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I recently bought a 2008 R320 with the OM642 engine 240k km/ 150k miles. I bought it cheap as it had a bit of a miss that I assumed was just a flaky injector.
The PO had taken the car to the dealer and they recommended doing a compression test and if that was OK, to replace injector #5.
I took the air intake off and first thing I noticed was damage on the compressor wheel. Not sure if it was related to the miss or not, I removed injector 5 and had it cleaned/flowed/tested. It came back OK. I used my borescope and found no evidence of damage in cylinder #5.
So far I’ve tested compression on the front 4 cylinders and they all come in at around 350 psi (24 bar) using a Chinese compression kit. The compression tester adapter isn’t an exact replicate of the glow plug so if the readings are low, it could be explained by that.
When loading the engine using the brakes in drive and rev to 1500 RPM you can feel the miss come and go. Full throttle the miss seems quite regular. The area around cyl 2/3 seems a bit noisy. Not sure if it’s mechanical, an injector, or some minor injector seal issues. No CEL (check engine light). No pending codes. Which I find strange given how noticeable the miss is.
No smoke, though the DPF may be making issues?
Fuel economy is poor. I did one 20 minute drive with the EGR valve unplugged and fuel economy seemed better (~9.5L/100 KM / 25 MPG). The past 500 km was 14.5L/100km (16 mpg) but that was under previous ownership, so who knows under what conditions. I thought it would set a CEL but didn’t. Engine would rev high, but no boost.
While working on it, I’ve also noticed the left valve cover has been resealed. And around cylinder 3 there are a bunch of aluminum shavings that weren’t cleaned up. Like someone fixed a stripped thread and didn’t clean up afterwards.
The plan is to finish compression testing the rear two cylinders. Assuming they check out OK, what’s next??
Remove injectors one by one and borescope the remaining cylinders? Send the remaining ones out for cleaning? Or swap in a brand new one, one by one, to maybe identify a bad injector?
Remove valve cover and have a look?
I have more experience with gasoline engines. I’d describe it as a plug with too large a gap, or a leaky ignition wire. It’s not a ‘hard’ miss if that makes any sense.
Unplugging an injector will set the CEL, so the ECU can detect that. But could it detect a connection with say poor connectivity? Or a weak driver?
Any troubleshooting tips would be greatly appreciated!
It will 'rattle' what seems like one cylinder occasionally. I'm thinking of checking compression on #3 & #6, and assuming they are OK, put a new injector in say cyl 1. Test and see if it's any different. Then put old #1 into #2, and repeat until a difference is noted. It's probably a good time to replace the seals anyway.
As it seems intermittent, I'm leaning towards electrical. Is there a procedure to check injector resistance at the ecu connector so I can verify the harness and injector?
Do you have a scan tool that can turn off each injector individually?
A slightly loose connection on the injector electrics will do what you describe without setting a code.
Got a new scanner (Thinkcar Pro). Took it for a highway cruise today. Ran great even though I only erased a soft transmission code (low voltage from a dead battery a month ago). No miss but still has a slight vibration (weak cylinder?) when brake torqued to 1200 RPM.
After about 20 minutes, headed home and it started running rough. Quite a noticeable miss on one hole.
Parked in the driveway, and one cylinder started knocking quite loudly. I popped the hood and by the time I got out, the cylinder stopped knocking. It was loud enough that I should have been able to identify which one was the culprit. I jiggled some injector wires and couldn't reproduce it. Definite leaky injector? Or could it also be electrical?
If the scanner had the ability to deactivate cylinders then I would have identified the offending cylinder. It can code injectors so I recoded them to the existing markings, resetting the correction values. Maybe it will identify something. The previous corrections:
The live injector corrections show injector #2 typically at 4 to 5 mm3/HUB, with a max of 5.82 after a 20 minute drive. Limit is 5. Injector 4 showed similar max correction (5.77) but it’s less of an outlier when driving around.
A video showing the roughish idle and testing: https://share.icloud.com/photos/0409...hXhU82JVyRRA-Q
Are there any other diagnostics that I should do before just replacing it? Still no codes.
Test of compression was 158 +/- 1.
The “Quantity correction values for smooth running control over several pressure levels has a limit of +3 mm3/HUB. I ran it several times. Warm engine, not much to report. I tried once putting it in drive and managed to get values of 4-5 for injectors 2 and 4 with the additional load.
