specsalot

I've just gotten my 88 951 up and running after a difficult no start. Electronics went bad, rebuilt DME/KLR. lots of other under hood PM work. The car is basically stock. I did opt for the Ransant chips sold by Specialized ECU when they had my electronics for repair. I've only had the car up and running for a couple weeks. I started noticing some loss in boost at WOT. Boost guage used to hit 1.6 or better under WOT. I took the car on its first road trip (160 miles) since the no start. Car ran OK on the highway, but it really started to be a dog in traffic under boost conditions. Boost gage was definitely flagging (not making more than 1.3-1.4 and exhaust note was also off. I'm going to elevate the car and do some test runs to verify waste gate leak by. When I had the pluming apart (fixing no start issues) the turbo seemed to be in good shape by feel, so I don't think I have a turbo issue. CAT is OEM, car has ~ 120K miles.

I figure I may have either a damaged seat / valve. Or more likely debris up along the valve stem causing the valve to hang up. My guess is that the new chips have up'd the exhaust temps a bit and contributed to the recent appearance of this problem.

Questions

1. Can the waste gate be dismantled / cleaned? I had a look at it years ago (while doing the clutch). It seemed a fairly primitive device. Obviously if I have damaged sealing surfaces I have to rethink any rehab efforts.

2. Anything else I may be missing in my thinking on this issue?

3. How much better are the dual port waste gates for these cars. Do they make sense as an upgrade if I'm retaining the stock Porsche timing valve and KLR boost limit controls?

Any recommendations based on experience with this issue?

specsalot

Took a nasty tumble helping a friend doing pool maintenance - bruised ribs. Won't be crawling under the car until I feel better which defaults me back to driving the hybrid. It's a nice car but its no 944. Updates / pictures to follow

Sixline

The easiest test to verify if the wastegate is sticking is to clamp off the line going to it. Go gently drive the car with it clamped and see how well it builds boost.

If it still won't boost over the 4-6 PSI that you were seeing then it's possible that the wastegate is stuck open, you have a pre-turbo exhaust leak, a piece of the double walled exhaust has collapsed, or you have a clogged cat.

If it boosts fine then it's possible that what you were seeing was the KLR pulling boost because of excessive knock. Possibly a bad tank of gas or something else electric failing(i.e. cycling valve or knock sensor).

I am not familiar with that chip that you mentioned. Did they give you a chip for the KLR as well? I am not here to force anything down your throat but I personally would of stuck with something a little more well known like Rogue Tuning or Vitesse. Who knows what they did to "improve" performance.

Lastly, I personally wouldn't bother trying to rebuild or service the 26 year old wastegate. Lindsey Racing can take it and turn it into a shiny dual port but why bother when you can get a Tial with adapter plates for less. Although more power to you if you want to attempt to fix it.

specsalot

Sixline - Thanks for your response Sounds like a good end to end summation of possibilities.

Regarding the chips, the DME and KLR both got new chips. I'm sure most of the (very minor) performance gain comes from boosting red line by ~ 500 RPM. The folks who sell the chips have a deep background in electronics repair, but they do not have the performance stature of Rogue or Vitesse. The car initially ran well and delivered decent MPG following the install. So I'm hoping the chips installed have nothing to do with this issue.

I had the waste gate off ~ 5 years ago when I did the clutch. I think I may have taken it apart back then to inspect it. If I find issues, I will probably not consider a repair. I think the valve unscrewed from the body (trying to remember), so it may have just loosened up. (but I think this is unlikely).

I can't rule out electronics issues or cycling valve problems, but I'm hoping these are not the issue. The exhaust note of the engine is definitely changed as this problem evolved, as if lots of exhaust was shunting by the turbo. That said, nothing in the change in exhaust note suggests an exhaust leak. Plugged cat is possible, but the on-set of this condition is relatively sudden (maybe 5 hours total drive time).

Thanks for your input. I'll post continuing results of my investigations into this situation. I don't have any reason to expect I have a turbo issue, but the right sequence of malfunctions could easily damage the turbo. Up till now the turbo has always performed well. When I've had the plumbing off, I've always grabbed the rotor for a quick feel. Always smooth turning and slop free.

Laust Pedersen

You can test your specific concern of a sticky wastegate (WG) without starting or crawling under the car, by finding and disconnecting the direct control line for the WG. Then pressurizing the line with 10 to 25 psi, listening for it to fully open, release the pressure and listening for the valve to hit the seat.

With this simple method you can also check for hose and diaphragm leaks and exercise the valve to get it unstuck, if it was stuck and the leaks were small.

Other failure types are loose seat, cracked seat and bad valve-seat sealing, although they are rarely bad enough to significantly lower the boost pressure.

