I just bought a 97 cherokee sport with a 4.0 for an offroad truck it had a blown head gasket so i fixed that now when it gets warm it starts missing and if u put it to the floor from idle it just dies like it loads up real bad with fuel. And also if u try to drive it in 4lo it doesnt like to run under about 1500rpm. Anyone have any ideas what would cause this has a new fuel pump with 50psi at the rail and a new crank sensor, distributor, and fuel pump. Im stumped thanks ahead of time for any pointers
Are all the tune-up parts fresh ? Tested the ignition coil ?
Test your Throttle Position Sensor.
You may have one or more of these Physical Symptoms:
1) The engine loses power and is stalling.
2) The engine will idle, but may die as soon as you press the gas pedal. When driving, it seems as if all power is gone.
3) Sometimes it feels as if the transmission is failed or isn't shifting properly, if at all. If you quickly jump on the gas you might be able to get the transmission to shift, but it won’t shift properly by itself. Shifting manually, the transmission goes through all the gears.
NOTE: The throttle position sensor is also DIRECTLY involved with transmission shifting characteristics. The TPS function should be verified early in the troubleshooting process, when a transmission issue is suspected.
It is best to use an analog meter (not digital) to see if the transition from idle to WOT is smooth with no dead spots. Locate and identify the TPS ground wire. 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 power input. You should have 5 volts going into the Throttle Position Sensor (TPS). Test the remaining TPS output wire. At idle, TPS output voltage should be greater than .26 volts but less than .95 volts. Move the throttle and look for smooth meter response up to the 4.49 at WOT. The ground wire should show no voltage.
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:
-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 accordingly 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 faulty TPS can report values outside the acceptable range causing the ECU to incorrectly fuel the engine. This is noticeable 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 excessive misfires resulting in one or more cylinders being shut down to prevent engine and catalytic converter damage.
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So i put a new tps on tonight and nothing changed im completely lost it wont do it when its cold only once it warms up. Also it has no rear cat. Would this cause it? When its sitting there idling if you just put it on the floor it dies right away like there is a huge load on the motor all the sudden. Thanks for anymore advise.
One component that can suffer from "thermal" (heat related) failure is the ignition coil. They can be tested for both primary and secondary resistances with a meter and a manual, but testing would have to be done IMMEDIATELY when symptomatic; otherwise testing data may be of no value.
I'd certainly try it.
99 Cherokee, 4.0 AW4, NP242
Past Jeeps: 49 Willys, 81 Scrambler, 88 Comanche Without "data", all you have is an opinion!
Its not the coil not the temp sensor and tonight it was so bad it wouldn't even start. I pulled the plugs and they were like charcoal so i put another set in and then it started but still same issue. Unplugged the upstream o2 changed nothing? Im lost...
FINALLY figured it out somebody put the distributor in just enough to make it run but it was a few teeth off so i pulled indexed it like your suppose to and it fixed it. Thanks everyone for the helpful hints.