2 PSI of Boost, but no blink code. Borrow KLR in MA?

[benzor]

HI Folks -

I've been working on low boost for a year, many posts here. Car is stock. The summary:

- Replaced all vacuum lines, but not Jboot. Link.
- Pressure tested at intercooler inlet, holds boost at 12 PSI (aftermarket gauge in car)
- Tested CV on bench, clamped line to WG, no change in boost
- Tested WG: xover pipe cold, actuate WG via external pressure, xover pipe warm. Good click when pressure removed suddenly
- BOV holds vacuum (new)
- Blink code tester on car, blinks when throttle signal removed, but intermittent blink or no blink otherwise.
- Turbo was off the car last year, vanes seemed fine.
- ISV seemed a bit leaky (blowing backwards through) on the bench, but car held 12 PSI for a couple minutes so I discounted it. Link.
- On a cold start, there was an exhaust leak under car near xover, but seemed to disappear when car warmed. I only checked at idle.

I'm wondering if the KLR could have failed, limited boost, but then no error code shown? I'm in Boston, MA in case anyone could lend a KLR to test.

The other hypothese I have not tested are:
- Exhaust leak (see above)
- Collapsed exhaust pipe
- Weak spring in waste gate - not sure how to test.
- Could a leak in the Jboot cause this behavior?

[Dean924s]

Collapsed Cat ?

[benzor]

I guess that's on the list - we'll see how rustwelded that exhaust is !

[cockerpunk]

big header leak?

[notMyScreenName]

Originally Posted by benzor

clamped line to WG, no change in boost

* * *

I'm wondering if the KLR could have failed, limited boost, but then no error code shown? I'm in Boston, MA in case anyone could lend a KLR to test.

If clamping the line to the WG does not affect the boost then whatever the KLR/CV is doing when the line is unclamped is not controlling the boost anyway. With that line fully clamped the max boost should go way,way up (it becomes very difficult for the wastegate to open with that line fully clamped). For now, I think I would concentrate my efforts downstream from the cycling valve.

[benzor]

Downstream of the cycling valve ie. WG with a weak spring, exhaust leak, cat, turbine failure, etc?

What's really poisoning my brain is the idea that a computer fault is holding it at 2 PSI - sounds like such an easy fix ! I guess it was not to be.

[kdjones2000]

Sounds like a leaky wastegate.

Collapsed exhaust "generally" only happen on high HP cars. I wouldn't rule it out completely, but less likely.

[benzor]

Will be retesting the bypass tonight to see how hot it gets.

kdjones2000, how many hours do you figure to remove a rusty wastegate? 3 hours?

[kdjones2000]

You have the 1-piece crossover?

3 hours at least...

[benzor]

Probably have the 1 piece (can't remember) - I have an '86, and I understand they didn't change to the 2 piece until later.

[benzor]

Looks like LR optimistically says 1-2 hours to remove and reinstall a WG! But they weren't pulling the original LINDSEY WASTEGATE at LINDSEY RACING - Your Porsche Performance Parts Center

[notMyScreenName]

Originally Posted by benzor

Downstream of the cycling valve ie. WG with a weak spring, exhaust leak, cat, turbine failure, etc?

Yes. At this point I don't think that there is any good way to know if the KLR and CV are working correctly but if fully clamping* the line to the WG doesn't give lots and lots (dangerous amounts) of boost then almost certainly I think something else is likely wrong.

What's really poisoning my brain is the idea that a computer fault is holding it at 2 PSI - sounds like such an easy fix ! I guess it was not to be.

I totally sympathize.

As for removing the WG... I recently had mine off and if the fasteners are in good shape it's not hard. If they are badly rusted or break off, however, it's pretty bad (ask me how I know).


*Be really sure that nothing is getting past the clamp. If the CV or KLR has failed then the CV should be in a failsafe state that applies some pressure to the WG diaphragm - which tends to push the WG open. I've never actually seen this happen myself but according to the documentation the failsafe state will limit the boost to about 1.2 bar (about 2.9psi). Anyway, if air is getting past the clamp it could affect the test. For the test to work you want the WG diaphragm to be trying to pull a vacuum against the clamped spot as the valve tries to open, thus making it really hard for the valve to open.

[benzor]

Well, some fairly obvious progress tonight. I have an exhaust leak in the crossover pipe. I had felt it before, but the black stain on the oil pan gave it away.

The leak is right the bottom - anyone know if this can be welded when on the car?



