bumped

 

If you are so set on it being injector related, why not just start there?

Swap the injector to another cylinder. If the problem migrates, then its the injector. If not, then its not the injector. And you go from there. All you have lost is some time.

 

I never said it was injector related. I put up a link where the symtoms were the same, that guy replaced his injectors to metal bodied ones at $65 a pop.
I want to find a place to start without ripping things apart and buying assundry tools for a poke and hope.
WHY would it only misfire at hot idle, only, has been my recurring question. It screams down the highway. No one seems to want to answer "that" question. Am I the only Dakota owner with this issue?
I took it from getting 12-15 mpg to 19-20mpg.
Built my own ram air solution for under $50, half that being the cost of 4" hole saw. I found $7 spark plugs that beat the snot out of the expensive platinums.
I am not set in stone by any means, but if I wanted to throw my money away, I would I take it to my stealership, they could not even do an oil change right.
Only one guy has posted anything worth considering, TY much, and I want other input before I spend my hard earned cash. Why else would I participate in the forum, doh!
Theres alot lot of parts to unhook just to get fuel rail off, I do not leap easially.

 

Causes for hot only misfire -
Plug Coil shorting out when warm - You can check the coil by checking the resistance
Shorted Spark Plug Wire when hot - The wire could be broken in side, or have some insulation rubbed off that could be arcing on the engine
Fouled Spark plug - You already checked for this you said
Carbon Deposits in head or valves - This would be tested by compression test and or leak down test

A leaking fuel injector or one that is plugged would cause a misfire at all times. I doubt it's an injector, but the possibility is always there.

Curious question. I know you said you checked your spark plugs, but have you changed them recently? What plug did you put in if you did? You may have a bad plug. Sometimes they are bad from the factory. It does happen. Spark plugs are cheap, and if you replaced them recently, you may have a bad plug.

 

Oh I forgot, there is a very simple test for a burned exhaust valve only by the way.

Take a sheet of paper, like printer paper, when the engine is idling and mis-firing. Take the paper and hold it 2-3" from the end of the exhaust pipe. Watch the flutter of the paper with the engine pulses. If the paper is drawn TOWARDS the exhaust pipe, this may indicate a burned exhaust valve. It's a cheap. easy test. Won't hurt anything.

 

Plug Coil, your not talking about the injectors solenoid are you?
I have a distributer in the truck, spark plug wire from distributor cap to plug. Its all old school distributor layout, to me its all a mechanical style distributor parts.

I use HALO sparkplugs, used a set for 25,000 miles. Two summers ago I replaced with a new set, used about 10,000 miles. There was nothing wrong with old set, they were in beautiful condition. They all looked alike. I kept them. When misfire began, I pulled the #3 new one and replaced it with old #3. No help. New #3 was in beautiful condition.
No carbon on any of them.
I use Dixie Caps in the injectors.
New plug wires with new plug set.

I'll try the paper test, but the plugs were in such good shape and the acceleration is fine. Whenever I reset the trucks puter, I would drive a hundred miles with no light coming back, but when I would stop at a toll booth and waited in line , boom it would pop while idling in line.
Fuel vaporization in the injector is the only thing I've come across that makes sense. And your idea about a plug coil????? I will find out where it is and check it.

TY

I am thinking about trying "Duners Fuel Rail Mod".
I need new front rotors, I might need a new govenor pressure sensor and transducer. Thats why I do not want to waste money on maybe's.

 

By plug coil I meant ignition coil. I brain farted. Forgot we were talking about the 3.9. excuse that comment. The 3.9 doesn't have the ignition coils. My mistake. I'm tired buddy. long day.

You replaced the plugs, plug wires, but did you check the distributor cap? Maybe the cyl 3 electrode is a bit burned. Could possibly be cracked too.

If it is indeed an injector, you can check by checking the resistance of the injector, but this will only check the electrical side of the injector, not the mechanical side. You most likely don't have access to a DRB 3 Chrysler scan tool, but if you can get your hands on one, you can do a power balance test but shutting off individual fuel injectors one at a time and see if it affects the misfire at all. With the other cylinders you should feel a significant difference in feel. With the bad cylinder, you won't feel as large of a difference. That would be one way to check the injector.

I'm sorry man, but I'm starting to run out of ideas on how to test the mechanical side of the injector without just taking it out and swapping it to another cylinder and see if the misfire follows it. That'll be the easiest way to make sure it is the injector. If the misfire does follow the injector swap, then that solves your issue. If not, it's not the injector.

 

TY Much CS,
Swapping the injector will be the last test, I just wanted to double check and exhaust all the easiest checks first, before I start taking things apart.
I thought you might have meant the ignition coil, but with all the new fangled puter components,,,,,,,,,,,,,,, a coil issue would have affected the entire ignition system.
When I added new plug wires, I tried to replace the distributor cap and the rotor. Its a pain to get at them and I fought with it a bit. After taking out the old parts I started to put in new. I opened up the new rotor box, started to put it in and realized it had no metal any where on it. DOH! I had bought it online and did not look at it till I went to install it. Man was I pissed. I had to put back in the old one and I think I put back in the old cap as well. That was gonna be my next look see, but I figured I try and gather some more info, anyways.
I emailed a pic to the company where I bought the rotor and they wanted to know why I was disatisfied, bleepin idiots. Will buy nothing there ever again!
Because it runs so nice down the highway, I will be surprised if its the cap and rotor, but WTF.
I still want to think its fuel being vaporized in the injector due to heat, but cylinder #1's injector is 2" away and no issues with #1.
Its truly the only scenario I've come across that fits my symptoms.

 

My 2 cents I guess and don't fault me for trying to help. Replace the cap and rotor since it needs it anyway. Still missing? Check for a plenum leak. Spray a little carb cleaner or starting fluid around the #3 cylinder and listen for the idle to change. Still missing and idle doesn't change? Pull #3 injector and swap with another. Missing moved to another cylinder? No? Perform compression test. The first 3 options cost nothing but your time since you were going to change the cap and rotor anyhow and any of them could very well solve or lead you to the problem. The last will cost you the price of a compression tester which if you are like most of us you'll get more than one use out of.

To my knowledge there is no inherent problem with fuel vaporization on the 3.9. It's a pretty tried and true design. basically a 318 with 2 cylinders lopped off. Injectors do go bad but test #3 will tell you if that is the problem without spending money

I'm all about not wasting money and just throwing parts at something but any diagnosis does take some hands on time. There are alot of knowledgable folks contributing here and they like me are just trying to help out a fellow Dakota owner over the internet. There are some very straightforward suggestions being given and I know how frustrating it gets trying to chase down a problem sometimes but don't be so hard on those trying to help otherwise people tend to stop helping.

 

TY,
Not trying to be a hardass, just trying to get advice that I can use. Use a couple of different types of online forums. Many people do not answer the question you are asking.
I am a little mystified by the fact I have only one cylinder mis-firing, whilst many of the ignition components are fed by the same means, distributor, fuel rail or regulated by common sensors. Also, its not mis-firing when cruising or cold. Fuel pressure is constant. Fuel filter is common to all cylinders. Even the vaporiztion I refer to should extend to the #1 cylinder, its injector is 2" away. The plenum gasket should affect all, no.
Its about heat somehow, that should affect more than just 1 cylinder. Maybe the injectors o-ring is bad......................................
You can't blame a guy for trying to get quality info, even if I have to push a little for it.
In order to see a germ correctly, you have to focus the microscope correctly.
Salute