Turbo Boost Guage higher than normal

[motorscuba]

As I was leaving last night I noticed that my turbo boost gauge was higher than normal. It normally is nearly all the way to the left until the turbo kicks in and then it goes up to almost half way and then drops down. Now it starts out at half way and goes up from there. I even noticed a little difference in how it felt upon starting up....a little shaky and unusual sound. I drove a couple of blocks and decided not to drive it until determining what this could be and if damage could occur.

It's a 1987 951 that's stock just so you know. Any ideas out there??

Thanks

[sketchers356]

Not to be offensive, but I am having a really hard time understanding what you mean by half way (1 bar?) etc. When the turbo kicks in it should be higher than 1 bar more like 1.8 bar.

It sounds like you have a vacuum leak to me. Check out this youtube video. https://www.youtube.com/watch?v=AL3jbcrqY8g

[motorscuba]

No offense taken. By half way I mean in terms of the gauge. In essence half way would be 12:00. I'll check out the video. Thanks

[sketchers356]

Ok Im still not really understanding you, but good luck!

[motorscuba]

12:00 is straight up on the gauge.....it's a fairly common term. Right in the middle of the guage. I just looked at a pic of the gauge and in terms of bars it normally starts all the way to the left of the gauge or .4 bar and goes up to towards the middle of the gauge about 1 bar but now it starts at 1 bar and goes up to close to 2 bar.

Now from what you are saying that is normal operation? I understood from previous info that the way my turbo was operating was normal for a stock turbo. Please clarify.

Thanks

[Ga 951]

Motorscuba,
I'm no expert but I have a 951. The factory gauge reads absolute pressure. At sea level with the engine off, your gauge should read ~1bar (ie 12 o'clock). When you start the car and run normally (ie no boost) your gauge should read less than 1 bar ---that is vacuum in your intake system. When the turbo is boosting, your gauge should go to 1.7 or 1.8 bar around 3-4000 rpm and back off slightly as the rpm increases toward redline. This means under full boost you should see almost full deflection to the right!

If yours does not do that, then you need to check it out

Good Luck,
Bruce

[sketchers356]

Bruce, exactly what I was going to type.

At idle the boost gauge should read .4 not 1 bar (12 oclock)

[motorscuba]

We'll mine would never go to full right on the gauge which would be 2 bar...the most it would go is in the area of 1 bar..maybe a little higher as far as I know. I didn't regularly look at it at full boost though. At idle it would be at .4 bar. That was my norm. So if everything seems to have shifted upwards as described is that from a vacuum leak and if driven to my mechanic as opposed to being towed could damage be caused??

[motorscuba]

Anyone out ther know if driving it under these conditions even to a mechanic would cause additional damage to the turbo?btrying to make the choice between towing or driving.

[sketchers356]

If you have a bad vacuum leak it will cause the engine to run very lean, which is a very bad thing for your engine.

[motorscuba]

I decided last night to tow it to be on the safe side and did that this morning. Thanks Sketchers for the info though. They're going to check vacuum and the rest of the turbo for me.

[sketchers356]

Would be interested to know what the problem is.

[DannoXYZ]

Originally Posted by motorscuba

We'll mine would never go to full right on the gauge which would be 2 bar...the most it would go is in the area of 1 bar..maybe a little higher as far as I know. I didn't regularly look at it at full boost though. At idle it would be at .4 bar. That was my norm. So if everything seems to have shifted upwards as described is that from a vacuum leak and if driven to my mechanic as opposed to being towed could damage be caused??

Driving it at low-throttle no-boost should be fine.

One of the 1st things to check is to verify the gauge is correct. It's electronically driven by the KLR, so everything along the way could be bad:

1. plastic hose between intake-manifold to KLR is cracked, loose, etc.
2. MAP-sensor in KLR is bad
3. KLR is bad
4. wire-short somewhere between KLR and dash-gauge
5. dash-gauge is bad

If you still had the car, and maybe the mechanic will do this as well, is to hook up a vacuum-gauge to the intake-manifold and verify what the actual readings should be.

Most likely they won't match the dash gauge. Which leads to troubleshooting the next step towards the KLR. Hooking up the vacuum-gauge at the KLR to the hose coming from the intake will verify the signal that the KLR sees.

Most likely it won't match the readings taken from the intake-manifold. This will indicate that the plastic-line is leaking. Things get crispy with age and cracks form. It may be leaking enough that it doesn't hold vacuum and will send 1.0-bar atmospheric pressure to the KLR, thus the 1.0-bar reading at idle. This will also send extra air into the intake-manifold, thus the cause of the new stumbling at idle.

But the leak isn't so bad that it can't hold boost. So under boost, the hose can still send some pressure to the KLR to make it drive the gauge at +1.0-bar, even to stock 1.6-bar settings under boost.

[motorscuba]

Thanks Danno for that info. I'll pass it on to the mechanic. I'll be sure to update Sketcher once we narrow it down.

[motorscuba]

Ok here's an update...we checked the guage for proper operation and it passed, we checked the vacuum and it seems fine. The next step is to check the waste gate and circulator valve. Opening things up to get to them. They believe the waste gate is possibly stuck.

The condition did worsen enough that the car shut down due to excessive boosting which is what it's supposed to do. So we are marching on inspecting piece by piece.

Suggestions are greatly appreciated.

[RRRacing1970]

Hi... yes I agree with all the above descriptions of unknown turbo BOOST problems.
1) Remove the waste gate vac line and put (air hose) 10-25 PSI on the waste gate vac fitting.
2) Remove banjo bolt in turbo inter cooler discharge pipe to inter cooler.
3) Take a leaf blower and stick it in the tail pipe... you should feel and hear air coining out the
banjo bolt opening. (Waste gate is open) turn off leaf blower -
4) Remove (air hose from waste gate vac. fitting) (leave it off)
5) Re-install banjo bolt
6) Remove Inter cooler intake side 2.3 " pipe at the inter-cooler - install leaf blower and turn on as to induce pressure to the intake manifold... if there is air coming out of the waste gate vac fitting port at the wast gate... waste gate is stuck open... or may have a busted diaphragm. Or... just stick the leaf blower up the tail pipe and see if air is coming out the vac port on the waste gate... also means waste gate is bad!
Good Luck... Ron

[motorscuba]

Thanks Ron. I'll pass it on to the shop!!!