6.4 broke down, need diagnosis help

[EriikK]

Wife was towing on the interstate, chime and check engine light, she aimed for the exit. It died on the off ramp a mile later. Trying to start it, it turns over fast, tries to start but won't quite stay lit.
We had it towed to a shop, they got codes for throttle body, replaced it, no better.
They disconnected some sensors (MAF?) and they can get it to run but badly, very rough, and now it has a loud knock. Uh-oh. It wasn't knocking before and the engine has 80k miles on it.

1.. The only code is for the throttle body. Any clues what could cause this behavior and not throw a more useful code?

2.. The knock is a big surprise and worry. I put the used engine in the truck 10k miles ago and it has been flawless until now. It just doesn't make sense to me that a big knock would come on so quickly. Yes it has the proper oil in it. Maybe it's knocking because the spark timing is way off, or it has a severe fueling problem?
Any suggestions?

 

[Wild one]

Wife was towing on the interstate, chime and check engine light, she aimed for the exit. It died on the off ramp a mile later. Trying to start it, it turns over fast, tries to start but won't quite stay lit.
We had it towed to a shop, they got codes for throttle body, replaced it, no better.
They disconnected some sensors (MAF?) and they can get it to run but badly, very rough, and now it has a loud knock. Uh-oh. It wasn't knocking before and the engine has 80k miles on it.

1.. The only code is for the throttle body. Any clues what could cause this behavior and not throw a more useful code?

2.. The knock is a big surprise and worry. I put the used engine in the truck 10k miles ago and it has been flawless until now. It just doesn't make sense to me that a big knock would come on so quickly. Yes it has the proper oil in it. Maybe it's knocking because the spark timing is way off, or it has a severe fueling problem?
Any suggestions?

Might be time to boroscope the cylinders,and if nothing like a broken piston shows from that,then it's probably time to pull the oil pan and start checking main and rod bearings.The only reason i'd start up top looking at pistons is the fact you said it turns over fast and tries to start,that kind of points towards a lack of compression,from either a broken piston/dropped valve etc.
What was wrong with the original engine that caused you to replace it,if you still have it,it might be time to rebuild that one,and stick it back in the truck

 

[EriikK]

Yup it doesn't sound like a quick fix. So I'll have the truck and camper towed home then dig into it. Do I remember correctly that I can't get the oil pan off without pulling the engine?

I don't know that it's cranking faster than usual, I just meant it was cranking well. But yeah, check the easy things first.

The original motor had a knock or big tick at 160k miles. Being new to the hemi I thought it would be easier and definitely cheaper to swap in a motor from a low miles wrecked truck than take on a rebuild. Not so sure now if that was the right decision or not... it's all rolling the dice.

 

[Jeepwalker]

I wouldn't jump to conclusions just yet. I've burned myself on repairs thinking worst-case out of the chute ...leading to a lot of unnecessary expensive work.

As far as why it died, could be a failing crank or cam sensor. Or bad wire ..battery, etc. That can certainly result in an engine running like you describe. The shop probably pulled off the MAF sensor wire b/c it's an easy way to get a vehicle (generally) to run in 'open loop' ...basically a pre-programmed default operation routine which bypasses emission system and other sensors. But since it didn't run any better in open loop, that means its more than likely not other sensors, etc. Of course it still could be the crank sensor (I'm not sure about the cam sensor in open loop). So I would definitely look at the codes (besides MAF), and see what it shows. Do you have an ok scan tool? If not, this might be the time to invest in one. Or AlfaOBD ...or an MX Plus tool you can use with a phone or tablet.

Knock? This is where it's time to take a deep breath, slow down & do basic inspections one at a time. Knock can be different things to different people. Could be real bad, might not be??:

1) Pull the valve covers off first. Have someone crank or start the engine, and watch the rocker lift at EACH cylinder. See if there's a bad one, a barely moving rocker, indicating a cam issue or lifter issue? If you see that, then you kind of know where to start. Go to Y/T and look up "Hemi Cam Issue or problem" ...there's no shortage of videos on the subject.

