I have a 1998 Dodge 1500 5.2 Auto.

When I first drive down the road when cold and it is still in Open Loop, the truck bucks and stumbles at low rpms. Almost sounds like a misfire... but if that happened then a code would have come up for that and it never has.

I also find that it will stay in open loop for almost 10 minutes before it gets warm enough to go into closed loop.

Also periodically I will get a code about excessive voltage on the 02 at the cat. I usually goes away.

The mileage is around 14.5 mpg, new plugs, wires, cap, rotor and K&N filter.

Any ideas?

 

Well if it's acting up when cold and the engine takes longer than usual to warm up, the coolant temp sensor could be a problem although a code will usually show. The sensor is cheap...You could also check the connector/wiring to make sure it's working correctly.

High voltage on the o2's can be set when a coolant temp sensor goes bad as well.

My truck used to buck all the time when cold (and knock once in a while) and it turned out to be a faulty ign. coil...If the coil is original, I'd look into replacing it anyways-just a thought.

 

Why would the coil only act up when cold?

Should I put an aftermarket coil on it then or just a replacement stock style?

 

It just seemed to be buck more when cold idk why. It still did once in a while when warm though.

I don't know if the aftermarket coils like MSD's would improve much with all of the other ignition being stock...I just got an oem one, works fine.

And I'm not saying the coils your problem... With the codes you have, in conjunction with everything else, it sounds like a bad coolant temp sensor/wiring. Either that or a mix of different things that just happened to occur at the same time; one causing the code (bad o2/heater circuit?), the other causing the bucking (bad coil, plenum, etc.), and another causing slow warming (bad t-stat, coolant sensor, pcm, etc.)

 

I talked my my mechanic ( who is a huge Mopar guy)

He is starting to think it might be a fuel issue. The other day on the highway I tried passing a truck and the truck just stayed at about 70-75 and would not speed up no matter how much gas I gave it.

He said this could also be the problem when it is cold..

He is gonna take mine for a drive and compare it against his 1998 Dodge truck and try to see if their is a difference from the seat of the pants feel..

 

In any case where fuel may be considered a problem, checking the pressure at the fuel rail is a good starting point.

 

Well a dirty injector(s) will cause a misfire and stumble (usually at low accel.) when in open loop so that is definitely a possibility. It'll sometimes throw a p0171 too but I don't think a High Voltage code...Fuel pressure should be at ~49psi as well.

 

thanks for the help.. I will let you know how it turns out..

BTW.. has anyone seen an increase in mileage by putting on headers but stuff using the stock exhaust ( cat,pipes, mufflers)?