Truck is an 87 F150, 302 EFI, 100k miles on a rebuilt short block

Last fall I converted my truck to MAF and basically made my own K&N intake assembly. Since I no longer had the stock airbox to connect the crankcase breather pipe, I knocked a hole in the side of the intake pipe and connected the breather pipe into that. The hose from the PCV valve is routed to the intake as well, just before the throttle body.

Is this a bad idea? I noticed recently there is smoke coming from the oil fill when I remove the cap, and wondered if the vacuum might have sucked in a gasket somewhere allowing exhaust into the crankcase. Thinking I might be getting blowby, I checked compression on all cylinders, all are between 155 and 170 PSI. I then removed the breather pipe from the intake at idle and lots of smoke came out the breather.

Should I have just put a filter on the breather rather than routing it to the intake?

Brian

 

On my MAF,

The hose comes from the oil fill neck over to the air intake tube between the throttle body and MAF sensor. It doesn't have a filter on it, and doesn't need one. It's just tapped in.

 

Adding to what Justin said, the PCV should be attached to manifold vacuum, after the throttle body, not in the intake hoses. The breather should attach to the intake hoses.

 

Yeah, my PCV is under the upper intake in the middle. Some were behind the upper intake which led to problems with unbalanced cylinders. I think the air from the PCV went more towards the #8 cylinder and caused premature wear. I put mine in the middle to prevent that.

 

So I can leave the breather going to the intake before the throttle body, and move the PCV to the manifold "tree".

Thanks guys!

...now if I can figure how to get the sparkplugs our of my Ranger

Brian

 

As long as the breather going to the intake before the throttle body sees filtered air, you're all set.

If it taps in downstreem of the airbox, it's already filtered air (MAF application). The speed density system has the PCV breather going over to the airbox and has it's own filter because it taps in upstream of the engine's air filter.

The PCV hose doesn't originally go to the vacuum tree. I guess you could put it to the vacuum tree but I don't know how because there isn't an available opening on the tree for it.

If it were me, I'd take the upper intake off, and tap a hole in the bottom of it and screw in a barb fitting so I could attach the hose there. My edelbrock intake came tapped and threaded so I just put the barb in there and hooked it up. It also had the hole in the back for the stock PCV location, I blocked that with a plug.

 

MAF vehicles have to pull the crankcase vent after the air mass meter so the air coming through the PCV valve is accounted for.

 

My MAF has the little Y where it splits from 1 tube into 2 tubes before the throttle body, which is where the PCV taps into the system, which yes would be between the MAF sensor and TB.

 

That's where I connected the PCV on mine as well since I got used a y-pipe from a 95 MAF F150, and there was a connection. I have 2 spots on the tree that are capped so moving it is no problem. I had it on the tree at one point but moving it before the TB seemed to lower the idle speed a little.

The breather is currently connected downstream of the air filter but before the MAF.

Sounds like I need to move the PCV to the manifold and move the breather to the connection before the TB, after the MAF of course.

 

I think the idle sped up because the pcv was acting like a vacuum leak. Hook up to the nipple in the 'y' pipe for the breather and you should be good to go.

 

After putting way too much brain power (and some beer) into the whole subject I decided two things:

1. In order for the PCV system to work properly there needs to be more vacuum on the PCV connection than on the breather connection, and

2. I don't know how there would be such a difference in vacuum, or pressure, when both are connected to the same pipe before the throttle body.

So I connected the PCV to the manifold tree and the breather pipe to the y-pipe after the MAF sensor. Now there is no smoke with the cap removed, smoother idle, and for some reason higher oil pressure(yes I have a real gauge).

you guys knew all that right?

Later
Brian

 

I am intrigued by the higher oil pressure. Glad to hear you got it working correctly!

 

Yeah, now you got the right idea! In order to have PCV (Positive Crankcase Ventilation), you have to have lower pressure at the PCV valve than at the breather. That ensures a good flow of air through the crankcase to remove that "smoke" you mentioned. During engine operation, the oil is agitated so much that an oil mist or vapor (or smoke) is produced. Also, all engines have a tiny amount of combustion gas (blowby) that slips through the ring gaps into the crankcase and raises the pressure, and thats why we have PCV systems to begin with, to release the pressure created by blowby and protect the gaskets. The valve itself is there to keep the engine running at idle (high vacuum) by restricting the flow of vapor and gases back to the cylinders. As the load increases (low vacuum) the valve opens up to allow full flow. But like EPNCSU2006, I'm puzzled at the increase in oil pressure, because that seems unrelated. If anyone can offer an explanation I'd be interested to hear it.

 

How much more pressure?

 

The gauge was reading 15-20PSI at idle when warm, now reads around 25PSI. At about 2000RPM it was reading 40PSI now almost 50PSI.


I noticed it last night after reconnecting everything, and today coming to work. I asked a few people here at work, they have no explanation other than slightly faster and smoother idle.

Brian