2) If they all (rockers) are articulating well and the same, that's good. Then a compression check for all of the cylinders (or leak-down even better) is in order. That's basic inspection. Let us know what you find once you get it home.

3) Make a note of the oil pressure too if you get it to run or stumble enough to run.

4) Sounds stupid, but I would check/clean the battery terminals real well. Do a load-test on the battery, and ensure all the fuses in the fuse-box are pushed down all the way. They have a habit of working lose on these Rams. If that doesn't make a difference, give the big umbillical cord of wires underneath the fuse box a good wiggle. Make sure it's seated well to the TIPM.

Best of luck
.

 

[Wild one]

Yup it doesn't sound like a quick fix. So I'll have the truck and camper towed home then dig into it. Do I remember correctly that I can't get the oil pan off without pulling the engine?

I don't know that it's cranking faster than usual, I just meant it was cranking well. But yeah, check the easy things first.

The original motor had a knock or big tick at 160k miles. Being new to the hemi I thought it would be easier and definitely cheaper to swap in a motor from a low miles wrecked truck than take on a rebuild. Not so sure now if that was the right decision or not... it's all rolling the dice.

I'm not sure what all's involved in pulling the pan on a 2500,on the 1500's if you drop the front diff,it's easy to pull the pan,whether that's needed on a 2500 i can't say though

 

[62Blazer]

Really need to know the exact code in the engine. There is no code that states "you need to replace the throttle body", rather a code will say there is some type of out of tolerance signal in the throttle body circuit ext... A code scanner is not a tool that tells you what parts to replace, just where an unusual signal is coming from. Unfortunately a lot of people use it that way.

 

[Jeepwalker]

A code scanner is not a tool that tells you what parts to replace, just where an unusual signal is coming from. Unfortunately a lot of people use it that way.

I agree with that.
In addition, reading codes w/o doing the basic look-see and troubleshooting can lead a guy down expensive dead-end rabbit holes. Which is one reason customers often pick their truck up from the dealer service dept, they changed the most obvious part, per a code or a scanner reading, but didn't 'fix' the actual problem. I've chased a few dead ends in my day. Had simple things like cracked vacuum lines or PVC lines give all sorts of errant codes.

So, to sum it up, try to avoid jumping to conclusions. Investigate the basics before pulling the oil pan.

 

[HOSTAGE81]

Wife was towing on the interstate, chime and check engine light, she aimed for the exit. It died on the off ramp a mile later. Trying to start it, it turns over fast, tries to start but won't quite stay lit.
We had it towed to a shop, they got codes for throttle body, replaced it, no better.
They disconnected some sensors (MAF?) and they can get it to run but badly, very rough, and now it has a loud knock. Uh-oh. It wasn't knocking before and the engine has 80k miles on it.

1.. The only code is for the throttle body. Any clues what could cause this behavior and not throw a more useful code?

2.. The knock is a big surprise and worry. I put the used engine in the truck 10k miles ago and it has been flawless until now. It just doesn't make sense to me that a big knock would come on so quickly. Yes it has the proper oil in it. Maybe it's knocking because the spark timing is way off, or it has a severe fueling problem?
Any suggestions?

Contaminated gas ??

 

[EriikK]

I have the MX+ OBD reader and Torque app. Would AlphaOBD give me more detail or not? I'd be happy to invest if it does.
And yes I understand that diagnostic codes do not tell what part to replace, they are a starting point.
At this point I do not know exactly what codes it is showing, the mechanic was using his Snap On scan tool and I was kind of following along but I didn't want to get in his way too much.

Right now I just don't know enough. Is it a serious problem or is the shop not competent to diagnose it or are they not honest? I can't tell. So I'm having the whole mess towed home so I can go through it methodically in my own shop on my own schedule. Not something I can do in their parking lot.

