2012 GL350 with 126,000 miles on the clock. I know that the swirl motor is malfunctional and fixing that is on my list of things to do this fall. I'm keeping it out of limp-home mode with the resistor trick, but it does give me that warm MIL glow. =) I do not recall ever having heard it make any unusual noises at start-up like those described for the timing chain stretch and I've kind of been listening for it. There is a slight exhaust leak right past the turbo that I know about, but I figured I would take care of that here when I pull the turbo off to do the m55 job.

This weekend it started making a noise when off-throttle going downhill that was an almost-imperceptible ticking. At first I wasn't even sure I was hearing it, but as soon as I would hit the accelerator, the noise would go away. Yesterday, however, the noise was very metallic and very pronounced. At first I was only getting it in the lower RPM range but as it spun up to about 1800-2000 rpm, the noise would abate. After a couple miles, though, it was appearing at pretty much any point. It isn't constant -- it seems to come and go, but I haven't been able to correlate the coming or the going with anything else just yet. My initial thought was lower RPM = slower turning oil pump, but I have checked the oil level and it's within spec. Oil and filter have been changed with Pentosin about 2 or 3k ago. I might be slightly overdue on my fuel filter, though -- I didn't have my notebook with the part number written in it near my computer to get my rock auto order placed and it kind of slipped my mind, so I might be about 2-3k over on that. So far, that's the extent of my troubleshooting. I plan to get my stethoscope in there and listen around, but I was hoping that I might get a good direction on where to start and things I should consider. This is my first diesel to wrench on so while I can play the audio daily double all day with a gas engine this one isn't completely familiar to me. When it's ticking, it sounds like a fairly gnarly hydraulic lifter tick like on a Miata with really old and slightly low oil. Or a rod knock -- but I've never had a rod knock noise come and go.

My plan of attack is to first get it ticking again and then to probe around and listen. I was going to start in the timing area, check the valve covers, try to get down to the block. Any good hints on other places to which I might want to be listening?

 

Back up. Does the sound correlate to engine speed? If not, it's a whole lot less likely that's it's anything internal that turns/moves with the crank speed. Sure it's not a heat shield or broken exhaust mount or something like that? Nothing different there as compared to a gasser, so proceed as you would normally. And, really, there's not a whole lot different in terms of the engine (diesel to gasser) in this instance. All the basics apply.

And... "Brutal"? Really?

 

Yeah, I think "brutal" is the best adjective to use for this one. It's not as bad as a ventilated block, but it's up there. Definitely more "tick" as opposed to "clunk" or "knock".

It does change in relation to engine speed, but not in relation to road speed. I haven't tried neutral while rolling yet, but different gears at the same road speed produce different rates of ticking. Heatshields, etc are a good think to check though - I could see a bad motor mount, for example, allowing the motor to create a harmonic. I'll add that kind of thing to my checklist!

 

A little poking around tonight. It is definitely not coming and going at this point -- the noise is there at startup and through the RPM band. It is definitely louder/faster with higher engine speed. I nosed around with my stethoscope and it seems loudest on the right side valve cover and fuel rail. The ticking noise was present on the front timing covers, but not as loud as it is on the turbo-to-DPF pipe or the right side valve cover/fuel rail. My guess right now is that it really sounds like a collapsed lifter. I moved my phone around the motor while recording to see if I could determine where the sound was coming from but it's telegraphing all over the place. Hear it here: Any and all speculation is welcome!

 

While I'm not as adept at figuring out the "why" in this case... I, unfortunately, agree with you that this sounds internal. Add the data of "different gears at the same road speed produce different rates of ticking" furthers the notion of it being internal as it sounds like you're saying the noise correlates with engine RPM.

 

I unplugged each of the injectors one by one tonight and the noise remained. So I think that rules out injectors. When I first started it up during that process, it sounded like a bag of wrenches for about a second before going back to its tickticktickticktick. Best guess now is timing chain.

 

Did you check the oil? I had a catastrophic oil leak which resulted in terrible clacking and ticking.

 

I did check the oil and the level is spot-on. I haven't checked oil pressure, but I assume there is at least some pressure in the system since I'm not getting a light.

 

 

The oil cap is definitely on and sealed tight. I noticed a while ago that they sound kind of comical with the cap off, though!

Thanks for the tip. I was a little hesitant to put anything in the crankcase, what with the dpf and all that, but I'm getting ready to pour in the seafoam now. Fingers crossed!

I have to say... I really do love driving this beast. It tows so well and has great manners. I just wish it didn't have such an extensive list of special tools!
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I drove the beast the 3 miles over to my workshop last night where I put the seafoam in and let it idle for a bit. On the way over it started running rough and popped a code for misfires in cyl 2. As soon as Singapore quali is over, I'm going to go back over and see if the seafoam was the trick. If not, I guess the misfire could be caused by the injectors, valves, or some problem with the cylinder or piston. I'll build my slide hammer adapter and swap injectors 1 and 2 and see if the misfire follows the injector.

