Intake Manifold Gasket change 258 -
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post #1 of 3 Old 10-20-2002, 05:46 PM Thread Starter
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Intake Manifold Gasket change 258

Intake Manifold Gasket change 258

I think my intake manifold gasket is leaking a little and would like to change it. Does anyone out there have experience with this project on an 85CJ with a stock 258ci engine?

1. are the intake and exhaust gaskets two separate gaskets?
2. can the intake be changed without changing the exhaust gasket?
3. do some people use no gasket, just PVC?

The reason I think my gasket is leaking is after being on the freeway for a few miles and coming to an exit, the idle becomes very rough. The RPM don't seem to decrease - if anything it increases slightly but is rough. After a couple of miles of driving the surface streets it smoothes out at idle. So, I think when it is running at the higher RPM for extended periods the intake manifold must develop a leak probably somewhere near the exhaust manifold where it gets the most heat. After cooling a bit by driving at the slower speeds, it goes away.

2004 Rubicon, 6" lift, 35s, winch, hard top, full doors, bumpers, tire carrier and rock sliders.
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post #2 of 3 Old 10-21-2002, 09:08 AM
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it may not be your intake gasket. '85 would have a computer (unless you removed it...) possibly it could cause a problem? i dont know anything about vehicle computers, but it might be something to check into.

now, for your question...
'81 and up 258's should have separate intake and exhaust manifolds/gaskets. mine is an '81, and it does.

yes, you should be able to change the intake without removing the exhaust. the exhaust is bolted to the block with (4?) bolts/nuts, and the intake seats between the ports of the exhaust, using bolts with washers that seat on a metal lip cast into the intake. there should be (8?) of these. as a side note, when you replace the gasket, you probably would want to replace these with new, grade 8 bolts(+antiseize compound). forgive me if this description does not make sense, when you look at it, you will see what i mean. to get some of the bolts out, you will have to use some u-joint ratchet extensions, this is fun...

PVC? i am supposing you mean RTV, this would not be good (or necessary) to use on the intake . when you start the engine after charging the gasket, it will smoke a little, this is the gasket heating up and sealing itself.

if you buy the gasket at a place like autozone, it will probably come with both intake and exhaust gaskets, + a little o-ring and gasket for the manifold heater. if you into the motor that far, you might as well change both while your at it.

i hope that i have been a help, good luck!

'81 CJ-7 Got it when I was 16!
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post #3 of 3 Old 10-23-2002, 12:34 AM Thread Starter
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Well, I found the problem. I drove it several times at high speeds and when I'd come to a stop I'd adjust the air mixture screws. Sometimes it would help a little and sometimes it got worse. Finally, today I was doing it again and when I came to a stop, I could hear a high pitch whistle noise coming from under the hood. I raised the hood and sprayed brake cleaner at the intake manifold and carb base plates. Well, low and behold, the idle changed drastically when spray touched the rear two pieces of the intake manifold. The idle smoothed out and the whistle noise went away. I will change the gaskets tomorrow.

PS - I did bypass the computer since I run a Weber carb and have no need for a computer to control mixture settings.

2004 Rubicon, 6" lift, 35s, winch, hard top, full doors, bumpers, tire carrier and rock sliders.
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