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Will exhaust make jeep run bad?

9K views 24 replies 10 participants last post by  I6CJ7 
#1 ·
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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#2 ·
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.
 
#3 ·
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.
 
#5 ·
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.:cheers2:
 
#6 ·
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...
 
#9 ·
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?
 
#10 ·
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.
 
#11 ·
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
 
#12 ·
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.
 
#13 ·
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.
 
#15 ·
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!
 
#16 ·
Like I say, it's what you want out of your engine.

For a 4 banger
lots of HP at High RPM look at a short 4-2-1 header lots of scavaging

Lots 'o torque lower RPM? long individual runners into a single collector.

Exhaust are interesting. Matching them up with intakes and cylinder designs even more....
I got a book about 300 pages just looking at the scientific aspect of designing an exhaust system.
Helps when I cant sleep at night....

Actually Bosch has the best book out there on engine and automobile design.
incredible info

http://www.amazon.com/Bosch-Automotive-Handbook-8th-Edition/dp/0837616867
 
#17 ·
Ok so I have a question. My manifolds both intake and exhaust are both stock. I would love to replace the exhaust manifold with headers if that make better sense. But reason I haven't is because I keep hearing from everyone that they end up breaking from bouncing around and even normal driving?? Then I was told that there are header out there that have stress relief built in the headers and you can buy them off ebay. But even then I hear those eventually break and only after a few years.

Is this true?

John S. thanks for the advice I will look into that reference and learn a little more. Right now I have all my braces disconnected on the exhaust so that I could move it around a little. It ended up sliding on me and burnt a hole in my front brake line just off the proportioning valve. Thank goodness for E-Brakes!

Got the brake line replaced and the exhaust moved and mounted again. The jeep still feels like not as much power as it should and there are no leaks in exhaust anymore. Got those fixed. So now I am back to wondering if I should just disconnect the exhaust from the header and drive around and see what happens?

Thoughts?

Again, this all started before the jeep exhaust was leaking. Jeep studdered and lost all power while driving. Have to pull over usually and give the jeep a second. Then I could only drive around 30-40mph. Next day its fine again. Usually i could get it up to around 50mph right after the jeep had a small break but it would just choke out again and slow me back down to around 30mph. Then when exhaust was leaking, it stopped having that issue anymore. Then I fixed the exhaust leaks and its back to choking again.

.
 
#19 ·
Personally, I don't think your performance issues have anything to do with the exhaust.

Have you done any other diagnostics? Have you checked fuel delivery and vacuum pressure when it acts up?

How do the plugs look? They often give clues to what is going on.

Good luck,

Matt
I agree Matt. I was thinking a short, plug wire or coil wire, temporarily arcing. Plugged exhaust will affect the engine 100% of the time... IMO.
 
#21 ·
4.2 straight 6's dont crack or break headers only the newer 4.0's do. I don't know why that is though...
And our 4.2 can be had with a real long tube header. Like Hedman headers, which is what I've had for overs 7 years now, and even 2 different 258's and I've never had a crack or anything develop on it. They make alot more power, and really makes the 258 sound mean!
 
#22 ·
Well lets move on then.

skerr I never have replaced the plug wires. They look cheap anyways. I have replaced plugs with either autolites(sp?) or champions. I will pull one two of them and take pictures for you to look at. Distributor cap and roder replaced. Coil replaced.

strenk you actually helped me out several years back when I started my rebuild. You learned me on the heat riser. I went to local auto parts store and they took me to back of shop and in an old dusty cigar box was a spring for the heat riser:). However that spring has already deteriated and fallen off. So now heat riser is open all the time if I remember the default position properly.
 
#24 ·
Well guess what, went down to take out a spark plug for you guys and found a huge vacuum leak! I don't know what it is or if I even need it anymore but it is what has been causing my bad idle! I have not been able to keep the jeep idling for chit and its been so bad the past couple days it ISNT idling at this point.

I saw it was pulled out and barely hanging and so i pushed it back in and boom! I started jeep and it idles perfectly!

Mabe you guys know what this is and can i just silver plate(cap it off) the thing and forget about it?

http://www.jeepforum.com/forum/f8/intake-manifold-part-what-1560536/

.
 
#25 ·
If you're asking what that diaphragm looking thing is in the first pic on that thread, it's the EGR valve. And it isn't needed. Mines just plugged off with no line going to it on my weber 38. I did see a guy who made a block off plate for it just because it looked better. But if there's no vacuum on it, it wont be open anyways.
 
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