I did unplug each injector one at a time as part of the troubleshooting so I suppose I could have borked something up in that process and created a second unrelated problem, but I've reset the electrical connection to no avail.

 

I'm back to where I started. I swapped injectors 1 & 2 which eliminated the misfire entirely, but the tick remains. My side hammer adapter worked perfectly though and it only cost me about $10 to make. Old harbor freight slide hammer plus a 10x1.00 coupling nut welded to two 14x1.5 nuts. One end threads onto the side hammer and the other on to the injector.

 

 

I listened around with my stethoscope as my first diagnostic step and I couldn't quite determine exactly where it was loudest. The right bank was louder than the left and the injectors and the fuel rail seemed to be louder than the other areas on the valve cover, but it could just be telegraphing. I'll throw the injectors and fuel rail back on and try to get a better listen on the fuel pump itself.

I really appreciate the diagnostic help - I've never worked on a diesel so I'm a little out of my element here!

Does it mean anything that when there's no fuel in the lines and the starter is just cranking the engine that there are no unusual noises?

 

Sounds like an exhaust leak to me.

 

It sounds a lot more metallic than exhaust leaks typically do when probing around with the stethoscope. The high pressure pump isn't really making any noise, it's really loudest on the right valve cover. I got the cover off so I could inspect the tensioner and when I turn the engine by hand I swear that I periodically hear a metallic noise.

View of tensioner

If I understand correctly, a stretched chain should be shooting more tensioner than that, right?

 

Following the procedure in AR05.10-P-7600GZB, I have confirmed that the timing chain is within spec. The book calls for locking the cams and then rotating the crank pulley. If the crank pulley moves 11 degrees or fewer after tdc, the timing chain is "OK".

I know that a lifter that makes a squishing sound indicates bad, but should the tensioner make a squish? Seems to me like that could indicate trouble.

EDIT: I'm going to go with failed chain tensioner. I can compress it with one hand and it sprays its oil everywhere.

 

I decided to also pull the cams to see if there was anything funny there. On the exhaust side of cylinder 1, the little lifter retaining clips on the rocker arms were not secure on the arm:



I crimped that back down and rotated the engine by hand a few turns. No noises. I did discover that there are two sets of timing marks on the can sprockets. Hopefully I don't have this thing 180 out.

 

Apparently the problem was not the tensioner or the clip on the rocker. It's all back together and there is absolutely no change. I pulled the belt off to rule out the water pump and accessories and it's still ticking like mad. I'm getting low on ideas.

 

Bear with me while I think out loud a bit here. Here's what I've been able to test and verify so far:

• Noise is related only to engine speed
• Not related to any pulley-driven accessories (operated with serpentine belt removed)
• No change in noise when disconnecting injectors (that should rule out an injector nailing, right?)
• Runs rougher when each injector is unplugged (rules out a misfire? I would expect that if there was a misfire, there would be at least one cylinder that would have no change in running when the injector was disconnected. Also, no more misfire codes from the ECU)
• Before I started working on it, it ran just fine for about 20-ish miles. I fiddled with unplugging injectors one at a time, cleared the codes and drove it 3 miles to my workshop. About halfway there, it started to misfire. After swapping injectors around a bit, and eventually putting them all back in their original locations, the engine was running smoothly again, albeit with that infernal ticking.
• Injectors have been externally cleaned, new copper washers and rubber return seals have been installed, and the injectors were installed with the Special Ceramic Grease (really creative naming there).
• There were a handful of burnt wires left over from a previous exhaust leak that came with the car when I bought it a year-point-five and 30k miles ago. I cut out the burned wires and crimped in new automotive wire in the same AWG.
• I've got a code for the O2 sensor heater shorted to positive that existed for at least 2 months before the ticking noise started.
• I've got codes for the swirl motor, but am avoiding LHM with the resistor trick. Also all before the ticking noise started - for the last year or so.
• After doing all the work so far, I have a new code indicating incorrect sensor voltage. I don't have the number handy (I think I left the bit of paper that I wrote it on over at the workshop) but my recollection is that it wasn't referring to a particular sensor. That is a new one.
• The engine is running a little bit rough now to the point where the interior lights will sort of pulse with the engine. This is also a new thing. Related to the last point?

