XJ lost power and will not start

I just had a new Exhaust system installed yesterday morning and I'm unsure if this created this issue. I was driving on the highway doing about 75. After about 40 miles driving on the highway I started losing power. I had the gas pedal almost all the way down. The tach would not go past 2k rpms and the the Jeep started slowing down. I managed to get into the break down lane and then the engine shut down. I opened the hood and checked the oil and transmission fluid. They where fine. I checked the plug wires and the seemed fine. The Jeep started again and I got about 20 feet and it died again. I tried again and the engine turns but engine did not start. I have had the engine light on for about a week and when I checked the code last week at autozone it was for a gas cap evap thing. Any suggestions? I'm leaning towards fuel pump or filter which I think is in the gas tank?

It's a 1999
4.0
and a limted
4 door

Well, you didn't specify how much of the exhaust system was worked on, like the exhaust header? Take a look at the CPS/CKP crank sensor harness and see if it has been burned against the exhaust. Unplug and plug the connector a few times to freshen the contacts.

After cranking some, check at the Schrader valve on the fuel rail to see if there is fuel pressure.

Check for spark at the plugs. Use a spare plug and attach a spark plug wire, ground the metal body of the plug to the engine and crank the engine, watch for a spark. If you don't have a spare plug just remove one from a cylinder.

Can you hear the fuel pump prime when you first turn the key to ON?

The Exhaust was replaced from the front pipe back. Where is the CPS/CKP crank sensor harness located? Is that the thing that connects to the distributer?

I Checked the Schrader valve on the fuel rail and it squirted out fuel till I emptied it. Then I turned the key on and waited for a minute. Checked the rail again and it had fuel in it.

I will check the for spark

The brand new cat could have fractured and plugged the exhaust.

True on the CAT. But would that prevent the engine from starting more than 24 hours later? I did find the CPS and it is not damaged, but it could be the issue. I am having my brother come over tomorrow with an inline spark tester to check the coil and the wires etc.

If the engine doesn't start, testing the crank sensor should tell the story on that. It is definitely job #1. Without the proper input signal from the crank sensor, you won't have spark and you won't have fuel going TO the injectors (you may have good fuel pressure at the fuel rail however)

Here is a link to a thread that gets into what is involved here....worth the read.

http://naxja.org/forum/showthread.php?t=1025391

Thanks I will look into the crank sensor today

I have spark, bought and installed a new CPS, I'm getting fuel? Still will not start? Any other suggestions?

Even though you have fuel pressure to the fuel rail and replaced the CPS; that doesn't mean that the fuel injectors are receiving a pulse from the PCM.
The CKP (Camshaft Position Sensor) inside the distributor sends a signal to the PCM so that it knows which cylinder to fire.

The information below was removed from Tim_MN response as reference above by birchlakeXJ.



The most likely cause of it cranks and cranks but won't start up is the Crankshaft Position Sensor (CPS) located on the transmission bell housing. Often this part is also referred to as the CranKshaft Position Sensor (CKP) CPS/CKP failure is very common. The CPS/CKP can stop working with no warning or symptoms and the engine will not run or the engine may randomly stall for no apparent reason.

Crank Position Sensors can have intermittent “thermal failure”. This means that the CPS/CKP fails when engine gets hot, but works again (and will test as “good”) when it cools back down.

Begin with basic trouble shooting of the start and charge systems. Remove, clean, and firmly reconnect all the wires and cables to the battery, starter, and alternator. Look for corroded or damaged cables or connectors and replace as needed. Do the same for the grounding wires from the starter to engine block, and from the battery and engine to the Jeep's frame/body. Jeeps do not tolerate low voltage or poor grounds and the ECM/ECU may behave oddly until you remedy this.



Symptoms –
- Starter cranks and cranks but engine won't start up and run.
- Fuel gauge and voltage gauge may not work or display properly.
- You sometimes will have No Bus on the odometer after 30-60 seconds.
- A failed CPS/CKP may or may not throw a CEL trouble code.
- No spark at the spark plugs.
- Fuel pump should run and prime for 3-5 seconds.

If the CPS/CKP is failed sometimes the OBD-II trouble code reader cannot make a connection to the ECU/computer or cannot read Check Engine Light/MIL codes because the CPS/CKP has failed. Disconnect the code reader, disconnect the CPS/CKP wire connector, and reconnect the code reader. If the code reader establishes contact with the ECU and scans, your CPS/CKP is failed and needs to be replaced.


Diagnostic steps to confirm the CPS is the cause of your no-start


You should be able to verify a bad cps, by unplugging it, and turning the ignition key to on. If the voltage gauge and/or the fuel gauge now displays correctly, replace the CPS.

