Porsche-O-Phile

Latest update on my 951 "n/a". . .

I pulled the wastegate off to check it - it is okay. The valve starts opening at about 8psi or so (gauge on the air compressor isn't very accurate), but it does open. The diaphragm and hose hold pressure and vaccum perfectly with no loss.

When I pulled the CV off, I noticed that the nipples were all busted off; a replacement is on the way courtesy of NZ951. . .

According to Clark's Garage, the exhaust gas normally should force open the wastegate valve at pressures above 1.2 bar and that in the event of a CV failure, that would be the maximum attainable. The values I'm getting as a maximum are about 1.15-ish (maybe it's 1.2) bar. As such, I think everything is okay (other than the CV). My question is, how does the system accommodate pressures above 1.2 bar? If the wastegate spring is overcome by boost pressures above 1.2 bar, then does the CV switch somehow from carrying pressure to the wastegate (forcing the CV open) to carrying vaccum (forcing the CV closed)? This seems to make sense, since it has a pressure (banjo) and a vaccum (J-boot) source.

I've also heard that if you "pinch off" the wastegate line from the CV on a 951 that's working properly, you'll obtain maximum (unrestricted) boost since there's now no way for the CV to force the valve open by pushing pressure to the wastegate. That said, why would the wastegate be able to exceed 1.2 bar, since the CV would similarly have no way of holding the valve closed (via vaccum) at pressures above 1.2 bar?

Am I missing something? Someone explain this plz.

Gator_86_951

The cycling valve has a duty cycle which will dictate where you are running boost pressure to the wastegate or intake. In this way you control how much boost the intake side is seeing. This is my general guess on how this works, the specifics of it with the KLR should be directed at somebody that didn't think about it for like 5 minutes.

This is a duty cycle (Bad illustration)

_____|-------|_____|-------|_____|-------|_____|-------|_____

So when the line is up (for instance) wastegate, when the line is down (intake). The duty cycle is the usually expressed as the percentage of time a signal is expressed for a given period. So, in this case, a lower duty cycle would give more boost. I hope maybe this helps.

Porsche-O-Phile

I think I might have figured it out. Let me know if this sounds plausible:

Under normal conditions, the exhaust gas is pushing down on the valve in the wastegate trying to force it open, but the spring doesn't allow it to move until 1.2 bar. At this point, the exhaust gas pressure is high enough to overcome the spring, but if the valve tries to open, the diaphragm has to move down with it. As the diaphragm tries to move down, it creates a vaccum in the wastegate-to-CV line. If the CV is in its normal "open" state, there is nowhere for the pressure in this line to go and the vaccum or otherwise lowered pressure in the line created by any movement of the diaphragm will contribute to "fighting" the valve's movement and the valve will stay shut well above 1.2 bar.

In my situation, the wastegate-to-CV line is open to the atmosphere. As such, when 1.2 bar is reached, the exhaust gas just overcomes the wastegate spring and shoves the valve open, dumping out the exhaust pipe. This is possible since the valve moves down, moving the wastegate diaphragm down (as described above), but there is no reduction in pressure above the diaphragm to resist the movement, since the other end of the line isn't plugged. As the pressure drops, ambient air pressure rushes in to replace it - nothing "fights" the movement, and the valve opens and the boost is limited only to what the spring in the wastegate can provide.

There's a simple way to test this - clamp off the wastegate hose. This is exactly what Clark's Garage says to do, but the distinction I didn't see before is "clamp off" versus "disconnect". There might be a very big difference. I'll reconnect everything tomorrow and put my hand vaccum pump on the wastegate hose and put a partial vaccum on the line to see if boost jumps up when I rev the engine. If so, this will go a long way to my (and hopefully others') understanding of exactly how this system works. If not, it's back to the drawing board, but this analysis seems to explain all my symptoms and observations and what I've read and been told up to this point.

UK952

Are Clarks garage talking 1.2 bar above atmospheric or 1.2 bar on the guage 0.2bar?
As far as I am aware the factory wastegate only gets a pressure signal to open from the cycling valve (or no signal to stay closed).
With a boost enhancer or reliaboost this signal is held off until the preset pressure is reached.

Did the actual valve look ok on the wastegate was it seating properly?

0.2 (1.2 on guage) sounds like the maximum you would see with the cycling valve saying open - should be the same as connecting the banjo bolt on the hard pipe to the wastegate opening port.

Have you got your new intake hoses yet?

For you to be loosing so much boost (if its being generated - I.e. exhaust not going out the wastegate bypassing the turbo) you want to look carefully at the pipes aound the inlet side of the engine.

Ideally pressure testing the system but if this is not available check carefully,

The pipe that comes out of the turbo to the hard pipe.

