My 1992 Plymouth voyager 3.0

My 1992 Plymouth voyager 3.0 looses power when it gets hot I put a straight pipe thinking it was the catalytic converter and still doing the same thing also it backfires

Must be running too rich. U got a bad choke. Or coolant temp sensor. Could be bad fpr too.

If I recall correctly, that OBDI engine has multiport fuel injection, along with a distributor (w/cap, rotor & module).

I would start with the basics, especially when you mention it’s backfiring. Specifically make sure your plugs, plug wires, cap & rotor are all good.

Specifically make sure your plugs, plug wires, cap & rotor are all good

Agree totally. Hot (and old) electronic ignitions can act much like you describe. I’d add the ignition control module (link below) to that list, too.

https://rockauto.com/catalog/moreinfo.php?pk=931224&cc=1244203&jnid=426&jpid=1

This engine does not have the super long life pugs of today. They are also prone to MAP sensor malfunctions.
If you cycle the key on and off three times and leave it on, a light on your dash will flash in 2 digit patterns. The last pattern displayed will be 5,5. anything but a 1,2 ( low or disconnected battery in the last 30 starts) or 5,5 (end of test) will hopefully lead you to the trouble area.
You can look up the codes by simply Googling 2 digit trouble codes.

Oldtimer11 I have the codes and they are 34, 35

The meaning of those codes is:
34 speed control servo solenoid, open or short detected
35 radiator fan control relay circuit, open or short detected

Question:
Does your cruise control work? A bad speed control servo on that vintage Chrysler will cause the cruise control to stop working.

Do you know if your radiator fan is coming on as it should?

Well, if the radiator fan isn’t turning on, that could definitely cause engine operating problems. Have you done a visual check to see if it is turning on or not? Usually the radiator fan turns on in stop and go driving, not on the freeway.

And a defective speed servo could cause the engine to appear to lose power, depending on what exactly the speed servo does in this car. If I had this problem I focus on those two problems first.

Backfiring … I’d be suspicious of valve problems too. Suggest to do a compression check.

Joe mario the cruise control is not working it use to and I will check the fan