*****update***** We have checked timing, grounds, sensors, everything suggested. New idle control valve, and reset computer. Truck turns over- wont start. Seems like our only option is to replace the PCM? any thoughts?

I put a used engine in my 03 dodge ram 1500 (3.7). Before putting it in I changed the oil pick up tube, oil pump, belts and all the seals. It started up right away, drove it down the rode and it ran fine for about a mile then died. Towed it back home and now it is backfiring and will not stay running. Any ideas what the problem could be? it sounds like the timing is off but I'm not sure if there are other problems that should be checked out first?

  • 2
    Go on. Tell us more. What page of the service manual are you using to troubleshoot the no start condition?
    – zipzit
    Commented May 30, 2016 at 16:14

2 Answers 2


I'm not familiar with this engine specifically, but here are the areas I would be looking in. Remember, you need 4 things to run - Spark, Fuel, Air, Compression. Feel free to comment with your findings.


  • Since this engine was recently reassembled, I would be looking at timing marks to make sure the timing belt didn't jump. I've had a timing belt jump when I didn't put enough tension on it.

  • Check compression, might give you a clue as to a cylinder having an issue.

  • Pull the valve cover and rotate the crank by hand to make sure all the valves are opening/closing properly


  • Check fuel pressure at the rail. If this is low, it could be the fuel pump, filter, or Fuel Pressure Regulator (FPR).

  • You can pull the rail and crank it to see if the injectors are all firing.

  • Bad gas. Assuming the truck sat for a while, did you drain the tank?


  • Check base ignition timing (not sure if you can even do this)

  • pull the plug wires one by one to see if one makes a difference.

  • pull the plugs, make sure they are clean. They should be tan, if not, that might point to an issue.

  • an inline spark plug tester to verify plugs are firing


  • Vacuum lines

  • Idle Valve

  • EGR

  • Plugged cat


  • CODES! I'd be surprised if there aren't any.

  • The best thing, would be if you can get your hands on a scanner that can give you a live output of the sensors to see what is going on.

  • ensure all wires are connected to the correct sensor

  • You may need to start back probing sensors, but I would think anything too far out of the norm would cause a code.

  • check grounds. Bad grounds can cause weird issues, I normally install some heavy gauge cables directly from the battery to the body and the block. Ensure all wiring harness grounds are connected. Follow the harness with a fine tooth comb.


You're going to have to verify spark and fuel injector operation. Use a scope and backprobe the signal wires for any cylinder. You should also look at the cam and crank signals for irregularities or drop outs.

You could use a multimeter or noid light to test the injector signal. Don't use a test light on the signal driver circuits.

Replacing the PCM may or may not fix your problem, don't throw away money unless you can verify the PCM is the problem. If you don't have access to a scope you may need to take the truck to a garage and pay some money for a diagnosis.

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