Thread: 96 3.9 V8 Breather Mystery

Originally Posted by MMEJ

Hi, I'm considering removing the breather from the LH rocker cover to the air filter as oil entering the air box post filter element cannot be doing the MAF any good, and installing a catch tank or small filter for the breather pipe to vent into.

Should, the board members think its not a good idea to remove the breather pipe from its factory location is it advisable to remove the small 'T' connector to the inlet plenum as it seems too small to be a breather and I can't workout what function it performs?

As a foot note, should a 96 D1 3.9 V8 have a fan cowl around the radiator as my D1 isn't currently fitted with one?

Cheers

You've got gas on and the gas fitter thought it was a good idea to shift the breather upstream of the gas mixer. Well, it's not a good idea. Fit the breather back to its standard position on the throttle body and it will work just fine. It is perfectly safe there.

Shifting the breather is important on vehicles with PCV systems, which the D1 is not. Despite what some people think, it is not the cause of backfires on gas. And the tee piece arrangenemt is just fine in the standard setup so leave it like it is.

A fan cowl is useful in slow traffic conditions with a good viscous fan coupling. Otherwise some D1 owners have been successful using EL-AU Falcon twin electric fan set-ups instead of the viscous.

Hi, don't understand your reply for the breather, as it doesn't really address the questions.

Yep I can see that standard fitment maybe the easiest but is it the best as SMOG kit can reduce the efficiency of the motor? Just wondering what the benifits of removing the pipe are (if any) and what the 'T' piece into the plenum does (how does it help with the engine breathing). The engine bay would look a whole lot better with this kind of stuff removed.

Many thanks for the advice on the fan cowl, I'll see if I can track one down.

Originally Posted by MMEJ

Hi, don't understand your reply for the breather, as it doesn't really address the questions.

Yep I can see that standard fitment maybe the easiest but is it the best as SMOG kit can reduce the efficiency of the motor? Just wondering what the benifits of removing the pipe are (if any) and what the 'T' piece into the plenum does (how does it help with the engine breathing). The engine bay would look a whole lot better with this kind of stuff removed.

Many thanks for the advice on the fan cowl, I'll see if I can track one down.

I don't see why you want to remove the breathing system. It is mandatory for the engine type to have a system of combusting breather fumes. The main thing was your post below said

"the breather from the LH rocker cover to the air filter"

This is NOT the standard breather. The standard breather, including the tee piece, are connected around the throttle body. The 16mm hose should bend around from the tee to the inlet side of the throttle body. You should find a cap there, fitted by the LPG fitter. Remove the cap and reconnect the breather here. It works fine and on a healthy engine the fumes are minimal and won't affect performance.




The breather I am talking about is the one in the extreme lower left corner of the picture.

Dont remove breather system I did it in my landcruiser turbo diesel that was fine stoped sucking oil into turbo but i did it in my d1 v8 just letting it free vent all it does is give you bad oil leaks leave it in factory position I have returnd mine back to factory no performance increase and just gives the fuzz somthing to pick on if they pull you up on it

Yes, you should have a fan cowl.

Sorry but I can't help with the other issues.


Phil

Just realised you could be talking about the weeny hose that goes from the back of the passenger side rocker cover to the air cleaner box. If that's the one, sorry about the misunderstanding.
The early D1's and RRC's had a small intake filter on the rocker cover instead which keeps falling off. If oily fumes come out of this breather then you need to clean all the fittings on the main breather , including the flame trap on the DS rocker cover. That usually fixes it, unless your rings are stuffed.

I am not sure what the arrangement of the D1 is but an RRC 3.9 with V belts has a small hose to the plenum from a originally plastic T piece in the main vent line. A coomon cause of uncontrolled idle is when some "bright spark" replaces the T which has a tiny hole with a normal T .

AFAIK this hose is to provide some vacuum in the vent , and its purpose MAY be to reduce oil fumes to the throttle butterfly at idle or high vacuum and when vacuum is reduced under hard throttle to then let the fumes through to the throttle body. Cannot think of anything else.
Regards Philip A

Attachment 35245

Attachment 35246

Hi all, please find enclosed 2x photos of the breather system as fitted by our friends at Solihull.

As can be seen, the breather runs from the rocker cover to the 'T' piece, and then from the 'T' piece to the air filter case.

Now when I first owned the D1 I read (on this very forum ) that the small bore pipe and the connection to the plenum needs to be clear or the tick over won't be correct. I checked the pipe and the plenum connection found it was blocked, un-blocked and the tick over was the same. So what function does this pipe perform, can I run just the large bore pipe from the rocker cover to the filter case and block off the plenum connection?

A little more controversially for some, say we forget that the boys and girls in blue () may get little upset if i was to run the main breather pipe into a catch tank () and block the connection to the filter case, would this help the way the motor runs as it wouldn't be ingesting oil laden air from the engine? I also assume that this modification reduce the ammount of debris coating the MAF and the inside of the plenum chamber?

Cheers