View Full Version : Intermittent engine knock noise

07-04-2019, 05:09 AM
My T1N 308 611 , 2006 Sprinter developed an intermittent engine knock. Its most noticeable when starting in 1st gear just as I put my foot on the accelerator , then disappears. But you can also hear it when you rev the engine a little when van is stationary. At times it can sound loud like metal on metal and is noisy. Scary. But it disappears as the revs build and you can't hear it at idle or when the van is cruising along the road.
I took it to 4 different mechanics and they all thought it was either a big end or rod bearing. So with sinking heart I took it home , drained the oil (at 3000kms) and sent off an oil sample to an oil Lab for analysis .I pulled out the oil filter and checked. No sign of iron filings or metal bits. Clean as. I bought a magnet and put it inside the sump and moved it around. But it came out clean with no metal filings at all. The oil test came back confirming this stating the engine was in great condition with no signs of wear !. Relief !!. So I'm assuming that rules out bearing issues.
So where to from here. I checked the injector tops for black death and clean as. In fact the injectors look like new. But haven't pulled them out yet. There is no obvious smoke coming out the exhaust when I rev the engine. A little bit but not black clouds. I had someone else drive the van up a hill while I drove behind to see if black diesel smoke came out under load but nothing much. So wondering if I should pull the injectors . The injector shops asked if the van was pumping out smoke too , so perhaps its unlikely its the injectors ?. I also added some Wynn's EDT fuel treatment to the fuel tank about half a tank ago. Since the noise arrived I've only driven it 400 kms or so.
One thought is the oil pump. Wondering if the oil pump seals are going and its not picking up oil
quick enough ?. But that would mean the red light would show up on dash right ?. Another mechanic said the big end bearing if failing , would not necessarily show low oil pressure. But it would show metal in the oil . The sound is usually there at the beginning of a drive. But sometimes it there later on too when hot.
I asked the Merc mechanic if it was the cam chain tensioner maybe making the noise . He said no.
There does seem to be more than normal blow by when I take the oil filler cap off. Plenty of oil jumps out but I don't know it thats a sprinter thing ?
So I'm wondering where to from here ?. I guess I could get the scan codes to see if that points to anything . Any ideas ?.
The van has 242,000 kms on the clock. But the previous owner wasn't great with maintenance. I've owned it for 6 months and only done 6000kms . Since I had it its had a new cam sensor.
Any thoughts would be appreciated thanks. :thinking:

Gabe Athouse
07-04-2019, 05:58 AM
I’d check all the pulleys and the harmonic balancer real well, best tensioner, and accessories mountings. Fan clutch? Motor mounts? Fuel pump sucking air? Or maybe even disintegrating CAT or other exhaust rattling?
I think your oil report rules out bearings for sure.

07-04-2019, 01:30 PM
harmonic balancer/pulley
Engine/trans mounts
exhaust hangers
flex plate
driveshaft center support bearing/hanger