Ram 1500 cant rev > 3,000 RPM


#1

Its a 99 Dodge Ram 1500 with 5.9 gas engine w/ 115K miles.

The truck started running really rough and I was 60 miles from home. The issue was bad plug wires, dist cap, rotor. These items were heavily corroded. I was able to get the truck home and then replaced the typical tune up items. Truck was running good as new. I drove it around and everything seemed fine until I took it out to the highway. Runs great at low RPM but cuts out and cannot accelerate above ~3,000-3300 RPM depending on the gear. When I get to ~ 3K rpm it starts cutting out and surging and feels like I am riding a bucking bronco.

The CEL has been on the truck for a couple of years and I have not checked it due to mice chewing up my wires a couple years ago (the joys of country living). I never rewired up the OBD2 port. It has run great and gas mileage has been normal until last weekend. Funny part is when it started running bad, the CEL went off.

I have had suspicion that the catalytic converter has been partially blocked because it has made noise before it gets warmed up. My thought is that when the engine was running rough, my gas mileage went really low for that trip home. My thought is all the extra gas that ended up in the exhaust has finally killed the cat and now i have a significantly restricted exhaust.

I am open to ideas. My next step is to install a test pipe and see if that solves the problem.


#2

Yes, the catalytic converter could be the problem, or it might be the result of fuel system problem.
When was the fuel filter last replaced?
If you don’t recall, or if it was more than 30k miles ago, I would suggest replacing that filter.
I would suggest that you also test the output of the fuel pump, as it could be failing.


#3

A vacuum gauge can be used to test for an exhaust blockage. It’s far easier and cheaper than rigging up a test pipe.

The sixty miles of driving with an engine gasping could have done the converter in.


#4

Excellent points. I will check the fuel system while I have a Y-pipe on order.


#5

I forgot about the vacuum test. I just loaned out all my vacuum gauges to my brother to synchronize his carburetors on his boat. I have a manifold of 8 liquid filled gauges that I made years ago.

The cat has been making a banging sound for a couple of years now. This is a farm truck and doesn’t see many miles in a year. I have always been afraid of the cat catching my fields on fire as I drive through tall grass. It is not uncommon that I drive through waste high grass and brush. A couple of weeks ago I was driving through grass taller than the cab of the truck.


#6

It might not be a bad idea to carry along a small fire extinguisher in the truck considering the use in high grass and brush.

Here in OK a few years ago (where it’s almost always hot and dry) a state trooper in pursuit of a suspect slammed to a stop in a field and took off after the suspect on foot.

A few minutes later the hot converters set the grass on fire underneath the patrol car and burnt it to the ground.


#7

My recommendation? Start by fixing the things you know are bad and go from there. Hope it isn’t too late. Hope you don’t have irreversible damage.


#8

Start by fixing the wiring to the OBD II connector so you can take advantage of the manufacturer’s self diagnostic software. You paid for it when you bought the car, so you might as well use it. Straight piping the cat might be something you need to try at some point, but the first check is what dB mentioned above, the intake manifold vacuum. That will usually show up a major-plugged cat. I think you already understand that anything that impedes the free flow of air and gasoline into the engine, and exhaust gasses out can cause this symptom and will show up most at higher engine rpms and loads.

My guess – and just a guess — some remaining ignition system problem. Maybe a marginal coil/ignition module. The ignition system is stressed more as well at higher rpms. Crank/cam position sensors should also be considered. But don’t go down those pathways until you fix the OBD II so you can read all the diagnostic codes.


#9

Don’t give ME any credit

I haven’t even part of this discussion

:laughing:


#10

I plan to fix the port and any remaining wiring issues (radio, power mirrors, mirror defroster, and dash cluster are intermittently working) when I replace the dash. It is one of those years that the dodge dash cracked into a million pieces. Mine is in a million pieces. Driving down the rough dirt roads don’t help. The whole dash is going to come crashing down into the floor if I don’t fix it soon. My issue is there is limited time to keep up on everything that needs attention. There is always something more urgent than fixing the luxuries on a farm truck.

Other than the dash it has been a pretty good and reliable truck. As long as I can keep the pack rats away from it hopefully I will get another 10 years out of the truck. This truck is basically farm truck and is only driven about 3000 miles a year.


#11

Years ago I worked at a cattle ranch in Colorado. As a “no nothing newbie” ranch hand, I got lots of odd jobs. I thought I’d at least get to ride a horse, but instead I was equipped with a VW Beetle. I’d have to haul some feed- hay in the backseat of the Beetle from time to time, and you probably know that hay tends to host families of mice. So every morning I’d have to chase the mice out of the Beetle. Eventually I decided this mice chasing event every morning was taking too much time, so I decided to just let the mice stay in the car if that’s what they wanted. I’d sit in the driver’s seat, rolling down a country road, and two or three mice would ride along in the passenger seat with me. When I’d come to a gate I needed to open, I’d stop & get out of the car and leave the doors open so the mice could get out, but they preferred to stay in and ride back w/me. The other ranch hands couldn’t get enough of this, they’d tease and tease me about my Beetle being a “Mouse Car” … lol …


#12

I got the test pipe installed this weekend. I made it myself using a magnaflow 2-1 collector and a short piece of 2.5" pipe. I welded in some bungs for the 02 sensors and truck runs great!


#13

Great detective job, sounds like you’ve definitely narrowed it down to the cat.