Just rebuilt 5.9 magnum, rebuilt trans, runs extremely smooth when it’s cold but as it starts to warm up the timing starts to jump so it starts to put and idle drops until it finally dies. New distributor rod, cap, and rotor, all new spark plugs, and wires. New TPS and ICV. Completed cleaned the throttle body. I have an actual scanner coming tomorrow to look at the timing and fuel pressure. I’ve read that you need to do a fuel timing sync but idk. Do you?

 

Fuel "sync" merely tells the PCM which 4 injectors need to be fired in the next revolution of the crank. All timing for injectors and ignition is derived from the crank position sensor. The method for installing the distributor described in the service manual is usually close enough, IIRC there is more than +/- 10 degrees variation that the PCM can deal with.

Having said this, my money is on the crank position sensor going wonky when it heats up.

 

I've had this happen in the past with a non OEM crank sensor. When the engine cut off consistently, I plugged in an ODB2 scanner right after the engine shutdown and got a code from the PCM flagging the crank sensor as an issue.

 

I don’t have any codes as this presents time so I’m not entirely sure

 

is there a way to test this?

 

Not easily. The best way would be to monitor the crank position signal with an oscilloscope but that's not realistic for DIY or even many shops. Indirectly the "tach bounce" during cranking or a scan tool with live data would indicate the PCM is reading some signal but you can't tell if the signal has dropouts etc. Does the truck start right up after it died or do you have to wait for it to cool down ?

 

Itll start again just fine. We haven’t been able to fully tune it. Right now we sitting at +/- 15 degrees before TDC so it takes a little to start

 

Sounds like your timing is off a fair bit. You can adjust the distributor slightly to make it start easier.

If you can find someone in your area with an old Snap-On MT2500 scanner, along with the cartridges that cover your year Dodge Ram, it has a function to set fuel sync. You can also find these scanners used on Craigslist, FB Marketplace and eBay.

 

After some more diagnosis we got it to stay running when the MAP sensor is unplugged and when it’s plugged in it’ll stall out. Gonna replace that tomorrow and continue to work on timing

 

Did you fix the plenum issue? If it leaks it will affect timing. How are you seeing the timing? You can use a timing light and check the balancer. You can set the distributor like this on #1 CYLINDER TDC COMPRESSION STROKE to get the fuel sync. With worn parts use a scanner.