Check engine light still on after replacing cap

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DJ_Playing

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2017 Ram 3.8 L V6 120K Miles
I recently had the check engine light come on, I replaced the cap and reset the code. a couple days later it came back on. When I went to get the truck inspected they said the Purge valve was bad and needed to be replaced. So I did it. Check engine light is still on and the gas cap light is on as well.

When I cut it off to get gas the truck takes 4-5 times to get it to start, its like its out of gas.
When filling it up as it runs the tank has a LOT of pressure when the cap comes off, The engine surges between 500 & 1500 RPM and it fills very slowly.
I'm sure this is a common issue, I just don't have the tools to diagnose it,and being out of work right now I cant afford a big mechanic bill
 

GTyankee

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If you can drive it, take it to an auto parts store, like Autozone, oriellys, etc.
ask them to use their scan tool to check your truck.

they should give you at least code number, like P 0456
with that code, a list of possible causes will show up
 

Nicoleincali

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This isn't necessarily A reply, but I'm running into the same thing with mine not with the gas cap but it's a misfire on cylinder 2 and yet everything has been changed and replaced and the check engine light is still coming on
 

Atcer2018

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This isn't necessarily A reply, but I'm running into the same thing with mine not with the gas cap but it's a misfire on cylinder 2 and yet everything has been changed and replaced and the check engine light is still coming on

When you say everything has been replaced, what exactly has been replaced?
 

Nicoleincali

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Started a few months ago have had spark plugs changed, ignition coil changed, checked the cap auto repair shop had it for about a week said they fixed it nothing was done. So I disconnected the negative cable from the battery waited 15 minutes hooked it back up drove it the light came back on. I am at a total loss
 

Nicoleincali

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As a side note....84k miles, no issues, runs great! Just can't figure out what is causing the misfire code for cylinder 2
 

KevinInVT

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Had a misfire on cylinder 2 with the wife's Pacifica with the 3.6 Pentastar, forgot the specific code unfortunately, P0302 maybe, but I replaced the fuel injector and it ran smooth since. Replaced at around 34k, just over 60k now and no issues since replacement.
 

Rlaf75

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P0152 & P0157 are bank 1 & bank 2 upstream O2 sensor codes indicating the engine is running very rich.
P0440, P0456 & P0457 are EVAP codes.

The engine could have a vacuum leak somewhere that's causing the EVAP & gas cap codes to keep coming back & depending on where that vacuum leak is it is telling the computer to dump more fuel which in turn will cause the rich codes.

Each set of those codes could be a coincidence but more than likely not. Diagnosing EVAP leaks can be a real pain to locate without the proper equipment. You can keep throwing parts at it but it will more than likely cost you a lot of money only to not actually fix the problem. A simple tiny hole or crack in a line can set the codes and can be next to impossible to find. My suggestion would be to take it to a reputable dealership or repair shop and have them diagnose it. More than likely they will have the proper equipment to do so.
 

Atcer2018

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Started a few months ago have had spark plugs changed, ignition coil changed, checked the cap auto repair shop had it for about a week said they fixed it nothing was done. So I disconnected the negative cable from the battery waited 15 minutes hooked it back up drove it the light came back on. I am at a total loss

The gas cap won’t set a misfire code unless it’s associated with something else. You state the repair shop replaced the plugs and ignition coil. Did they replace all the coil packs or just the coil pack on the cylinder showing the misfire code? Is the new coil pack OEM or aftermarket? The reason I ask is chasing a misfire code on a single cylinder it’s typical to swap coil packs with another cylinder to see if the misfire code moves to the cylinder with the suspect coil. If the shop simply replace the coil pack on the cylinder with the misfire code it’s possible the new coil is bad especially if it’s aftermarket. You don’t give the actual misfire code so no way of knowing which cylinder the misfire is on. Bank one coil packs are easy to get at for coil swaps but bank two are under the intake manifold so not so easy to swap coil packs. You also don’t state the code your truck has now after the shop replaced parts. Is it the same code you took the truck into the shop for? Unless you read the present code it could be a brand new code not related to the previous code. Misfires are fuel, spark or air delivery issues. Occasionally it’s a faulty sensor of some sort. If you have the same code as before the parts replacement it could be the fuel injector. Try running some fuel injector cleaner through a tank of gas. The best cleaners have PEA in them so try to find Red Line Si-1 or Amsoil Pi as they have high PEA content. If you can’t find those use Chevron Techron Complete Fuel System Cleaner. Don’t use one of those miracle in a bottle cures as they don’t work.
 

