enlarging PTC vac line—opinions?

[JimBee]

Redoing my PCV on the 93 850 turned into a much bigger project than I'd imagined because the original oem plastic line was kinked near one end to align it with the rubber adapter at the oil separator box. This resulted in very little vacuum actually getting to the box and extremely clean box and rubber hoses. There was zero sludge, not a speck of anything in the ports at the side of the engine, just a tiny bit of oil. I bought this car in 2008 and had no record of maintenance, but when a camshaft seal I'd replaced (along the the other 3) just after I bought it, began leaking I assumed the PCV was clogged.

Why did the last person sharply bend the end of that long plastic line to align with the rubber adapter?

The 93/94 850's used a manifold mod that included vanes in the manifold runs that are vacuum activated to adjust air flow for increased performance (there's an MVS post on this which I wasn't aware of until I found it on mine). Mounted on the underside of the manifold, there's a vacuum can with a diaphragm and linkage to activate the vanes with a small vac line running off the throttle body. That assembly blocks the space beneath the manifold, so some creative bending of the plastic line is needed to get around it—including a sharp bend to align with the rubber adapter at the oil trap nipple. The installer must have heated the hard plastic line to make that sharp bend, but in the process it was kinked, reducing vacuum, probably close to zero, allowing no escape for excess crankcase pressure.

That line needed to be replaced, and clearly there was no space under the manifold to get a line of any thickness directly through—so what to do?

First, I'm assuming the approximately 3/8" ID plastic line size was a design compromise needed to get a line through that space which is tight anyway even on the later 850s without the manifold vacuum can. But downsizing it to 3/8" creates a built in restriction of vacuum between the 5/8" nipples on the PTC and the oil trap box—not to mention the kinked bend at the end.

But, now I'm wondering if the physical space limitation was the reason they downsized that link to 3/8"? OR, would a 5/8" line allow TOO MUCH vacuum on the crankcase? This is the question.

Anyway, I decided to replace that link with a full 5/8" ID line. To do that I'm running a 5/8" fuel rated rubber hose vertically from the oil trap box up through the opening between the first and second manifold runs to a 90 degree brass barb L into a lateral length of hose along the top of the manifold and down to the PTC. It's a bit tight at the throttle body end, but seems okay.

So the question: will this wide open vac line, a) pull too much vacuum from the crankcase, or b) report a vacuum leak to the ECU?

If, needed, with this assembly, I can easily downsize the lateral link to 1/2" or even 3/8". There are brass barbs available for that.
I'm just finishing putting it back together, so I haven't run it yet.

BTW: the 93/94 850s used a oil trap box with only one nipple—they didn't have a second hose to the top of the engine.

Opinions?

[jreed]

I used the 5/8" fuel rated rubber hose too on my 1997 and it has been running great for the past 3 years. No problems or codes noted.

[JimBee]

Thanks, J. Reed! A testament to my whimsy!

[JimBee]

J. Reed. Follow. up question re PVC hose refit: I also have a 96 850 NA and a 96 turbo 850. I'm also thinking about doing a similar re-hosing on those two. How did you route your upgrade hose?
Thanks,
JB

[erikv11]

Same thing on my 98, the line to the PTC is just fuel hose. Not sure how I routed it but didn't use any fittings etc, just a run of hose.

[abscate]

I think the vacuum is controlled by the PTC orfice (often called a PTC valve here, which is incorrect,,,its just a hole with an electrical heater to keep it clean). I dont think the size of the hose will matter at all.

[erikv11]

PTC = Positive Temperature Coefficient ain't no valve in there

thank you jreed!
viewtopic.php?f=1&t=68898

[jreed]

Here's a photo of the fuel line and two 90 degree fittings I used on my 97 855 in Dec 2022. Still working with no issues noted yet.

[JimBee]

Thanks, J.Reed the pic is helpful. On the 93 (probably 94, too), that's not an option due to the vacuum can mounted under the manifold that closes off the space by the starter.
Also, due to the top-side vac hose on the 96s to the oil separator box, going under the manifold looks like the only practical route for the 5/8" hose. That was actually my plan for the 93 until I got in there—with a big oh, oh sigh!

Fortunately, the 93 doesn't have the topside hose so it's a clean run along the top of the manifold from a straight up vertical hose from the oil separator box.