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Misfire/Lack of power....Gettin Frustrated...

rugidone

NAXJA Forum User
This has been a bit of an ongoing problem lately and is sort of a compressed post from another forum.

(Intermittent problem)
After heading to work, the jeep runs great for the first couple kilometers then picks up a lack of power attitude until it reaches higher RPMS then takes right off, Plugs/wires/cap/rotor button are all recent.

Shut jeep off, restart and normally, problem goes away.

Now Friday, while it was in one of its gutless moods, it actually broke down, and had a hitching misfire til I got to where I was going, shut it off, restarted and ran fine the rest of the drive.

After this weekend.

This past weekend, I changed the exhaust manifold, downpipe, 02 sensor, center sections and muffler to eliminate all the leaks.

Cleaned intake, throttle body and the IAC, I also changed fuel filter and CKP.

Problem is still there, if not worse, it wants to die when rolling up to a stop sign.

Still behaves like before though. Intermittent boosts of power, its really sluggish and getting hard to drive. While cruising and slowly getting up to speed, sometimes it will take off like it should for a few moments then when it upshifts it goes back to the sluggish misfiring pile of metal.

Any insight before I burn it to the ground?
 
Make sure the vacuum hose to the map on the firewall isn't leaking. Unplug and replug all sensors. Take off the coil on the passenger side of the block and inspect it. Clean the metal bracket it was living on. Remove, clean, and tighten all grounds. Make sure battery terminals are clean and tight.
 
So, I changed the temp sensor and the coil tonight, still no change, drove it home, and just decided to unplug the 02 we just put in, drove around the block a couple times, and there is no longer any stumbling/power loss.

Would I be correct in saying theres a good chance the 02 was the culprit? Or is unplugging the 02 just screwing with the electronics.
 
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Very high chance. I would imagine that the 02 was bad so the Jeep was in limp mode. I have had rigs do that and they run like crap till fixed.
 
Check the compression in all 6 cylinders. If you have a couple that are low and they are beside each other, then you have a blown head gasket. It will crack between the 2 cylinders and bleed compression off into the adjacent cylinder..... if just one is low, then do a wet test on that cylinder-- pour a teaspoon or so of oil in the spark plug hole, the do a nother compression check. If the compression comes way up in that cylinder then you have bad/broken rings in that cylinder. If it stays about the same, then you have a bad valve, cracked head, blown head gasket.... check the compression, make note of the number for each cylinder and report back.
 
If this were mine, the first thing I would do is test the throttle position sensor. It can give flaky symptoms at certain areas in the throttle band, then work great in others.
Here is more....
----------------------------------------------------

The throttle position sensor is connected to the throttle shaft on the throttle body. It sends throttle valve angle information to the PCM. The PCM uses this information to determine how much fuel the engine needs. The TPS is really just a simple potentiometer with one end connected to 5 volts from the PCM and the other to ground. A third wire is connected to the PCM. As you move the accelerator pedal with your foot, the output of the TPS changes. At a closed throttle position, the output of the TPS is low, about a half a volt. As the throttle valve opens, the output increases so that, at wide open throttle, the output voltage should be above 3.9 volts. Testing can be performed with an electrical meter. Analog meter is best. You are looking for a smooth sweep of voltage throughout the entire throttle band. While slowly opening and closing the throttle, take note to the movement of the voltmeter needle. There should be a direct relationship between the needle motion to the motion of the throttle. If at anytime the needle moves abruptly or inconsistently with the movement of the throttle, the TPS is bad

You should have 5 volts going into the TPS. At idle, TPS output voltage must be greater than 200 millivolts. At wide open throttle (WOT), TPS output voltage must be less than 4.8 volts.. The best is to use an analog meter (not digital) to see if the transition from idle to WOT is smooth with no dead spots. With your meter set for volts, put the black probe on a good ground like your negative battery terminal. With the key on, engine not running, test with the red probe of your meter (install a paper clip into the back of the plug of the TPS) to see which wire has the 5 volts. One of the other wires should show .26V (or so). The other wire will be the ground and should show no voltage. Move the throttle and look for smooth meter response up to the 4.49 at WOT.