The hard pipes themselves (I have seen one holed underneath though only small hole),

the rubber couplings to the intercooler,

The intercooler, does it have rock damage on the front is it heavily corroded?

The large pipe to the intake from the hard pipes.

The pipe to the divertor valve ( and the 'plunger' inside the divertor valve to make sure it is seated and not allowing air back through to the J boot.

The pipe that comes off the hard pipe to the idle stabiliser? (sorry doing this from memory could be inlet manifold).

The inlet manifold itself any open pipes?

And the connection from the hard pipe banjo bolt to the metal line that runs under the manifold to the cycling valve.

If all else has failed I would be tempted to plug the banjo bolt hard pipe take off and the the line to the wastegate and see if you still fail to raise any boost.

Also try removing the thin pipe (and plugging it) from the divertor valve to ensure its not opening early for some reason.

I guess you could also try plugging the large pipe to the divertor valve

If this fails to raise any boost, I would check the turbo spins freely by removing the J boot and turning it by hand.

A leaky J-Boot is not good - it allows unfiltered and unmetered air into the turbo inlet but shouldn't affect the boost as it is before the compressor.

HTH
Tony

Porsche-O-Phile

1.2 bar on the gauge; atmospheric plus 0.2 bar. Factory spec is 1.75 +/- 0.05 bar max. boost.

Yep, looks fine. I cleaned it up a bit just to make sure it was sealing fine. I sprayed WD-40 in there and none leaked out so it was sealing tightly anyway, but it never hurts to clean stuff.

Well, if I ran the line directly from the banjo bolt to the wastegate pipe I would still protect the engine from overboosting but I'm not sure it would be much different from the present situation. I suppose it'd have the advantage of "plugging" the banjo line though. For the time being I'm just going to run the banjo line to the J-boot line which simulates the "open" or normal position of the CV for testing.

A few; I still need a couple more. It's a step-by-step process due to money and availability limitations. I've replaced the worst ones and I'm working on replacing the rest as I can. I get maybe one or two a week and will continue this until they're all changed out & new. AFAIK Nobody sells the entire set of hoses except for 944Online and they want something like $150 for it which I consider a rip-off. It'll actually be less at the dealership for the ones I need, especially once shipping costs are considered.

I agree. The stuff on the inlet side all looks pretty good with two exceptions. The hose from the stabilizer to the intercooler pipe is badly trashed to the point of being worthless. It's plugged off for the time being, as is the nipple on the intercooler pipe. The J-boot connections that look bad are sealed up well with silicone to prevent any foreign matter from getting sucked in there. I'm reasonably certain there are no leaks in the J-boot (I'll check it with the vaccum pump) but even if there is a small one someplace, it shouldn't affect boost level, since it's upstream of the turbocharger.

Replaced, it's fine now - brand new.

Tested it - it's fine. You can't blow any air through the diverter valve until you apply a vaccum to the connection point on top.

They're fine, I actually did check those too.

Ditto - those are okay. They're clamped tight too. I double and triple-check all the clamps before testing.

Nope; I have brand new intake gaskets (where it sits on the head) and new seals for the injectors where the fuel rail plugs in. All vaccum lines are connected. Intake is in good condition (no cracks or holes).

That connection is fine, although the hose at the other end of the metal line to the CV was trashed. Both of them in fact (there's one from the other metal line that goes to the J-boot). Those lines were so old and brittle they literally shattered into a million pieces when I tried to "disconnect" them from the CV before realizing they were already snapped off of it. They must've broken off cleanly at the CV nipples ages ago and never drew my attention because they had broken off cleanly. I'm certain they were leaking at that point though. The problem here is the CV - it's dead.

My thoughts exactly. I'm going to "jumper" the banjo line to the J-boot line (simulating CV "open state" position) and plug the wastegate line. I'll bet dollars to donuts I'll make boost above 1.2 bar.

Did that. Didn't change anything.

I could do that but I don't see what that would accomplish other than forcing boost into the engine during shifts and "spiking" the RPMs.

Turns fine, I checked it. No damage, no play.

Yep, I completely agree. I will eventually get a new J-boot but they're over $100 so it'll have to wait a while. The fixed one I have now will work okay for the time being, I'm certain no foreign objects can get in it, but I'll eventually replace it with a new one so it's fixed the "right" way.

Thanks for the input though.

Porsche-O-Phile

SOMEONE out there has to know the answer to this - what allows the wastegate to stay closed and build up pressure beyond the 1.2 bar limit provided by the wastegate spring? Is it the drop in pressure created above the diaphragm as the valve tries to move downwards and open or what?

fortysixandtwo

The wastegate is opend by pressurizing the diaphram. Now take that same diaphram and plug the port. The exhaust gasses would now have ot overcome the spring pressure (at ~1.2bar) AND the vacuume on the other side of the diaphram. The CV will let air in, to regulate the position of the wastegate vavle.

