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I have an 89 5.0 tpi swap with no emissions. The engine runs strong and smooth but the PCV circuit is building excessive amounts of condensation when hooked up to the top (passenger side) port on my throttle body. PCV valve is new, no vacuum leaks, throttle body is clean. The top port just doesn’t pull enough vacuum to suck in the blow by vapors. Now if I un-cap the port just below it (where vapor tank used to plumb to as I’ve read) there is plenty of vacuum. When I hook up PCV to that port all seems well and no condensation. I am just concerned with that amount of vacuum I will suck in too much vapor/oil and pre-maturely dirty up my throttle body? Thoughts on this? The gasket on top of the throttle body is good too, maybe not having the vacuum canister is why there’s no vacuum at the PCV port on my throttle body? The pCV is located in what looks like a breather on the passenger side valve cover btw.
I cant see the PCV valve plumbing, but the hose from the PCV Valve, should go to the drivers side rocker cover. The hose from the top of the throttle body, should go to the left side rocker (valve) cover.
Thanks for the reply. Sorry bad pic. If you look behind the ac lines the pcv valve is right there(inside the breather looking oval). The hose is currently routed to the middle port on the passenger side throttle body where there’s vacuum. It was routes to the top port (where it’s supposed to go) but as stated above has been giving me problems with condensation and oil/water sludge in the pcv valve and hose(and probably next would be sludge in the motor if I left it).
Your PCV system isn't quite right. The throttle body connection should be the top and no PCV and then you need the PCV on the driver's side cover then to the manifold port for vacuum.
Last edited by Tootie Pang; 05-24-2019 at 03:23 PM.
Interesting. Thanks for the info. I guess I will need to make some adjustments as my drivers side valve cover doesn’t have any provisions for a breather/ pcv valve. So from the looks of the diagram the PCV doesn’t route to the throttle body, but manifold vacuum? Is that how you guys have yours set up out there?
OK great, I will give it a shot and report back. Thanks for the help! Final question, are you routing your PCV hose to the intake manifold port near the fuel pressure regulator?
There should be a 3/8" or so nipple for the PCV hose on the left/driver side of the intake manifold base, between the two sets of runners. It's in that last pic. Not sure which vac port by the fuel pressure regulator you're referring to, there should be two nipples there and one should be for the fuel pressure regulator and the other is used for the HVAC vents and cruise control if you have it.
The large upper connection on the throttle body is a fresh (filtered) air inlet for the connection to the valve cover on that side, and that port below it is full manifold vacuum and typically used for the charcoal canister purge line.
Glad to help. Cool TPI install. Would love some pics. The diagrams show it but yes, driver's side manifold base to the PCV valve in the driver's side valve cover. Passenger cover just has an elbow which connects to the top port of the passenger side throttle body ports.
Thanks! Gotta do a liitle fab work to get it right again, might just give in and buy the proper valve covers. The passenger side that says “filtered air,” is confusing me. Is that hose some type of filter? Cause clearly the vapors enter the throttle body after the air filter.
Here’s a few pics.
By "filtered air," it just means don't leave it open to the air without a breather or filter. In the case of a TPI/LT1 throttle body, the big upper port on the throttle body is equivalent to putting a fitting in your air cleaner / intake tubing.
The PCV valve on the driver side valve cover is sucking air from the crankcase, and the crankcase is letting new "filtered air" in through the passenger side valve cover. The idea is to circulate fresh air through the crankcase.
Having all this hooked up correctly is particularly important on a MAF system. If you use a typical hot rod style breather element instead of connecting it to the throttle body / air cleaner duct, all the air getting pulled in by the PCV valve is "pirate air" because it's air entering without the MAF's knowledge. With the filtered air pulling from the intake duct (in the case of TPI/LT1, the large upper fitting on the throttle body), the MAF can account for it.
By "filtered air," it just means don't leave it open to the air without a breather or filter. In the case of a TPI/LT1 throttle body, the big upper port on the throttle body is equivalent to putting a fitting in your air cleaner / intake tubing.
The PCV valve on the driver side valve cover is sucking air from the crankcase, and the crankcase is letting new "filtered air" in through the passenger side valve cover. The idea is to circulate fresh air through the crankcase.
