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Unread 08-04-2013, 11:39 AM   #1
twildt
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Will exhaust make jeep run bad?

I have been fighting a few problems lately. Lack of power of overall regular and intense driving. Take off is really bad, I had to ride clutch longer or the engine wants to choke and jerk. More like its sucked a ton of air and takes a second to get gas and then finally takes off.

Another issue which I have had for quite a long time now is lack of power while driving long distances. This is a little different than above. It usually happens when I drive over 200 miles or so. I'm usually traveling around 60MPH on interstate. I will be driving along and all of a sudden the jeep engine starts choking(chug chug chug) and I lose most power of engine. It takes me all the way down to around 15-30 mph. Finally I can get the gas pedal(slowly working with it) to finally give the engine gas and the engine stop choking and actually get the jeep to start moving again. But I can't push the gas pedal down hardly at all. It will start choking again. Even if I pull over and let it sit for a half an hour. I start the jeep and take off and 10 minutes or even less it will start doing it again.

Then when I let the jeep in town and start driving at slower speeds it is fine. Takes off and drives under 40MPH just find without choking. Also if it sits over night its fine to drive on highway again for another 200-300 miles again. Its crazy!

So a month ago I got a leak under manifolds and found the exhaust manifold and intake manifold gaskets had completely burned out, dried out and huge pieces were gone. I knew it had an exhaust leak for several months but continued to drive it around town thinking it was the exhaust flange leaking. It kept getting louder and I found the real problem.

I had just replaced these gaskets 3 years ago!! I couldn't believe they were already that far gone. Excessive heat is the only thing I could think of. So I replaced the gaskets again.

Now I realized I had driven 2-3 times over 400 miles on interstate while these exhaust gaskets were leaking. The engine never choked during the exhaust leaking. I figured others things fixed it and kind of forgot about it until I fixed the leak. I replaced all the exhaust and intake seals. Donut gasket. And I replaced the exhaust flange bolts and got a nice seal for the tail pipe connecting to the exhaust flange.

After I got the seals fixed I drove it home which was 130 miles away. On that very trip home it started choking on me again which it had not done the whole time its exhaust was leaking!!

So my question is maybe its my exhaust? It's shot. Its rusted up and looks like hell. I took it to an exhaust shop and they said it was terrible. No cat, just a muffler and tail pipe.

Could my exhaust be clogging and causing backed up exhaust back to the engine and causing it to overheat? Or causing that engine choking?


PS: I have the following:

258 with new weber 38/38
replaced spark plugs, new fuel filter, no FPR, gas tank is clean, new fuel pump(manual), new coil, new distributor cap and roter, new thermostadt, radiator flushed and 50/50 mix used, removed A/C(yeah, that old 1980's add-on unit), and a new ECM. This is the stuff I did trying to figure out the engine choking problem last year before the exhaust leak.

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Unread 08-04-2013, 11:49 AM   #2
JustDandee
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I have had experience with the catalytic converter clogging and causing some of these same systems(really bogging down the motor, significant loss in power) and I have talked with people that had mufflers clog up. Sometimes due to rodents not just age. If your up to it and will probably replace the exhaust anyway, you can cut the exhaust pipe before the muffler and run it open to see if that is it.
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Unread 08-04-2013, 11:53 AM   #3
twildt
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Quote:
Originally Posted by JustDandee View Post
I have had experience with the catalytic converter clogging and causing some of these same systems(really bogging down the motor, significant loss in power) and I have talked with people that had mufflers clog up. Sometimes due to rodents not just age. If your up to it and will probably replace the exhaust anyway, you can cut the exhaust pipe before the muffler and run it open to see if that is it.
I thought about doing this, I am a little worried about how loud its going to be. I also don't have a saw... I tried unbolting all the clamps and its on there pretty good, couldn't just pull it apart.
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Unread 08-04-2013, 12:01 PM   #4
JustDandee
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Buy a cheap Hack saw and it will do it in short order, then a local auto part store might have this

http://www.jegs.com/i/Dynomax/289/33...FbF_QgodsX0Aow

so you could patch it back together, but yes it will be loud. IMHO that might be fun to drive until you get into the exhaust shop.
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Unread 08-04-2013, 12:38 PM   #5
hmantractors
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Exhaust

You could have a clog between the manifold and the tailpipe. I would start unhooking the muffler and work back to the manifold trying to find a clog. I would be concerned about having run the engine with bad intake gaskets. An air leak at the intake will cause the engine to run lean. Very lean will burn the pistons. Exhaust manifold gasket leaks would not concern me other than the load noise. I would however fix that also.
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Unread 08-05-2013, 10:13 AM   #6
twildt
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I looked back on the pictures I took when repairing the gasket leak and it appears that the intake manifold gasket was ok, the broken/missing pieces of gasket were the exhaust manifold gasket only... Thank goodness.