Incidentally, while I was there, I noticed that the heater valve is leaking and dripping down. Hopefully I haven't toasted the clutch in the process, will have to replace it ASAP.

[benzor]

I'm taking the waste gate off while I'm in there, so we'll bench test it to see how its doing.

[benzor]

Wastegate tested out fine, opens at 5PSI, no other obvious leaks.

I called around to a couple of shops - they said it was likely I would need to take the crossover pipe off in order to weld it - see photo above. Even if it is on the seam (as opposed to the top of the xover), there is only 3-4 in of room to the oil pan.

[DannoXYZ]

the default state of the CV is fully OPEN and pumping all manifold pressure to wastegate. This will have effect of opening wastegate and dumping all boost.

When system is working correctly, the KLR sends a PWM signal to CV to divert pressure away from wastegate back to intake. This then closes the wastegate and builds boost.

In this case, with hose between CV and wastegate clamped and no boost, would seem to indicate a weak wastegate spring and/or clogged exhaust.

With cooperative bolts, wastegate removal is 15-min with 1-piece crossover. Just be sure to remove the 3 hanger bolts, the dump-pipe bolts in addition to the wastegate-to-crossover bolts. Then disconnect exhaust from downpipe and slide back. You can then slide the wastegate back also to remove. Check out this recent recent Exhaust Crossover Removal thread.

Simple test at this point is to bolt in a block-off plate to the crossover at the wastegate port. With no wastegate in place to dump exhaust, you should get +25psi boost easily. If not, then bad turbo or collapsed crossover inner tube.

Although in this case, it appears the crossover leak can be significant enough cause low boost.

[notMyScreenName]

Originally Posted by benzor

Wastegate tested out fine, opens at 5PSI, no other obvious leaks.

I called around to a couple of shops - they said it was likely I would need to take the crossover pipe off in order to weld it - see photo above. Even if it is on the seam (as opposed to the top of the xover), there is only 3-4 in of room to the oil pan.

Be sure to tell the welder that the crossover is made from Inconel (specifically Incoloy 800) so that he/she can use the correct filler. I once had a welder use the wrong filler on an Inconel exhaust part and it immediately (before even being put back on the car) cracked. Some guy on another forum went so far as to have the crossover material analyzed to be sure. The heat shield is stainless.

[kdjones2000]

Someone is selling a 2-piece crossover for I think $100 on this forum. Just get one of those and put it in...

944/951 Parts

[benzor]

Thanks for all the suggestions on finding the leak. I've done a bunch of work, but haven't fixed it yet.

- I bench tested the WG. Starts to open at ~4-5psi, couldn't see anything obviously wrong with it. I didn't take it apart or attempt to shim it.
- I pulled the xover pipe and inspected it. The exhaust leak was coming from the test fitting, which is now plugged with a new lug nut. Rolled a golf ball through the xover, that's not collapsed.
- There was a small exhaust leak also at the manifold to cross over, replaced with new stainless steel rings.

The car now boost to 5psi (2psi at 3200rpm, 5psi at 4750rpm).

- I pressure tested the intake again, found a pinhole leak on the intake, now fixed.
- I re-ran the test with the clamped CV line, no difference.
- I manually checked the turbo - spins fine, no obvious damage, no end play. Was apparently rebuilt by PO.

So from the above suggestions:

- Have a block off plate made the the WG and test
- Check headers for leaks

Any other suggested tests?

[DannoXYZ]

From your testing, we can assume the following:

- WG is fine, quite good actually. Most WG I've seen with this age starts opening at 2-3psi.
- WG control isn't an issue, since pinching off the hose still doesn't raise boost
- issue is exhaust-related as indicated by boost going from 2->5psi when test-fitting plugged.

Just to confirm WG isn't leaking exhaust, an easy block-off plate can be made using electrical-panel plate. The kind that's used to cover junction-boxes. Trim the 4x4" plate down to same dimensions as WG flange, drill 4x holes for mounting bolts. Slip in between WG and flange and bolt all together.

Now if boost doesn't build, we can assume it's turbo, downpipe or exhaust after that. I've seen collapsed inner-walls on the downpipe and the section between downpipe and catalytic can get squashed from being bashed on speed-bumps.

Or catalytic may be clogged? Simple enough to remove it for a test drive, will be really LOUD, but will be quick and simple test of catalytic & catback exhaust to rule those out as contributing factors.