My Car - Maintenance - Air hose replacement

On day, while driving, I noticed an intermittent hissing sound coming from the right side of the car, behind the dashboard. It was only present at small throttle openings and would cease under decceleration or harder acceleration. It also disappeared above about 3000 RPM. After deciding that it wasn't going to go away by itself I popped the hood and listened for the source. It appeared to emanate from behind the air pump, and was accompanied by a muffled "putting" sound, sort of like the sound made by the air pump. Not knowing what the normal air pump sounds were like I didn't know if the putting was normal, but the hissing definitely wasn't.

I was apprehensive that one of the myriad air lines under the intake manifold had split or popped off and was not at all keen to remove the manifold to check them. For some guidance I posted a description of the noise on the RX-7 mailing list, and Derek Vanditmars suggested that I have a look at an air hose that wraps around the 'Y' pipe (turbo outlet).
	Armed with this bit of knowledge I decided to have a look at the back of the air pump. It is hidden by the air relief valve return air hose and the rear turbo's intake hose. Unlike the intake manifold these are easily removed, and reveal the top of the 'Y' pipe and nearby parts.
Once the two hoses were off the problem was obvious. The hose Derek had described, which supplies air to the air control valve, was split like a bratwurst.
	After removing the damaged hose I could see that the tubes it connected are not very well aligned. The hose must distort quite a bit to bridge the gap between them as it is curved in only one plane. This no doubt contributed to the hose's failure, and will probably contribute to its next failure as well.
Since my local dealer didn't have the hose in stock I attempted to make a temporary repair with duct tape. This turned out to be a complete waste of time; the combination of heat and air pressure destroyed my repair within a few minutes.
	The new hose arrived the following weekend. I found it to be much more reluctant to slide over the metal tubes than the old hose. After struggling to get each end over its respective tube I resorted to lubricating the inside with a bit of water mixed with dish soap and this helped some. I found that the only way to get the hose over both tubes was to first slide the hose as far as I could onto the tube that goes to the air control valve (the top one in the picture). Then, using the fading strength in my fingers and the handle of a pair of pliers as a blunt prod, work the free end of the hose in front of the lower tube until the tube finally slipped inside. By this time the water/soap mixture was pretty much dry, but I managed to drag the hose off the air control valve tube toward the air pump to get its tube into the hose far enough that the clamp would seal it.
While I was there I checked the tightness of the worm gear clamps on the hoses from the 'Y' pipe to the intake elbow and found that several of them had loosened up a bit. It's a good idea to check these clamps at least once a year.

I put the rest of the hoses back on and fired the car up. No more hissing!

Created on ... July 19, 2003