Alright all you 5.9 experts, I'm in need of someone to either confirm my diagnosis or point me in a different direction. I'm calling fuel pump, but I'd like to get more opinions from the knowledge base here before my friend shells out $260 on a fuel pump.

The particulars:
1996 Ram, 5.9 with Automatic and overdrive. 210,000 miles.

The symptoms:
When cold, truck seems to run fairly well.
After allowing it to reach full operating temp at idle, we drove it 6 miles or so before the following began to happen:
RPMs dropped 3-400 momentarily, began to spit and sputter followed by backfiring through the intake. Power began to disappear quickly, and eventually (about 1 minute from onset of symptoms) got to the point that it would not even pull itself at all.
At that point, it would idle, but VERY roughly. When he attempted to rev the engine, he could get it to idle up somewhat if he depressed the pedal slowly, but if he goosed it to 1/2 throttle and tried to hold it the RPMs would jump up to about 2500 and slowly begin to drop while backfiring through the intake again.

We let it sit for about an hour, and it fired up and ran as well as before this all started. We turned around and headed back to my house, but it only made it about half-way before it began to exhibit the same symptoms again. The longer we let it sit, the better it would run and for longer. If we tried to "force" it, eventually it would get to the point that it wouldn't even idle.

Truck does not smoke, knock, ping, burn oil or anything else. Oil is clean and water-free.

Parts that are less than 1,000 miles old:
Plugs, wires, distributor cap, rotor button, coil, IAC. IAC and coil were replaced today to eliminate them from possible causes of this problem.

Help, lol.

 

Forgot to mention this:
About a month and a half ago, his fuel gauge read 3/4, but it was actually empty. Up til that point, it had always worked, but for some reason it got stuck at 3/4 that time. Long story short, after running out of gas, he took it to fill it up... Went from 3/4 to full and has worked correctly ever since. Not sure if it could be related, but worth mentioning.

 

Do a pressure test on the pump. It sounds more like a Catalytic Converter problem to me though. Crawl underneath and tap the CAT with a hammer to see if there is some rattling sounds coming from it. You can also (if you have an infrared thermometer) test the temperature in front of the cat and behind the cat. If the cat is working right, the temp before the cat should be colder than behind it. (Make sure the motor is warmed up first)
Welcome to DF, and remember, the search button at the top of the page is always your friend.

 

My '94 did some of this as well when my fuel pump started to go out. The more i would let the gas tank empty the worse the symptoms got. after awhile i could only keep it above 1/2 tank and they would it would start to act up. I was told the pump needed to work harder to get the gas from the bottom of the tank and when it was trying to work hard it would cut out and make the trucks rpms jump up and down

I never got it fix so i couldnt help you with that but they were about the same problem your friend is having

 

lol, I'm quite friendly with the search button.

Forgot to mention...there is no CAT. It's been gone for quite some time, now.

 

Ah, well then do a pressure test on the pump, and I would test it with a volt meter too while I was under there.

 

Will be doing this in the morning. Thanks for the input guys, and anyone else who has any further suggestions or input is welcome to leave them.

 

My O2 sensor senses are tingling ... sounds like when it goes into closed loop is when it starts to get screwy.

 

+1 to bill. front o2 sensor is a major player during closed loop. do that next.

 

Check O2 sensor as mentioned. If that don't fix it, try replacing the coolant temp sensor.

I never realized how important that coolant temp sensor was until I snapped one off in the intake. truck ran like absolute crap without a singnal from that one little sensor. All the symptoms you described happened with a bad coolant temp sensor.