94 Ram 1500 360cu 200k

My girlfriend has had an issue with her truck.It had been maintained well ,as it was a fleet truck.
When it reaches operating temperature it begins to run very badly. It feels as if it is not getting fuel, (or perhaps dumping too much fuel?)
I don't know much about mechanics.
I looked to see if had thrown any codes there is a "37" but I don't see how that would cause the backfires,sputtering and jerking or as my gf says chitty chitty bang bang.
It runs well from cold until temp.
We did replace the plugs , wires cap and rotor. However we are financially unable to start replacing all of the usual suspects. I need to check the fuel pump pressure but if it were the pump...wouldn't it do it all the time?
I am writing to ask if it can be the coolant temp sensor ? The dash gauge works properly. From reading your site I understand there are two, one which goes computer.
My confusion stems from that there are no codes and it only does it when it is warm.
Are OBD1 reliable? It should indicate sensor failure,?
Another thought was a 02 sensor. The cat was changed a while back.
I appreciate your time in reading this and any thoughts you may have.
Thank you
Bob

 

Depends on the sensor..... For the O2 sensors, so long as voltage is switching, the PCM 'assumes' its good. That may not necessarily be the case though. I would suggest unplugging the front O2 sensor, and see if the behavior changes. (being as how yours is 94, I think you only have one O2 sensor, right on the front of the cat.)

 

Thank you for your response and knowledge.
I will try that.

 

The early trucks have a quirk in that they have separate temperature sensors for the instrument panel and the PCM. If the PCM sensor is bad the PCM keeps the mixture too rich for normal operation. You can measure the resistance of the two pin temperature sensor, it should be ballpark what the table below shows.

 

Thank you I wasn't aware that there is a way to test it.
That is very helpful.

 

I unplugged the O2 sensor as recommended, brought the truck up to temp. Then drove it around the parking lot for a while . The issue did not occur.
I ordered a O2 sensor that. you-all recommend from Napa and will pick it up tomorrow.
Well I pulled the O2 after PB ,heating, and PB installed the new one. I was sure it was going to take care of the problem ...but it did not.
I will get to the two wire coolant temp sensor, ( I think I see it down behind the alternator) and check the resistance.
Also will check fuel pressure to rule that out.