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Unread 02-26-2015, 07:28 PM   #1
Colt44
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258 with MPFI conversion smoking at certain times - valve cover plumbing the culprit?

My '83 CJ-7 has the full 4.0 head/MPFI upgrade. Donor vehicles were 91-95 YJ (and a few parts such as computer and what passes for the distributor cap from 95-98 Grand Cherokees). Runs fine, but it occasionally blows some blue smoke, sometimes a pretty big cloud. Not all the time, so probably not rings. Not every morning, so probably not a valve guide. However...

After I did the upgrade I smelled an awful lot of gas fumes, so I pulled the charcoal canister and associated plumbing from the '91 Wrangler. There is now a tube running from the rear of the valve cover to the intake manifold, and a breather filter at the front of the valve cover.That did away with the fumes, but I suspect that the tube from the valve cover to the intake manifold might be sucking a lot of oil and dumping it into the fuel/air mix, resulting in smoking and increased oil consumption. A look into this plumbing shows evidence of a lot of oil present in that tubing.

So - I've heard a lot about "baffles" and enlarging certain holes, etc. in relation to oil escaping from the valve cover (which came from a 95-98 Grand Cherokee).

Would it help for me to run the tube out of the front (higher) end of the valve cover, and put the vent at the rear?
Do I even need a vent?

Do I need to modify my valve cover, or get one from another year or aftermarket?

Sound, fact-based advice from someone with knowledge on this particular wrinkle would be much appreciated.

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Unread 02-27-2015, 04:35 AM   #2
gmakra
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Are you using a PCV or the 4.0 tubing kit? The kit is calibrated for the 4.0 and crankcase ventilation.
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Unread 02-27-2015, 11:11 AM   #3
Colt44
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I pulled the plumbing - including the canister - right off Wrangler/Grand Cherokee donors and grafted it on per the emissions chart from the Factory manual. (Technical or Service, don't remember.)
The whole system, from gas tank, rollover check valve, etc. right up to the valve cover is per the diagram for a YJ, so I don't think the plumbing, per se, is the problem.

IIRC, I used the fittings off the Wrangler, and I think some tubing off the Cherokee because the length was a better fit.
But the PCV is the same as what was already on the valve cover. The grommet was hard as a rock and needed replacing, so I went ahead and got the PCV.

So, the emissions parts are correct for the valve cover - it's just a matter of whether the valve cover is correct or not, and causing the problem because of the way it's scavenging oil improperly.
I think, if this is what's causing the problem, it would come down to the valve cover itself and whether the configuration of this particular cover is causing excessive oil to be pulled from the top end and fed into the intake.

I know I've heard people talking about baffles, or lack of same, causing this kind of problem.

Can anybody speak about this from experience?
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Unread 02-27-2015, 12:16 PM   #4
gmakra
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The 4.0 does not have a PCV per say it does have a calibrated tubing system. You can pull on from the junk yard or buy one from the steelership. That should make your problems go away
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Unread 02-27-2015, 12:28 PM   #5
Colt44
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Dude - did you read my post? I did in fact pull that whole system from a 4.0 donor. And though I said PCV, I was referring to the 90-degree fitting that comes out of the valve cover and connects to the tubing system.

So again, I don't think that's the problem per se.

Does anybody know about the valve cover(s) and any problems with excessive oil being pulled out of the the top end and dumped into the intake to cause smoking?

Quote:
Originally Posted by gmakra View Post
The 4.0 does not have a PCV per say it does have a calibrated tubing system. You can pull on from the junk yard or buy one from the steelership. That should make your problems go away
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Unread 02-27-2015, 01:11 PM   #6
jeepwhore
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I've seen reference to different generations of 4L having different valve cover baffling. Does the cover you have match the head being used (I assume so as it was a complete assembly)? It might be something to look into, perhaps a later year cover will have better baffling to keep the infiltration to a minimum.
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Unread 02-27-2015, 03:11 PM   #7
Colt44
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I bought the head from an aftermarket source; although it is a 7120 casting I know of no way to determine the exact year.

Quote:
Originally Posted by jeepwhore View Post
I've seen reference to different generations of 4L having different valve cover baffling. Does the cover you have match the head being used (I assume so as it was a complete assembly)? It might be something to look into, perhaps a later year cover will have better baffling to keep the infiltration to a minimum.
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Unread 02-27-2015, 04:19 PM   #8
Matt1981CJ7
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Does your PCV plumbing look like this?

If so, the rear hole is the one that needs a baffle. You should be able to remove the rear grommet and see the baffle inside the valve cover.

Matt
yjvacuum.jpg

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Unread 02-27-2015, 04:45 PM   #9
gmakra
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Quote:
Dude - did you read my post? I did in fact pull that whole system from a 4.0 donor. And though I said PCV, I was referring to the 90-degree fitting that comes out of the valve cover and connects to the tubing system.
Quote:
But the PCV is the same as what was already on the valve cover. The grommet was hard as a rock and needed replacing, so I went ahead and got the PCV
Dude read your posts its unclear as to what you have done and now I will leave up to you to figure out.
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Unread 02-28-2015, 11:03 AM   #10
Colt44
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Jeez everybody's always so touchy. Really not trying to be rude, but I thought I'd already done pretty much what you were telling me to do, and said as much.

If that was unclear, my apologies. But I basically just pulled all the original vacuum tubing, along with the valve cover, from a 1991-1995 Wrangler and/or Cherokee. Whether it's a PCV or just a 90-degree fitting, it's what came off that model year 4.0 with MPFI.

Quote:
Originally Posted by gmakra View Post
Dude read your posts its unclear as to what you have done and now I will leave up to you to figure out.
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Unread 02-28-2015, 11:16 AM   #11
Colt44
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Quote:
Originally Posted by Matt1981CJ7 View Post
Does your PCV plumbing look like this?

If so, the rear hole is the one that needs a baffle. You should be able to remove the rear grommet and see the baffle inside the valve cover.

Matt
No, more like this:

The tube mates right up to the throttle body. The "fixed orifice" line goes to the intake manifold as shown.

The YJ airbox won't fit in my CJ's engine compartment, so I used the fresh air tube from a Cherokee (the big rubber 90 tube that goes from throttle body to air filter box) and fitted a cone-type air filter on the end. So, the line to the valve cover that shows being routed from the airbox attaches to a fitting I installed on the intake tube.

The lines from the evap can go to the intake manifold and air intake tube, as appropriate.

So functionally, everything is hooked up as functionally equivalent to the above diagram.

From what y'all have said, it looks like it might indeed simply be a matter of getting the right valve cover with a suitable baffle.
vacuum-diagram-1994-yj-xj-manual-full.jpg  
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