TJ check engine light

[Boludo]

It came on the day after some rallying around town. It was running a little rough after rallying. I checked for diagnostic codes and got 12 and 43. I checked and cleaned dist. cap and rotor, spark plugs, air filter, battery terminals, and air intake at the intake manifold.

The check engine light went off due to disconnecting the battery. Then came back on after about a week or less of very normal driving.

I got the same diagnostic codes as before;

12 - Direct battery input to PCM was disconnected within the last 50 Key-on cycles. (I get this one everytime I have ever checked for diag. codes. Even random checks when I've had no problems)

43 - Peak primary circuit current not achieved with maximum dwell time.
or
43 - Misfire detected in one or more cylinders 1 thru 6.

Anyone know what else this could be and where a good place would be to have someone plug into the computer and run a diagnostic on it?

Thanks!

 

[mikeh]

check the fuel cap.my wifes liberty did the same thing.I put a new cap on and havent had a problem since.hope thats what it is.cheap fix.

 

[waynehartwig]

It came on the day after some rallying around town. It was running a little rough after rallying. I checked for diagnostic codes and got 12 and 43. I checked and cleaned dist. cap and rotor, spark plugs, air filter, battery terminals, and air intake at the intake manifold.

The check engine light went off due to disconnecting the battery. Then came back on after about a week or less of very normal driving.

I got the same diagnostic codes as before;

12 - Direct battery input to PCM was disconnected within the last 50 Key-on cycles. (I get this one everytime I have ever checked for diag. codes. Even random checks when I've had no problems)

43 - Peak primary circuit current not achieved with maximum dwell time.
or
43 - Misfire detected in one or more cylinders 1 thru 6.

Anyone know what else this could be and where a good place would be to have someone plug into the computer and run a diagnostic on it?

Thanks!

What year TJ? How are you checking codes?

A dirty/faulty injector can also cause a misfire code.... You'll have to pull all the injectors and see if one appears to not be working or replace them all with a known good set. I do have a good set here that I use for testing....

So can a faulty cylinder/valves. Compression check can eliminate this as a probability.

Also what are you doing it the light comes on? Do you notice the engine run any different?

 

[Boludo]

What year TJ? How are you checking codes?

A dirty/faulty injector can also cause a misfire code.... You'll have to pull all the injectors and see if one appears to not be working or replace them all with a known good set. I do have a good set here that I use for testing....

So can a faulty cylinder/valves. Compression check can eliminate this as a probability.

Also what are you doing it the light comes on? Do you notice the engine run any different?

It's a 1997. I checked the codes by turnibg the ignition on and off 3 times wihin 5 seconds, then leaving it on....the check engine light shows the codes by how many times it flashes and the odometer shows the code numbers.

The light came on the after some harder driving around town. Nothing too serious...I never hit the rev limiter, but was on the gas a bit. The engine started running a little rough and the check engine light popped on.

It's running pretty smooth now, but not as smooth as before the light came on. I get a little put, like a small misfire every few seconds...moreso when the engine is cold. It is very slight, probably almost unnoticable to others, but I can tell there is a difference from before the light came on.

Oh...on a side note...2 summers ago I was climbing the sand hill in moab. Went up as far as I could 5 or 6 times, hitting some high RPMs. The check engine light came on with in a few minutes after an it was running rough. It later went off. About a week later it came back on. I checked the dist. cap and rotor...the rotor was melted and in bad shape. I replaced cap and rotor and it fixed it.

I think I will try to clean the intake more and see if it helps clean out the injectors.

Let me know if you have any other suggestions.
Thanks a bunch!

 

[waynehartwig]

The reason I asked about the year, is because it should be a P code, and that code should say cylinder 4 has a misfire - not a cylinder 1-6. Jan 1 96 and up are all OBDII's, making your TJ and OBDII rig for sure.

It almost sounds like you have a stuck valve....

Go do a compression test....


BTW!? Why are cleaning the intake? Is there something in it???? Or are you talking about the intake filter? Or manifold??

 

[Boludo]

BTW!? Why are cleaning the intake? Is there something in it???? Or are you talking about the intake filter? Or manifold??

I guess I should have said throttle body instead of intake. I took the air tube off the throttle body and there was a bunch of black gunk all over. I didn't have much cleaner left in the can so I probably didn't get it all clean.

I have a K&N filter in the stock air intake box. I've heard that you can suck oil out of the filter into the air intake and get things dirty and even mess us sensors. I have a neighbor who messed up his mass airflow sensor in his truck because of a K&N. Not sure if TJs have a mass airflow sensor in there or not.

 

[waynehartwig]

I guess I should have said throttle body instead of intake. I took the air tube off the throttle body and there was a bunch of black gunk all over. I didn't have much cleaner left in the can so I probably didn't get it all clean.

I have a K&N filter in the stock air intake box. I've heard that you can suck oil out of the filter into the air intake and get things dirty and even mess us sensors. I have a neighbor who messed up his mass airflow sensor in his truck because of a K&N. Not sure if TJs have a mass airflow sensor in there or not.

Ahh... Don't worry about that stuff, it's not going to cause the issue your having.

No, TJ's don't have mass airflow sensors... If they did, they would be between the intake and throttle body and you would see wires coming off it.

 

[Boludo]

Thanks for your help. I will find somewhere to have the compression test done. Any suggetions?

 

[waynehartwig]

Thanks for your help. I will find somewhere to have the compression test done. Any suggetions?

You're backyard with a rental from Autozone? Seriously, rent a compression tester from one of the parts houses and then do it yourself.

Just pull all the plugs

Insert the compression tester in cylinder 1, hit the starter for 3-4 revolutions (you'll see the guage bump each time), then record the number.

Do that for all cylinders. You're looking for differences more than like 5 psi across the board. Chances are the dead one will be 90 while all of the others are 140. If you have two dead ones near each other (3 and 4), that most likely dictates a blown a head gasket - which could also cause a misfire code.

If I recall, spec is 120-150.... But you don't want to see that much of a difference between them all. More like 140-150. But as long as the numbers are in that range, you should be fine.

When you are done, post the numbers and I'll give you my opinion... If you can, take a picture of the plugs, so I can see what the electrodes look like. Might have to take a picture of them sideways or at an angle to get a good picture.....

 

[Boludo]

Sounds easy enough. Thanks for your help. I'll post the results.

 

[waynehartwig]

Sounds easy enough. Thanks for your help. I'll post the results.

Absolutely! Call me if you want and I'll do what I can over the phone... ...Number is on my website or PM me and I'll give it to you there.

 

[Boludo]

It must have been a plugged injector and/or the Jeep likes my wife. I dumped some fuel system and injector cleaner in the tank. I burned through about 3/4 of a tank. My wife took the Jeep out one day to go shopping. I started it the next morning and the light was off. It's running perfectly now.

 

[waynehartwig]

It must have been a plugged injector and/or the Jeep likes my wife. I dumped some fuel system and injector cleaner in the tank. I burned through about 3/4 of a tank. My wife took the Jeep out one day to go shopping. I started it the next morning and the light was off. It's running perfectly now.

Or a stuck valve, etc, that unstuck it'self...