Small pressure pipe rot. All V8R models.

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Small pressure pipe rot. All V8R models.

Postby J44EAG » Sun Mar 27, 2016 2:32 pm

My car has done it again as described below! This time I knew where and what to look for.

This small but irritating issue will affect all V8R models as they age. My 350R is now thirteen years old and has covered 80k miles. The rubber pressure pipe from the pressure plenum to what I believe is the by-pass actuator has disintegrated due to heat for the second time now. The rubber pipe is now well past its best and needs urgent replacement. I clipped the bad bit off but now the pipe is getting rather short! There are several other small 3mm bore rubber pipes around the throttle body area which will probably also need attention shortly. All pipe ends should be secured with clips or a small cable tie to prevent the issue from recurring. Just as well I`m due to remove the throttle body, super-charger elbow and the charger itself for porting, and deep service shortly. I can renew the pipework at the same time.

First signs of pipe failure will illuminate the dash MIL light and the check engine symbol. PO171 and PO174 fault codes will probably be found with a diagnostic tool and will be described as "Lean, banks A&B". This implies a leak possibly just after the supercharger outlet and before the inlet tracts on both cylinder heads. Its not suprising if the rubber pipe off the charger output plenum has fallen of the metal stub pipe due to a split, crack or pipe internal diameter expansion. Old rubber does that sort of thing. Old pipes should be replaced with new.

To find this pressure pipe follow the photo sequence here.
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Disconnect the inlet pipe from the top inlet plenum. A Jubilee clip secures the plenum to the throttle body throat. It is not that easy to access and you will need a spring drive 8mm hex socket to slacken off the clip. Left the plenum up from the throttle body and slide towards the front of the engine. A horizontal dowel which locates at the front of the plenum, holds the front end of the plenum to the car. WD 40 will help a rubber grommet on the plenum slide along the dowel. The supercharger plenum outlet plenum or "cowhorn manifold" is then exposed. A metal stub pipe is on the near side. An old rubber pipe will often drop off that pipe. replace the rubber pipe or secure as required. This shot shows the plenum inverted and details the circular part of the plenum which engages the throttle body plenum to the left with the grommet lug to the left.
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This is the "cow horn" manifold. with the sub pipe just over the top and downwards around the two o`clock position in this image.
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Here is the pesky swollen ended old rubber pipe and the "cowhorn" stub pipe. The two items need fixing back together again to cure the air leak and persistent fault codes.
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The worst part of the job is locating the upper plenum back into the collar above the throttle and holding the Jubilee clip in position. Use WD40 on the collar to ease refitting of the plenum. It can be a fiddly job.

Right. I`m off to Halfords to try to source some replacement pipe.

Late edit. Halfords stock rubber pipe in their pre-pack section. Lengths are about one metre. ID sizes are 3.2mm, 5mm and one rather larger size. The 3.2mm would appear ideal for my needs. Not fitted yet as the Easter Bank Holiday Monsoon has started again but worth the trip just to get it in stock.

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