94 960 3ltr 24v Heavy knock on start

father ted · Post by **father ted** » 02 Jun 2014, 11:34

Hi all,
had this 960 for seven years and has a current mileage of 125k and has always been pampered with no expense spared when required. On start up today there was a heavy knocking from within the engine which lasted for about five seconds on tick-over. It disappeared and the engine began to rock as if it were misfiring. After a minute it went to proper idle speed and has been ok all day across the rev range.
Having not experienced this before my imagination was running wild wondering what it was. My first thought was a failing oil pump but no oil pressure warning light came on. A blocked oil filter maybe or a blocked sump strainer. It wasn't tappet rattle or "pinking" but felt more like big endish. Its due for an oil change about now but I don't feel its something i should ignore. The engine is still as sweet as a nut and pulls like it should with no issues. Any ideas out there please. Cheers.

Ethan Rode · Post by **Ethan Rode** » 02 Jun 2014, 18:52

How are your ignition coils? any cracks or carbon tracing? How does the wiring look to the coils? Any OBD codes?

father ted · Post by **father ted** » 03 Jun 2014, 04:07

Hi,
coils look good, although i have'nt tested them (not sure how to frankly) all clean and no signs of any issues. The wireing looks good also apart from the plastic protector sheath which is brittle in places with the heat in that area. No OBD codes. Car started perfectly this morning and sounded sweet from the get-go. Decided to go for an engine flush/oil change as i have in the past experienced lifter rattle from time to time but nothing serious. See how it go's. Cheers.

danr960 · Post by **danr960** » 03 Jun 2014, 22:24

I am with Ethan on this, most likely, there is a miss on start up but is sounds as though it is more than one cylinder. But it clears up quickly, could be a leaking head gasket and some coolant is getting into a chamber or two? A bad power stage is another possibility.

DanR

93Regina · Post by **93Regina** » 04 Jun 2014, 22:43

father ted wrote:On start up today there was a heavy knocking from within the engine...

Heavy knocking, then one shuts down engine immediately.

Timing belt would be suspect, but vehicle was driven afterwards, with no complaints. Timing belts must be changed on 24v.

Can your fuel rail pressure be checked; maybe an injector is leaking. Check your radiator fluid, maybe a blown head gasket, which is not uncommon.

Fuel knock normally is due to advanced timing, but with ECU, knock sensor, and CPS, one should not hear knocking due to ignition system.

Pull spark plugs, let it sit overnight, then have someone crank engine while you watch with your safety glasses.