Having all this hooked up correctly is particularly important on a MAF system. If you use a typical hot rod style breather element instead of connecting it to the throttle body / air cleaner duct, all the air getting pulled in by the PCV valve is "pirate air" because it's air entering without the MAF's knowledge. With the filtered air pulling from the intake duct (in the case of TPI/LT1, the large upper fitting on the throttle body), the MAF can account for it.
With any "V" engine, the concept is manifold vacuum to PVC in 1 valve cover - and "filtered" fresh air (breather) in the other valve cover. The fresh air ENTERS at the breather and gets pulled through the engine, picking up blow-by gasses along the way, and EXITS through the PCV valve at the opposite side of the engine, getting sucked into the intake to be burned. Actually simple once you understand it.
Perfect. Great explanations! Thanks for taking the time to share some knowledge. You guys have a great holiday weekend! It might be a little while with work and family but I will update when I get everything up to snuff.
PCV Crankcase breather filter, from the 70's. Inside the plastic housing was a removable polypropylene gauze filter element. When I was a Union Auto Parts Journeyman, in a Teamster Union Auto Repair Shop, the mechanics, called the filter a "Kotex".
The good old days, when all large Auto Shops and Parts Stores, in SF and Marin County Ca, were UNION!
Ok so after evaluating what I need to do to the valve covers I have to make it work, I’ve decided to look for some used covers online because I’m pretty certain that mine would look butchered after modifying them to work. I found some nice covers from an L98 350 vette motor with spacers and perimeter bolts that will clear my roller rockers. Those should bolt right on to my 305 TPI if I’m not mistaken? Just thought I’d check with you guys first as they are a bit pricey, but will look nice and have the provisions I need to get the PVC plumbing correct again. Thanks
For my TPI conversion I used stock early style TPI valve covers (perimeter bolt) with extra thick gaskets from Summit Racing. The extra thick gaskets give more clearance for my roller rockers. My Trick Flow heads have raised valve cover rails also. I have searched for aluminum aftermarket valve covers that would work with TPI, and have found nothing that works with the TPI configuration.
Thanks for the info Fred. I ran into the same problem with my search as well. So I ended up going with the valve covers from a C4 vette with some spacers. Can’t wait to put them on they should look pretty cool and function properly
Thanks! Gotta do a liitle fab work to get it right again, might just give in and buy the proper valve covers. The passenger side that says “filtered air,” is confusing me. Is that hose some type of filter? Cause clearly the vapors enter the throttle body after the air filter.
Here’s a few pics.
It's always nice when you can say, "Problem solved!"
You changed your steering wheel. The previous one is my favorite wheel. But the new one looks good too.
Good eye! I like that style wheel too, I have the GMC version of it in my 89’ Jimmy. It didn’t quite fit the build though. I wanted to get my dad involved since I built the truck for him... so he turned the wood pieces for the tilt, shifter, and turn signal on the lathe. I think it came out pretty good. That 90’s Chevrolet steering wheel is taking up space in my shop if anyone wants it let me know happy fathers day to all the dads out there! Mine got me hooked on wrenching when I was just a lil guy.
We had a big car show here in Idaho this weekend. Got to break out the Oldsmobile I built back in 2003. Used to be my dad’s...I helped him restore it to to a driver back in the early 90’s. Then I got a hold of it
I cant see the PCV valve plumbing, but the hose from the PCV Valve, should go to the drivers side rocker cover. The hose from the top of the throttle body, should go to the left side rocker (valve) cover.
Anyone else have advise?
You are correct. The hose from the top side of the throttle body is the air SUPPLY line which goes to the pass side valve cover. The PCV valve itself sits in a grommet in the driver side valve cover and the hose goes to a port on the bottom of the plenum I believe. By pulling the supply air from the TB, it gets metered by the MAF since it ends up as combustion air anyway.
05-24-2019, 09:49 AM
With any "V" engine, the concept is manifold vacuum to PVC in 1 valve cover - and "filtered" fresh air (breather) in the other valve cover. The fresh air ENTERS at the breather and gets pulled through the engine, picking up blow-by gasses along the way, and EXITS through the PCV valve at the opposite side of the engine, getting sucked into the intake to be burned. Actually simple once you understand it. 
happy fathers day to all the dads out there! Mine got me hooked on wrenching when I was just a lil guy. 
