A lot of parts with little results misfiring on cyl 6

Jeep 4.0 misfire on Cyl 6: low compression on cylinders. Oh by the way it is a 2000 TJ Wrangler

Pulled head and took to a reputable machine shop , he looked at the head and seen problems with the exhaust valves and seats. The valves had beat the seats down into the head about a quarter inch, he put new hardend seats and valves in also trued the head. Came home put the head on and felt as though I had bought a new jeep on the test drive. Very happy. A couple of days later going to work and started misfiring bad on #6 cyl ,,and here we go, checked fuel rail,,had 47 lb ,took fuel rail out of intake fired it over all injectors spraying really well,put that back together. Went to the spark plug side pulled and changed plugs,no good,changed coil rail,no good ,changed distributer sensor,no good,getting ready to change crank sensor,,will let you know. Oh I did check wires to coil rail connection cleaned and looked for damage.

 

Welcome! Interesting jeep adventure from the sidelines....inspect spark plug wire routing and/or replace spark plug wires? Damage from arcing can lead to misfires too.

 

Welcome to the forum @dbucknerc. Interesting post. Curious to your fix and hope it all works out for ya. Looks like you have everything covered. Post up if we can help.

 

Last night went to install the crank shaft pos sensor,knowing in my heart it did'nt need one,desided to check and clear codes,low and behold there where 2 codes instead of the usual 1 code. There was a second code telling me I had a open circut #6 injector,, so I have a new injector on the way. Mo money mo money mo money ,but thats ok, now it gives me the chance to probe the wire coming from the ecm because the way it is going ,it will not be as easy as just changing out an injector. Broken wire maybe.

 

Are you getting any codes to go with the misfire?

 

Misfire on cyl 6. And for the first time last night I got a open circuit on #6 injector,, have not looked at that yet but coud be a bad ecm ,broken wire or bad injector,,,thoseare my thoughts.

 

Mine too. Try switching injectors and see if the code follows the cylinder.

 

Hey Joe
Thanks for the info yesterday,made me feel more confident about what I was doing.
My results where ,,,integrity of wiring was good using a seal beam light,
Found that computer was not providing a pulse to the injector buy hooking test light to positive battery and probing control wire with motor running.

Had to go to dealer ,talked to service manager,naturally he told me he had problems flashing modules that people have brought in from advance auto,long story short after talking to advance auto, I ended up back to dealership and orderd a module from them for big dollars,, and when it comes in ha will call and get me to bring it in . Module was $729 plus tax and programing service will be $115 dollars.

I have seen where there is a programmer out there you can buy,they won't give a price without contacting them called Flash2 but I feel that the computers can be reflashed to fix problems but to get setup would be exspencive.

Sent from my iPadQ

 

Welcome to the site. Its been a little while since i did a computer r&r but what i remember if you had a code calling an open inj circuit that is hard wired (circuit board in side the computer (ECU). Barring no bkn wire from ECU to injector. I would assume that you a least have a 12 month 12,000 mileage warranty buying from the dealer. Even thou this costed you more IMO I feel you made a good choice. Good luck -

 

Thanks ,,I am waiting patiently for new ECM to come in. I think it will solve my woes.almost thinking if we could go back to the old way and get the computers out of the loop.

 

Yes you can. Cjs are one way or if you will is strong and have extra cash you can change to a carb and bypass computer stuff. There is all kinds of opinions on carbs vs injected etc... Yes it would be nice thou.

 

Well guys the new PCM didnt fix the problem. I still have a code p0206 witch is open circuit on injector 6. When checking plug with noid light noid light does not flash, checked control wire to pcm and integrity is intact. Checked for battery pos to injector and power is there. At the end of my rope.

 

Sure could be chris4by4, thats why I went to the dealership $$$$$$$$ to make sure it was right, funny thing though, when I left the dealership I noticed something odd, I pull into a gas station and poped the hood and all my vacuum hoses were diconnected ,even the rubber cap on the intake. Why would they have to take my vacum lines off to install the pcm and program it. Just seemed odd to me. And then leave them off. Job security maybe ,,, maybe not. But anyway when I reinstalled all the vacuum lines it still is throwing a open circuit on cylinder 6 injector. I did put a noid light on it to check for pulse from the new pcm and it does nothing, I am getting battery voltage to a new injector and no responce from the pcm. The control wire checks out fine. Really has me puzzeled.All points to a bad driver in the pcm. No grounding pulse.

 

Since the dealership did the PCM install they should be able to explain the disconnected vacuum hoses. While in the shop the service tech should have discovered the open circuit issue as they would have performed a multi-point inspection of all systems. A missed opportunity to charge for the repair of the p0206 is unusual.

 

There are 4 things that will cause this. You have fixed 2 of them the ECM and the Injector. Bad ECMs are rare, yet people replace them all of the time. Injectors are more common, but you replaced it as well as the ECM. That leaves poor connections at the plugs (try using Dielectric grease at all plugs that you disconnect and reconnect if you have not done so already. the fourth is a shorted or open wire or faulty wire. The ECM is picking up resistance outside of the normal parameters and therefore is throwing a code. I know that you said that you checked voltage and resistance, but did you check the voltage and resistance of the other 5 cylinders and then compare #6 to them. This might show you a difference in the from the other 5 enough to throw a code from the ECM. If so you will need to check the wiring harness find the problem and replace (splice in new wire) in that section. Electrical can be so frustrating. Good luck.

 

If I remember right the power to the injector is constant and the computer switches the ground to turn the injectors on and off. Have you verified that this is happening like it should? I will usually unplug the injector while the Jeep is running and use a test light hooked to the positive post of the battery and test the ground side of the injector plug. If the test light flashes then the wiring should be good (minus an issue with the connector)

It might be worth unplugging #5 injector and plug in #6 and see where the miss fire goes.

@OFFGRID Do you remember when they switched from batch fire injectors to sequential on the 4.0?

~Jeff

 

Thanks for all the input,I did check the ground pulse from the pcm to pos battery and got no pulse with a test light,also tested battery voltage from power side of injector to control wire at pcm and have power all the way through the circuit with the pcm disconnected,but no ground pulse from pcm

 

I am not that familiar with when jeep did what so much after the CJ, but I do know to run sequential you need both a cam and a crank sensor. This should narrow the year down in aiding when they started sequential.