4.slow95

Just as the title says... I have a 96 cherokee country 4.0 aw4. It will crank strong and attempt to start but immediately shuts down. I am at a loss and starting to suspect the pcm. any help would be great. thanks!

landude

CPS.
Was it bucking and running poorly prior to this?

RTorrez1

You said you have fuel pressure and spark. But do you have the right pressure? Your year should have 39psi + or - 5psi. Also the spark you have is it a blue spark. Any other color spark can cause many problems including a no start.

tjwalker

1. Verify quality of spark. As mentioned, you should have a strong, BLUE, snapping spark. Yellow/orange/white indicates a weak spark which may not be strong enough to start the engine (ignition coil is primary suspect for weak spark).

2. If spark checks out (and only if), then splash a little gas into the intake. If the engine starts and runs for a few seconds, you clearly have identified a fuel delivery problem. Early 96 models need 31 psi of fuel pressure to start, sometime during the 96 year they switched fuel systems and those need 49 psi of fuel pressure to start. If you have a fuel pressure regulator in the engine bay, you have the old style.

3. Do you have a security system? They can inhibit starting when they are on the fritz.

Good luck and keep us updated!

freegdr

When you checked codes what did ya get ?

Bustedback

Check the condition of the battery first. It should have a static voltage of at least 12.6 volts. Check the voltage with a DVOM while cranking, it should not drop below 9.6 volts.

Roler

Do you have the engine immobiliser feature and do you mean it will run for 1-2 seconds and then shuts off, like you take out the key?

If so, we're talking about a whooole different issue. If you don't have the immobiliser, we move on.

96blackxj

having the same exact problems as my friends zj 4.0

it started off no spark, replaced the coil no difference, replaced the cps, no difference, then out of nowhere it ran got it almost all the way home and it died, replaced distributor, no change..

took it to a shop and they said pcm is bad, replace pcm.. no start

dont dump money into it, there is another issue we are still trying to figure out my friends zj if we figure it out before you figure yours out then we will tell you what it was...

like others have said, check your fuel pressure and check your spark, and try putting a little bit of fuel into the intake manifold through the throttle body

4.slow95

Ok got it started... had to have my foot in it at first. After I took it around the block I came back and it idles fine. Turned it off and it started right up. This is my wife's so I need to be sure this doesn't happen again. Anyone else had this issue??

tjwalker

Having to "tip in the throttle" to start the engine can indicate a problem with the throttle position sensor.

It's possible to have problems with engine management sensors that don't set codes.

Here is more on this sensor. I'd start with testing of it.
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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 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 fault TPS can report values outside the denied 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 excessing misfires resulting in one or more cylinders being shut down to prevent engine and catalytic converter damage.

4.slow95

Thanks. I understand how the tps works. I just don't understand why it would happen suddenly. I have had one go bad and do exactly the symptoms you described but not anything like this. Could this be a battery or ground connection issue??

xjvicks

I had one that did this exact same thing. It turned out to be the coolant temp sensor had gone bad. The way I would get it to start was to mash the gas all the way down.

4.slow95

Hmmm. well that does make sense as well. I can look into that. it does read a bit lower than it should. can a poor battery connection cause this?

Kalali

A faulty coolant temp sensor does not behave this way but a marginal battery definitely does. If it were me I would load test the battery before spending a dime on anything else. YMMV

4.slow95

Brand new battery. BUT! I cleaned the terminals real well and cleaned up all the other battery connections and problem solved! Thanks for the help guys!