Low Compression on Cylinder - 65k miles

[ramrebel0528]

2019 Ram Rebel 5.7L rough idle and tripping malfunction indicator light. Brought to shop and there is low compression on cylinder 6 with only 65k miles. Now haven't had my truck for 3 weeks and the dealer called and said they are working with Chrysler because they aren't sure what is going on. Anyone else having cylinder pressure issues at only 65k miles? Seems like this shouldn't be happening at such low mileage. Is there any TSBs? Should I try to get a Ram ticket open? Guessing its going to be at least a few thousand to fix and just lapse my powertrain warranty

 

[vincentw56]

2019 Ram Rebel 5.7L rough idle and tripping malfunction indicator light. Brought to shop and there is low compression on cylinder 6 with only 65k miles. Now haven't had my truck for 3 weeks and the dealer called and said they are working with Chrysler because they aren't sure what is going on. Anyone else having cylinder pressure issues at only 65k miles? Seems like this shouldn't be happening at such low mileage. Is there any TSBs? Should I try to get a Ram ticket open? Guessing its going to be at least a few thousand to fix and just lapse my powertrain warranty

It's not common. As for it not happening because it only has 65k on it, stuff happens and you drew the unlucky straw. It's unfortunate.

 

[Cbty2050]

The dealer can't figure out low compression?

 

[Rick3478]

Low compression is usually caused by a leaky valve. Could be warped, burnt, carboned up, or maybe seat has come loose and tilted a bit. Or could be a broken spring, jammed lifter, or other valvetrain problem causing valve to not open/close properly. In any case, it will probably need at least a little disassembly to diagnose. Could get pricey.

 

[ramrebel0528]

The dealer can't figure out low compression?

Was a little concerned when they said that …

 

[6of36]

Was a little concerned when they said that …

They probably meant they aren't sure whether it could be warranty or not. They would want to see if they could get warranty, to know who is going to pay for tear down. Unless you agree to pay for tear down, if not warranty.

 

[BowDown]

Broken valve spring, take the valve covers off and look

 

[Jwolford303]

@ramrebel0528 Did you ever find out the problem? My truck is having the same problem, popped up with P0306 so I fixed the spark plugs and still has the code coming up. Went and got a compression test done and it’s low on cylinder 6.

 

[BowDown]

@ramrebel0528 Did you ever find out the problem? My truck is having the same problem, popped up with P0306 so I fixed the spark plugs and still has the code coming up. Went and got a compression test done and it’s low on cylinder 6.

Does the truck smoke? If not, check the valve springs

 

[Jwolford303]

So I’ve gotten a few answers, my mechanic told me it had a computer wiring problem, they are driving it around for a day to make sure that’s it. Said it was running normal since.

 

[BowDown]

So I’ve gotten a few answers, my mechanic told me it had a computer wiring problem, they are driving it around for a day to make sure that’s it. Said it was running normal since.

A ECU wiring problem isn't going to cause low compression, that's a mechanical problem. Don't let them BS you

 

[Scram1500]

A ECU wiring problem isn't going to cause low compression, that's a mechanical problem. Don't let them BS you

Possible it was the wiring to one of the solenoids that controls MDS? Cylinder 6 is an MDS cylinder

 

[BowDown]

Possible it was the wiring to one of the solenoids that controls MDS? Cylinder 6 is an MDS cylinder

Wouldn't that fail closed, not hanging a valve open? MDS disables both the intake and exhaust valves so the cylinder acts like an air spring so I wouldn't think you'd experience a loss of compression from MDS. I'd also think they'd notice that during troubleshooting

To rapidly swap engines in a practical way, the Hemi ECM is commanding a sequence of events that starts first with cutting the fuel to the deactivated cylinder. Next, the intake valve takes its last "gulp" of air to fill that cylinder, sans fuel. It's the last time the intake opens until the cylinder is activated again. The following compression stroke is followed by no ignition source, and all the energy used to compress the pressurized air in the cylinder is returned to the crankshaft on what would normally be the power stroke. The final move by the ECM is to deactivate the exhaust valve—all of which happens in a split second. From here on out, there are only two strokes: down (expansion), and up (compression). In that operating regime, the cylinder has a net power consumption near zero; the only cost to the engine is ring and bearing drag—but most importantly, no energy is lost due to the chore of pumping volumes of air in or out. That's where the fuel savings actually comes from.

What Is Hemi MDS?

We explain how Chrysler Hemi MDS cylinder deactivation works, what goes wrong, and how to fix it when it breaks.

www.motortrend.com

 

[Scram1500]

Also if I could read I would have picked up on Jwolford403 writing that they had gotten a compression test

 

[BowDown]

Also if I could read I would have picked up on Jwolford403 writing that they had gotten a compression test

Honestly, I hope what you said is the problem, hate for the guy to need a new engine and have to go through that but a compression test tells me its mechanical. Sucks

 

[6of36]

Cam phasers are also electrically controlled. Possible valves close at the wrong time, causing low compression.

 

[BowDown]

Cam phasers are also electrically controlled. Possible valves close at the wrong time, causing low compression.

True but like scram said, the OP says they did a compression test, the cam phaser only advances or retards a single cam. If this were DOHC cam engine then that would be a possibility. Advancing or retarding the cam wouldn't change the LSA or overlap so you'd still be able to check compression with the valves closed.

Hopefully the shop treats him right

 

[6of36]

True but like scram said, the OP says they did a compression test, the cam phaser only advances or retards a single cam. If this were DOHC cam engine then that would be a possibility. Advancing or retarding the cam wouldn't change the LSA or overlap so you'd still be able to check compression with the valves closed.

Hopefully the shop treats him right

If it is out of phase, the valves may not close, until the piston is part way up the compression stroke, therefore having less compressing time. I haven't looked at the engineering of the engine, to see if it would advance or retard, but late closing intake valve would result in lower compression.

 

[BowDown]

If it is out of phase, the valves may not close, until the piston is part way up the compression stroke, therefore having less compressing time. I haven't looked at the engineering of the engine, to see if it would advance or retard, but late closing intake valve would result in lower compression.

There's not that much timing in the phaser, 5° to 7° and its still controlling both intake and exhaust advance / retard in the same phase (single cam). Also, if it was the cam phaser, cylinder 6 wouldn't be the only cylinder with low psi.

But, if what you say was correct, you'd have a loss of cranking pressure across all cylinders, not just one. Even out of phase, both valves still wouldn't be hanging open. You simply wouldn't build max cylinder pressure but across all the cylinders

 

[6of36]

There's not that much timing in the phaser, 5° to 7° and its still controlling both intake and exhaust advance / retard in the same phase (single cam). Also, if it was the cam phaser, cylinder 6 wouldn't be the only cylinder with low psi.

But, if what you say was correct, you'd have a loss of cranking pressure across all cylinders, not just one. Even out of phase, both valves still wouldn't be hanging open. You simply wouldn't build max cylinder pressure but across all the cylinders

True, it was another case of not going to the beginning of the thread. My memory isn't that good anymore, and I hadn't read the original post, since October, but got the notification of a comment, since I commented back then. I only knew it was about low compression, and saw the comment about electrical, which yes, would be all cylinders of at least the same bank. I need to slow down, when I haven't been on for a few days, and trying to catch up.