Hands up who remembers THIS
Sprinter with the OM646 Dual Stage Turbo Engine that had me head scratching ???????
To Recap, it came to me last year, with "chokka blocked" DPF and a bunch of Fault Codes. Very Poor Starting, needed a ton of Cranking.
Back then I did every SDS Test possible and fixed all but one Code, but still the beast was very very hard to start !!
But when it finally started, after fixing all the other Codes and getting DPF to Re Gen it ran lovely, pulled OK but kept flagging "Air Flow Offset Drift" Code.
It always sounded like it was Cranking OK, no ups and downs on Cranking RPM, and passed SDS Compression Test which monitors Cranking RPM and Graphs it ............. IIRC it did show #2 Cyl was slightly borderline, but bearing in mind when I blew a big hole in a piston on another CDI, and that still started up quick, I wasn't convinced it was a Compression issue, nor was anyone else !! Everyone was saying Fuelling issue.
It also idles sweetly, smoothly and sounds great when it is running !!
Well, since the last post on it, it was left Parked Up taking up space, the Owner understood I couldn't physically get it into the Workshop due to my Doors only being 8ft high, so we decided to resume works once the Winter Weather broke.
Got back at it yesterday and I now know exactly what is wrong with it
I had meanwhile done a ton of research and actually got some real meaningful figures for various tests on the Fuel System, also I bought the MB Glow Plug adaptor for my Diesel Compression Tester Kit, so I could actually make sure we weren't flogging a "dead horse".
So, yesterday I repeated the Injector Spill, Fuel Rail Regulator, and Pumps Tests, all checked out fine, well within the "Leak Off CC's Specs" and "Pressure PSI Figures" I was given.
As I had kinda expected, so glad we didn't go chucking expensive bits like Pump, Fuel Rail etc at it !!
OK, so lets look at these Compressions then with a Decent Pressure Gauge.
The bear of this is you gotta get them Glow Plugs out without snapping, so got it really hot, and got 'em out
Here we go ............
Cyl #4 = 650psi
Cyl #3 = 650psi
Cyl #2 = 150psi
Cyl #1 = 150psi
Yep, the aforementioned "Dead Horse" has been well and truly flogged
Ok I don't get how it runs so sweet once it's started, but yeah, losing 2 of it's 4 "Suck Squeeze Bangs" while Cranking will cause it to be a bitch to start, and also, if, as I suspect now, it is a Head Gasket / Block Face / Head Face issue, then the fact that the 2 Cylinders are probably pumping across into one another while the other Cylinders Valves are open, yeah, that will give the Airflow Offset Drift Code !!
Plan of action now...................
I don't wanna do it !!
If I had more space I would love to but it won't go in my Workshop, once I strip the Head off it it is immobilised, I can't push it outta the way, so I'm seeing the owner Monday to discuss the way forward.
I'm going to recommend he takes it to a big Engine / Head Re Mfr in Inverness, will speak with them first, first thing Monday !!
I suspect, as this is a long standing problem, and he literally drove it for ages like this, the Head will be Burnt and possibly the Block, across the Gasket Face between the Cylinders, so will require the Block Deck Skimming, maybe a new Head etc etc ...........................
Nope, I haven't the room to store it and do the job ................... Farm it out
But, at least it didn't beat me
I sussed out what is wrong wi' it
So, anyway, DO NOT
rely on an SDS Compression Test !!
But, like I said, and I'm sure some of you know, if an Engine is down on Compression, normally you can here the RPM hop up and down as it is cranking, normally it will idle rough, but this beasty didn't do that ...............
That I cannot explain
IIRC waaaaay back, it also passed the running Cylinder Balance Test on SDS too
Cheers for now,