Unplugging and reconnecting the CPS sensor where it connect to the main harness near the back of the intake manifold usually resets the ECU and if the jeep fires right up after doing this you can bet that the CPS is faulty and needs to be replaced.

Exchange the fuel pump relay and the ASD relay with one of the other similar ones in the PDC to eliminate the relays as the cause of the no-start. Confirm that the fuel pump to runs for 3-5 seconds when you turn the ignition key to ON.

Eliminate the NSS as a cause of no start. Wiggle the shift lever at the same time you try to start. Put the transmission in Neutral and do the same. Do the reverse lights come on when the shifter is in Reverse?

Inspect the wires and wire connectors at the O2 sensors on the exhausts pipe. A short circuit from melted insulation or from broken O2 sensor wires can blow a fuse and the ECU/ECM will loose communication. Don’t get tunnel vision and assume the sensor is bad (unless it tests bad with a meter). Damaged wiring or a dirty connector can inhibit the signal from making it to the computer. Inspect/test/clean/repair wiring or connectors as necessary.


CPS Testing


Crankshaft Position Sensor Connector (CPS/CKP)





TESTING PROCEDURE 1991 – 2001 4.0L H.O. engines

1. Near the rear of intake manifold, disconnect sensor pigtail harness connector from main wiring harness.
2. Place an ohmmeter across terminals B and C (See Image). Ohmmeter should be set to 1K-to-1OK scale for this test.
3. The meter reading should be open (infinite resistance). Replace sensor if a low resistance is indicated.

I replaced CPS sensor with a new one and still the engine not will fire up Someone suggested that I make sure all of my ground wires are properly grounded and are in good condition. I am trying to avoid bringing it to a local shop because I am low on cash at the momment. I am trying to get my brothers friend to come over with his scanner and see if it can tell me what the issue is.

seg501 said:

I replaced CPS sensor with a new one and still the engine not will fire up.

Click to expand...

The CP(K)S you replaced is the one that is inside the distributor OR is it the CPS sensor that is bolted to the bell housing at the 11 o'clock position ?
They are two different sensors....

I replaced the one bolted to the bell housing. Should I replace the one inside the distributor? Where inside is it?

You are getting spark, you have fuel pressure to the rails and the fuel pump runs for a few seconds when you turn the ignition switch on, but still no start.
The CKP is what the PCM uses to know what cylinder injector to pulse and when.
Several years ago my CKP shorted out against the curved trigger plate inside the distributor due to a bad distributor shaft bushing. This caused the injectors to stop pulsing.
Replaced the distributor and CKP and the engine fired right up.
A bad CKP doesn't always generator a CEL; so using a scan tool may not indicate a problem.

I haven't seen where you have CONFIRMED fuel pressure. Put a gauge on the Schrader valve and confirm the correct operating pressure.

You can test the synch sensor in the distributor. You can use a NOID light to check for a firing impulse to the injectors. You can use a volt meter or test light to check the injector harness to see if you have 12 volts to the injectors.

Lots of testing to do BEFORE you started swapping parts, and there is lots of testing to do BEFORE you find the problem.

Good luck.

There's no point on checking on the electrical stuff without verifying the engine's good internally. Sounds like it could have nearly seized, or overheated and killed the piston rings.

Quick check- does it sound about the same while cranking it over as it used to? Don't laugh, I've had people bring in fried engines who told the service writer "Won't start and the starter sounds funny."

It sounds the same cranking it over. The oil is clean, no burning smell. Also it wasn't running hot at the time of breakdown. I am going to check the sprak plugs themselves and then check my ground wires as well.

It sounds the same while the engine turns. It was not overheating at the time of breaking down. I checked the oil and it's clean. The only thing I noticed is that when I stop turning the key to start it the engine sounds like it's going to start for a split second. Not sure if it's because everything is stopping? Other than that it sounds normal.


Where is the Schrader valve located? We used a inline spark tester and I have spark on all plugs and coil. I will check injector harness with volt meter. I have a spare distributer and fuel injector rail, but don't want to replace them unless they are the problem.

The Schraeder valve is on the fuel injector rail and has a screw on cap to protect the valve and threads.

I am going to replace the CPS that is in the distributer, clean all ground wires and straps tomorrow morning. If the jeep still doesn't start I am taking it to a mechanic. I am just doing my best to not bring it in if it's something easy.

It was the CPS in the distributer and the coil was giving too low of a spark. Both replaced and the Jeep is alive. Thanks for all of your help!!