Ok, this is going to be an odd one I believe. 93 dodge ramcharger with a 5.9 liter engine. Port fuel injected, stock other than a K&N air filter. 160 K miles and has always run great.

Last couple of months she got new plugs, cap, rotor.
Last 12 months, new bosch fuel pump and associated filter assembly

Now that it is cold out, when I start the truck it idles as it always has (a slight lope to the idle almost like a cam lope, it has always done this when cold) If I give it any throttle at all it starts to backfire through the intake, very bad. I am not able to get 15 miles an hour out of it. If I continue driving once the engine comes up to temp it is like a switch is flipped and the truck will take off and run fine. It is so sudden that if there is someone in front of me I would hit them. It takes off that fast and the change over to running well is that rapid.

Once it warms up if I drive down the highway at high speeds I.E. 70 mph and it is rather cold out 20 deg or less, it's like whatever warms up gets cold and then it starts missing and backfiring again and the speeds drop back to 15 - 20. Once it warms up again, the switch is flipped and off she goes like she is running a race.

I have just replaced the TPS and it did not make a difference. That was prior to noticing the correlation between warm and cold performance.

There are no codes coming up and the CEL is not coming on.

I have checked the fuel pressure while it is running poor and I maxed out my gauge at 60 psi

The obvious things don't make sense such as O2 sensors, coils, ignition etc due to it running perfect as soon as a certain temp is achieved. It's not a gradual change in performance, it is just like a switch is flipped and then it runs perfect.

Anyone have any ideas??

 

I have also searched the forums far and wide and have not found anything specific to this issue. I have found close, but not the same with relation to the cold performance.

I guess I should also say Hello to everyone, but in my frustration I forgot my manners!! lol

Anyhow, I'm glad I found this place and hope I can get some thoughts from all of you.

 

Have you done the Hughes plenum fix on yours? Sounds like yours has already sucked the gasket in!

 

War wagon, I had thought of that, but this thing runs absolutely perfect once it comes up to temp. As I said, in the post, it is like a switch is flipped and it goes from not running to running absolutely perfect. From everything I have read, once you blow the plenum gasket out they just run like **** period. Would it run perfect once it is warm if the plenum gasket blew out? Not meaning to say you are wrong, I am asking for your opinion...

 

It will run BETTER warm... but then, I've never heard of a MPFI engine backfiring, so I grasped for the obvious first.

 

Dodge motors are the coldest naturally cold nature. Does it still do it when warm is the question