When I get it home my steps will be something like: check codes and chase those rabbits. If in doubt change suspect sensors, I have spares of some and I wouldn't mind ending up with spare cam and crank sensors. Since the codes I saw beside the road made no sense, I wondered if it was the ECU. I re-seated those connectors, no change. But if my spare ECU is usable I might try that.

Seems to me I ought to be able to get it to idle decently whether or not it has a mechanical problem. Once I have achieved that, I can evaluate the knock and find out what it is or isn't, and check oil pressure.

Speaking of oil pressure.... Did you know that the oil pressure reading on the dash is fake? The sensor on the engine is just a switch. As long as there is any pressure to activate the switch, the computer makes up an oil pressure number to show you, based on RPM and temperature and I don't know what else. It's an idiot light pretending to be a gauge.

Absolutely this is not BS, you can check it yourself. I have this info from a very experienced technician at Chrysler HQ. And from my days as an engineer at Ford, I know they do the same thing on at least some models, I have personally verified it.

 

[EriikK]

Contaminated gas ??

Well that's an interesting idea I had not thought of! Thanks! Not common anymore in the USA but it could certainly cause bad running, and depending on what the contaminant is, even knocking. And it might not throw a useful code from the computer, how would it know? Hmmm...

Back in the old days I could just hang a quart tank of good gas above the engine and try it. Not so easy now with fuel sensors, closed systems, in tank pumps, etc. Anybody got any ideas of how to test this short of draining and refilling the big tank?

 

[CanRebel]

Speaking of oil pressure.... Did you know that the oil pressure reading on the dash is fake? The sensor on the engine is just a switch. As long as there is any pressure to activate the switch, the computer makes up an oil pressure number to show you, based on RPM and temperature and I don't know what else. It's an idiot light pretending to be a gauge.

Absolutely this is not BS, you can check it yourself. I have this info from a very experienced technician at Chrysler HQ. And from my days as an engineer at Ford, I know they do the same thing on at least some models, I have personally verified it.

One is an Oil Pressure Switch
One is an Oil Pressure Sensor

People confuse and call them same thing, but they are not.

Switch is diaphragm/spring based, which will be either close circuit or open it, depending manufacture. Turning Light on or off. Some/Newer switch's do calibration over certain period, detecting low pressure.

Sensor has pressure-sensitive element, like piezo or capacitive sensor. It converts pressure to electrical signal which gives 'real' time changes to ECU/Dash gauge.

 

[Torque]

Wife was towing on the interstate, chime and check engine light, she aimed for the exit. It died on the off ramp a mile later. Trying to start it, it turns over fast, tries to start but won't quite stay lit.

Turns over quickly means low compression on one or more cylinders. I'd suspect broken valve spring(s), camshaft or dropped valve (my most likely guess) because of the loud knock. Pull the spark plugs and peek into each cylinder and I bet you'll find the answer.

 

[Dusty]

"Speaking of oil pressure.... Did you know that the oil pressure reading on the dash is fake? The sensor on the engine is just a switch. As long as there is any pressure to activate the switch, the computer makes up an oil pressure number to show you, based on RPM and temperature and I don't know what else. It's an idiot light pretending to be a gauge.

Absolutely this is not BS, you can check it yourself. I have this info from a very experienced technician at Chrysler HQ. And from my days as an engineer at Ford, I know they do the same thing on at least some models, I have personally verified it."

Disagree. A switch is an open OR closed device and that is not the type of component that is used on Ram trucks. Many people have witnessed different oil pressure indications over the course of the year due to temperature at the same RPMs, or when changing to a different oil viscosity.

I would suggest looking at the service manual which describes how the system works, regardless of what a "Chrysler" tech. has told you.

(P.S. Ford does in fact have computer manipulated oil pressure reading systems on some of their engines and vehicles.)

