Turbo intake pressure test

[amrbose14]

Has anybody out there tried this?

Following a you-tube video (https://www.youtube.com/watch?v=AL3jbcrqY8g) I made myself a cap to fit into the 'J-boot' and connected it up to a compressor.

I have to say I'm a bit puzzled. I thought I would be able to actually pressurise the system, but I'm not sure it build any pressure. I have a couple of pressure gauges in the system, including one fixed into the adapter in the J-boot. None of them register any pressure at all when the line from the compressor is open.

According to the video this also pressurizes the crank case. Certainly air comes out the filler cap if I remove it. I guess that might make it difficult for the system to hold pressure. The other alternative I suppose is that the system is shot full of leaks, but the car does generate boost on the road so I think not.

Despite this I can use it to find leaks! There's one in a pipe junction under the manifold, and my cycling valve also seems to leak.

Does anybody have any experience of this? I'm not sure how much further I can take the diagnostic as it's difficult to see/hear/spray soapy liquid very far under the manifold.

This is really just a preamble to replacing the vacuum hoses... but I wanted to try the diagnostic first. I'm not sure if its working or not at this point!

Chris

220T

 

[944Scott]

I have just done this and I could not hold pressure either. I did manage to maintain a constant 1 bar from my air compressor which allowed me to search for leaks. I found about six in the end, a couple of odd ones were a leak from the body of the idle control valve and one of the connection points for the hoses that connect on to the inlet manifold had become loose and had to be bonded back in place.

 

[TTM]

Did this a couple of years ago on my rebuilt engine, we put up to 4 bars which it held remarkably well, but normally you shouldn't need more than 2, and anyway the pressure well necessarily decrease even on a new engine, but by then it's the rate of decrease that is interesting to watch. Ok it was easier in my case as the device we used also generated smoke in addition of pressure.

Throttle body seals are often overlooked. The hose coming out of the AOS is often cracked from below when it has not hardened like stone after years of heat cycles. The cycling valve leaks from new. The J-boot also happens to crack though it's not always easy to spot.

 

[Eldavo]

I hate threads like this as I always end up writing another item onto the "to-do" list on my garage whiteboard!

 

[amrbose14]

It seems like a method worth mastering. However at the moment I'm not sure it is much better than squirting soapy water with the engine running. I could hear the leak from around the cycling valve (which would be impossible with the engine running), but ultimately it was the soapy water than localised the leak.

Are there any obvious sources of leakage I should be checking? How does the air get into the crank case?

I also gather there is a point in the 4-stroke cycle where inlet and exhaust valves are both open slightly. I'd have thought I would have been unlucky to stop the car at that point.

Chris

 

[bmnelsc]

ORIGINAL: amrbose14

...
I also gather there is a point in the 4-stroke cycle where inlet and exhaust valves are both open slightly. I'd have thought I would have been unlucky to stop the car at that point.

Chris

Yes there is - valve overlap is common in all engines. The intent is to start opening the intake valve while the exhaust is still "exhausting" which helps create some suction on the intake side for better cylinder filling. Remember that this is happening on each cylinder once per two crankshaft revolutions so I think its pretty easy to hit that point.

Firing order 1-3-4-2
Cyl 1 Cyl 2 Cyl 3 Cyl 4
TDC comp BDC power BDC intake TDC exhaust
BDC power TDC exhaust TDC comp BDC intake
TDC exhaust BDC intake BDC power TDC comp
BDC intake TDC comp TDC exhaust BDC power

 

[Eldavo]

I've got a vacuum manifold with everything on it's own feed so can easily disconnect a port and use that to pressurise the system with the engine off.

Given you can buy an external one for a tenner or so on eBay and bolt it to the firewall I'm amazed more people haven't done it.

 

[amrbose14]

So given the car is immobile, and the air flow meter and air box is off, can I just pull the main ht lead and crank the engine for another try at the lucky dip?

ORIGINAL: bmnelsc

ORIGINAL: amrbose14

...
I also gather there is a point in the 4-stroke cycle where inlet and exhaust valves are both open slightly. I'd have thought I would have been unlucky to stop the car at that point.

Chris

Yes there is - valve overlap is common in all engines. The intent is to start opening the intake valve while the exhaust is still "exhausting" which helps create some suction on the intake side for better cylinder filling. Remember that this is happening on each cylinder once per two crankshaft revolutions so I think its pretty easy to hit that point.

Firing order 1-3-4-2
Cyl 1 Cyl 2 Cyl 3 Cyl 4
TDC comp BDC power BDC intake TDC exhaust
BDC power TDC exhaust TDC comp BDC intake
TDC exhaust BDC intake BDC power TDC comp
BDC intake TDC comp TDC exhaust BDC power

 

[amrbose14]

I've gathered that you can pressurise the system upstream, but unsure how to do it.

ORIGINAL: Eldavo

I've got a vacuum manifold with everything on it's own feed so can easily disconnect a port and use that to pressurise the system with the engine off.

Given you can buy an external one for a tenner or so on eBay and bolt it to the firewall I'm amazed more people haven't done it.

 

[944Scott]

Could you not just block off the exhaust?

