2005 Liberty Runs Rough ~ DTC P2305

[TurboRay]

Hi ~ I'm a semi-retired ASE-cert'd "Master Mechanic" and I'm trying to help a friend with his 2005 Liberty 3.7 He brought it to me running rough, with the CEL lit. He scanned it and found codes P0300 (random/multiple misfires) and P0302 (cyl 2 misfire). OTOH, I scanned it and found P0302 AND P2305 ("Ignition Coil ‘B’ [cyl 2] Secondary Circuit").

I initially suspected either the sp/plug or the coil. I swapped the plug with another cyl (#1), and the misfire remained with cyl 2. I then installed a new coil in cyl 2..... to no avail (still misfired). Next, I checked for "key-on" 12V at the coil = good. Then, I checked for coil triggering (noid light) with the engine running and found NONE (with a good signal at all other coils).

For shíts and giggles, I also checked for 12V at the injector (good) and for triggering = NONE, altho a good signal @ other injs). Seeing evidence of past rat/rodent infestation, I ASSumed wires had been chewed. Fortunately, I found a link to the factory service manual, which included a wiring schematic with the ECM pinouts (orange/black harness connector, pin 9 = coil control AND pin 11 = inj control. So, I tested both wires for continuity between the ECM plug and the coil & inj connectors, and (drum roll)...... both wires are good.

Soooo......... I'm faced with the possibility that the bad coil (zero ohms = shorted) failed the coil driver in the ECM ~ BUT, why is there no injector signal? I ASSume that the coil and inj drivers are separate, but..... DUNNO! Is there a possibility that either the cam or crank sensor isn't providing a "signal" for JUST the #2 cyl position/sequence? Seems unlikely. If an ECM is needed....... does it need to be programmed for this specific vehicle? <shrug>

Whaddaya all think? SORRY for the dreadfully long post, and..... TIA for the anticipated help.

 

[blackhawk]

This is an interesting case
What I understand you got 12 v in the connector of coil and injector of the cyl 2. And the negative pulse is not present in both?
The continuity is good from pcm to both connectors. Right?

My suggestion is to swap both coils and injectors, if the problem is still present, you have a problem in the pcm

 

[TurboRay]

This is an interesting case
What I understand you got 12 v in the connector of coil and injector of the cyl 2. And the negative pulse is not present in both?
The continuity is good from pcm to both connectors. Right?

My suggestion is to swap both coils and injectors, if the problem is still present, you have a problem in the pcm

Your "understanding" is correct, Blackhawk! I DID swap out the #2 coil AND the #2 sp/plug, to no avail. Afterwards, I checked for key-on 12V at the #2 coil, and it was okay. Then, I discovered no intermittent ground triggering at the #2 coil AND injectors (noid light) when cranking. Sooo..... after finding a wiring schematic online, I ohmed both trigger wires between their respective plugs to the appropriate pins on the ECU/PCM connector and they were both okay. I also "ohmed" the #2 coil and found the primary winding almost completely shorted (0-.2 ohms) ~ IOW, no good!

I had hoped to get a response from you experts here, but ~ after several days ~ gave up, relied on my own diagnosis, and purchased (1) A rebuilt/exchange PCM from "All Computer Resources", and (2) A new coil. The reblt PCM was security/immobilizer-programmed via VIN for my customer's Liberty and it fixed the problem. My WAG is that the defective coil shorted the solid-state coil driver in the PCM..... causing it to fail. I still don't understand why the injector driver ALSO failed, BUT........ all's well that ends well, I suppose. <shrug>

TTFN ~ Ray Casner, dba "Ray's Garage"