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PCV connections on '86 5.0L?

theshadow

Sr. Member
Joined
Jun 30, 2006
Messages
358
I've been having some idle issues after installing a new painless mass-air engine harness and Ford racing computer/mass-air sensor combo on my '86 5.0L that used to have speed density. Ive checked fuel pressure its at 40 pounds, re-set the TPS to .98v. Recently I just found the hose that goes from the underside of the upper intake to the PCV valve is cracked so tomorrow im going to replace the hoses and the valve. im wondering if this could have been my problem. Also, im trying to figure out what this vacuum connection is on my throttle body. Its a 3/8'' connection and ive got it plugged right now. I looked through a few books and found that it is a PCV valve connection supposedly. Is this true? Im really confused as to where the PCV valve connects to. Any help much appreciated.
 

Broncobowsher

Total hack
Joined
Jun 4, 2002
Messages
34,835
On the 5.0 (car type port injected) the PCV system has 2 parts. Fresh air into the crankcase, polluted air coming out of the crankcase. The PCV valve and cracked hose you found (probably you bad idle) is the part that takes care of getting the stale, polluted air out of the engine (and burns it). The extra fitting you found on the throttle body (non-vacuum side of the blade) should be routed to the valve cover that has the oil fill on it. That lets fresh air (filtered by the air filter) flow into the engine. It is also a vent to let excessive air out of the engine at times of prolonged full throttle (low or no vacuum).
 
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theshadow

theshadow

Sr. Member
Joined
Jun 30, 2006
Messages
358
Broncobowsher said:
On the 5.0 (car type port injected) the PCV system has 2 parts. Fresh air into the crankcase, polluted air coming out of the crankcase. The PCV valve and cracked hose you found (probably you bad idle) is the part that takes care of getting the stale, polluted air out of the engine (and burns it). The extra fitting you found on the throttle body (non-vacuum side of the blade) should be routed to the valve cover that has the oil fill on it. That lets fresh air (filtered by the air filter) flow into the engine. It is also a vent to let excessive air out of the engine at times of prolonged full throttle (low or no vacuum).

Ok, that makes sense. But neither valve covers have a fitting for the PCV hose. Is it possible that ive had the wrong oil caps this whole time? Also, I forgot to mention my initial problem (which you broncobowsher guessed anyway;D ). Its had a really unstable idle ever since I did the conversion from speed density to mass-air. It will start idle for about 5-10 seconds and then die. Consistent results every time.:p
 

904Bronco

Contributor
Bronco Guru
Joined
Sep 28, 2004
Messages
5,749
Loc.
San Martin, CA
theshadow said:
Ok, that makes sense. But neither valve covers have a fitting for the PCV hose. Is it possible that ive had the wrong oil caps this whole time? ]

The factory 5.0 motor has (passenger side) a valve cover with a raised oil fill tube that the cap screws into. The raised oil fill tube has a 3/8 fitting on it that the port on the TB connects to. Change valve covers or add a fitting to the exsisting ones...

The excessive vacuum leak maybe the cause of your idle problems? 86 yr motor will be hard to find a factory hose for. Most Mustang owners upgrade to the 87-93 style, those hoses can still be found new. You will need to find a donner car for the fittings.
 

Broncobowsher

Total hack
Joined
Jun 4, 2002
Messages
34,835
OK, the mass air conversion adds another step. That valve cover to throttle body hose must be routed correctly. It must pull air from the intake between the mass air meter and the throttle body. The port on the throttle body is perfect.

If you are running a vented valve cover (oil fill with a breather) you will have the startup idle issue you describe. What is happening is the engine is getting air (from the breather, throught the engine and PCV) that is not metered by the mass air meter. Cracked PCV hose does the same thing, allows unmetered air to enter the engine. since the computer doesn't see this air entering the engine, it doesn't know to add fuel for it. After it runs for a little it, it adapts to it.
 
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