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Cannot Figure Out Why 4 Back Cylinders Won't Fire

13150 Views 77 Replies 31 Participants Last post by  drakej
About 3 weeks ago, while driving home from work, my 4 back cylinder ( 5, 6, 7, 8 ) abruptly stopped firing (found this out once I made it home to diagnose it).
I tested the coils for 12V and spark as well as tried switching the coils and plugs around, no change.
Limited on time to diagnose (I had to travel for work the next day) I left it at that point.
Fast forward to this afternoon and I go back at it. I first test the injectors to make sure they have both 12v and a neg pulse from the computer. Both being present, I pulled the injectors out and energized them with a battery to make sure they all sprayed/worked. I then swap the front 4 around with the back 4. No change, the back 4 cylinders still aren't combustible.
I read somewhere (I've done a bit of searching ) that it could possibly be the CKPS (crank position). I've only dealt with one of those on a Mercedes I owned. When it went bad, the car simply shut off and would not start at all.
So, I'm asking if anyone has seen this (or similar) and if not, any ideas on what I could possibly check out next?
I'm literally at a stopping point and out of ideas.
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I think the CKP would throw a code if it was off.

Have you tried disconnecting and reconnecting the battery (I'd leave it off for 30+ minutes)
Did you test the injectors with teh PCM firing them?

Pull the fuel rail out and put some blue shop towels under the injectors. Unplug the coil packs and try to start the car for a couple seconds and see if the towels are wet under all the injectors.
Have you checked the intake manifold for cracks?
I was just asking because I was curious. I wasn't trying to help troubleshoot.
Have you checked your muffler bearings? I'm just asking because I am curious. I am not trying to help troubleshoot.

Gerry
Don't make fun.
Did you test the injectors with teh PCM firing them?

Pull the fuel rail out and put some blue shop towels under the injectors. Unplug the coil packs and try to start the car for a couple seconds and see if the towels are wet under all the injectors.
I've checked the injector wiring with two different sources. Once with a noid light. Secondly with a computer safe test light. It's simply a 12v powered test light with resistors and LED's. Attach it to positive it lights red. Attach it to negative it lights green. The fact that it has LED's allows it to be used like a noid light to read the negative pulse from the computer to the injectors. The non firing ones all have positive from battery and are getting a pulse from the computer.
BUT have you verified that they are actually spitting out fuel, when fed by your pump and your PCM?
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