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Unread 08-18-2012, 11:29 PM   #1
Forum16
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1997 TJ Wrangler 
 
Join Date: Aug 2011
Location: San diego, Ca
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Need help! Loss if power / gas mpg

My 97 tj with a 2.5l is giving me alot of heartache. It keeps giving me a engine code: p0171 (high voltage reading in upstream o2 and lean fuel mixture) so far I've swapped out both o2 sensors, All my injectors, plugs, wires, cap, rotor, tps, and cleaned out my throttle body. The tps may have helped a little, but still when I hit any kind of hill over 50 mph my engine/power/revs starts hesitating/sputtering. And is usually followed by the CEL: p0171. The only thought I have left is the fuel pump and Id really rather not drop the tank if I don't have to. Any ideas? Thanks in advance

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Unread 08-19-2012, 01:15 AM   #2
mukluk
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CEL code P0171 can be caused by any of these:
Fuel pressure out of specs
Fuel pump inlet strainer plugged
Restricted fuel supply line
Faulty fuel pump
Faulty O2 sensor
O2 sensor signal circuit shorted to ground
Faulty O2 sensor heater operation
TPS voltage > .92 volts with throttle closed
Faulty TPS
Faulty MAP sensor
Faulty temp sensor
Engine mechanical fault
Faulty PCM

I'd say start with checking and cleaning the connections on the sensors listed above as well as your battery connections (TJs are funny about proper battery power), followed by a fuel pressure & flow check. As an aside, if you do decide to replace any sensors, it's recommended to use OEM as non-OEM sensors have shown themselves to have generally poor reliability.
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Unread 08-19-2012, 02:58 AM   #3
ASUjeepDevil
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Quote:
when I hit any kind of hill over 50 mph my engine/power/revs starts hesitating/sputtering.
This is a new occurrence? My 2.5L does this all the time without throwing codes. Did you completely replace the TPS with an OEM unit? The TPS can't just be cleaned out like the IAC valve and sensor can.

I would do as mukluk said and make sure battery connections are clean and tight, then proceed to the fuel system. It sounds like the issue takes place only under the most stressful load, so problems may be hard to diagnose when the Jeep is sitting still. You may be able to connect a fuel pressure gauge to the rail and use a long enough hose so that the face of the gauge can be taped to the windshield or run into the cab, then cruise a hill on the highway to see if pressure drops or jumps around when you notice the sputtering. You may need to bleed the pressure before attaching the gauge though, maybe someone else can chime in for safety's sake.

The in-tank fuel filter is supposed to be a lifetime filter but I suppose it could get restricted somehow. FP regulator is a more common point of failure though (which sits right on top of the tank so you'd still have to drop it). I know you can test the check valve by trying to blow both ways through it, which you shouldn't be able to do if it's working properly, but your symptoms don't sound like they're related to a bad check valve. You may be able to check this before dropping the tank by having a buddy turn the ignition on so you can hear the fuel pump fire up for a second, repeat on-off several times in succession to draw fuel into the lines then keep your head near the tank and listen for fuel to trickle back into the tank through a possibly faulty check valve. Not sure why that would cause problems under load though - usually bad check valve is associated with problems starting the Jeep. Hopefully someone else will chime in, good luck!
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Unread 08-22-2012, 02:14 PM   #4
Forum16
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Thank you for the great input, this should keep me busy for awhile. I haven't had time to do alot yet. However, I did run some seafoam thru my vacuum/induction and barely got any smoke from the tailpipe. I did get almost as much smoke coming from where the pipe bolts to the end of the mAnifold. This among other things is giving me the feeling I have a problem with my catalytic converter, maybe it's clogged. Also after the engine is hot, and I turn it off, I've noticed a consistent ticking from the cat. So I banged on it a little (it's probably trash anyway) and from there the jeep ran perfect for about 100 miles. It seems obvious to me now to replace the cat??
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Unread 08-22-2012, 02:36 PM   #5
ASUjeepDevil
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Quote:
Originally Posted by Forum16 View Post
I did get almost as much smoke coming from where the pipe bolts to the end of the mAnifold.
Then you've got an upstream exhaust leak, which is consistent with the symptoms you described. Hopefully that's the only reason you threw the P0171 codes; perhaps the 02 sensor readings were so out of range that the computer interpreted it as a faulty 02 sensor. Get the exhaust leak fixed and reset the computer and hopefully it goes away. Otherwise you might be looking at 02 sensors again or continuing to diagnose the fuel system.

You said the smoke was coming from the point where the exhaust downpipe bolted up to the exhaust manifold? Your cat may be shot as well from what you noted but before replacing that you should probably address the known leak first. If there's an exhaust shop around that you trust you could take it in to see if it's cracked or the manifold bolts have just loosened up or something else that can be repaired. I always seemed to get rolled for a full exhaust system in these kinds of situations so a few minutes getting recommendations on honest shops in the SD area might save you a lot of money in the long run. I don't personally know of any but there's a lot of SD and SoCal guys on here that can probably give you a name to seek out.

Even though you didn't get a huge cloud of carbon smoke from the Seafoam I think you got the maximum benefit possible from that product - diagnosing an exhaust leak you didn't know you had! Good luck!
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