Here's what I think might be true:

• Tensioner is new and thus should be good. I did not prime the tensioner, though. Since that's a pretty easy job, I may try that real fast.
• Old tensioner was easy to collapse and sprayed oil which I think indicates a problem, but maybe not?
• Old tensioner did not appear to be hyper-extended.
• I set the engine to TDC and locked the exhaust cam sprocket into place. I could only turn the crank pulley to approximately 8-9 degrees ATDC. WIS says that the chain is stretched and needs replacement if you can turn it past 11 degrees ATDC. Does this mean that the timing chain is good?
• I removed each lifter one at a time and attempted to compress it by hand by putting the bottom of the lifter on the workbench and pushing down on the still-attached rocker arm. None of them made any noise or gave any movement. The only movement present was on the two lifters on the #1 exhaust valve where the retaining clip had come loose. Should this rule out lifters on the right bank?

Here's what is unsure:

• Where the heck the stupid noise is coming from! (okay, that's a little obvious)
• The noise telegraphs all over the engine, so while it seems like it's loudest on the right side, I can't say for certain that is where it's coming from. I have been using my mechanic's stethoscope to listen around and even with that I can't quite pin down the source location.
• The injection pump does not seem to be the source. Probing the body of the pump, the ticking noise isn't very pronounced. When I probe the output fuel line, the noise is present and somewhat pronounced, but it doesn't seem as loud as the right bank fuel rail or the area around the oil fill on the head cover.
• When turning the crank by hand, I notice that the chain tensioner is moving in and out quite a bit. I assume that it is supposed to be constantly moving, taking the slack out of the chain as the springs push back on the cams, but I've never watched an engine with a known healthy chain tensioner before, so I don't have a frame of reference. Should it be moving so much?
• All I have is a gasoline compression tester, so I have not been able to check compression on the engine.
• Is the timing chain check procedure in WIS valid? Is there a point where there is enough stretch to cause noise but when they wrote the book they got it wrong?
• I replaced the fuel filter while I was at it so it took a couple tries to get it to start. While the starter was turning the engine, there were not any abnormal noises. Does that have any diagnostic significance?
• Can chain issues come on this fast? Everything I've read seems to indicate that the timing chain problems start with months of a rattle that is only present for a brief time during a cold start.
• Did the lifter retaining clips on the rocker arms pop back off again?

And finally, wild theories:

• Exhaust leak? I know that when I had the turbo off last year, there were a couple gaskets for which I was shipped the wrong part numbers so I wound up re-using the metal gaskets. It's had a very minor leak, but it is within the realm of possibility that one of those gaskets has suddenly and catastrophically failed. The exhaust leaks that I've fixed in the past, however, all tended to have a noise that would change slightly in volume and tone as the engine was put under load, but this noise is very constant. With the stethoscope there is also a very metallic component to the tick, whereas I haven't heard that kind of a "ring" with exhaust leaks before.
• Bottom end? I've had a tiny bit of experience with spun bearings and broken rods in gassers, but they never sounded like this. That always seemed to have more of a "clunking" component to the sound, maybe better described as having a deeper note than this. The noise seems louder when probing against the head versus the block.
• Timing chain? If the WIS check procedure isn't all-encompassing or if I somehow managed to do it wrong, it could be the timing chain banging around.
• Can the lifters be stuck such that they won't compress or expand? Every bad lifter I've come across in the past was collapsed due to the check valve failing and not being able to hold oil. Could I have a different failure method here?
• Cam-driven air compressor? It is physically located in the primary noise area, but the stethoscope doesn't sound as loud there as it does in other places. I could test that fairly easily by pulling the compressor off the head cover and putting some tape over the hole.
• Broken bit of timing chain guide?
• Foreign object in the chain path? This seems extremely unlikely. The oil is about 3k miles old and it's very unlikely that I would/could have dropped anything into the oil fill. Other than adding some DEF, there was no other work or maintenance done to the car since that last oil change.

If I was dealing with a Chevy, I might be a little more willing to put a giant magazine into my parts cannon and start firing, but apparently the German rounds are a bit more expensive so I hesitate to open fire just yet. I'm tempted to throw a chain at it, but between buying the special chain tool and a chain, that's a pretty big nut to risk on a guess. I guess the upside is that if it is the bottom end, I'd want to put a new chain on it anyway as part of the rebuild. Right now I'm pretty stumped, but I think my next steps are:

1. Submerge the old tensioner in oil and see if it pumps up at all
2. Pull the new tensioner and submerge it in (new) oil and see how it behaves relative to the old tensioner and to how it behaves before submerging it. If there's a big difference, then maybe it's a priming the pump issue.
3. Run my phone with a sound level meter around the engine to see if I can pick up any spikes in volume that I can't discern with my Mark I Eardrum
4. Feed my stethoscope down the oil fill port and see if I can hear anything different
5. Pull the head cover again and see if the lifters are separated from the rocker arms again
6. ...?
7. Nuke it from orbit?

