westija

Need some help from the experts with a question about Intake Air Leak test.
I'm finishing my Intake Refresh and after so much fun with some challenging parts I came to the point to test for leaks, using Dwayne's instructions and device.
My intake is not holding pressure (it starts to build a bit but does not go beyond 1 psi and drops to zero in seconds- I'm using a bike manual pump as I do not have a compressor).
The question is: if by chance one of the cylinders is at the position in which we have an exhaust and intake valve overlap (both opened), I would not be able to maintain pressure, would I?
So, could there ve a condition in which pressure would not build up and yet have no intake (or somewhere else) leaks?
As I don't have a compressor, the low build up I got doe not show a leak that I can find.
Thanks

Mike Frye

I'm pretty sure there is no intake and exhaust overlap.

The intake should maintain pressure and if it's not, you've got a leak I'm afraid.

If you can't find it by pressurizing the whole thing, maybe take it apart and work in pieces. It's going to be a long and tedious process, and don't think that when you find one, that you're done. I found 3 or 4 big leaks and one or two small ones when I did my intake refresh.

You might also want to post the year and some details of your car, it will make it easier for people to give you more detailed responses.

Herman K

Sounds like you put the intake back on already? When you did the intake refresh and when it was of the car did you replace the TB valve and flappy bearing with new double side seals beside all the vacuum hoses and rubber connectors?
I did mine early this year and just found a clean brake ( sheared-off ) from the DS elbow plastic fitting connecting the brake booster see ( https://rennlist.com/forums/928-foru...w-stopped.html )

still may have to check the hose running from my ISV to TB to get steady idle at 675RPM.

Good luck

Dwayne

I agree with Mike - I don't believe there is any overlap. I've used the pressurization device many times without regard to crank position and it has always held pressure when all leaks have been addressed. Even if there were specific locations of overlap, you could always rotate the crank a bit and try again. But as Mike suggests above, you probably have a leak.

If you do not have a compressor, I would recommend using a solution of distilled water with a few drops of soap (such as dishwashing soap) in a spray bottle and spray hose connections, mating surfaces, bearing locations, fuel injector o-rings. Then pressurize with your pump and look for bubbles. If you can borrow a compressor, that would help give you more time to look for leaks while the system is depressurizing. I suppose you could get another person to continually pump the hand pump while you inspect for bubbles or leaks. Hope this helps.

FredR

I must be reading this lot half asleep! Are you chaps telling me that with 8 cylinders firing in rotation there is actually a point in the cycle where all the valves are closed?

That does not tally with my experience- if you want to run this test you simply have to put plenty of air in so that you can accumulate a [very] little pressure and thus tell if there are any leaks. I would think the 45degree BTDC position is the best position to do this given no valve can contact the piston at this part of the cycle [32V motors].

Even then it is not a perfect test as you want it to hold vacuum not positive pressure unless of couse you are FI'd but the idea is that you should be able to hear hissing from any localised leak correct me if I am wrong.

A bicycle pump? I'd like to see that one [LOL]- your forearms will drop off unless you are well practiced in cyclical arm strokes!

Regards

Fred

westija

Thank you for the tips guys, I will keep trying.

The car is a 89 5-speed S4.

I have followed Dwayne's write-up practically 100%, as I agree with everyone here that he does an awesome job documenting the repairs for us, non-experienced owners.

I replaced all gaskets, vacuum hoses and elbows, valve covers gaskets, injectors' seals , throttle and flappy bearings, return fuel line, besides some unrelated to the leak parts, such as Crank Position Sender, Knock Sensors, ISV (although mine seemed to be good). I bought parts from Rogers and except for a couple of fuel lines, I used his recommendation in terms of parts. The only hoses I have not replaced are the ones that connect the Air Filter Box to the Air Diverter valve and the ones that go from there (rear passenger side) to the front solenoid.

You are correct, I re-installed the Intake and am at the point that I am testing for leaks prior to installing the Fuel Rails and Air Filter (I'm on page 323 out of Dwayne's 353 write-up - almost there). I am using the spray bottle test to find the leak by looking for bubles and foam movement close to the joints, clamps, gaskets, etc.

I might have to bite the bullet and make an investment on a compressor. You are right that my forearms are killing me. And with such a low pressure that I can build, listening to leaks is impossible.

If there are valve overlaps, based on what you say, I would still have - with some good pressure from a compressor - leaks somewhere that I could detect.

Thank you for the tips and keep them coming if you think about something else. I need all the help that I can get.

Mike Frye

Nope, they don't have to be all closed. There just isn't a position where the intake and exhaust valves are open on any given cylinder at the same time. That's all you need. If the intakes are open the exhausts are closed on that cylinder and vice versa. Cam timing on a stock cam ensures this (pretty sure Jim B confirmed this in thread I had going about intake pressure testing.)

FredR

Mike,

According to Professor Louie the exhaust valves are open for longer than 90 degrees so de-facto something open somewhere no matter what. Doubtless some crank positions minimise the degree of opening thus why the need for a compressor to drive some volume through the system to accumulate a little positive pressure as it were. When I tried this procedure out of interest [no known problems] I struggled with a small compressor to accumulate any measurable pressure.

If known experience suggests otherwise fair enough. Louie was referring GT cams. Whether that makes a significant difference to the opening duration in terms of crank degrees I do not know. According to the workshop manual the S4 exhaust valve opens 17 degrees before bdc and closes 2 degrees before TDC which according to my arithmetic means it is open 105 degrees*8= 840degrees or 120 degrees more than two revolutions.

Regards

Fred

westija

Well, I bought the comporessor and found one leak so far.

I'll replace the gasket and continue the search, as the pressure leaking here was not too high , but could not hear or see more , so far.

Maleficio

Interesting approach. I wonder if it help by jamming a potato into the tail pipe?

Maleficio

Pressurize the entire system front to back with smokey air and look for leaks?

17prospective buyer

Lol smoke test, that's actually a good idea. Go to a shop and see if you can use their smoke tester for half an hour!

Fogey1

For this purpose, I'd think duct tape and the exhaust port of a shop vac are your friends in pressurization. You won't be able to listen for leaks very well with all the racket but ...

Maybe even a smudge pot at the intake port to initiate the smoke test.

Or make a bellows-type bee smoker that moves a lot of air.

17prospective buyer

Why not the exhaust test ports that come directly off the manifolds? Only problem is i don't think the smoke produced from a smoke machine actually rises. Wait what about the vacuum source for the vacuum system on the intake? Surely that would work for your smoke tester?

Mike Frye

He's using Dwayne's write-up. I think he's covered for suggestions.

The hard part is slowly and methodically going through and fixing each one (or isolating part by part, which is also quite slow) and then going back in.

Until you get them all, you aren't done, no matter how many you find and that's the hard part.
I found leaks in:
>>Oil filller cap O-ring
>>Oil dipstick (at the handle and at the base where it goes into the block)
>>Throttle body O-rings (the sides where the throttle plate comes through the throttle body has O-rings that were brittle and not sealing)
>>various leaks from hoses that go for the ISV and to the side of the oil filler neck.

This was after a complete intake refresh that included EVERY intake part including the cam cover gaskets, the washers for the intake bolts and the seals for the cam cover vents.

For me, the only way that worked to pressurize it was to pressurize my compressor tank then TURN OFF the compressor so it didn't kick on while I was pressurizing the intake because when the compressor kicked on I couldn't hear it leaking out anywhere.

Patience, grasshopper. It will be worth it. You will be rewarded with a smooth running and dependable car that will run well for years...