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Unread 03-22-2012, 10:09 PM   #1
aschubert
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Total loss for ideas! Anyone with deep knowledge?q

97 tj 4.0....prob: surge/hesitation (on acceleration) rough closed loop idle, power loss..rumbles along rather than smooth running...

Heres where it gets interesting: vacuum aces across all tests, compression 125,125,130,124,125,127...stable 40 psi fuel pressure, rebuilt and tested injectors, new Map sensor, tps sensor tests good, new plugs, wires and spark to plugs tested excellent with online tester, new cat, new o2 sensor, new exhaust manifold..no vacuum leaks anywhere...ran through all possible test variations with vacuum gauge. New gas tank and filters. Whining alternator, but output solid. Evap solenoid tested perfect with ohm meter..(only test I knew to run on it)..evap dry, unplugged. All new exhaust system, including cat. Had intake manifold leak for awhile, baked some plugs, but compression and vacuum testing indicates valves, rings good. Seems to be running rich..as if timing was off...but as u know, no adjustment on that..chain jump would cause far more problems...idle air control sensor clean, functioning unknown. Have not done leak down test, symptoms don't point to that revealing anything. Rough idle spotty, not patterned..as if rich...wondering if unburned fuel closest to intake leak that was fixed cartooned up valves and preignition is occurring..anyone got ANY FREAKING SUGGESTIONS! ARGHHHHH! Oh yeah..mileage is down, too.... :confused

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Unread 03-22-2012, 10:32 PM   #2
MattJeep
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Try a proper NTK O2 sensor. Mine had symptoms just like yours and the O2 sensor cured it. Just a thought.
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Unread 03-22-2012, 11:09 PM   #3
Knuckelhead
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Have you tried unplugging the upstream O2 sensor?...
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Unread 03-22-2012, 11:40 PM   #4
ratmonkey
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Isn't fuel pressure supposed to be 49psi?
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Unread 03-23-2012, 12:19 AM   #5
mrblaine
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Quote:
Originally Posted by aschubert View Post
97 tj 4.0....prob: surge/hesitation (on acceleration) rough closed loop idle, power loss..rumbles along rather than smooth running...

Heres where it gets interesting: vacuum aces across all tests, compression 125,125,130,124,125,127...stable 40 psi fuel pressure, rebuilt and tested injectors, new Map sensor, tps sensor tests good, new plugs, wires and spark to plugs tested excellent with online tester, new cat, new o2 sensor, new exhaust manifold..no vacuum leaks anywhere...ran through all possible test variations with vacuum gauge. New gas tank and filters. Whining alternator, but output solid. Evap solenoid tested perfect with ohm meter..(only test I knew to run on it)..evap dry, unplugged. All new exhaust system, including cat. Had intake manifold leak for awhile, baked some plugs, but compression and vacuum testing indicates valves, rings good. Seems to be running rich..as if timing was off...but as u know, no adjustment on that..chain jump would cause far more problems...idle air control sensor clean, functioning unknown. Have not done leak down test, symptoms don't point to that revealing anything. Rough idle spotty, not patterned..as if rich...wondering if unburned fuel closest to intake leak that was fixed cartooned up valves and preignition is occurring..anyone got ANY FREAKING SUGGESTIONS! ARGHHHHH! Oh yeah..mileage is down, too.... :confused
What brand of 02 sensor did you install?
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Unread 03-23-2012, 12:57 AM   #6
Sparkyman2000
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Fuel pressure should be 49psi or within 10%. Check volume of the fuel pump. Make sure pressure doesnt bleed off entirely after 10 mins of turning vehicle off. Is the fuel good? If the LDP is stuck open too much fumes can get into intake cause too rich. I would check vacuum hoses from rear of car to front. Is check engine light on or any codes stored? Charging system ok? not correct voltage and amps the PCM acts wierd. Throttle body clean and decarbonized same with intake?(a Service Bulletin) Oh as far as IAC is concerned I would remove it than plug it back in turn ignition on see if it moves.
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Unread 03-23-2012, 01:22 AM   #7
DevilDogDoc
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Early TJ, maybe weak exhaust valve springs?
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Unread 03-23-2012, 01:28 AM   #8
twofiveLO
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Quote:
Originally Posted by Knuckelhead
Have you tried unplugging the upstream O2 sensor?...
X2

I had the same thing going on for a couple months and replaced an tested just about everything. One day I unplugged the o2 sensor.... I haven't plugged it in since
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Unread 03-23-2012, 08:18 AM   #9
UnlimitedMatt
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I heard of people having random issues with 97's. Over in the Colorado section of NAXJA (North America XJ Association) they were saying to replace the ecu (computer). That was the last thing they replaced out of desperation and it fixed the random problems on their 97.
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Unread 03-23-2012, 11:30 AM   #10
Knuckelhead
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Quote:
Originally Posted by twofiveLO View Post
X2

I had the same thing going on for a couple months and replaced an tested just about everything. One day I unplugged the o2 sensor.... I haven't plugged it in since
That's a troubleshooting step, not a fix...
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Unread 03-23-2012, 01:34 PM   #11
NotURMailman
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A bad injector (or injectors) leaking fuel into the engine is also possible, although less likely than some of the other suggestions that have been made.
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Unread 03-24-2012, 02:12 PM   #12
aschubert
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LDP? 02 sensorwas whatever orielly's had on a frustrated Sunday....intake and upper engine had 64 oz of sea foam, throttle body pulled off and cleaned already...one other thing...no pressure released when fuel cap removed,but seems like people say that's the norm? Do you mean see if unplugging the iac while running to see if the idle speed moves? Not certain what u meant by that idea....gonna look at all suggestions...Thanks for responses! Will let y'all know...
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Unread 03-25-2012, 07:16 PM   #13
twofiveLO
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Quote:
Originally Posted by Knuckelhead

That's a troubleshooting step, not a fix...
"Fixed" my problem until I get around to replacing it
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Unread 03-25-2012, 08:07 PM   #14
mrblaine
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Quote:
Originally Posted by twofiveLO View Post
"Fixed" my problem until I get around to replacing it
So in other words, we should all go unplug our O2 sensors to fix our rigs?
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Unread 03-25-2012, 09:20 PM   #15
Knuckelhead
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Quote:
Originally Posted by twofiveLO View Post
"Fixed" my problem until I get around to replacing it
That didn't fix anything, it helped identify what needs to be fixed...
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