Regards,
Dusty
2019 Ram 1500 Billet Silver Laramie Quad Cab 2WD, 5.7 Hemi, 8HP75, 3.21 axle, 33-gallon fuel tank, 18” wheels. Build Date: 3 June 2018. Now at 106196 miles.

 

[EriikK]

Ok, I got the truck and camper towed home yesterday, today working with a friend we have got the diagnosis started. Bent intake valve on #3 cylinder. Cylinder 3 had many more misfire counts than the others so we put a borescope down the spark plug hole and there it is.
Of course there could be other problems, and we don't yet know the root cause of this problem.
Next is to pull the valve cover and see if there are clues there. Then how hard is it to pull the head with the engine in the car? That might be the next step if the piston isn't damaged.

 

[crash68]

Did you know that the oil pressure reading on the dash is fake?

A switch is an open OR closed device and that is not the type of component that is used on Ram trucks.

The gas engines have real oil pressure and temperature sensors, the diesel engines don't have oil pressure sensors(use low pressure switches) but the EcoDiesel has an oil temperature sensor.

 

[tron67j]

Ok, I got the truck and camper towed home yesterday, today working with a friend we have got the diagnosis started. Bent intake valve on #3 cylinder. Cylinder 3 had many more misfire counts than the others so we put a borescope down the spark plug hole and there it is.
Of course there could be other problems, and we don't yet know the root cause of this problem.
Next is to pull the valve cover and see if there are clues there. Then how hard is it to pull the head with the engine in the car? That might be the next step if the piston isn't damaged.

I think the best route is pull the engine and work on it without having to contort yourself. Doing this deliberately is difference between fixing it and making it worse. Yes, I know this is a pain. But there are things just aren't easy to find while engine is in truck. Bolts and all are not seized up since it was out recently, just my two cents.

Good luck.

 

[Wild one]

Ok, I got the truck and camper towed home yesterday, today working with a friend we have got the diagnosis started. Bent intake valve on #3 cylinder. Cylinder 3 had many more misfire counts than the others so we put a borescope down the spark plug hole and there it is.
Of course there could be other problems, and we don't yet know the root cause of this problem.
Next is to pull the valve cover and see if there are clues there. Then how hard is it to pull the head with the engine in the car? That might be the next step if the piston isn't damaged.

Bent intake valve,makes me wonder if the locating pin on the cam broke,and the cam is out of time.That would explain why it spins over and sounds like it's low on compression. The hemi is an interferance engine,and if the cam ends up re-tarded ,it will usually smack the valve,and bend it. As reconmended,it might be easier to pull the engine,and work on it. As i'd start by checking to see if the cam still spins,it's not common for a cam to seize and shear the cams locating dowel,but it's also not unheard of either.

Damn it looks like re tarded gets flagged

 

[EriikK]

Thanks for the advice.
The cam is spinning, the engine runs but badly.
Yes for sure I want to check cam timing, what is the easiest way to do that?

Yeah tron67j, that's the big question. It's not easy to work on the engine in the truck, and I know how to pull it. It would probably take me half the time it did a year ago.

The question behind that is whether to apply a quick fix or to go for a proper rebuild. Tough decision. 80k miles isn't that old... the truck isn't beautiful but I was planning to keep it for many more years... what might I miss with a quick fix... what can of worms might I open up with a rebuild...

 

[EriikK]

Wouldn't a skipped cam chain result in bending exhaust valves not intake valves?

 

[Wild one]

Wouldn't a skipped cam chain result in bending exhaust valves not intake valves?

Usually the hemi bends the intake valve,as it has a bigger valve head,and when the cam is re tarded,it ends up closer to the piston. It's more common to shear the cams locating dowel, then the VVT sprocket will turn slightly in relation to the cams centerline,then it is for the chain to jump a tooth on a sprocket. The most common cause of the locating dowel breaking,is improper torque on the cam bolt.