I have a 2004 Jeep Liberty. The motor is running on 3 cylinders, The 3 on the drivers side. I have checked the compression and all the cylinders are above 120 psi. I checked the spark using a new spark plug and the spark is good. Then I checked the sparkplugs that came out of the dead cylinders, and all produced spark. Those 3 plugs were dry possibly indicating no fuel. The motor runs like its in a limp mode. What could be wrong? Could it be the pcm? I accidently deleted my codes and after running it and even after driving it 100 feet no new codes came up. Can someone please help?
Help! Running on 3 cylinders.
- Thread starter LGB
- Start date
greg92jeepxj
Official Supporter
To check if the injectors for the three cylinders in question are firing , you will need a NOID light.
It is preferred to use a noid light on each injector harness plug while cranking but you can get away with using one light on one injector harness plug at a time. Even easier , get a computer safe test light and probe each injector harness plug while engine is running to find out if the PCM is firing the injectors on that side of the engine. It's odd I agree the one bank is not firing when the harness should be receiving equal signal since the driver should be powering all injectors in a sequential order . But confirm if injector pulse is read on these cylinders and no harm in checking all cylinders as well. Check the wiring harness for the injectors to see if maybe the power is not getting to each injector as that is supplied by a relay and a fuse which powers all the injectors together. The ground is supplied by the PCM which when grounded , energizes the injector. That is how the firing order works in a sequential port injection system . As for the 120 lb compression test result , I do not know the compression rate for that engine but it sounds low but look it up to confirm . A full compression check of all cylinders would be a good idea as you should be getting more than 120 lbs per cylinder . There could be a valve train problem.
It is preferred to use a noid light on each injector harness plug while cranking but you can get away with using one light on one injector harness plug at a time. Even easier , get a computer safe test light and probe each injector harness plug while engine is running to find out if the PCM is firing the injectors on that side of the engine. It's odd I agree the one bank is not firing when the harness should be receiving equal signal since the driver should be powering all injectors in a sequential order . But confirm if injector pulse is read on these cylinders and no harm in checking all cylinders as well. Check the wiring harness for the injectors to see if maybe the power is not getting to each injector as that is supplied by a relay and a fuse which powers all the injectors together. The ground is supplied by the PCM which when grounded , energizes the injector. That is how the firing order works in a sequential port injection system . As for the 120 lb compression test result , I do not know the compression rate for that engine but it sounds low but look it up to confirm . A full compression check of all cylinders would be a good idea as you should be getting more than 120 lbs per cylinder . There could be a valve train problem.
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