Atcer2018

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As a side note....84k miles, no issues, runs great! Just can't figure out what is causing the misfire code for cylinder 2

Does your engine have a ticking sound while it’s running? It could be hard to hear especially over the clatter of the fuel injectors. Since you state it’s cylinder number two that’s at the front of the engine on the driver side. You can take a really long screwdriver or an old broomstick handle and place it against the valve cover on the driver side front then put the handle to your ear and listen for a tick tick tick sound. A distinct tick sound could mean you have a failing lifter. Initially it won’t affect performance but it will get worse until it destroys the cam. It will set a misfire code. Hemi tick also plagues the 3.6 Pentastar engines.
 

Sherman Bird

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All Generic errors
P0175
P0172
P0456
P0457
P0440
Crawl under the truck.
Find the larger diameter hose coming out of the charcoal canister that goes towards the fuel tank.
Get a drain pan, don some nitrile gloves, have a roll of paper towels at hand, and remove the hose at the canister. Expect to have liquid gasoline run out. upwards of a quart.
Allow the hose to drain and reinstall. You are done under the truck. Remember to be VERY VERY cautious with gasoline waste. Dispose of said gasoline according to hazardous waste guidelines for your locale, and same for the rags.

IF you got liquid fuel, you must replace the fuel tank AND the charcoal canister, because the rollover valve has gone kaput.

IF there is no fuel and the hose is dry, reassemble and look elsewhere for the problem. The rich DTC for the engine alludes to a malfunction of the EVAP system given the other DTC's.
 

Nicoleincali

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Does your engine have a ticking sound while it’s running? It could be hard to hear especially over the clatter of the fuel injectors. Since you state it’s cylinder number two that’s at the front of the engine on the driver side. You can take a really long screwdriver or an old broomstick handle and place it against the valve cover on the driver side front then put the handle to your ear and listen for a tick tick tick sound. A distinct tick sound could mean you have a failing lifter. Initially it won’t affect performance but it will get worse until it destroys the cam. It will set a misfire code. Hemi tick also plagues the 3.6 Pentastar engines.
Hey thank you, now what I'm running into is the check engine light comes on and off intermittently. I did a hard reset, the light went off for a few days, now it's back on. What about some of the wiring? From the PCM or the ECM? No one can figure out what's going on with the truck.
 

Nicoleincali

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The gas cap won’t set a misfire code unless it’s associated with something else. You state the repair shop replaced the plugs and ignition coil. Did they replace all the coil packs or just the coil pack on the cylinder showing the misfire code? Is the new coil pack OEM or aftermarket? The reason I ask is chasing a misfire code on a single cylinder it’s typical to swap coil packs with another cylinder to see if the misfire code moves to the cylinder with the suspect coil. If the shop simply replace the coil pack on the cylinder with the misfire code it’s possible the new coil is bad especially if it’s aftermarket. You don’t give the actual misfire code so no way of knowing which cylinder the misfire is on. Bank one coil packs are easy to get at for coil swaps but bank two are under the intake manifold so not so easy to swap coil packs. You also don’t state the code your truck has now after the shop replaced parts. Is it the same code you took the truck into the shop for? Unless you read the present code it could be a brand new code not related to the previous code. Misfires are fuel, spark or air delivery issues. Occasionally it’s a faulty sensor of some sort. If you have the same code as before the parts replacement it could be the fuel injector. Try running some fuel injector cleaner through a tank of gas. The best cleaners have PEA in them so try to find Red Line Si-1 or Amsoil Pi as they have high PEA content. If you can’t find those use Chevron Techron Complete Fuel System Cleaner. Don’t use one of those miracle in a bottle cures as they don’t work.
The primary code was P0302 , had the fuel injector replaced, the code is still P0302. No new code. They did move the coils to check if it follows, no ticking. The truck runs really good I just don't understand?
 

SteveBlack

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I had the loose gas cap warning and check engine light for the evap codes. First I replaced the gas cap ($9), and that did nothing. Then I replaced the Vapor canister purge valve under the hood ($24) and that didn't fix it. Finally I replaced the Evaporative System Integrity module ($21) over the has tank on the charcoal canister and that did the trick. Thankfully all of these were easy to change and inexpensive.
 

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