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post #1 of (permalink) Old 02-21-2003, 06:54 PM
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Blow By?

Ok, I need some real help now. My mechanic has been doing various things to my '84 CJ7. I Nuttered it, TR TFI'ed it, replaced the Carter with a Weber and I still have a serious problem. It appears that it is running very rich, smell of gas, fouls out plugs in a week, etc. Adjustment of the Weber per instructions makes little difference. The real problem is the atomized oil that comes out of the PCV, the supply air and the oil cap when removed. I even put on a vented oil cap to help with the problem. My mechanic believes that it is blow by. The thing that makes me suspicious is he did a compression test and all six cylinders showed around 125. The catalytic converter does not show any back pressure.

He is beginning to think that we should replace the engine. Is this where I stand?

Any insights are GREATLY appreciated.

Sharps
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post #2 of (permalink) Old 02-21-2003, 07:13 PM
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Re: Blow By?

If it's running as rich as you say and you have bad blow-by, I'd think the oil would smell of gas.
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post #3 of (permalink) Old 02-21-2003, 07:54 PM
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Re: Blow By?

Taz:
Just stick my nose over the oil fill hole to check?

Thanks

Sharps
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post #4 of (permalink) Old 02-21-2003, 07:59 PM
 
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Re: Blow By?

With 125 psi on all 6 holes, I would rule out blow-by. Replacing the PCV valve would be the next step and it's cheap too.
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post #5 of (permalink) Old 02-21-2003, 08:02 PM
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Re: Blow By?

Pull the dipstick and sniff.
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post #6 of (permalink) Old 02-21-2003, 08:08 PM
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Re: Blow By?

Ddieken:
Brand new PCV. First thing in the morning I'll pull the dipstick and see if I can detect a gas smell.

Smaller jets in the Weber?

Sharps
post #7 of (permalink) Old 02-21-2003, 08:43 PM
 
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Re: Blow By?

If it runs strong and has that compression (not seriously low), I wouldn't let a little blowby dictate that I replace the engine. I'd set up some kind of a catch can for the pcv filter. and have the filter dump into it. If you have the stock type air cleaner I'd move the pcv filter away from it as it must be just fouling the air filter. Or if you can set up a sealed can with a drain on the bottom and the filter on the top, it will keep the filter from getting so clogged with oil that it doesn't vent well anymore. I'm sure you know this, but that filter is supposed to be drawing air in, not venting fumes out, but given enough crankcase gasses (to obverwhelm the capacity of the pcv system), it's better it leaves thru the filter than blowing out gaskets. Also, valve covers typically are baffled at one end and that's where the pcv valve should go and the other end is for the line to the filter. I imagine a creative guy could remove his valve cover and tack weld on a sheet metal baffle beneath both openings to reduce the exposure to oil.

Is it rich overly rich at idle? I'd imagine there is somewhere a web page explaining the various circuits on a weber and how to tune them. You will typically set up the idle mixture with a pair of mixture screws and alter the mid to wide open throttle with jets. If there's something in between on this carb, you will have read up on that. I know that jet kits are available for the webers. You just don't want to be leaning out the jets if the idle mixture is all that's off or vice versa. Maybe consider investing in a 02 sensor based mixture gauge. They seem to be getting reasonable in price. Would soon pay for itself in gas at todays prices.
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post #8 of (permalink) Old 02-21-2003, 09:13 PM
 
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Re: Blow By?

</font><blockquote><font class="small">In reply to:</font><hr />
Pull the dipstick and sniff.

[/ QUOTE ]
Sage advice for a Jeeper in need, or an explicit, get-your-face-slapped pick up line? [img]images/graemlins/grin.gif[/img]
Sorry Taz, I had to...
[img]images/graemlins/givemebeer.gif[/img]
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post #9 of (permalink) Old 02-21-2003, 09:47 PM
 
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Re: Blow By?

I agree with TiminMb. Run a catch can. I've got a bit of blow by on my 258 as well, and I'm getting that atomized oil you mention through the pcv back into the Weber. I cut some filter material and fit it inside the pcv tube to cut down on the residue. It still runs strong though, and I'm not ready to pull the engine just yet. I just found a catch can in my Jeg's catalog which I'm going to be installing along with a breather filter.

As for the rich condition, I'm experiencing similar conditions. I think part of it has to do with the cold temps and my manifold heater not functioning properly. After it warms up it's not as bad, but it's rich enough at startup to foul the plugs pretty bad. I just installed an MSD 6a which helps cut down on the unburned fuel at startup, and it doesn't seem to burn as rich now overall. I'll also be getting a jet kit for the Weber. How far in is your idle speed screw? I remember reading in the instruction manual about false rich condition when it's actually lean, I guess due to the idle speed screw being too far in and too small a jet size. I'd have to check that though. Doesn't make sense. Hope I haven't confused you more. I'm still figuring out my Weber also... [img]images/graemlins/blush.gif[/img] You're not alone, though...
and I don't think you need a new engine...
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post #10 of (permalink) Old 02-22-2003, 08:30 AM
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Re: Blow By?

Morning all, I checked the dip tube and I don't get a distinct gas smell. Is there a possibility that all the oil being sucked into the carb through the pcv and the air cleaner could be the problem with fouling out my plugs? I am going to locate a catch can. What are the implications of putting breathers on all three of the crankcase holes (oil fill and pcv in and out) and just letting it breath without going through the carb? A no-no?

Brick, right now the idle screw (the low speed one up on the linkage) is set where they recommend at around 1 1/2 the mixture screw is at about 2 1/2 but moving it seems to make very little difference. I was thinking about going to the MSD 6 ignition module but was worried about how complicated it would be to wire. There sure a bunch of wires that go to the existing module. Was is bad?

Thanks all,

Sharps
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