Here is a reference to the collapsed double walled exhaust that “Sixline” was talking about.
https://rennlist.com/forums/944-turb...aust-pipe.html

Laust

specsalot

Thanks Laust,

I was helping a friend test his electronics and haven't had time for the car otherwise. That sounds like a good test for the mechanicals.

While I had the computers unplugged, I tested the electrical value for the knock sensor. Its supposed to read ~ 270K ohms to 330K ohms when measured between KLR Plug Pins 11-13. Mine reads ~ 4.6M ohms. I also shunted the sensor connector pins and verified continuity of the wiring in the harness. Sensor wiring is new - but it still made sense to rule out a broken wire.

Questions:

• Has anyone seen these sensors go bad?
• Will a higher resistance value cause the KLR to deliver my symptoms (low boost)?

I guess my next step is to verify this with blink codes and begin to shop around for a replacement sensor.

specsalot

Just ordered a new knock sensor from FCP Euro
Porsche Saab Volvo Knock Sensor - Bosch 0261231006 $33.44

Sixline

You probably could of saved the money. The sensor at some point got updated and the self-impedance changed to greater than 1 MΩ. I bought a new one as well from FCP Euro and the resistance measures around 4.8 MΩ. More info in the thread linked below.

https://rennlist.com/forums/944-turb...ymptoms-4.html

specsalot

Sixline - Thanks for passing along the above info. Didn't realize these were piezo electric crystal units. Oh well it's only money I guess now I have a spare. Have to start looking at other stuff after I put this knock sensor issue to bed. I'm still going to swap out this sensor with a new one (since its already on the way). For now I'm going to try to re-torque the sensor and see if things improve.

Here is what my shop manual says on these sensors:



I love this cryptic quote, "Exact inner resistance of the knock sensor does not rule out a defect in the sensor." This makes the specification of a Control value kind of dubious.

Per the manual pre-MY88 units are torqued to 9Nm. MY 88 and beyond are torqued to 20Nm. Piezo electrics are based on crystal deformation and voltage. I'm going to have to check the torque on my sensor. Perhaps it has loosened up or is otherwise not correct. Based on the full thread you provided, my car is definitely operating in safe mode as described in thread you referenced in your post. The P/N on my sensor is the new style unit P/N 0261 231 006 old style P/N 0261 231 001. I guess the output is the same as far as the KLR is concerned because its the piezo element that creates a source signal vs modifying an external current source.

It seems these cars always deliver lessons - one problem at a time. That is why this forum is such a gift - being able to tap the collective experience here makes a difference. Thanks for posting the linked thread which helps point the way.

BR/
Paul

TurboAngel

I've been scouring the forum trying to get info regarding knock sensor issues. I've just recieved a new updated bosch sensor and it too is reading 4.8M. Has anyone used a sensor with this value with success?

specsalot

Swapped out the sensor, no improvement. Had the car in the air. Waste gate bypass was cool to touch while the crossover warmed up. So I have to start really looking. I'm going to have to give things a good look over before the next road test. Prior to the test I will clamp off the actuation line to the waste gate and take the car for a "careful" test drive. I will also check for blink codes after the test drive before shutting off the engine. I'm starting to worry at this point about other potential problems.

TurboTommy

How old is the cycling valve. As they age the symptoms are what you describe.
If your car was operating in limp mode or knock sensor activating the CV you would only get 1.2 bar on your gauge; not 1.4 as you describe.
Also maybe change back to the stock KLR chip and drive the car and see what happens.

Dougs951S

The easiest way to test the CV is just to bypass it with some plumbing bits from lowes turned into a makeshift MBC, then plug the line that goes from the J boot to the CV and take it for a drive with the wastegate line clamped.

specsalot

Thanks TurboTommy for your feedback above. I can't positively date the CV. It looks like a replacement part probably not original to the car. The PO did a lot of refresh work in 2005-2007 before selling the car. I suspect the CV dates to that time period. Based on that the CV is 9 years old with maybe 20K miles usage. The car sounds much different since this problem began. Yet it idles very nicely and the engine runs smoothly. If I was experiencing a turbo issue I would expect some kind of additional symptoms (turbo distress / tail pipe smoke / etc). Same would apply if I were experiencing other major engine issues (ie burnt valves). The car ran strong prior to my "no start" and the swap out of my electronics (KLR & DME rebuilding to ultimately fix things). I'll keep posting as I dig into this situation (in my spare time - of which I have very little).

specsalot

Thanks Dougs951S - If I don't find anything major under the hood, my plan is to plug off the waste gate line, get the car back on the ground and go for a short careful drive. Before I lower the car, I'm going to exercise the waste gate with a vacuum pump (per Laust's suggestion above) to listen for the sound of good mechanical closure. I'll keep reporting back results as I have time to get answers.