 

Priming the tensioner had no effect. It doesn't make the slurping sounds that the old one did, so maybe it's marginally better, but it wasn't the fix.

After removing the right head cover again, I used my GoPro to record manually turning the engine and then watched the process on the laptop with the volume cranked up. At a certain spot in the rotation of the camshaft, there is a metallic click every single time. It takes 720 degrees of crankshaft rotation to make the noise happen, so that likely means it is not originating in the bottom end. With everything quiet, though, it sounds like it's coming from the left side of the engine. I pulled the injection pump off the left head, but the click is still there. Also, turning the gear on the pump by hand doesn't unveil any rough spots or noises.

I feel like I'm getting closer.

 

as i mentioned before- this sounds 100% like when the oil filler cap is off.

my guess is you have a turbo/ exhaust leak somewhere on the right side. diesel exhaust is very dirty pre-cats. look for soot...

maybe now is the time to buy yourself a chassis ears set. the wireless one is very well executed.

 

Let me preface all of this with the fact that I greatly respect your opinion and expertise and very much appreciate the help that you're providing. I try really hard not to be the typical internet dope that asks for advice and then goes off and does his own thing anyway. Before proceeding with any further troubleshooting, I scoured the engine compartment for signs of an exhaust leak and before I opened it up for the second time, I did a physical check for air disruption.

I have taken the oil fill cap off when the car was running before this all went down and this noise is pretty different from that. With the oil cap off, that noise has a similar rhythm but seems a little more throaty and thumpy while this is much sharper and more metallic. I've run my hand and some thin paper around the various flanges and manifolds but haven't felt or seen any significant airflow disruptions. I am also not seeing any accumulations of soot anywhere. I'm not saying that it isn't an exhaust leak, but if it is, I can't find it. I've done some big block Chevy and modular Ford exhaust manifolds before and by the time they make this sort of noise, they're so opened up that it's like a bicycle pump in there -- it's not typically very subtle. With a diesel's compression ratio, I'd expect that an exhaust leak wouldn't be able to hide very well.

There is absolutely a clack or tap coming from the left bank exhaust valvetrain, though. With the head cover on, there is a tap at the exact same point in the cam rotation. Taking that cover off, I pulled the lifters & rockers from the intake cam, put the cam back in and the tap remains. When I take the lifters and rockers out of the exhaust side, the tap is gone and there's no tapping when I put the intake lifters into the exhaust side. I'm going to try six new lifters since they're not that expensive. Since there's no noise with the intake lifters pushing the exhaust valves, that should rule out broken valve springs or other valve-related problems. I also did a physical check of the valve springs as best as I could and didn't see or feel any cracks or breaks.

While my experience with this engine is essentially non-existent, I have hand-spun plenty of pushrod motors, some flat fours, a few V-6s, and a bunch of overhead cam inline fours in boats, cars, trucks, RVs, and motorcycles. Not once have I ever heard an otherwise healthy engine make a tap in the valvetrain that wasn't a bad lifter or a valve that needed a new shim or an adjustment.

Parts will arrive on Monday, in theory, so I'll get the injectors, head covers, and heads cleaned up and prepped over the weekend and should probably have it back together and ready to test again by mid-next week. I also am going to double and triple check the cam timing to make sure nothing is off. I also need to track down a glow plug connector. Part of the process here has been replacing some wires that got burned up when the PO had the turbo disconnected from the exhaust for some reason. It melted some wires, the swirl motor, and the fuel rail pressure sensor. I was able to splice in new wires to replace the burned ones, but cylinder 3's glow plug connector was completely melted down and needs to be replaced since the alligator clip that I'm using while it's parked here in the workshop probably won't go over too well in the real world!

 

Still nothing. I put six lifters in on the cam that appeared to be making noise when turning the engine by hand. While it runs perfectly smoothly, it's still making the ticking noise. I've removed the heat shields and triple checked for exhaust leaks. I don't feel any air movement, I see no soot, and with my stethoscope and with a bit of hose, I hear nothing around the exhaust. There is a tiny bit of oil between the exhaust manifold Y-pipe connector and the turbo, but there's no noise there.

Using a stopwatch and some estimating, I'm getting about 350-400ish ticks/minute which should be at about half-speed of the engine. Videos of timing chain noise that I've found have a much more rapid stacatto.

Honestly, I am pretty much out of ideas at this point.

 

Sounds like you are running out of ideas. I have a similair noise in my mazda miata. The community there calls it the "lifter tick." (you can hear it on youtube, sounds like a sewing machine). All I am saying is, maybe the noise is normal?

If I were you, I would throw in some thicker oil in the engine and see it if shuts things up. I dont know what viscosity you use in your truck, (I am an E class guy) easy enough to try. thicker oil wont harm things in the short term.