Rx7 Project: Vac Hose Job

Well, let me start out by referring you to a few web pages:

Rob Robinette's Vacuum Hose Replacement Page has a very good overview of of how to do the job and has notes on a few things you should watch out for (it kept me from pinching a couple of hoses).

You might also want to look at Rob's Page on removing the extension manifold (you need to do this to get to the hoses).

Max Cooper has an excellent page with information on suppliers and brands of vacuum hose and cable ties.

I would suggest the silicone vacuum hose from Baker Precision and the cable ties from Web-Tronics.

UPDATE: So far, I have done two jobs with the Baker Precision hose and one (my own car) with hose from Hose Techniques. The HT hose was much more kink resistant and fit better. It was also more resistant to tears and abrasion. HT sells a kit for the RX-7 which has all the different size hose that you will need. I will be using them for any future vac hose jobs. Note: The BP hose is a quality product, I just like the HT hose a little better.


What you'll need:

In addition to a good set of metric tools (especially 10mm, 12mm, and 14mm stuff) you should have the following:

tools-tn.jpg (49267 bytes)

I would also replace all the gaskets that you remove. Often, replacement is not necessary (they are metal gaskets), but they are not expensive and replacing them isn't a bad idea:

Throttle Body Gasket             N3A1-13-655

Throttle Body O-Ring            N390-13-W69

Extension Manifold Gasket    N3A1-13-112

Air Control Valve Gasket       N3A3-13-996                

There are several one-way check valves (green & white plastic) that often go bad and cause turbo problems. These same check valves often break when you are removing them, so you may want to buy a few just in case. Be sure that you test every valve when you have them out. You will need a vacuum pump to do this properly (Mity-Vac is a good one that can be purchased at most parts places). To test them you just need to be sure that the flow air in one direction and that they do not flow air (and do not leak) in the other direction. Since the check valves are one-way, you need to make note of which way they were installed and make sure you put them back that way. The Shop Manual has diagrams in case you forget.

Small diameter check valve    HE41-13-995

Large diameter check valve    N390-13-995A


Getting Started:

You will need to remove the following parts to gain access to all of the vacuum hoses (see Shop Manual for details):

Be sure you cover all intake openings. I used masking tape and paper towel in these pics, but I prefer masking tape and zip-lock bags. You do not want to accidently drop a nut or bolt into the intake. If you realize you dropped something in there it is a pain in the rear to get it out. If you don't realize you dropped something in there then you will probably be buying an engine soon.

The Air Control Valve needs to be removed to access a hose or two that are underneath it. Be careful when replacing it as it is easy to pinch the wiring harness for the solenoids here. In the picture below, the thing with the red dots on it is the Air Control Valve.

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The solenoid rack needs to be removed for two reasons: 1) There are a few hoses underneath it that need to be replaced and 2) It it much easier on your back to remove the solenoid rack, take it inside to a table, and replace its hoses. If you are having odd turbo problems, you may also want to test each solenoid for proper opertation (see Shop Manual for details) while you have the rack out. Also, when removing hoses from the solenoids, you must be very careful. The solenoid nipples tend to break and they cost about $50 to replace. I used an x-acto knife to split the solenoid hoses lengthwise. Then insert a small screwdriver into the cut and twist gently. This should loosen the hose so that you can safely remove it. If it doesn't, keep slitting the hose until you can get it off without applying any pressure to the solenoid.

To remove the solenoid rack you will need to remove several phillips head screws at the front and rear of the rack. Some people have had trouble rounding these screws out. You do not want to do this is they will then become very hard to remove. I used a #2 phillips bit in a 1/4" (I think) socket and a ratchet. Apply as much force as you can (to keep it from rounding the slots) and remove each screw. I didn't have any trouble this way. You then need to disconnect the electrical connections and a few hoses from the rack. Below is a pic of the solenoid rack.

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Replacing the hoses:

Replace the hoses one at a time. Make pictures and/or sketches of everything you take apart. Label any hoses or electrical connections that you think you might forget. I have also found that paint pens (in various colors from your local craft shop) are really great for color coding connections and hoses). Also, I have found that Mazda was really good about using keyed electrical connectors in the car... which basically means that its hard to plug the wrong electrical connection into a sensor. Look around well and make sure you replace all of the old vac lines... you might as well do the job right while you're in there (there are probably more than 60 hoses to replace).

There are two sizes of hose used on the car. It will be obvious whether you need to use the 4 or 6 millimeter hose. Mazda also felt the need to use hoses with different diameter fittings on each end. When you run into these you will enjoy the fact that silicone hose is very stretchy. You might have to work at it but you can stretch the silicone hose over the larger fitting. This may sound a little confusing, but you'll see what I mean when you get there.

The long needle nose pliers are your savior. You can use them to install hoses in places where you can't get with regular pliers. They are also great for pulling hoses off.

The 6mm vacuum lines for the Wastegate and Turbo Precontrol may have restrictor pills inserted in them, depending on the year model of your car and the age of the turbos. If your car has the pills, you must be sure that you remove them and put them (oriented correctely so that air can pass through them) into your new hoses. The pills are different sizes, so make sure you put them back in the correct hose. See the picture below for the lines I'm talking about.

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Watch for kinks. Make sure the hoses are not kinked. If they are you will have problems. Lengthen or shorten the hoses so that air can flow easily in them. If you have a hose than wants to kink no matter what, you can insert a small spring (try a ballpoint pen) to give it some rigidity.

Use your handi-cut pliers to cut the silicone hose at a ninety degree angle. The sharp handi-cut pliers (or a good razor blade) will make a clean cut and prevent the hose from splitting.

Some people advocate cable-tieing each hose end while others like to glue them in place. Well, they are both correct and incorrect and I will tell you why. There are two types of hose fittings on the car. Most of the fittings are straight pipes with no flares on the end. I don't think it does any good to cable tie this type of pipe as you can still pull the hose right off. With this type of fitting, I put a small amount of 3M Weatherstrip Adhesive (get it at any parts place) on the outside of the metal pipe. Then you just push the hose into place and the adhesive will become tacky and hold the hose in place. Be sure that you don't get ANY adhesive inside the pipe. The other type fittings (of which there are few) have flared ends on them (they bulge out at the end). This type fitting is an excellent place to use a cable-tie instead of adhesive, as the hose will not come off unless you cut the tie.



Be sure to torque the extension manifold bolts in the proper order and to the correct torque (see Shop Manual).

Don't split the silicone vacuum hoses. Silicone is great for many reasons, but its only major weakness is that it splits easily. Be careful not to pinch or scrape the new hoses when you are re-installing parts (such as the alternator). Once silicone gets a nick, it will split wide open.

Watch out for pinched hoses. The extension manifold has a low spot in the middle than can pinch two hoses against the solenoid rack. In the picture below, the hoses with colored dots are the ones you should watch when re-installing the extension manifold (It was easier to mark the old hoses rather than the new ones).

hosepinch-tn.jpg (62126 bytes)



Finally, the link below will take you to all of the pictures I took for the vac job. They might be useful if you forget where a hose went. You might also want to use the pics to make sure you replace all of your hoses (you may see some you didn't realize were there).

Vacuum Hose Replacement Pics