13 ram hemi help please

[Ashkon]

Hello ram ram. Iam in need of you guys help desperately. Long story short, I had a bad rod knock and I had the engine rebuilt at a reputable shop. Heads worked also. All
New oem lifters cam and mds solenoid.

I put everything back and the truck ran good but had a cylinder 6 mis fire. I checked and checked and could not find our way. Compression is good, passes leaked down test. It was firing and also was spraying fuel. Swapped coils, plugs, and Injectors and the miss is still here. So I ordered a new ecm pre programmed. Go it in today and same bull crap. The miss goes away when you drive and put a load or rpms on it. But if you let it idle, it will miss enough where it through a Chex
Engine light. It is damn near a dead miss. If you u plug the coil or injector to the cylinder, you here no difference. Ram fam, where is my next step? I am pretty knowledgeable, so any ideas or test you have I will attempt. Thanks

 

[Ricks Ram]

Hello ram ram. Iam in need of you guys help desperately. Long story short, I had a bad rod knock and I had the engine rebuilt at a reputable shop. Heads worked also. All
New oem lifters cam and mds solenoid.

I put everything back and the truck ran good but had a cylinder 6 mis fire. I checked and checked and could not find our way. Compression is good, passes leaked down test. It was firing and also was spraying fuel. Swapped coils, plugs, and Injectors and the miss is still here. So I ordered a new ecm pre programmed. Go it in today and same bull crap. The miss goes away when you drive and put a load or rpms on it. But if you let it idle, it will miss enough where it through a Chex
Engine light. It is damn near a dead miss. If you u plug the coil or injector to the cylinder, you here no difference. Ram fam, where is my next step? I am pretty knowledgeable, so any ideas or test you have I will attempt. Thanks

Is it possible you have some type of intake vacuum leak near that cylinder? If you have compression, spark and fuel it should fire. The fact that it runs better at RPM and worse at idle would definitely indicate it could be a vacuum leak. I have had intake manifolds leak on the inside at the actual port and they are very difficult to detect. You sound pretty knowledgeable so you may have already check for it but just another possibility if you haven't.

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[Ashkon]

Let me ask you this. Hypothetically speaking. What would happen if I had the non mds lifters on 6 and and the mds lifters on 8?

 

[MoPowered]

I tend to agree with Ricks Ram as what you’re describing is symptomatic of the intake plenum leaking, you pressurize the system this way:
The safe way to find an elusive vacuum leak; is to pressurize the intake manifold with about three lbs. of regulated air. This can be done by attaching a regulator to yourshop air hose; then attaching the hose to a vacuum fitting or the (PCV) valve fitting on the intake manifold; carburetor or throttle body.
If you have a leak you’ll hear it either whistle or a staccato type of hiss.

 

[Ashkon]

Well I pulled the intake off hoping to see something but I didn’t. I will install the intake in the morning and see what happens.

 

[Ricks Ram]

Well I pulled the intake off hoping to see something but I didn’t. I will install the intake in the morning and see what happens.

Make sure you check intake for any cracks while you have it off and also check the intake port. Make sure it has a good seal and gasket when you re install it. Another trick is to take carb cleaner and spray it around the intake and hoses while the truck is idling warm to see if it affects it. Obviously if it does you have a vacuum leak. Since its only missing on one cylinder you can pretty much rule out having the wiring switched somehow on a coil pack or injector.

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[Dodge 1500 4X4]

Sounds like a internal crack in the manifold, Did you do the 3psi test and check for any hissing or not holding pressure?

 

[Ashkon]

No sir, I don’t have a regulator to try that but am going to throw the intake back on first thing today and try it again. If it still misses I will try to go buy a regulator from
Home Depot.

 

[Ricks Ram]

No sir, I don’t have a regulator to try that but am going to throw the intake back on first thing today and try it again. If it still misses I will try to go buy a regulator from
Home Depot.

If it still misses you may want to try the carb cleaner test around the intake base and vacuum hoses and valves as well

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[Ashkon]

Well I did it and still missing on 6. New gaskets and sprayed carb cleaner on the hoses, around Intake. Still missing

 

[Wild one]

Pushrods in the right holes,they are differant lengths between intake and exhaust

 

[Ashkon]

The miss is almost unrecognizable when you start it after sitting over night. First 10 seconds is good. Then it runs bad on 6. Watching the scanner. What about if I put a slightly smaller push rod on Both intake and exhaust? Maybe 1 of the valves is staying open slightly? Just grabbing straws now

 

[Ricks Ram]

The miss is almost unrecognizable when you start it after sitting over night. First 10 seconds is good. Then it runs bad on 6. Watching the scanner. What about if I put a slightly smaller push rod on Both intake and exhaust? Maybe 1 of the valves is staying open slightly? Just grabbing straws now

That would make no sense because your compression test was normal plus the fact that it idles normally when cold. You also didn't make any changes that would constitute a different length pushrod according to the info you have posted so far.

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[Ashkon]

I was thinking. When it sits a day maybe the lifters drain down. Causing the push rods to be not as long vs when fully primed.

 

[PoMansRam]

Sorry if I missed it, but what about the leads TO the coil for that cylinder? I'd check for power or put a scope/scan tool on those to chart some data. If that cylinder is indeed firing at some points and not others, it doesn't likely seem compression related, but more data needs to be collected to tell.

 

[Ashkon]

So I’ve had the coil on a spark tester and it seems to never stop firing.

 

[Ashkon]

Just feels like it’s compression related at this point. But machine shop performed a leak down test and it passed

 

[Wild one]

Just feels like it’s compression related at this point. But machine shop performed a leak down test and it passed

For ***** and giggle pull 1 plug out of each cylinder and do a compression test yourself. Pull the starter relay in the fusebox and you can jump the starter right from the fusebox,makes it so you can do a compression test by yourself

 

[Ashkon]

Ideally. What should my compression be?

 

[jws123]

Compression normally like 180 If I remember correctly . I had a 2012 a yr ago do exactly what this is doing after I did a cam/rebuild except I removed mds. I went nutz I never figured it out i sold it lol will be watching this thread.