1993 XJ Rough idle

[ifoundastick]

I have this 1993 xj I purchased a while ago due to the guy thinking there was a bad fuel rail. Long story short and various parts replace I'm still getting intermitent performance and reliablility. What I'm seeing is when its running rough and seems like its missing the spark from the coil. When it does start its is not as bright as it should be. I've been able to get it to run right for a bit and all is well i turn it off and then try to start it again and its back to running rought.



I think there might be a problem with the coil wire Dark Green Orange cable when running its getting around 9-11 volts flucating.

The dark green wire is getting a full 14.35 volts.


Any ideas why this would be happening and do you think the PCM might be bad ?

 

[Saudade]

So sometimes it runs ok and other times not so much?

Could be a short/open wire somewhere. When it's running rough, disconnect the #1 fuel injector. It should run a bit rougher. If so, reconnect it. It should improve. Then disconnect #2 and see if it runs rougher. If so, reconnect. Repeat for #3-#6. If one of them doesn't make a difference (try disconnect/reconnect a few times) you've identified the cylinder that's not firing properly. Could be fuel, could be spark, could be something else.

The dark green/orange wire comes from the alternator and also goes to the PCM. Check the connections for any corrosion, insulation breakdown.

 

[Anak]

Check your grounds. Battery grounds, engine grounds, any you can find.

This was my dipstick ground: Intermittent Stalling Issue

 

[ifoundastick]

I've updated the grounds with the big 7 and also re crimped the grounds on the dip stick side and that seems to have helped a little bit but I'll revisit them again and see if I can improve the connection. It was initially wired very terrible.

I replaced the injectors and tested every wire to see if the constant 12volts is getting there and that is good when its in the weird state. 5 and 2 don't seem to fire.

I did notice that sometimes if i wiggle the coolant temp sensor that will fix it after its in the limp home mode but it doesn't seem to help long term I've replaced the sensor and when i remove the wire i'll get the CLE and the aux fan will turn on.

It only seems to happen on starting so i was thinking some how there's a surge somewhere that puts the PCM into limp home mode. I've pulled the PCM and installed it into my OG 1994 XJ and it fires right up so its something electrical on this jeep.

I replaced the igition switch cause the accessory connector wire (purple) looks like it was running a bit hot and melted it. I'm getting a new connector for it today and may try and install and check everything out.

the yellow wire that only makes contact when on start goes to instrument cluster and then to the Engine coolant temp sender ( so think some how its giving it the wrong voltage cause it might be +12v rather than the 3volts needed ? or that whole circut has an intermittent ground ?

 

[ifoundastick]

Okay check this out. I checked the wires on the passenger side block again and found that with out the motor running i'm getting 0 ohms when the engine is running like shit i'll be getting 11-9-0 ohms. When the engine is running okay the ohm meter will say 0 but after some time of running it will return to 6-7ohms. What would cause this ?

 

[Marcass]

So sometimes it runs ok and other times not so much?

Could be a short/open wire somewhere. When it's running rough, disconnect the #1 fuel injector. It should run a bit rougher. If so, reconnect it. It should improve. Then disconnect #2 and see if it runs rougher. If so, reconnect. Repeat for #3-#6. If one of them doesn't make a difference (try disconnect/reconnect a few times) you've identified the cylinder that's not firing properly. Could be fuel, could be spark, could be something else.

The dark green/orange wire comes from the alternator and also goes to the PCM. Check the connections for any corrosion, insulation breakdown.

Homie is correct. I will also put my two cents in and say to clean your throttle body and it's IAC Valve/Sensor. Small easy preventative maintenance that may be in the realm of what you are dealing with.

 

[ifoundastick]

I changed the IAC with another good one and it worked for a bit and now it's back to running like shit. For a test cause the guy who sold it to me said it was a bad fuel rail. I attached a pressure tester to the fuel rail and found that with the pressure regulator off I'm getting 40PSI. So i was like its good and ran to the DVM to get plates for the Jeep. drive it 6 miles to there get the plates come out and try and start it nothing.. detached reattached the gauge nothing idling like crap sputtering. then i finally get the right combination and blam runs like a champ i drive it around town getting after it running fine for a good 30 mins get it home park it and turn it off and then come back in 5 minutes and it's back to running like caca.. So I was thinking maybe its a bad fuel rail/fuel return to the tank ? or if the ECM came from a newer XJ that doesnt have the ballast resistor ? I've also replaced that and replaced the relay but that didnt fix it.

Once the thing is running she purrs and I can get after it. I got it up to 75MPH with out a problem while testing today.



I did no