960 Engine Knocking When Engine Cold

lehmanra · Post by **lehmanra** » 07 Apr 2004, 07:16

I have a 93' 960. Recently when the engine is cold it knocks while under load during acceleration. After about 15 minutes of driving the knocking goes away. Then the engine runs well. Could this be due to the timing belt?

petershen1984 · Post by **petershen1984** » 07 Apr 2004, 22:30

You may need to go premium on fuel. an FAQ site I read up on suggests treatment using fuel additives, but those add to your fuel costs considerably (you probably won't notice the difference). In the long run, I've switched to Premium and almost never hear engine knock.

Although, with the recent hikes in gas prices worldwide, premium has become proportionally more expensive than the lower grades

Volvord · Post by **Volvord** » 08 Apr 2004, 22:25

The knocking you describe could be caused by two items.
1) a carbon build up in the cylinders which essentually increases the compression to a level when knock or detonation occures.

2) a lean mixture when cold which will induce a detonation.

I agree that you should be running premium fuel in you car, that and a good run on the highway to remove some of the carbon deposites should do the trick

lehmanra · Post by **lehmanra** » 09 Apr 2004, 08:21

I do not think that it is the grade of gasoline. The knocking only happens during the first 15 minutes. After 15 minutes the engine runs find and accelerates great. However there are times when the engine starts it sounds like it barely runs.

Could this be do to a timing belt? Any suggestions?!?

petershen1984 · Post by **petershen1984** » 09 Apr 2004, 09:33

Symptoms from a bad timing belt would be much more obvious and last much longer than 15 minutes. I'd say check your fuel octane or the fuel/air mixture levels.

Volvord · Post by **Volvord** » 09 Apr 2004, 12:53

The question is, the knocking you describe is it detonation or a mechanical engine knock? After re-reading your post I would say that you may be hearing a slight piston slap. When the pistons are cold there is more clearence between the piston skirts and the cylinder wall, as the engine runs the piston will rock slightly in the bore and produce a slight knocking sound. As the engine warms up the piston will expand and the noise will dissappear. The noise will be more noticable because of the rough running and low rpm's you describe when the engine is cold. In this case the noise it not causeing the rough running, about the rough running probably increasing the noise.

The rough running is not your timing belt, although it is important to replace the timing belt at the recommeded intravals to prevent being strabded on the side of the road. I would recommend a complete tune-up with plugs, checking ignition wires & cap, cleaning throttle body, and even having the valve clearence checked.

ozzimark · Post by **ozzimark** » 10 Apr 2004, 18:31

well if it takes like 15 min or so, this could indicate that the oxygen sensor is warmed up, so before this, a bad air flow sensor or something could be causing it to run lean

lehmanra · Post by **lehmanra** » 13 Apr 2004, 08:00

Actually the engine sounds like it has a large hole in the muffler. I have put a tank of premium gas with an additive it in and no change. My next stop is to change the fuel filter and injectors.

92 960 · Post by **92 960** » 15 May 2004, 14:32

Hi guys, I'm sure you are all aware that most mechanics are on the learning curve with 960. The valves being hydraulic require very different driving habits in this car. I know this is not normal but I would stay away from aditves. Stick to a premium grade if you can and use sythetic oil at 5K interval to prevent further problems. To solve the sticking exust valve rpoblem, warm the car up and take it on the freeway, at about 35 shift to "L" which is (second gear at that speed, not first) get it up to 5000 RPM and keep it there for a good ten minutes. This will rotate the valves and and loosen things up. You cant damge the engine, on the contraire it will idle better and run much smoother after this. Also don't ever start the car to move it a few feet and shut it off befotre warming up. You risk serious valve sticking problems from doing this. I always drive it atleest a few miles before shuting it down. Its a great car as long as the timming belt is changed every 30K (uptil 1994) and the cooliing sytem is new. http://www.brickboard.com

Al 92 960 200K

92 960 · Post by **92 960** » 15 May 2004, 14:36

Hi guys, I'm sure you are all aware that most mechanics are on the learning curve with 960. The valves being hydraulic require very different driving habits in this car. I know this is not normal but I would stay away from aditves. Stick to a premium grade if you can and use sythetic oil at 5K interval to prevent further problems. To solve the sticking exust valve rpoblem, warm the car up and take it on the freeway, at about 35 shift to "L" which is (second gear at that speed, not first) get it up to 5000 RPM and keep it there for a good ten minutes. This will rotate the valves and and loosen things up. You cant damge the engine, on the contraire it will idle better and run much smoother after this. Also don't ever start the car to move it a few feet and shut it off befotre warming up. You risk serious valve sticking problems from doing this. I always drive it atleest a few miles before shuting it down. Its a great car as long as the timming belt is changed every 30K (uptil 1994) and the cooliing sytem is new. http://www.brickboard.com

Al 92 960 200K