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L26 swap PCM question

wstefan20

wstefan20

New member
Alright, so I've been trying for a long time not to post a question as stupid as this one, but I think I'm not wrapping my head around the PCV system correctly so please humor me. I swapped to a L26 on a series 2 a few thousand miles ago, and I think everything is running fine, but I have no reference since I've never driven a stock working gp. (mine was blown up when purchased).

I read that you have to drill into the side and plug the drilled hole and cap the upper pipe, and others say just put a breather on it. I currently have just a breather so my air isn't pre-metered or anything so I don't know if this causes problems.

I've also seen those who have both and drill/tap the side and have the breather.

From my understanding, the upper breather goes to the pcv valve via a small internal passageway, and that there's another passageway in either the throttle body neck or going to the throttle body directly. My throttle body adapter blocks everything so I want to make sure that I'm not essentially canceling out the pcv system and threatening blowing a gasket.

My other loaded question is I've always been a fan of catch cans, although how our pcv system is set up, there is no stock way to hook one up, and I don't want to do the valve cover breather method.

I've seen some ls guys run a vacuum tubing and run the map sensor external. If that is possible, you could potentially add a tube coming up from where the map sensor used to be. If I'm not mistaken, if you could do this, you could epoxy the ports going to the pcv vacuum and run it to a tapped vacuum port through a catch can. This would give us the functionality of running a catch can finally! I know this would probably be a pointless mod to most and wouldn't help much out, but I really want a catch can cause I'm tired of the sludge that builds up on our throttle bodies!

If anyone has done this or attempted this, please let me know. I'll try to post some pictures to clarify things as I go.
 


So maybe I'm thinking about this wrong. For both pcv and map sensors to work, there needs to be a vacuum source. From what I can tell, this tiny hole in the side is the vacuum hole that leads somewhere in the manifold:

EyOE2n.jpg


Unless I'm wrong, there needs to be a inlet for air going to the other head to relive pressure. Not sure where the inlet goes to....

Any thoughts?
 
Ok. So I think I've almost got this figured out.... I'll be taking a trip to the junkyard today or tomorrow to confirm my theory. Way too complicated to explain in words, so here's a crap ton of pictures with circling to demonstrate paths of airflow:

The air intake starts here in the throttle body

IMG_3208.jpg


Then passes to the rear here:

hqdefault.jpg


Then goes to the upper intake manifold via the gasket here:

IMG_5291.jpg


On the L26 the air intake starts at the top stack and some people tap into that here:

UIMProj005_Mod.jpg


That's the only difference in pcv at all between systems. Both travel down through the gasket here, and I've also circled the pcv valve intake location:

zz_l36uitk.jpg


Here's where the vacuum source comes from to the pcv and map sensor, as well as the location where the intake runs:

81n_YMnzg_VSL_SL1500.jpg


Next it enters the lower intake here and also here's the entrance to pcv:

AM_2712131917.jpg


Here's a closeup on that vacuum hole for pcv we saw earlier, and the hole for pcv going to the head:

20171129_130815_747x1328.jpg


Here's where both pcv ports come out. not sure which side is which and wether they cross (I don't think they do):
s_l1600.jpg


And here's where the pcv passes through the lower intake gasket to the heads:

gasket2.jpg



I'm going to try pouring liquids and using flexible straws at the junkyard to prove my theory. Then if that is true, as long as we can use the ls folk's way of re-routing the map sensor, we can simply seal the vacuum source hole in the upper intake, remove the map sensor and use it's old location to tap into for a catch can, then simply drill for vacuum to complete the circuit!
 
Ok, so I got bored and went to the yard. Here's what I found. To make things clearer, I've added marks to show air flow.

Just in case anyone is curious, here's the air intake routing for the L26 from the top cap to the intake. Note that this is before the throttle body and after the maf sensor (pre-metered air).

20171130_095111.jpg


Here is the main difference in pcv between the L26 and L36. The blue arrow indicates the L36 pcv intake path to the throttle body, and the red indicates the path continued from the prior image. Note they both exit the same location on both.

UIMProj005_Mod.jpg


The vacuum intake for both L26 and L36 that feeds the pcv is fed through this pipe. Also shown is the bottom of the air intake from prior picture. As you'll see later on, the air intake goes to the rear head, and the pcv intake (not vacuum) is taken from the front head, and the vacuum is taken from the manifold via the pipe as shown. Top is pcv in, bottom is air intake (drew intake arrow backwards).

20171130_100721.jpg


From the upper manifold, there are two separate paths as described above. Here is where they flow. Note, that the red arrows are drawn the wrong way as the air intake flows into the head from above. The crankcase pressure travels out via the blue arrow to the pcv.

AM_2712131917.jpg


The rear head is the air intake, and the front head is the crankcase pressure release to the pcv. The holes in the head allow crankcase pressure from the rear head to travel to the front head for expulsion traveling in the lifter valley as shown. Also shown is the port that both heads use for transferring either air intake or pcv pressure to the lower intake manifold.

20171130_102304.jpg


The funniest thing about this is that everyone who has been laughed at for putting a breather on top of the L26 nipple instead of the "preferred" method of drilling through the side of the L26 (see prior post) into the vertical air column and plugging the outside hole is completely negating their pcv system because they are routing their pcv air intake to vacuum!!! While this will equalize the pressure in the crankcase, you are in a sense completely bypassing the pcv system entirely!