Porsche-O-Phile

Makes sense then. I get what's going on, it's what I suspected. Thanks. Amazing that all this comes down to cheap crap plastic pieces (actually it's amazing how many of my problems are caused by cheap crap plastic pieces). I swear, plastic has no place in automobiles except maybe for trim. It's only good for one thing - breaking.

The stupid plastic nipple connections on the CV caused all this crap. Grrrr. I'll plug the line and give it some throttle; I'll bet anything it'll build boost above 1.2 bar. I'll check into whether there's a way I can jury-rig the CV for the time being or not. Maybe I can get some plastic tee ends and jam 'em in there tight and silicone them enough to prevent leakage. If not, at least I know what the problem is now. Mucho thanks.

Tom M'Guinn

I have not read everything in this thread.... so if I missed it, just ignore me. But, have you tried clamping (the snot out of) the line that runs to the wastegate, and/or removing that line and plugging it? On a healthy car, doing that should result in way too much boost. If you are still low, then your trouble is making boost rather than controlling it (e.g., turbo, wastegate, exhaust leaks, etc.).

Porsche-O-Phile

My problem seems to be that the wastegate line was not "clamped off", it was disconnected - as in open to the ambient air. As such, my suspicion is that the only thing opposing the building boost pressure was the wastegate spring (no vaccum on top of the diaphragm) so at 1.2 bar, the valve opened and whoosh - out the boost goes down the tailpipe. I have materials to seal up the CV and provide a seal for the wastegate line; I'll test that but I'm willing to bet it builds boost fine once I do it.

Claus Groth

Jeff,

I repaired a CV by drilling the broken port to accept a nipple from a tube tee. I epoxied it in place and it held for years.

Bret 944

Jeff, I think I'm in the same boat as you, see my topic "I need help with boost". I've ordered a new diverter valve cause I know that things no good (failed the "blow" test). Next thing I need I guess is either a new CV (or some way to eliminate it). How much was the new CV, and where did you order it from ?

Porsche-O-Phile

Thanks guys - that's pretty much the repair I'm doing also - I picked up a few 3/16" vaccum connectors and have them siliconed in the three holes on the CV. I think they'll hold; they are pretty solid. If not, I'll try again using brass ones (the AutoZone I went to only had plastic ones, but they hold pretty well and I suspect once the silicone cures there won't be any blow-by). I will soon know. . . I'm taking a little breather and it's back down to finish bolting up the intake manifold and associated air plumbing and then road test it. If this ends up being the problem after all this, I'm going to have a good laugh - it's been a great learning experience though!

special tool

Dude - take that silicon and throw it in the river. SILICON??? And you have it all over the j-tube also?
Your cv jury rig is NOT going to fix anything. You will still have no boost. You have to put everything back to factory first at least.
And saying that Someone has to know? When you have glue stuffed in your intercooler-idle stabilizer???? Over the internet, no less. You HAVE to be 17 years old.
There is no magic miracle in the cv holding the wastegate closed - it is a very simple solenoid that the klr throws open when it thinks (not closed loop) the correct boost pressure should be there.
You are quikly approaching Hosrom gogo status, sport. Get a new cv for fort bucks, and fix everything correctly and stop fvcking around!!!!

Some of you kids over complicat the hell out of these cars. Don't. They are simple. Don't go reading Sport compact car about WOTM's Supra and think you stock 951 is ANYTHING like it.

-cranky this morning, no coffee yet

Bengt Sweden

Porsche-o-phile
Sorry but your assumptions are not correct.
First of all you do not have a good vacuum source in the J-boot and if you had you wouldn't know what the vacuum was at different situations. Even changing air filter would create a problem, remember that the KLR is controlling without feedback loop.

The WG opens at a certain exhaust gas pressure which occurs at a certain exhaust flow which is not directly related to the inlet pressure, i.e. it could be at inlet pressure of 1.2 bar above athmosperic at 3000rpm or .7 bar at 6000rpm since the exhaust flow is so much bigger at higher rpm.

1.2 bar above athmosperic is what you probably will experience if you remove the wg line. If your WG spring is not too old and weak you will go out of the scale on the stock gauge.

The connection to the J-boot is there to make sure that the measured air do not escape the system.

You can't create vacuum in the lines to the WG by pulling the WG valve ( or pushing with exhaust) the CV is not that tight. If you disassemble your old one you can see why.

Bengt