Engine dies and backfires on highway

My 95 dodge ram recently quit on the highway. It lost power and backfired if I gave it gas. Wait 10 minutes and I can make it a few miles before it dies again. Wait a day and it runs fine until it drive for about 20 minutes on highway. From the various postings it sounds like either the fuel pump or the catalytic converter. Any ideas on how to narrow it down. No check engine lights come on, and all guages are OK. Local mechanic put fuel pressure guage on truck and drove around but could not reproduce problem.

Sounds like the cat to me. Anything fuel related probably wouldn't make it act like that.

Any suggestions on how to check the cat before replacing it?

Simplest way to check the Cat is to just take it in to a good muffler shop. They will be able to tell your right away. They just usely drill a few hole in it and take a look inside. Then they weld the holes back up if nothing is wrong. If it is bad I would have them change it out. IMO it is well worth the money to have them do it. They have all the stuff there that they need. I usaly have to make several trips to the local parts store before i am finished.

easiest way to check cat is to install an old type vacum/fuel pump gauge you know the type you use to use on carburated engines or something that could read low pressure up to approx 10-15psi and install it on egr back pressure port and running in neutural snap throttle wide open bring rpm up to about3500-4000 rpm rapidly back pressure should not exceed 2.5 psi best way i know and 100% accurate never failled back pressure port is the lower port on egr solenoid

easiest way to check cat is to install an old type vacum/fuel pump gauge you know the type you use to use on carburated engines or something that could read low pressure up to approx 10-15psi and install it on egr back pressure port and running in neutural snap throttle wide open bring rpm up to about3500-4000 rpm rapidly back pressure should not exceed 2.5 psi best way i know and 100% accurate never failled back pressure port is the lower port on egr solenoid but i would bet my money on a fuel pump not cat any fault codes???

Thanks for the suggestions. I will try the guage and then the muffler shop if necessary. I will be away for a week, but I will post the results in case anyone else has similar problems.

The way I check the cat is to stand by the pipe or pipes and see if there's anything coming out while you have the motor running. If the pipes fill up before the cat and stall the motor out, and nothing ever came out of the end, then the problem should be obvious to you.

Bleed knows the cats. I'd use his method first.

I take it this would only be apparent when the problem with power loss is occurring, since the truck seems to run fine until I take it on a longer drive at high speeds.

Next time the problem occurs, just pull off the road (it does idle, right?) and check the exhaust flow; if it's restricted I think that'll be your answer.

If the cat is broken inside like mine was, the motor will run depending on what you drive over, and how the truck shakes to make the inside move around.

Kinetic molecular theory right? You drive it enough so that the catalyst gets hot enough and shakes around inside, and expands and gets stuck in a certain position that prevents exhaust exit. Wait a while and it cools down and moves perhaps, until you crank the motor over a couple more times and it clanks out of the way. Everything seems fine and the motor runs like normal until it happens again. That's the only explanation I can come up with. My own truck has acted like this.

Thanks. I am almost looking forwarded to the truck breaking down again.

When it does, post back and let us know.