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Discussion Starter · #1 ·
HELP please :(

New exhaust fitted ( well not new but new to me ) by my mechanic friend and it sounds great but I have noticed significant loss of top speed. wont pull past 60, but feels and drives great. I dont believe in coincidence but can poor back pressure cause this? I am booked in to have a new custom build by a professional in 2 weeks but I want to figure this out.

Any ideas? Please help guys....
 

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Backpressure in the exhaust can easily cause a major loss of power. One of my pre-cats came apart internally and plugged up the main catalytic converter just below it and my speed was limited to about 5 mph after that happened. It happened suddenly on while on the highway 75 miles from home. I had to limp to a friend's house at 5 mph on the side of the highway for something like 10 miles to fix it.
 

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loss of back pressure really only effects low RPM areas and torque..

Higher RPM and the engine will come alive..

You got something wrong other than that...
vacuum leak or fuel problem
 

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Discussion Starter · #4 ·
Thanks guys, I am pretty sure there isnt a vacuum leak, no other symptoms and my revs are steady. Again I thought about fuel pump, but surely there would be other symptoms? Not just a drop of top speed? Hmmm
 

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look to make sure the injector harness on the right way and snapped to every one.

be surprised on vauccum leaks... they can be tricky mf
 

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Discussion Starter · #6 ·
Cheers blackbox will go check now. I would have thought there would be a missfire if the harness wasnt on right though? I will check around the throttle body etc spray for air leaks.
 

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Discussion Starter · #7 ·
Daft question but I'd better check. I did change my coil pack myself, the springs that go in each slot were a huge pita but I managed to get it finally, but could it be possible one of them is bent or not making a good connection with the plugs?
 

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Backpressure in the exhaust can easily cause a major loss of power. One of my pre-cats came apart internally and plugged up the main catalytic converter just below it and my speed was limited to about 5 mph after that happened. It happened suddenly on while on the highway 75 miles from home. I had to limp to a friend's house at 5 mph on the side of the highway for something like 10 miles to fix it.
To clarify, that problem was caused by excessive backpressure due to the clogged catalytic converter.
 

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Discussion Starter · #9 ·
Checked everything as best I can and nothing is showing up. It ticks over so sweet and pulls nicely, just will not go past 60mph, doesnt accelerate at all in 5th but it probably needs a re gear as I have larger tyres but it shouldnt stop pulling at 60. It didnt before I had my exhaust messed about with. Was hoping to avoid the mechanic :(
 

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Discussion Starter · #11 ·
Willl try this later this evening. I used NGK plugs, noticed a difference instantly on how smooth it felt, sure it isnt an issue with these..
 

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This could be a long shot but, could it maybe be your O2 sensors? Mine wasn't accelerating over like 65 the other day, but it threw on the check engine light. Took it to Oreillys so they could pull a code and it ended up being the O2. I purchased the upstream sensor cause I think that's the one messing up. If not I'm probably going to replace the downstream as well.
 

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The upstream sensor is the one closest to the engine, it should be the front.

Also, Bosch sensors are known to cause problems in Jeeps.
 

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Also, how many O2 sensors does your '01 have? My '06 has 4. Two upstream and two downstream.
 

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Sorry Chris, just saw this. My 97 TJ only has 2 sensors, my upstream being close to the front oil pan and front drive shaft. I just went to rockauto.com and bought it off of them. Not good hearing Bosch causes problems because that's the one I bought haha! If you do decide to replace the sensors, soak them in penetrating oil a day prior to taking them off. Mine was stuck in there, it's currently soaking over night.
 
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