I guess I will cut the pipe in front of the muffler. I was assuming that while I had the muffler and tailpipe under water a couple of times and the exhaust is really old that the muffler may have chunks of rust or something in it and when I'm driving along the bigger chunks blow around and clog the muffler enough to cause issues.

I didn't even think about rodents! After I got the exhaust leaks fixed I can't get the darn thing to idle right also. It runs fine but idle is terrible. Usually dies until its warm. Then when warm it barely idles and takes a while to get it to take off from a start with not much power. But when it does get going a little and engine decides to run ok all the power comes back and its fine at higher speeds.

Ugh...
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Unread 08-05-2013, 11:05 AM   #7
John Strenk
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A plugged muffler may also explain why the exhaust gaskets blew out...
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Unread 08-05-2013, 07:50 PM   #8
tiny1985
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My exhaust is detached right at the manifold, and it isn't nearly as loud as I Hugh it would b
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Unread 08-07-2013, 08:31 AM   #9
twildt
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Being detached right at the manifold, doesn't that pose a risk to sucking cold air back into the engine and causing some kind of issue?

Also, the engine rely's on the muffler back pressure too right? So without the muffler connected it's not going to run very well correct?

Or am i wrong about the 4.2 straight-six and the 1978 particular setup?
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Unread 08-07-2013, 11:07 AM   #10
John Strenk
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If you have ever seen the exhaust manifold on a stock '78 4.2 you wonder how the exhaust ever got out in the first place.

Usually the rumor risk is cooling the exhaust valve to fast that it might warp. I've never had it happen to me.

Under normal driving, probably not notice it too much but at WOT or high RPM, it could get a little leaner than anticipated with stock carb.
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Unread 08-07-2013, 11:36 AM   #11
LumpyGrits
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Hook up a vacuum gauge to the intake manifold and note the reading at idle.
Now, run the engine up to 2K, RPMS and let it stay there for a bit.
You should have pretty much the same reading at idle, IF your exhaust is not restricted/clogged.
LG
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Unread 08-07-2013, 11:46 AM   #12
dhubbs
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My personal opinion and some of what I have read is that the exhaust cooling too quickly will warp valves is a myth. Nor have o really understood why you would want back pressure in the exhaust. Headers and such are designed to improve air flow and yeild higher performance. Basically removing back pressure. It seems to me that if you can reduce exhaust pressure, the pistons will have to work less hard to push the exhaust gasses out which can't be a bad thing.
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Unread 08-07-2013, 01:23 PM   #13
John Strenk
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I agree with the first statement, I've never seen a valve warp because of open 'Exhaust'

But I have personally seen the improvement in torque with exhaust back pressure.

Flashback to 1980 and I'm running a Pinto with a warm 2.0 with a Weber 38 and 2" headers with Isky cam, trick head grind

I was running open headers in trial runs at a Autocross and it was pointed out that the track required closed exhaust. After bolting on the rest of the exhaust system on I was able to spin the tires shifting into 3rd, something I was not able to do before. I actually broke the seat back accelerating so much harder.

Ah those were the days...

But some back pressure is good depending, and repeat, depending upon your engine setup, Sure an engine can be built to run Zero back pressure and too much is bad but usually there is an in between balance.

I remember adjusting the back pressure on my VW 1600 by cutting header right were it starts to turn blue.
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Unread 08-07-2013, 02:02 PM   #14
dhubbs
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That's interesting for sure. I have always heard that it would help, but just doesnt make sense to me. I am sure there is a lot more science to it than I am knowing.
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Unread 08-07-2013, 02:23 PM   #15
I6CJ7
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Its not to much the back pressure you need. Its scavenging that becomes the issue. If the exhaust is too big, it cools the gases and they slow down. Losing power. Ceramic coatings will keep heat in the headers/exhaust and keep flow up, so a bigger diameter could then be used.

Exhaust systems are alot more complicated than most people know.
Just look at a 2 stroke bike header. Anf Google how that works!
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