I have a 1999 Ram 1500 with a 5.9. I have a K&N cool air intake. I have slightly larger than stock tires. I have considerably sluggish low end performance. My wife normally drives my truck as I need to commute daily. Because of this I am not sure exactly when this problem started. From a complete stop you can accelerate hard. The truck feels as though you are towing a heavy trailer for the first 10 seconds or so, and then takes off like a bat out of hell. You can watch the RPM's come up slowly as you start to accelerate. I do not believe the torque converter is slipping. I have tried manually shifting or turning the overdrive off with no effect on this problem. I have no codes coming up. I did have a number five missfire code come up. I don't know if this would have anything to do with the problem I am experiencing.

 

Welcome to DF.

Check your plenum, see if it is blown. (many threads on this, a quick search will turn up TONS of information.)

 

i'd look at fuel pressure.. sounds like you're bogging down..

could be vacuum related...

I'd start, though, by looking at your catalytic converter.. pull the upwind o2 sensor and see if it improves.. it could be that it's clogged up some, and when the engine produces enough pressure to 'break through', you're on your way, but before it gets that kind of pressure going, you bog..

 

you're ninja fast Hey You.. Imah start saying: "Hey, You- NINJA!"..

 

HeyYou, thank you for the suggestion. How do I go about checking the intake plenum? Replace the intake manifold?

Drewactual, I checked the vacuum by installing a vacuum gauge. I haven't driven it with the gauge installed, but initial tests in the driveway read 20 solid. Fuel pressure on the rail, again sitting in the driveway, is 47psi. I did not drive around with the gauge installed, only a stationary read in the driveway. Is there a way to test the O2 sensor? I know how to test the Cat be measuring with an infrared thermometer.

Thanks for the awesome help.

 

Look down your throttle bores, see any oil? Plenum is blown..... fairly standard repair on these trucks. Get the plenum plate from hughes, gaskets, bolts and such from your local parts store, yank the intake, replace the plenum plate, put it back together, and down the road you go.

Also a good time to change various coolant hoses, thermostat, and such that are difficult to get to otherwise.

 

I've seen oil control problems behave this way -- plugs that are fouling will clean up a bit at higher RPM and begin firing again. If the truck's consuming oil it's a good time to pull the plugs for a look. If it's an oil control problem, the cat and O2 sensor will foul, then the fouled (clogged) cat will cause higher combustion chamber temperatures that often lead to cracked heads. It gets expensive fast, which is why I suggest looking at the plugs first.

If it's oil in the cylinders, the most common causes are a blown plenum gasket, failed PCV valve (particularly when the misfire is on the cylinder nearest the valve's port in the intake manifold) and/or leaky valve stem seals.

 

I had a chance to use a FLIR camera a few minutes ago. I brought the engine up to operating temperature. Temp from the header to the very front of the catalytic converter was 550 degrees. Temperature from the outlet on the cat was 230 degrees. Looks like I have a bad converter. Is there anything else I should replace at the same time? Is there a high flow brand you can recommend?

 

Magnaflow has a high flow cat. You can get it at summitracing.com. I think the part number is 94004 or something. Its about $80

 

Yes, your plenum plate. Since that's the most likely reason the cat has gone bad.