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

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?

Collapsed Cat ?

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

big header leak?

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.

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.

Sounds like a leaky wastegate.

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

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?

You have the 1-piece crossover?

3 hours at least...

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.

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

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.

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.

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?

http://forums.pelicanparts.com/uploa...1412653125.jpg

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.

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

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.

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.

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.

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

http://forums.pelicanparts.com/porsche-924-944-968-used-parts-sale-wanted/820677-944-951-parts.html

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?

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.

I had a very similar problem and it turned out to be a clogged cat.

DannoXYZ -

Thanks for the rundown. Have purchased a 4x4 junction box cover - nice trick. I was always visualizing a thicker plate with the pipe behind removed, but you've solved that by sandwiching.

Will thereafter take a look at the downpipe / cat. I had the turbo off 2 years ago, annoyed that I didn't look down the downpipe.

Will have to figure out where the downpipe separates from the cat

My car was maxing out at 5psi....found it to be clogged cat. I actually put a piece of steel across the WG's piston to stop it from opening period, still did not fix the boost. When I finally took the cat off it was almost totally blocked. This was a piece that came out of the cat.
Sox
http://forums.pelicanparts.com/uploa...1418276858.jpg

That was the answer! Took the cat and downpipe off, car acceleration and boost were all there. And it was loud! Prior to that, I had blocked the wastegate off with a flange, did not make a difference. Man, was it exciting to drive the car with full boost - I wanted to stay out longer, but it was going to break some windows if I did. I've been looking for this issue for at least a year - Danno, looks like I owe you a beer if you find yourself in Boston!

At this stage, unclear to me if its the downpipe, the cat, or both. Here's the evidence:

1. Can't roll a golf ball through the downpipe (diameter 1.68 in, but I could put a flashlight through (diameter 1.25in). External diameter of pipe is 2.12 in, so seems likely it collapsed at the corner, where it goes from vertical to horizontal under the car towards the cat.

2. I was able to see light through the cat - like 16 pixelated cells out of 10,000 - see picture below. Surface didn't "look" clogged. First picture in cat is with flashlight on engine end, no light used on rear end. Second picture includes light from rear as well, to show relative size of 'light hole' coming through the cat.

So my hypothesis is just downpipe, which means I need to find a muffler shop to cut it off and weld in a new section? Or better to but a new downpipe?

http://forums.pelicanparts.com/uploa...1418508354.jpg
http://forums.pelicanparts.com/uploa...1418508376.jpg
http://forums.pelicanparts.com/uploa...1418508397.jpg

Reading RL, technically I should be calling this the 'cat-pipe'. The turbo outlet pipe is still on the car, and was not collapsed.

I have the pipe you need that was removed at 70k. The cat was replaced 1k miles before I removed it so it is almost new.

PM me if interested.

Glad you found it!

Also thanks for sharing your efforts.... Helps us all build the community.

Mike

Glad you found the problem! That section between the downpipe and cat is problematic. It gets crushed easily and can collapse internally.

We used to live in Boston! Cambridge actually back in the '70s when my dad was at university. Looking forward to visiting some time; I miss the snow! And I skating on the Charles!

Uh-oh! Found out tonight that I also needed the cat-back exhaust. I put the new test pipe on, with no change. Took off the muffler, full power. Annoyingly, the top section of the exhaust muffler pipe was collapsed, from below it was still round and intact.

Will now be looking for mufflers!

That sounds like your catalytic converter honeycombs have fallen apart and blocked your exhaust.

I have never heard of a cat-back collapsing due to heat, only the catalytic converter pipe, and only in high HP situations.

I was surprised as well. However, it is not the cat, because I did the test last night with the cat-pipe installed, only the muffler removed.

If I get a chance, I'll post a picture of the the collapsed muffler pipe tonight. Was not a stock muffler, was an ANSA.

New muffler is on, all other pipes the same, and car is working great ! So it was definitely the muffler. Going to have some fun cutting it apart tomorrow to figure out.

For interest, here is the muffler that was blocked. Chock full of knotty fibre.http://forums.pelicanparts.com/uploa...1421201933.jpg

What is that? Did the muffler come apart internally?

Could be a fibreglass-packed muffler. Could've gotten blown around over time and clogged one end.