Should my engine be sucking or blowing?

[Smevans]

I tried searching this but I'm not really sure what to call it. When the car is running, if I take off the oil cap should the air be sucking in or blowing out? Someone told me it should be sucking in, I don't think he knows what he's talking about.

 

[94Jettameowpsst]

It shouldnt reallly be doing either.
If its sucking in you most likely have a bad pcv valve
If its blowing out, you most likely have blow by from worn out piston rings OR a bad pcv valve.
I've experienced the "blowing" and it was due to my number 3 cylinder having a LOT of blow by.

 

[silver eclipse]

Why are you taking off the oil cap while the car is running?
-Chad

 

[joe]

Why are you taking off the oil cap while the car is running?
-Chad

.... side note pvc valve should be open @ idle.

 

[silver eclipse]

I wasnt saying it would damage anything, I just dont understand why you would have it off while the engine is running.
-Chad

 

[joe]

that what I was wondering

 

[Smevans]

It wasn't doing either.
I'm trying to sell my car and so this guy had me pull over to take a look at it. He was acting like he knew all this stuff and took the cap off to see what was happening. Then he told me it should be sucking and I had never heard anything like that before. Just wanted to verify what I was thinking. The guy was an idiot. Thanks for the help!

 

[c4uldr0n]

yeah, dont' listen to him

 

[Sinner]

He's probably just trying to get you to go lower on your price and is being dumb about it. I have sold many cars and I always run into one of these idiot's and once they start giving me this crap I realize they don't have any money and usally want to offer you some rediculously low price that is probably about half of what you were asking and I always just cut them short and end the deal right there and tell them I have few other people interested but if they don't buy it I will give them a call.

 

[romeen]

Actually I think that guy was right. Unfortunately there is no such thing as a perfect piston ring. There will always be some level of blowby which ends up in the crankcase. Normally this pressure is evacuated through the PCV valve when at idle (under boost it gets sucked into the intake pipe). If your PCV is functioning properly then your intake vacuum at idle should create negative pressure in the crankcase, therefore there would be "sucking" when you take the oil cap off.

Have you modified your crankcase ventilation configuration (removed PCV, installed VC breather, etc.)? Does your oil dipstick ever pop out? How much vacuum at idle?
This could be a symptom of a potentially more serious problem.

If there is anything inaccurate in this info someone please correct me.

 

[Smevans]

If by VC breather you mean the little filter on the side, yeah I have one of those.

The best thing about this guy was the dumbass didn't even ask what's been done to the car as far as mods go. He got in my car, rev'd the engine and asked why he can't hear the bov in neutral.

 

[romeen]

You might want to pull your PCV valve and make sure it is not blocked. You can test by removing the valve from the VC but leaving it hooked up to the vacuum hose which connects it to the intake manifold. If you place your thumb on the end of it there should be vacuum. If not the valve is likely plugged up. If so you can try to unblock it until replacing it.

What does your boost guage read at idle? If your PCV checks out ok you may have vacuum leaks causing low idle vacuum (normal is 18-22 in/Hg).

The valve cover breather filters are not as effective as the stock setup (vacuum hose to intake pipe) at venting the crankcase. This shouldn't really affect it at idle but under boost (when the PCV valve closes) you are not getting full evacuation of the crankcase vapors with the breather filter.

 

[Smevans]

I'm pulling 14 in/Hg at idle. Is that a problem? I'll check my pcv too. Uh..what's the VC? The valve cover?

On a side note:
I'm gonna be in the Portland/Vancouver area this summer romeen. How is it?

 

[romeen]

Idle vacuum should be 18-22 inHg. Unscrew the PCV valve from the VC but leave it hooked up to the vacuum hose. Start the car and use your finger on the end of the valve to check for vacuum. You may have vacuum leaks that can be identified by performing a boost leak test. I would definitely recommend doing a boost leak test.

Also checking at the oil filler hole by hand can be deceiving. Try using a piece of paper over the hole to see if it really is blowing air out. Hopefully the paper will be held in place over the oil filler opening.

Let me know what you find.

 

[Smevans]

the guy put a bill over the oil filler hole. It did cover it with some oil It didn't just stay in place either.

 

[romeen]

The oil is normal, it's being slung off of the cams. But if air pressure was making the bill flutter away from the opening then there might be an issue. Most likely a clogged PCV valve. Go ahead and check it like I said. If there is no suction through it you can spray some brake cleaner through it and use a toothpick to try to unstick the plunger until you get a new valve (they're cheap). Check the valve and let me know.

 

[Smevans]

Okay, I'll check it today hopefully. Thanks for all the help!

 

[Eclipse98_RS]

Why is that, that on some cars you can hear the BOV in neutral and in some you cant? Is it just the way the car is setup?

 

[Smevans]

I checked my pcv valve and it is sucking. So it's not that.

Here's a bit more info for you too. When I take my foot off the gas and just cruise my gauge shows 20in/hg (.7 kpa). If I put my clutch in it'll sit around 14-16in/hg (my gauge shows about 50-52kpa)

 

[Smevans]

Why is that, that on some cars you can hear the BOV in neutral and in some you cant? Is it just the way the car is setup?

Yeah, does it have anything to do with the recirculation set up?

 

[romeen]

I checked my pcv valve and it is sucking. So it's not that.

Here's a bit more info for you too. When I take my foot off the gas and just cruise my gauge shows 20in/hg (.7 kpa). If I put my clutch in it'll sit around 14-16in/hg (my gauge shows about 50-52kpa)

As I mentioned previously I would do a boost leak test to identify any boost/vacuum leaks. If you get your idle vacuum back up to 18-22inHg and the crankcase is still pressurizing then do a compression test. It is possible (but not as likely) that you are just getting a lot of blow-by due to worn rings.

 

[Smevans]

I just realized this too, my idle rev's are 1000rpm's so that would have a factor on my vacuum being around 14in/hg right? I'll be getting my car checked out once I get my AFPR. Should be about 2-3 weeks. Thanks.

 

[romeen]

If your system is free of leaks then your vacuum should stabilize in the normal range regardless of the high idle rpm. I have my idle set at 1K (to get rid of felt vibrations from poly motor mounts) and my idle vacuum hovers around 51cmHg on my Blitz electronic guage which translates to 20inHg. Unless you deliberately set your rpms at that level then the high idle rpm is consistent with a vacuum leak. All the more reason to get going on that boost leak test.

 

[Smevans]

Which Blitz gauge do you have? I have the BLM ones and it rests at -50kpa at idle. Maybe my numbers aren't right? The higher rpm was set intentionally to compensate for my larger cams.

 

[romeen]

I have the old style Dual Solenoid Boost Controller and the Dual Turbo Timer, both of which show boost/vacuum. The units when under vacuum should be cmHG. To convert to inHg just divide the number by 2.54. You may want to double check, but if you are at 50cmHG at idle then you are right where you need to be. You may want to repeat the piece of paper over the oil filler hole again. If your cams are making your idle lumpy maybe what you thought was air pushing out was just vibrations from the performance cams.