Jeep is killing me

[nylyon-(Admin) 7,114]

After the new pistons, the Jeep has been running great.  Had a minor issue with the right rear self adjuster but other wise been great.  That is until yesterday.  My daughter took it out for a ride and the engine light came on (flashing) with a P0305 and running very rough.  I got it home, and checked the plugs.  Switched #3 with #5 still got the misfire on #5.  Switched with #2 just for good measure and still P0305. (yes I am resetting the codes each time).

 

With the engine idling, there's a noticeable miss, I took the wire off #5 injector and no change with the idle.

 

I then took the injectors out and swapped #1 with #5.  Put it back together and still a miss on #5. Checked with a test light and getting pulse on the injector wire. Pulled the valve cover off to insure that the intake and exhaust valves are moving and they are.  

 

Figured it must be the coil pack.  Replaced with new, now it's smooth at idle however when I drive it I can feel the miss still.  Gunning the engine will throw the P0305 code again, but it will come back to smooth idle when I let off.

 

I'm open to thoughts on possibilities. 

[KyBlue 652]

Since you swapped the Injectors I'd say its in the wiring ... Just because you get a pulse w/ a test light ... doesn't mean there is enough current flowing to actuate the injector ...

 

Just my thought. I'm by far no expert on wiring ...

[squonk 38,844]

I think you need to check for a vacuum leak / lean condition on cyl # 5 Also pull the plug and a couple of others and see if #5 plug looks different than the others

Edited November 30, 2014 by squonk

[19richie66 16,880]

If I remember correctly, you should have 12 volts at all the injectors....computer provides the ground. You would have power at the injector with a test light. Mine did but the computer couldn't ground it due to the driver for #4 was shorted. Put your test light lead on the positive battery post and touch the test light to the negative wire going to 5 and see if it lights then. That should tell you if you are getting a ground from the computer. Just my two cents

[redidbull 54]

Head on over to jeep-owner.com. Very knowledgeable group. Jim

[Terry M-(Moderator) 2,125]

Did you install new spark plug leads/wires during reassembly of the engine?

Edited November 30, 2014 by Terry M

[nylyon-(Admin) 7,114]

I think you need to check for a vacuum leak / lean condition on cyl # 5 Also pull the plug and a couple of others and see if #5 plug looks different than the others

 

There doesn't seem to be a vacuum leak, I checked the lines I could check.  I will plug the ports on the intake (except brake) just to check.  Plug #5 looked perfect.

 

 

 

If I remember correctly, you should have 12 volts at all the injectors....computer provides the ground. You would have power at the injector with a test light. Mine did but the computer couldn't ground it due to the driver for #4 was shorted. Put your test light lead on the positive battery post and touch the test light to the negative wire going to 5 and see if it lights then. That should tell you if you are getting a ground from the computer. Just my two cents

 

Correct.  I am getting +12V (checked with the meter) with the engine running.  The pulse side is the ground, and I tested that with a test light.  While I can't verify voltage, there is a pulse.

 

Head on over to jeep-owner.com. Very knowledgeable group. Jim

 

I did go to another Jeep forum, I'll check Jeep-Owner.com as well.

 

Did you install new spark plug leads/wires during reassembly of the engine?

 

This 4.0 has a coil pack, there are no plug wires.  The coil pack is a one piece unit which sits onto of the plugs and bolts to the head. This was replaced, and when I did that it ran a LOT better, but still has the miss.

[nylyon-(Admin) 7,114]

Any of you guys near me have a leak down tester?  I'm wondering if I have a valve problem?

[stevebo-(Moderator) 8,034]

No leak down tester here. Sorry-

[Geno 1,928]

Have you checked for a strong pulse to the coil at the connector?

[19richie66 16,880]

My daughters jeep problem was the connector at the coil but it was dying out because of all the connectors were spread open enough for a bad connection. Her miss was the injector driver which lead to another computer. But I believe the coils fire both sides of the coil at the same time. One is a wasted spark. If you had a miss on 5 and one coil connector wire was bad then I would think you should have two misses. Having two misses is bad though if the wife finds out. Couldnt resist.

Edited December 1, 2014 by 19richie66

[Geno 1,928]

Loss of the waste spark fire won't cause a miss, there's usually not one there anyway on older non-waste spark vehicles.   

 

Got anyone close who has a Sun Machine 500E Karl?  I have one.  It will run a complete test and give you a printout of what's wrong with it.  Makes life real easy but the test is expensive as the machine is over 50K.  

[C-101plowerpower 1,605]

How did you test for a vacuum leak? When i was still messing with mopeds we used deodorant spraying it at the area were we suspected the leak. If it started tot run different we knew there was a leak

[nylyon-(Admin) 7,114]

I am limited with the test tools.  For the Vacuum leak, I inspected all the lines, and there's no noticeable sign of a leak.  I will continue to explore that.  Geno I don't have that tool, nor know of anyone who does sadly.

[Geno 1,928]

If the problem is in #5, you would be looking closely for an intake leak in the #5 runner. 

 

These are real handy for checking injector and coil pulses - http://www.autozone.com/test-scan-and-specialty-tools/injector-signal-tester/oem-6-pcs-noid-light-set/948078/ 

[nylyon-(Admin) 7,114]

So after replacing the coil pack things were better but still threw codes.  Decided to upgrade the plugs to double platinum and it seems to be running just fine now.  Can't get it to throw a code (and it had done so very quickly before).

[JC 1965 1,528]

Great news Karl.    Hope it continues to run good for you. I hate car problems but in winter they're a real bear. 

[Geno 1,928]

Glad you got it fixed Karl.  Hopefully you won't have to back under the hood of that one for awhile. 

[squonk 38,844]

You may even had a defective plug that showed no external signs of being bad. I have been fixing things for 45 years. 95 % of the time when it was a real head scratcher is was something silly. Glad you got it fixed.

Edited December 3, 2014 by squonk