Scania Misfire

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Sharpy
OneWave
OneWave
Posts: 27
Joined: Sun Dec 23, 2018 9:59 am

Scania Misfire

Post by Sharpy » Thu Jun 20, 2019 9:40 pm

Today's subject is a 2005 Scania P380 DC11 Pde 32 tonne tipper, it come in with a fairly serious misfire and was breathing heavily and with a knock under load apart from the obvious breathing and oil staining around the breather pipe the visual inspection provided no clues and fluid levels were all good with no signs of contamination.
A scan with the dealer tool revealed nothing and the cylinder balance and cylinder shut down tests were inconclusive, the scan tool wouldn't allow a relative compression test as the coolant temp was below 50 degrees due to the misfire and knocking I didn't feel comfortable trying to warm it up.
It was clear by this point that it was likely to have low compression and it was being lost into the crankcase so out with the Pico to confirm that was the case and to identify which cylinder or cylinders were the problem.
First test was the relative compression and due to the lack of a cam sensor on these engines I decided to use the optical sensor from the NVH kit to try and get a sync on the flywheel, On these engines they have a handy window in the bell housing top and bottom and markings on the flywheel for engine position, I used the "tdc" mark and set the opti sensor up in the bottom window as access was easier.
Scania_P Series_2005_Diesel_Relative.psdata
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This confirmed a problem on one cylinder and having a position for reference was nice but really much use for ID,
This next capture was to confirm the pressure in the crankcase. After trying different things I decided to remove no1 rocker cover and put a current clamp around the trigger of the Pump Unit Injector. I also should add at this point initially I had the clamp around the wrong wire and was getting 1 spike per 360 degrees of rotation I then took the next capture with the clamp on the other wire and at first I thought it also had 1 spike per 360 and even commented that I had 2 humps in the crankcase per 720 before realising that in fact the injector current is now how I want it once every 720 degrees. I was having a doh moment so mate @ PB if I confused you earlier this is why :lol: you were dead right about the shared ground but I had missed that it had sorted it.
This is the crankcase with no1 injector the cc pulses are weaker and I believe this is because no1 rocker cover is removed letting some back pressure escape. So at this point it is clear the problem is on no.6 and just to confirm I also have the exhaust pulse overlay with the 4 stroke cycle, note the injector current when on the wrong wire firing twice but I have aligned the firing order in the right place.
overlay.png
Now as we are stripping that cylinder anyway it'd be rude not to grab an incylinder with the Wps, I did put a manual gauge on first and confirmed the peak to be 200psi so as not to damage the Wps if I was wrong about cylinder ID, the great part is the incylinder highlights the difference between a manual gauge being able to build to peak rather than actual pressure bearing in mind I was doing all these tests on my own so I just had to crank without seeing the gauge or the laptop. Now I was 100% confident I had identified the problem cylinder and I didn't need to take anything off that I didn't need to which compared to one I did last year before having the Pico with an identical engine and similar fault I removed all 6 injectors and leak tested them with diesel which worked just fine but took forever by the time I refitted them with new seals and reset the preloads.

This is what I found
IMG_1745.jpg
IMG_1747.jpg
In this one its quite hard to see but there is a crack in the edge of the crown, I don't think this contributed to the low compression but it isn't good. Again due to the age of the vehicle and the Ulez coming into full force next year in our area the customer doesn't want to invest in a full overhaul but has given the go ahead to fit a new genuine Piston kit & liner to this cylinder plus a full set of big end shells which all arrive tomorrow so hopefully I should be able to post up some after captures.

Sharpy
OneWave
OneWave
Posts: 27
Joined: Sun Dec 23, 2018 9:59 am

Re: Scania Misfire now repaired

Post by Sharpy » Sat Jun 22, 2019 5:39 pm

Well as promised a follow up for the Scania, it is all back together, road tested its all running great and ready to go back on the road Monday morning, Sadly I only took one photo during the repair showing the nice shiny piston & liner in place ready for the cyl head.
IMG_1748.jpg


I will add that since cleaning the rust from the flywheel I realised that I the tdc mark that I placed the tape on for the optical sensor to pick up on was actually "TDC UP" and as the opto was at the bottom window it meant that I was actually always 180 degrees from Tdc and had I had either set the opto in the top window or realised and found the "Tdc Down" mark I would have had the pickup on the dead cylinder first go but hindsight is great and at least I know for the next one. Here are some captures from after the repair, I haven't added any channels for cyl id but you can see everything is pretty uniform.

Relative Compression
Scania_P Series_2005_Relative after repair.psdata
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A nice crankcase waveform and its actually in a slight vacuum

Then a nice even exhaust pulse capture, this one was at 600 rpm so the peaks are higher than the before captures.

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