Perform the test procedure again and wiggle and/or tap on the TPS while you watch the meter. If you notice any flat spots or abrupt changes in the meter readings, replace the TPS.

The TPS is sensitive to heat, moisture and vibration leading to the failure of some units. The sensor is a sealed unit and cannot be repaired only replaced. A TPS may fail gradually leading to a number of symptoms which can include one or more of the following: -

NOTE: The throttle position sensor is also DIRECTLY involved with transmission shifting characteristics! It should be verified early in the troubleshooting process, when a transmission issue is suspected!

• Poor idle control: The TPS is used by the ECU to determine if the throttle is closed and the car should be using the Idle Air Control Valve exclusively for idle control. A fault TPS sensor can confuse the ECU causing the idle to be erratic or "hunting".
• High Idle Speed: The TPS may report faulty values causing the engine idle speed to be increased above normal. This is normally found in conjunction with a slow engine return to idle speed symptom.
• Slow engine return to idle: A failing TPS can report the minimum throttle position values incorrectly which can stop the engine entering idle mode when the throttle is closed. Normally when the throttle is closed the engine fuel injectors will be deactivated until a defined engine RPM speed is reached and the engine brought smoothly to idle speed. When failing a TPS will not report the throttle closed and fueling will continue causing the engine to return to idle very slowly.
• Engine Hesitation on Throttle Application: The TPS is also used by the ECU to determine if the driver has applied the throttle quicker than the Manifold Air Pressure sensor can read. The fueling is adjusted acordingly to cope with the sudden increase in air volume, however a faulty sensor can cause the ECU to ignore this data and the engine will "hesitate" when applying the throttle. In extreme cases with the engine at idle, a sudden application of full throttle can stall the engine.
• Engine Misfire: A fault TPS can report values outside the deined acceptable range causing the ECU to incorrectly fuel the engine. This is noticable as a slight misfire and can trigger the misfire detection software and/or Malfunction Indicator Lamp (MIL) light on the dashboard. Extreme cases can cause excessing misfires resulting in one or more cylinders being shut down to prevent engine and catalytic converter damage.
 
The power comes back in the higher revs because the pistons are moving faster and the power stroke comes before a lot compression can be bled off... check the compression...
 
Couldnt get the compression tester tonight, but I did test the TPS, .82 closed, slowly opening the butterfly, it increased but maxed out a 3.9 or so. No jumps, tapped on the sensor with a screwdriver as I was opening the butterfly, no changes.
 
Had a similiar problem in my 89. Fuel pressure showed within specs both key on and running. Tested every sensor I could, all within specs. Did full tune up just because it had been a couple of years (less than 20k though). Still no change. Damn thing kept acting like it was starving for fuel until around 2k RPM and would then run fine. I removed the access plate for the fuel pump and found the hose coming from the pump towards the injector rail had a 1/4" split in it, which was allowing the fuel pressure to fluctuate under throttle and cause my surging issues. Once I replaced the section of hose, I've had no issues since.

Not sure if this is your issue or not, but it may be worth looking into. Good luck.
 
Had a similiar problem in my 89. Fuel pressure showed within specs both key on and running. Tested every sensor I could, all within specs. Did full tune up just because it had been a couple of years (less than 20k though). Still no change. Damn thing kept acting like it was starving for fuel until around 2k RPM and would then run fine. I removed the access plate for the fuel pump and found the hose coming from the pump towards the injector rail had a 1/4" split in it, which was allowing the fuel pressure to fluctuate under throttle and cause my surging issues. Once I replaced the section of hose, I've had no issues since.

Not sure if this is your issue or not, but it may be worth looking into. Good luck.


x2...my was surging, bucking, misfiring, and left me stranded on the highway. Turned out the output line on the fuel pump had corroded and was sucking air up and pumping it through the injectors, which they did not like so much. Removed pump, had it soldered up for $20.00, dropped it back in and it started faster than it ever had and ran perfect.

I had the same symptoms as you do btw.
 
Well, as of now, it has to be fuel, I am running out of things to check! Fuel Pressure Test right after work.

But by output line on the fuel pump, is this above the surface of the tank or do I have to pull the pump to find the problem?
 
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