The better route (which I will be doing and I know some others have also done) is to tap into the throttle body before the throttle blades but after the maf sensor. This is the correct way to hook this up. You still have metered air, but you are not tying to vacuum.

I've also seen people tie to a tapped port on the throttle body adapter. This is also vacuum though, so you are also negating your pcv system. Don't tie in here for pcv air intake.

I've been running unmetered air with no "ill effects" just using a breather on the cap, but I'm going to tap a hole to see what affects it has on engine performance (my guess, it looks cool).

As far as adapting a catch can, it looks like the easiest and probably most effective way to do so is to use vacuum assisted setup. Basically, I'm going to relocate the MAP sensor to another vacuum source (basically anywhere on the intake manifold should work), plug the original vacuum intake, and run the catch can from the MAP old hole to another vacuum source.

Theoretically, this should run same as stock, but I'd be running the vacuum intake externally through a catch can rather than straight to the intake via the small hole and pipe.

For MAP relocation, I'm thinking I'm going to tap into the throttle body spacer same as the N* engines do. Note, they use the same exact MAP sensor. It should turn out looking pretty stock too.

20171130_112828.jpg


Anyways, I've babbled on long enough. While it's fun writing this stuff and talking to myself, I'd love to hear from anyone on their experiences! Any advice helpful!
 
Turns out I'm not insane. A bunch of the LS guys do this relocation all the time with almost the exact same sensor because some aftermarket intakes don't have the provision for the sensor. Some have made custom billet blocks with a barb running to them, but others have just run a hose with some clamps to it! I'm going to tee off the vacuum for the catch can and try that to start with, just in case it doesn't work properly. That way I can just temporarily plug the stock pcv vacuum intake and route a catch can temporary to see if it works first before I go drilling holes! :th_laugh-lol3:

Didn't realize this, but I forgot that the L67s have MAP sensors fed simply by vacuum. Same sensor, just connected externally like I'm planning!

If this works, that means anyone with a L26/L36 can easily adapt their pcv systems to run a catch can without running a breather, and without re-routing their entire pcv system! (plus could be easily reverted back) This method might be adaptable to the L67 but I'd have to do more research first.
 
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iirc the l26 intake uses a external map. could be wrong. the pcv hose need to be routed to the intake tube like you have marked out.

that other hole in the intake near the tb is for the evap solenoid. either block it off, use the old one you have or get a l26 evap solenoid.
 


Scottydoggs said:
iirc the l26 intake uses a external map. could be wrong. the pcv hose need to be routed to the intake tube like you have marked out.

that other hole in the intake near the tb is for the evap solenoid. either block it off, use the old one you have or get a l26 evap solenoid.
Click to expand...

Thanks scotty! I was wondering about the evap solenoid. I've been running this for a while now, I'm mainly just trying to see if I can hook up a catch can.

The L26 has the same MAP sensor location, but I think it can be moved so I can tap a catch can. I'll test it out soon!
 
dont waste your money or time on a catch can, its soooooooooooooo not needed at all. if you had a turbo, then it could be justified, or a v8.
 
Already got a cheap catch can lying around, plus have you seen the crap the pcv spews all over the intake? I'd love to get rid of some of that.
 


blueguy91 said:
Deleting the EGR takes care of all of that build up.

Nothing else.
Click to expand...

All the other car's I've run catch cans on have been much cleaner than the one I deleted the egr. Also, why would anyone delete the egr in the first place? It helps reduce knock, lowers emissions, and lowers combustion temperatures. When I'm at the junkyard, All the n/a intakes are covered in oil spray, not soot from egr. I'm not saying that the egr doesn't contribute, but I think the pcv is the lead culprit here. I agree, on a boosted application, it would be much more critical than n/a, but I've run a catch can on a honda 4 cylinder with 70,000 miles and caught more than I could imagine (about a quarter of the tank every 5,000 miles)! Idk. I'm just interested to see how much this catches!
 
Just got a chance to do a test today, and I think this might actually work!

To test, I just extended the MAP sensor out with some spare parts lying around. Yes, I know, it's going to hit the hood, this was just a temporary setup. I plan on using a 1/4" to 3/8" 90 degree barbed adapter running to the catch can. With the 90 degree, I can use a zip tie to secure it where the MAP sensor hooked to. Then I have a 3/8" barb for vacuum off the throttle body adapter for the other hose for the catch can completing the circuit. Here's the test:

20171201_181856.jpg


20171201_182747.jpg
 
because it skews fuel trims in a huge way when you are trying to tune, and it doesn't really make that big of a difference in gas mileage
 


i get the same mpg with out the egr and all my mods as i did when it was stock. it dont affect a thing mpg wise.

just how does it lower temps? its sucking in hot exhaust thats full of carbon. all that crap on the back side of your tb blade is from the egr. the na cars with plastic intake the egr stove pipe melts the intake and makes it fail too.
 
Interesting. I hadn't thought about tuning. Makes since because it only opens at high load.

It would be nice to clean up the engine bay a bit.... Thanks for the advice.

Anyone else have any input on the egr delete?

I still think the catch can will help with sludge. If you've ever removed a 200,000 mile l26 intake, you know what I mean!
 
Won't hurt anything by trying it, the way I'm going to hook it up is completely reversible, and won't cost me anything since I already have the parts.

Worst case scenario, won't do anything. Best case, it'll keep my intake clean and keep blow by oil from being burned. It's worth a try!
 
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