I have a 99 Dodge Ram with the 3.9l with the 5 speed manual transmission. When the temp warms up to 170 and goes into open loop circuit the truck starts bucking and jerking trying to drive it. It dies when I come to a stop sometimes, but it starts right up. Things that have been changed on it are the MAP sensor, IAC sensor, TP sensor, Cam sensor/ pickup plate, Crank sensor, Timing gears and chain (double roller set-up) New plugs, wires, cap, rotor, thermostat, I am getting ready to do the plenum pan gasket on it. It idles fine, but here is the weird part if you block off the air intake, the motor continues to idle just fine, the motor does not bog down, it just sits there idling fine. Anyone have any ideas? I am kind of running out of them. Distributor seems fine slight movement nothing crazy, the hall effect bracket is still good and not broken. Any ideas has anyone else had these issues?

 

The computer here info from the O2 sensors when it is warmer up. So they might be bad (pre cat one is the most important post cat don't need to be changed). Does it do it at a specific speed? If it does it above 45 (that is when od is engaged and is directly connected to the motor) what you are feeling is an engine miss. Also could be the coolant temp sensor that is faulty causing the engine to dump more fuel in and is flooding itself out when you stop.

 

Yeah, unplug the front O2 sensor, see if it runs any better. (it will set a code.)

 

I also replaced both O2 sensors and a new cat on the motor as well. It does it at all speeds, you can kinda get it to drive with light pedal pressure on the gas pedal, but if you go to get on it it just bucks and jerks. Its a 5 Speed Manual not an automatic. It runs fine till gets up to temp. I have also replaced the temp sending unit. Also when I block off the air intake the motor should die right? It just keeps idling like nothings wrong.

 

Then you have a pretty significant vacuum leak....

What brand O2 sensors?

 

I forgot when I did a compression test all the cylinders were right around 160-165 across the board I didn't do a wet test.

 

The O2 sensors are NGK

 

Your plenum could be really bad which would cause a vacuum leak

 

That is what I think but I don't hear a loud sucking noise I'm thinking its maybe coming from the back of the intake next to the firewall area I went around and shot starting fluid around it and you could hear the motor change pitch. I've done a ton of work to this truck to use as a daily. Its a 99 single cab shortbox, 2wd rebuild the 9 1/4 rearend with 3.90 gears and a lsd, it has a 4 1/2" lift in the front and 4" lift blocks in the rear, all new ball joints, tie rod ends, shocks, rubber brake lines, radiator, etc this is just the last issue with the truck.

 

I know why lift a 2wd? I have a 2006 wrangler that is lifted and rolling on 35" tires, so the dodge is ment to offroad its just I like sitting up higher and it looks pretty mean. The ram is on 285/70/17 basically a 33" tire.