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Got a 2007 nissan pathfinder . Was running good then it got to where it was running rough with no power . Tried to make it home and it completely quit . Had somebody say it seems like it's dead on 3 cylinders . What would cause that ? Idk where to start
 

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One of the first things to do is perform an ECU code readout with a portable scan tool to see if any fault codes are set. The tool can be purchased at most auto parts stores or online at Amazon.com. Post the actual codes here on the forum so that we may be able to help you further. If there is one or more fault codes set, they can help point to the malfunction. If you have a copy of the FSM for your vehicle, the code readout procedure is described there along with a listing of codes. You can download a copy of the FSM from this web site: Owner's Manuals. The section EC.PDF is the one to read.

If you suspect some dead cylinders, consider performing a compression test on all cylinders. The normal procedure for a compression test is to remove all the spark plugs, insert a compression gauge into the spark plug hole, and then turning the engine over about three times. Post the readings here on the forum. If there is more than a 20% difference in any of the readings, a further test would be required to determine if the variance problem is due to an issue with the piston rings, the valves or the head gasket.

If the compression turns out to be OK, then here are some diagnostic procedures you can perform:

* Testing fuel delivery:
An easy way to test the fuel delivery is to remove the MAF from the throttle valve body. Now spray starting fluid into the throttle body while trying to start the engine. If it starts up for a few seconds and then dies, then there's a problem with the fuel injection system.

The fuel injectors may not be firing. This can be tested with a "noid" light probe for each injector harness connector; the probe kit can be purchased at most auto parts stores or online at Amazon.com. If one or more injectors are not firing, the problem could be bad timing sensors, a bad ECU or missing 12V.

Tee-in a temporary fuel pressure gauge between the fuel feed hose and the fuel rail. Turn the ignition key to the run position but DO NOT TRY TO START THE ENGINE. The fuel pressure reading should be around 51 psi which would be a static reading. If the reading is very low or zero, the fuel pump may have failed or the fuel pressure regulator is defective.

* Testing ignition:
Pull several coil packs to test; use a spare spark plug in the coil pack to test; ground the plug base with a jumper wire to the engine block; see if you're getting a spark while trying to start the engine. If no spark, the coil pack could be bad, missing 12V, or a bad ECU.

* The cam timing may be incorrect:
Check the chain guide to see if it's broken or it may be cracked and has skipped some teeth.

* There may be a major intake system vacuum leak. Check the intake manifold nuts to make sure they are tight. The gasket may have failed. Also check the intake plenum bellows at the throttle valve and at the MAF for cracks or loose clamps.
 
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