Cold miss fire

[JMikk]

Hey all, new issue seems to have come up and scares me I might not be able to get to work! When the truck sits and gets to ambient air temps, first start up seems normal. The regular high idle and then comes down to 675ish but after a minute or two it’ll drop to 500 and lope and keep dropping rpm till it dies. If you hop in it and let it come down from 1000 and then take off you’ll get 500 feet down the street and it’ll start dying to 500 in gear and the only way to get the truck to go is floor it which it’ll pop through the intake and then take off like a bullet. It’ll do this twice in 2-3 miles, once it’s at running temp it’s happy as can be, no troubles to be found. Any ideas? Fresh tune up, no check engine lights. Tried sea foam if it was a clogged up Injector but no change.

 

[fastf]

Start checking for vacume leaks you would be surprised a fine little pin hole can make a engine run like crap.

 

[dapepper9]

These engines being efi and speed density, vacuum leaks have to be quite large to really affect them.

Pop through the intake is common with bad coil. I'd start by taking a multimeter and checking resistance between the brass tower and either one of the pins in the connector

 

[fastf]

When is the last time you cleaned the throttle body.Those butterfly valves are known to gum up and stick.EFI has nothing to do with it I have owned several Dodges with that set up.Also it isn't the coil believe me.Take the air box off the air intake and get a can of choke cleaner and crank it up and hold the throttle open and spray the body.Look at the butterflies if they are black get you a tooth brush and spray choke cleaner on it and scrub it and take a paper towel and wipe it off.The best way to really clean it up is take it off the manifold and clean it make sure your replace the gasket under the throttle body.

 

[dapepper9]

When is the last time you cleaned the throttle body.Those butterfly valves are known to gum up and stick.EFI has nothing to do with it I have owned several Dodges with that set up.Also it isn't the coil believe me.Take the air box off the air intake and get a can of choke cleaner and crank it up and hold the throttle open and spray the body.Look at the butterflies if they are black get you a tooth brush and spray choke cleaner on it and scrub it and take a paper towel and wipe it off.The best way to really clean it up is take it off the manifold and clean it make sure your replace the gasket under the throttle body.

Owning something does not make you an expert.

My post about vacuum leaks not being a major deal on these is very much because they're EFI. HOWEVER, it's the specific type of efi. Speed Density systems do not measure the amount of air coming into the engines because they do not have a Mass Air Flow sensor. Instead they use Manifold Air Pressure. The PCM only knows roughly how much air the engine is intaking. You can have a large vacuum leak and the engine will still run. Not great but it will run. Don't believe me go pull the brake booster hose off with the engine running. Idle will increase, it will lean out, but it won't die. In fact you can drive it like that.

What you've described raises engine rpm, not lower it. Pop through the intake specifically is quite common with a weak ignition coil. The symptoms he's described also point towards Throttle Position sensor particularly with the the way he has to stab the throttle to get it go. If the TPS is getting inconsistent readings such as when at idle it switches the pcm from using the IAC to using the TPS. However if no throttle input is actually there the IAC never opens and the engine will choke out. When moving if the TPS is not reading correct input it will also improperly fuel the engine, also killing the engine in many cases. Stabbing the throttle can basically get it to "kick in".

My suggestion regarding the coil is simply to verify healthy spark, something that gets lost in translation on the internet as a guy will say "yeah ive got spark i saw it" without realizing it may not be strong enough. Multimeter readings are free if you have one and if you don't most parts stores have one theyll bring out. The TPS can also be checked via live data or also by multimeter. I'll grab the link and post it below this

 

[dapepper9]

https://troubleshootmyvehicle.com/chrysler/3.9L-5.2L-5.9L/how-to-test-the-tps-sensor-1

It's not a bad idea at all to clean the throttle blades. However them being dirty won't cause an issue like this where it's both at idle and while driving and also dependent on temperature.

 

[fastf]

Question how many cars and trucks and motorcycles have you owned or worked on in your life.You are 22 years old and the truth you haven't seen nothing the problem is at the throttle body have you ever drove a car or tuck with a manual choke it will spit a back fire through the carb and such if the engine is cold and it aint the spark.I know all about the computerized junk heck if you take away the computer that thing wont run.

 

[dapepper9]

Question how many cars and trucks and motorcycles have you owned or worked on in your life.You are 22 years old and the truth you haven't seen nothing the problem is at the throttle body have you ever drove a car or tuck with a manual choke it will spit a back fire through the carb and such if the engine is cold and it aint the spark.I know all about the computerized junk heck if you take away the computer that thing wont run.

I work on cars all the time. Mine, my family's, my coworkers, my friends.

You can jump to the throttle blades thing if you want but the simple fact is that's not how there system works. There's way too many variables you're refusing to take into account. Like i said, cleaning it is a good idea yeah. But it's not going to solve this guy's problem. You're also comparing this to a carb engine which is greatly affected by vacuum leaks and such things as you've described. This is in no way the same or even similar to a choke issue. The fact is, the problem still exists WHILE DRIVING. You have to stab the throttle for the engine to run correctly. It's not a blade sticking issue, particularly being these are cable driven throttle bodies. Your foot controls throttle position manually and gumminess isn't going to change that. If it was strictly an idle issue there could be something to your comments and history has shown that to be the case but it's not. There is something electrically going on.


I never said spark would fix it. Not at all the case. Checking the spark health simply takes it out of the equation and makes sure it's not a factor making the situation worse.

Lol the digging at my age is completely irrelevant and shows your ignorance in arrogance

 

[fastf]

Go work on your friends junk I don't care like I said you haven't seen nothing and really don't know nothing.

 

[dapepper9]

Go work on your friends junk I don't care like I said you haven't seen nothing and really don't know nothing.

*anything and *anything. Jesus.

Rather than try to pick a fight with somebody smarter than you, maybe let the guy get the help he needs

 

[jbmobbs]

Damn come back after 2 years and a grown man is having a ******* contest with a 22yo of who has worked on more....... unfortunately age does not mean **** for knowledge.

 

[CincyAreaVance]

Go work on your friends junk I don't care like I said you haven't seen nothing and really don't know nothing.

Get a load of this guy! LMAO

 

[dapepper9]

JMikk. Test your TPS as i posted earlier or find somebody with a live scanner. Idle is roughly 12-14% and full throttle roughly 75%. Sounds weird i know.

 

[Merc225hp]

Question how many cars and trucks and motorcycles have you owned or worked on in your life.You are 22 years old and the truth you haven't seen nothing the problem is at the throttle body have you ever drove a car or tuck with a manual choke it will spit a back fire through the carb and such if the engine is cold and it aint the spark.I know all about the computerized junk heck if you take away the computer that thing wont run.

Wow how small minded you are. So he's only 22 wtf does that matter? Seems to me he knows lots more than u do.

Stop trolling and go **** off.