Engine died while checking oil and other Q's

[AFC-911]

Ok, I went to check the oil today (after an approx. 20 minute drive), and once I opened the oil cap, the oil pressure dropped and the engine struggled to idle and just shut itself off.

I'm pretty sure this is NOT normal...So I check the oil level (with the engine still off), and it's pretty low (slightly below the second mark). Could this be the cause?

By the way, the car runs fine, and has not given me any problems. Idles properly (when not checking the oil anyways).


On another note, my 915 sometimes makes a slight whirring noise, but I'm pretty sure this is caused by my occasional shifts that are anything but smooth. Or it could be caused by an early shift as I don't hear it when the revs are higher?

[86 911]

That's interesting because my car is similair, except it does not die. It struggles to stay idling (800-850 RPM) with the oil cap off. Once I put the oil cap back on, it idles fine. Maybe something to do with vacuum or suction?

[vash]

arvin, if you remove the oil cap and the car dies, you may be missing a small brass cone that sits inside the rubber hose that comes off the oil filler neck. take off the hose clamp, pull off the hose and peek inside. it may just be skewed. it is more of a vacumn issue, and not a oil pressure issue. i dont think you can get an accurate oil level reading otherwise. (maybe wipe dipstick, insert, start car, idle, kill car with cap removal, and immediately check level. but i dunno)

[bigchillcar]

arvin,
the engine is supposed to be running and it's also essential that you be on level ground and your engine at the correct operating temperature (180 degrees) otherwise your reading will not be accurate. this is due to the great volume of oil and how it varies with temperature. opening the oil cap should cause the car to momentarily run leaner, but it should not die. it could be that your car's mixture is currently set on the lean side and that removing the cap simply pushes this ratio too far..
ryan

[Tyson Schmidt]

When you remove the oil cap, it allows air to go through the breather and around the airflow meter. This means it's getting unmetered air, which causes the engine to run lean. If your engine is already on the ragged edge of lean, it will die.

If it's running rich, it will actually make the idle raise.

Also, like Vash indicated, it could be missing the restrictor that should be there to keep too much air from getting around the airflow meter while checking the oil.

[smestas]

I know for sure my car is running on the rich side and I suffer from engine shutdown when trying to check the oil. I must be missing this restrictor. Does anyone here have a part # for this little gizmo?

I currently get around the problem by adjusting the idle screw so it stays on and then back it off once the oil level has been checked. Probably no the right way to do it but its a work around.

[autobonrun]

Originally posted by smestas
I know for sure my car is running on the rich side and I suffer from engine shutdown when trying to check the oil. I must be missing this restrictor. Does anyone here have a part # for this little gizmo?

I currently get around the problem by adjusting the idle screw so it stays on and then back it off once the oil level has been checked. Probably no the right way to do it but its a work around.

I assume you are talking about the back fire grid that goes in the hose from the filler neck to the airbox. I posted on this subject back in March. The attached link includes parts numbers, diagrams, and photos of the part.

Need source and part # for flame arrestor.

[smestas]

Now Im going nuts.

I just looked at my air box and the mentioned hole has a rubber plug in it. Then I looked to the two hoses from the top of the oil filler and one goes to the top of the engine (breather) and the other goes to the top of the CIS rubber boot? Am I missing somthing? Where would a hose on the pluged hole go to?

[bigchillcar]

yeah, the one from the airbox normally leads to the filler neck..like it's for oil overflow back to the tank.
ryan

[DanS911]

I have the same plug

[vash]

not the backfire grid. it is IN the hose that runs to the filler neck.

part # 930 107 289 00 "restrictor"

it is a cone, sorta like a thimble, but with a small (maybe 1/8 inch diameter) hole in the end.

i think it is pelican part # H-107-289-00

maybe westy will post a pic, he has an extra. we put one in his car and it fixed the same prob.

[autobonrun]

My car is a 79SC. In the photo I've attached it shows a curved hose going from the oil filler neck to the side of the airbox where you guys have a plug. Instead, in mine there is a hole where the backfire grid fit and the hose clamped to it. There is another larger hose that is connected to the side wall beside the oil filler neck that goes around the back of the engine. I can't tell where it lands but it may be the hose that carries the vapors from the crankcase to the oil tank.

In my Clymer manual for the SC, it states:

"Engine blow-by and other fumes are channeled from the crankcase to the oil tank by a hose on all 1977 and later models. An additional hose then directs the fumes to the intake air system. On 1977 and earlier models, this hose was connected to the air cleaner... On 1978 and later models, the hose is connected to the rubber boot between the airflow sensor and the throttle housing ... The angled connector ... of the 1978-on hose contains a 6.5mm orifice, which restricts the crankcase vacuum under all operating conditions."

It appears although I have a 1979SC, that the vent setup is based on the 1977 and earlier design. The setup you describe is more like the 1978 and later description and would explain why that hole is plugged on yours. Why our SC's would be different is beyond me. Maybe John Walker or one of the other members would know why the same series of SC's would have different emission vent setups. Maybe the part the others are speaking of is the restriction orifice that shows to be in a cloth covered hose that connects to the back of the crossover boot. The picture in Clymers shows an angled connector in the end of the cloth hose just at the back of this boot that goes over toward the filler neck. I don't have this hose on my setup. If you have a cloth cover hose on your filler neck, you probably have this setup instead of the type I have. My production date is January of 79. Maybe the earlier production dates still used the pre-78 setup and the design switched over at some point in production of the SC.

[livi]

I am sure I read in some Porsche magazine that if the engine stalls and dies when opening the oil filler cap - it COULD be a sign that the engine needs a top end overhaul.

This is not a joke (I am not that vicious) but IF this is true it would be educational if someone better informed than me explained how that works.

[Ian Comerford]

I don't know if this helps but I have just been to an open day at a Porsche Centre here in UK and saw a 1982 SC being inspected by an experienced (on old cars) technician. The car had exactly the same fault as you describe on yours. I cannot remember the full explanation (something to do with vacuum), but he said that it was due to worn valve guides and would necessitate a top end overhaul to remedy.

Ian

[Wayne 962]

The bottomline is that many of these cars have been messed with over the years. Previous posts are correct - there should be a 'backflow' valve in that hose. When the hoses are replaced 99% of them are simply tossed out, and the valve is tossed out with the hose. The new hose allows for a vacuum leak when the engine oil cap is removed. It's quite common. In fact, it's more common to have this problem than to not. In general, it's not a huge issue, and you can install the valve, and/or simply press a little on the accel linkage if you've got the cap off. The correct way, of course, is to get the correct parts in there so this doesn't happen.

As for whether your engine needs a top end rebuild just because of this - that's a bit of black magic to me. Engine condition is best determined by running and observing a deliberate set of tests, like the ones I detail in this article:

http://www.pelicanparts.com/techarticles/mult_Engine_Rebuild/mult_engine_rebuild-1.htm

-Wayne

[AFC-911]

Well my PPI last month showed 175 on all cylinders on the compression test, spark plugs are fine, and the leak-down was around 10-18%....As far as needing a rebuild, I don't think I'm there yet.