n/a engine and started by removing the intake piping and bellows. Expecting to find possible carbon build up inside the bellows and the section of body that it fits onto, to my alarm I found a whole heap of oil instead. No carbon, but about 100ml or so of engine oil sitting in the bellows and adjoining section of intake pipe - it was very wet in there!

This is the first time I've dismantled the intake at the throttle end in 3 years of ownership and suspect it may never have been removed before, so it looks like a steady build up of oil over a very long period. The car has been running fine so the oil doesn't seem to be causing problems, but it strikes me as unnatural that it should be allowed to accumulate in the intake system. The only issue has been with the idle speed occasionally sticking at around 1000RPM instead of returning to 700, usually occurring after long running on cruise control. A quick blip on the go pedal returns it to normal, but it's annoying, hence some servicing of throttle body as a starting point.

Having read this thread I'm now keen to fit an oil separator of some kind, then I'll get back to tracing the cause of the high idle. Does anyone have any more feedback about the performance of the separator (e.g. how long do they last before splitting etc?) or any have any other solutions come to light since?

Cheers,