 

[Eldavo]

You can see mine in the top left of this picture - everything is on it's own vacuum line with no T-pieces.

Something like this would do the job: eBay link

You can then use a spare port to pressurise the system.

 

[Indi9xx]

We use a a cupboard full of gizmos for this.. We have a regulator and loads of fittings for putting different amounts of compressed air into engines, as well as a vacuum pump for pulling a vacuum, along with oil filler caps, coolant caps, varios expandable bungs, a smoke machine which pressurises oil based smoke for leak detection as well as varios gas canisters, but the lengths you sometimes have to go to so you can find a leak, especially an intermittant leak is crazy.

If you think a 944 turbo can be a nightmare to track down intake leaks, you should mess about with 996 and 997 turbos where the intercooler hoses often leak.. the back bumper needs to come off to actually see the intercoolers in the rear quarters, let alone the trouble finding leaks in anything under the intake manifold.

 

[amrbose14]

Good idea. It would need to fit nicely to be airtight but worth a go.

ORIGINAL: 944Scott

Could you not just block off the exhaust?

 

[amrbose14]

I found it hard enough to find a bit of plumbing tube suitable to fit in the J-boot. Actually it's two bits glued together. Plus I'd never played with compressed air much so I have a collection of those fittings now...by the time I know what I'm doing it would have been cheaper to pay a professional to replace all the vacuum lines (the ultimate goal) for me!

ORIGINAL: Indi9xx

We use a a cupboard full of gizmos for this.. We have a regulator and loads of fittings for putting different amounts of compressed air into engines, as well as a vacuum pump for pulling a vacuum, along with oil filler caps, coolant caps, varios expandable bungs, a smoke machine which pressurises oil based smoke for leak detection as well as varios gas canisters, but the lengths you sometimes have to go to so you can find a leak, especially an intermittant leak is crazy.

If you think a 944 turbo can be a nightmare to track down intake leaks, you should mess about with 996 and 997 turbos where the intercooler hoses often leak.. the back bumper needs to come off to actually see the intercoolership in the rear quarters, let alone the trouble finding leaks in anything under the intake manifold.

 

[amrbose14]

That sounds like an amazing idea. Presumably you can then dispense with most of the next of tubing under the manifold? Of course it relies on knowing what you're doing, which I clearly don't at the moment.

Nice idea though.

ORIGINAL: Eldavo

You can see mine in the top left of this picture - everything is on it's own vacuum line with no T-pieces.

Something like this would do the job: eBay link

You can then use a spare port to pressurise the system.

 

[944Scott]

ORIGINAL: amrbose14

I found it hard enough to find a bit of plumbing tube suitable to fit in the J-boot. Actually it's two bits glued together. Plus I'd never played with compressed air much so I have a collection of those fittings now...by the time I know what I'm doing it would have been cheaper to pay a professional to replace all the vacuum lines (the ultimate goal) for me!

ORIGINAL: Indi9xx

We use a a cupboard full of gizmos for this.. We have a regulator and loads of fittings for putting different amounts of compressed air into engines, as well as a vacuum pump for pulling a vacuum, along with oil filler caps, coolant caps, varios expandable bungs, a smoke machine which pressurises oil based smoke for leak detection as well as varios gas canisters, but the lengths you sometimes have to go to so you can find a leak, especially an intermittant leak is crazy.

If you think a 944 turbo can be a nightmare to track down intake leaks, you should mess about with 996 and 997 turbos where the intercooler hoses often leak.. the back bumper needs to come off to actually see the intercoolership in the rear quarters, let alone the trouble finding leaks in anything under the intake manifold.

I found that an 80mm diameter oil filter removal tool was a nice tight fit in the J boot, I also drilled a hole in it and fitted a Schrader valve.

 

[amrbose14]

There's a broken link to a write up on vacuum line replacement on the pelican parts forum. Does anybody happen to have it? By all accounts its very good.

Chris

 

[Eldavo]

Easiest way for me was to find the diagram that matche your setup on the Lindsey Racing site in their tech tips section and then go through each item methodically.

For example, unplug the line on the FPR and connect that directly to the vacuum manifold, then see what else the removed line tees into and unplug that too and put it in it's own line.

As I've got a Turbo S the intake manifold has 2 banjo bolts connections instead of 1 anyway and I found that I only needed 4 feeds from the vacuum manifold to do everything until I fitted my EBC and then used the 5th for the pressure sensor for that.

 

[TTM]

ORIGINAL: 944Scott
I found that an 80mm diameter oil filter removal tool was a nice tight fit in the J boot, I also drilled a hole in it and fitted a Schrader valve

I use an old fuel filter that I cut in two. Nice thing is that the fitting is already there for a connection to some source of pressure.

 

[amrbose14]

I find myself wondering why I didn't post BEFORE I went scouring Wickes for bits of drain pipe!

ORIGINAL: TTM

ORIGINAL: 944Scott
I found that an 80mm diameter oil filter removal tool was a nice tight fit in the J boot, I also drilled a hole in it and fitted a Schrader valve

I use an old fuel filter that I cut in two. Nice thing is that the fitting is already there for a connection to some source of pressure.