With a hot engine (97C), I was eventually able to get cyl #2 to give results around 2.0 for all pressures (600-1600 bar). Cyl 3 registered 3.9 at 1600 bar which is a ‘failure’.
It very definitely sounds like a fuel injection issue. It could be a loose intermittent electrical connection or the injector itself, but you're on the right track.
I haven't seen any common electrical connection issues to look out for regarding the injection system. I'll take a look. One cylinder is always a bit soft but it turns into a noticeable vibration that gets worse the hotter the engine gets. Except for a few days ago when it seemed to be quite fine for a long time. Symptoms seem to mostly support a bad injector vs a flaky connection.
To me, your original fuel smoothing values seem to show cyls 3 and 6 having the most extreme values.
(#6 has the min, #3 has the max)
When I had injector trouble it was these two as well - one had black death and the other showed excessive overflow to return line, when compared to the rest.
I would guess this to be most common scenario simply because they are at the back of the motor and likely more heat-soaked than the others.
If you'd like to do a leak down test to verify, there are a number of threads on this forum and elsewhere which show how-to.
It's not terribly complicated or expensive. Amazon has the syringes and tubing for cheap - it's just waiting for things to arrive...
The live corrections really seemed to point to #2 as being a strong outlier. The 'quantity correction value' test that runs at about 1500 RPM also seems to point to #2. My simple leak off test didn't single out #2, nor did it highlight a single cylinder (like it seems to be).
I'll probably start with putting a new injector in #2 as it's a strong suspect and is easier to get to than the back ones.
I'm still surprised at how noticeable this miss is and the fact there's no codes. Maybe it's overfueling and the system is more designed to detect underfueling/misfires.
The data in plaintext, I must have misread. Is the screenshot of the original values, or after resetting?
My understanding is, those smoothing values get adjusted by the ECU over time according to what the motor experiences.
The higher-pressure ones take longer to adjust (?). A forum user here from OK ( I think) went into some detail on another thread.
So I would have just gone by the original numbers, as they indicate the 'best effort' the ECU could do, given the condition of the injectors at to that point.
When I replaced mine I'd had a hard-starting issue and some roughness which were cured right away.
My scanner didn't support entering injector codes, so I'm trusting the ECU to adjust.
I didn't get you'd already done leakdown test, and didn't watch your video.
The tubes look pretty evenly filled to me.
On mine #6 ran over the top before the others got half full, so was obvious what I needed to do.
That user I can't recall said expect they'll all go bad roundabout 200K miles, we'll see...
Can't tell if it's worth investing the time to get the left cover off. (too much plumbing and this model has real accessibility issues!)
I'm not suspicious of PO needing to tap and coil holes for the cover bolts, it's easy to strip the aluminum if you're obsessing about surfaces sealing.
But why take it off, and did they get things right under it? (timing chain replacement? Look for the chain tensioner is under the oil fill - if it looks new maybe that's why)
BTW, this motor doesn't have cam bearing shells, the covers are the upper shells.
If you want to try replacing injector(s), the good news is the price is much better than a few years ago. Or was when I did it anyway,
Cylinders #2 and #3 are both off (technically only #3 is outside the allowable range and #2 is very close) - see correction values at 1600 bar. Anything over 3 mm^3 / cycle needs to be replaced - even the DAS screenshot clearly says so. Correction for injector #3 is at 3.9 so it flows OK at lower fuel rail pressures but once the pressure rises it chokes so something is blocking the fuel flow, and #2 is at 2.9 and is high across the board so is probably weak / has clogged nozzles. Your initial observation that "The area around cyl 2/3 seems a bit noisy" is spot-on... #2 and #3 seem to be having trouble at full operating pressures (~23,000 psi or ~1600 bar).
The plaintext values were a bit hard to read so I transposed them in Excel to be more in line with how the scan tool report. I reset them and drove around for a while but looked like it would take a while to do anything meaningful. That's when I ran the quantity correction test several times. There's a noticeable vibration at 1500 RPM (where the test is completed). Maybe #3 is the culprit? But #2 seems to act up more when driving. And there's what feels like a 'hard' miss at ~1800 RPM when driving on the highway once things get fully up to temp. I'm thinking it's #2 that's doing this as it seems to change the most when tested.
OK - so according to the 6:53PM / 89C (Tested in Drive) screenshot above, injectors #2 and #4 are bad. The 7:58 PM / 97C screenshot shows that #2 and #3 are bad. Something does not add up...
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