My van has about 146,000 miles on it. I will start from the top. On my way home on the night of 3/8/2021 I began to notice a misfire between 1000 and 2000 rpms. No code popped so we decided to do our research on all possible causes. We are limited at home on tools but decided to check the transmission fluid level. It was low but still a good color so we dealt with that but no fix. On 3/12/2021 I took it to the shop and they claimed it was a cylinder 4 misfire and changed the coil, "spark plug," and plenum gasket. I wasn't able to pick it up til after hours because of work so we had already paid for the repair without getting to see it was fixed. It as still misfiring. I asked my mechanic friend to take a look and we found they never changed the spark plug. We decided to change them all as they had signs of ware and rust but it still didn't fix the problem. Any ideas of what to do? I am afraid to take it to the dealer mechanic for them to tell me nothing is wrong when their clearly is or they miss the problem. My rpm needle also bounces some, not drastic but if it idles at 600 the needle will bounce up and down between 500 and 700.

 

Note that your only evidence of a misfire is that a shop that "didn't change the spark plugs" told you that you had a misfire. You need to confirm that you really do.

It is odd that the idle RPM's are unstable and not triggering the light. So I have to ask, do you know that the light is working? If you go to an auto parts store they will put a lower end scan tool on for free in hopes of selling you a part. You should do that much to confirm that there is or isn't a code. Also have you checked basic things like the air filter and fuel pressure?

Autozone and other shops will loan you a kit to check fuel pressure (you have to make a deposit in case you don't return the tool).
https://www.autozone.com/loan-a-tool...diagnostic-kit

 

I just recently had my ambient temperature sensor pop a code and changed it so I know the light works just fine. Also checked with autozone yesterday and it didn't show any recent codes according to them.

 

The tach movement is the best evidence to follow without a code. The tach signal is data fed to the cluster from the PCM, so unsteady or jerking movement of the needle indicates a problem with the crank sensor or related circuits (unless other cluster problems are apparent).

One possible reason why no misfire code has set is that the PCM relies on the crank signal for misfire detection, but the PCM must see a signal that shows a change in crankshaft speed in order for a misfire to be detected. If this particular issue doesn’t show that change in crank speed for whatever reason, the PCM is none-the-wiser.

As already stated, you need to verify the presence of a misfire first. If you can’t “feel” the misfire and it doesn’t seem to be in time with the tach movement, it may not be there at all.

 

​​​​​​I was at work when I posted, I have since left and had the chance to actually see if what I believe is a misfire is related to the small bounces of my RPM needle. So the two incidents are not related. It's not a heavy jerk, it feels like I am running over small potholes when they come but they are not constant. Any clue what could be causing this? I am not car smart, but I know when something isn't right with my vehicle if that makes sense? My friend is a mechanic and the one helping me try to fix this problem but between my husband and I we have short intervals we can actually work on it.

 

To the best of my knowledge misfires need to exceed a 10% threshold in 1000 rpm to set a fault as measured by the crank sensor. Since misfire is a continuous monitor bad trips do not need to be set to set a fault. Sounds to me like a road test and a scanner capable of showing live misfire data is necessary in this case which is what the shop that said cyl #4 misfire may have done. More investigation is required.

 

Did you find out what the issue was? I am experiencing the same problem with my van.

 

Try this. Remove one spark plug, one coil pack and one fuel injection. Be careful not to loose the O-rings on the injectors. So which ever misfire fire you have, Maybe cylinder number 1, Move the spark plug to cylinder number 5 and the same with the coil pack to number 3 and the injector to cylinder number 2. So is anyone of those is causing the misfire it will follow one of the parts. If the misfire stays on tha same cylinder, Than the problem with that cylinder.

 

Thank you for the suggestion. I tried everything you wrote about. Moving the spark plugs, injectors and coils. Unfortunately the problem still persists. I still have a misfire on cylinder #3. No trouble codes. Misfire is shown in Mode 6 data using my Blue driver.

I can feel the misfire the most when the car is running on low idle. It increases when it's in gear and standing still.

What I've also done is cleaned the throttle body, cleaned the PCV valve and also took the bank 1 valve cover off. I turned the engine so I could get all the lobes off of the rocker arms. All the rocker arms had the exact same play. The cam lobes didn't have any major wear.

I have also done a compression test. All the cylinders had the exact same compression.

Is there a possibility that a bad cam phaser would cause this misfire on only 1 cylinder? I haven't checked the phasers for play.

Would you recommend taking the camshafts off and inspecting the rocker arms more closely?

Is there a possibility of a bad cylinder head?

Is there anything else to look out for, please?

The car is a 15' Dodge Grand Caravan with 143k miles.

I am attaching a photo of the cams.

 

Check the rockers on the rollers see if they are loose. They shouldn't be. Looks like the intake camshaft that maybe cylinder number 5 is pitted badly. If you have never work on a 3.6 penastar motor. The timing is very tricky. Take it to the pros. Replace the cams and all lifters along with all rockers.