Hello everyone I am need of your expertise. My 98 ZJ 5.2 has started acting up. First it would just completely die on highway, it would feel like loss of spark. I would wait a while and crank right back up, so i did full tune up problem fixed. Then it started rough idling and would have the idle spurge when idling. In come new sensors IAC, TPS and MAP along with full throttle removal and cleaning also new distributor cap and rotor. Worked for a couple of weeks. Now when it sits overnight it will not fire up in morning. It will crank and crank to no avail. Two hours later come back and fires right up. One more thing any one know what the sensor next to distributor is, sorry tried to post image but don't know how to resize.

 

 

Have you checked for spark and fuel when it is cranking to no avail? One of those is not happening. It sounds like it is the crankshaft position sensor not working right. Next time it doesn't start, pull and ground the threaded part of a spark plug to the engine block to see if it is getting spark while cranking.

 

Do the wires from off that sensor lead up to and underneath of your distributer?

That's one of those weird parts. It goes by several different names depending on what source you are referencing. I guess the FSM calls it a camshaft position sensor. However, If you look in a parts manual, you may find this part or sensor is nowhere to be found. The other names it goes by is a distributor switch plate, or a camshaft pick-up plate. Sometimes it is just referred to as the 'pick-up', or 'sensor plate'.

On the 95-98 4.0/5.2/5.9L models the sensor is easily removed; remove distrib cap and rotor, then disconnect the connector to the camshaft sensor then just lift it out.

It is certainly capable of causing the exact symptoms you describe if it were malfunctioning.

 

That's the weird part there is both fuel and spark, however the spark is very weak. As for the sensor, it is not the camshaft, that one is on the distributor itself. This one has just the two wires coming from it and taps in to the main harness that runs to the ecm. Reason I want to know what it is, is because it has some play to it. I haven't been able to get it off because deep sockets don't reach far enough to catch the thread.

 

I am in my WJ. Been on the road. I'm about to be getting back to where my ZJ is tonight though. I have a lot of general maintenance to do to it, and will probably be starting on that after tomorrow. It helps when I can see things. I'll look to see where this sensor is, and at its wiring. If someone else here doesn't name it? I'll let you know if I figure out what it is.

I'm sure you've read the numerous other threads online of people having very similar issues as yours.. It seems the coil, crankshaft position sensor, and/or camshaft position sensor are all possible reasons. I think the only way you'll possibly know is if you start testing them all with a multimeter.

I've read about a lot of people having similar issues, and it was their crankshaft position sensor. When this sensor is acting up it can sometimes also cause gas and voltage gauge reading abnormalities along with it too, as a sign. I guess if this sensor is acting up, it can also cause an OBDII scanner to not be able to link up to pull any codes. If the OBDII is not working. You can disconnect this sensor and try again. If the OBDII now successfully links up to be able to pull codes afterwards, then it basically points out that you have a bad crankshaft position sensor that way. There is a wiring harness pigtail leading to this sensor in the engine bay at the back of the intake I believe.. to make this easier, that can also be used for testing purposes.

Having weak spark makes me think of looking at the ignition coil. I know if you have a bad or failing camshaft position sensor, it can ruin the coil too... Sometimes those two go hand-in-hand.

Not sure if any of that helps?

(edited to add):
One other thing.. What you describe does sound like it could be a malfunctioning crankshaft position sensor. I have read of more than one person having these similar symptoms. It tuns out that the wiring off the oxygen sensors can come through the insulation and short out.. This can cause the crankshaft position sensor to appear to act faulty and be malfunctioning, when the reason is because of a shorted out oxygen sensor wire. It's just something easy to look into as another possible reason, according to what other people have reported.

 

So I finally figured out what that sensor is. It is the engine coolant sensor. So that solves one mystery. I have read about the crankshaft sensor, but would that cause weak spark at wires. As for the ignition coil, I am running an MSD coil with MSD 8.5mm wires installed last year. Also once it has started for the first time, I have cycled off and on with no problem.I checked all sensor wires for breakage and or kinks but all is good, even pulled the corrugated wraps back, not fun.

 

It's the engine coolant sensor. That sensor..

(edited to add):
If me.. I would test Crankshaft Position sensor for its reading in Ohms. Check any new one in the store before walking out with it too. I would test the Camshaft Position sensor the Pick Up however that is done. I would check the coil however that is done for the two different voltage readings (one with it resisted). I would verify Camshaft Position Sensor is installed/set correctly (so timing...). I would verfify the distributor and rotor is set up correctly. I would make sure spark plug wires are new, or in good condition (sounds like if you did a full tune-up, these are new or good). I would put in new spark plugs if needed (extended crank - bad running conditions related to bad spark, fuel, and air may ruin the spark plugs). I think that is your whole direct spark pathway verifed? From here, I would start considering other external influences. The Throttle Position sensor has the ability to mess with bad spark like running conditions. I would consider testing the TPS. Your throttle body and the different sensors located here have been cleaned, replaced, and are good. They wouldn't really do how you describe the recent symptoms anyway though, but good for your idle and all of the other possible contributor issues... At this point, testing probably all of the many components.. If still same? What do you do? You would have to consider spraying all connectors with electrical parts and connectors cleaner and brass wire wheeling everything, making sure you didn't miss any of the grounds. This is what I am doing to my new ZJ today is cleaning like this all of the electrical and grounds. Inspecting everything closely as I go along. Testing my battery static and with a load cranking etc... And new spark plugs, oil, coolant, and cleaning the IAC and throttle body.

Fuel pathway could be explored next. Using a fuel psi gauge and test looking for a good check fuel valve, fuel psi regulator, fuel pump, fuel filter, fuel lines, and the fuel injectors.. With the gauge. I would do that if you haven't done that at this point. You need to chase down the spark pathway I think in my mind first though. If all components are turning out to be testing and proving to be normal and good, then must also consider the general electrical. Such as a short or open etc in any portion of the electrical may stumble up some modules, or even the PCM. Could be the PCM?

Whats great though about this thread you have here.. I know there are plenty of the most specifically knowledgeable individuals to the XJ, ZJ, and the WJ Jeeps here that you'll ever find anywhere! If you have the mechanical ability? Sounds like you do.. And you look into and post back your findings? Sounds like you do and you have..

A lot of threads on this type issue, but also with a lot of Different answers.. and individual results.

We should be able to figure this out.

 

Well thanks for all that help with what to test and look for. So I decided remove everything again cleaned everything all out. Checked all sensors as mentioned, plugs and sensor wiring had battery removed scraped metal for clear ground. Wife was going back work now that school is starting. So put it all back together again, starts right up. No problems since. Going on three days now with no symptoms what so ever. Thanks for all you help. Greatly appreciated.

 

Thats cool!

Definitely keep an eye on things.. but, that should be normal routine.

(edited to add):
I believe sometimes some parts may be getting blamed, when it was never the parts fault in the first place. It's that after removing to replace some multitudes of parts, all these connections and connectors are being somewhat cleaned up as a group, as well as having cleaned up the battery some removing and replacing the cables a few times. It's a theory.