97 850 GLT - PTC diagnosis?

Post by **kcodyjr** » 28 Feb 2010, 13:55

Question is: how can I check the PTC's correct operation on the bench?

Background:

Before buying parts I went on a cleaning spree. The PTC looked like it had been installed by a bricklayer, using oil for mortar. I mean, it took 30 seconds with brake cleaner before I could even -see- the electrical connector.

So, I took it all apart, and went nuts with the cleaner until I didn't think I could get anymore. Put it back in.

Still smoking at the dipstick, but only depending on the pressure conditions. During spin-down there is no smoke; at idle or revving it up, it smokes gently. There is no perceptible pressure either way when I put my thumb over the hole, just a gentle stream of smoke.

To me, this seems like there is no operative check valve, and-or maybe a vacuum leak somewhere.

Should I be able to blow through the PTC when it's off the car? What does the connector do, is it solenoid or is it sensor?

Thanks,
- Kevin

Post by **charlyW** » 28 Feb 2010, 14:06

PTC I'm assuming thats the same as the PCV ? Did you clean the two ports one at the side and one at the rear of the oil seperator box? First time I replaced mine it still smoked till I blasted carb cleaner in both ports then gave it a week to reduce any built up condensation in the engine.

Post by **kcodyjr** » 28 Feb 2010, 14:10

No, PTC is the part of the PCV job that usually gets missed.

It is uncertain whether the PCV has been done lately but I tend to think it has. The hose leading from the PCV box to the PTC nipple looked clean inside, though I didn't take it off the car yet.

The PTC nipple is on the side of the intake hose, nearer the turbo end, where the PCV hoses connect.

Come to think of it... anyone know what "PTC" stands for?

-Kevin

Post by **Ozark Lee** » 28 Feb 2010, 14:14

The PTC should be clear, car on or car off, The electrical connector powers a heater that surrounds the passageway. A bench test would be a resistance test across the terminals. If it reads open it is bad if it reads low resistance - a few ohms - it is likely OK. In your case, based on the description, it sounds like the intake snorkel tube is physically done.

...Lee

Post by **Ozark Lee** » 28 Feb 2010, 14:18

Come to think of it... anyone know what "PTC" stands for?

Positive Temperature Coefficient. It is the turbo version of the thermostat on the intake air box on a N/A car and I think it is equally as worthless.

...Lee

Post by **kcodyjr** » 28 Feb 2010, 14:20

What signs should I look for on the snorkel tube?

It looked decent once I sprayed it down, though it looks like someone put some of that vacuum seal chewing gum onto the two ports at the airbox end of it.

Could the intermittent PCV performance simply be a symptom of major vacuum leaking? Shouldn't I be getting mad codes about it?

Post by **kcodyjr** » 28 Feb 2010, 14:22

OK, if the connector is a heater, I can't imagine it interfering with PCV performance.

How about the additional vacuum connector on the side of the PTC? Does it do anything, or just a vacuum pick-up point?

Is there an overall vacuum system design document somewhere, and I mean more than just a hose routing diagram?

Post by **Ozark Lee** » 28 Feb 2010, 14:33

The line from the PTC valve routes back from the PCV system as a vacuum line into the intake - it is essentially the line where all of the PCV gases get sucked back into the combustion chamber to be burned off.

I think that the diagrams on FCP's site shows how it all hooks up.

...Lee

Post by **kcodyjr** » 28 Feb 2010, 14:38

Ahh... just crossed my mind.

"Positive Temperature Coefficient," you say... they're trying to prevent the crankcase vapors from encountering cold air too suddenly upon mixing with the intake stream. In order for it to be mathematically "positive" they've got to be talking about some ugly calculus, it's more intuitive to think of it as "oil vapor pre-mix heater".

Colder air has a lower saturation point, and must cause the oil to condense out because the vapors are saturated by definition. If the air carrying crankcase vapors can be kept from becoming subcritical long enough, it would thoroughly mix with the clean intake air, and prevent condensation entirely simply by rarefying the vapors below the saturation point.

That may explain the clean PCV hose, actually. +1 to digging up an ohmmeter and checking that it has heat.

Post by **kcodyjr** » 28 Feb 2010, 14:45

Ozark Lee wrote:The line from the PTC valve routes back from the PCV system as a vacuum line into the intake - it is essentially the line where all of the PCV gases get sucked back into the combustion chamber to be burned off.
...Lee

Why put the PTC nipple on the intake hose at all, then? Why not just vent to the manifold?

At the manifold, pressure can become greater than ambient. That's therefore not a very good place to pick up vacuum on a turbo. Where the PTC nipple already is, makes more sense, because the compressor intake must always cause pressure to drop below ambient.

That's why I was thinking the secondary hose should be serving some kind of control function, to boost vacuum at an idle, but prevent manifold pressure from blowing back into the crankcase when you step on it.

- Kevin