I have another question about my new 1993 940 with 81,xxx miles. I replaced the timing belt and also the exhaust system.
I notice that the car shakes sometimes when I am waiting at the light. I also hear a low knocking sound. It drive OK otherwise.
I have replaced the timing belt and the exhaust system on this car. I also have stepped up from 87 to 89 octane fuel.
What could be the problem?

As mentioned check your mounts including the tranny mount. The car's low miles make a bad mount unlikely but not out of the realm of possibility.

You might want to check the car's fuel delivery. A friend of mine's 740 would shake at idle. It turned out to be a bad fuel pressure regulator.

Make sure the flame trap and its hoses are clear. A clogged flame trap or a flame trap hose might cause a rough idle.

The engine shaking might be causing the knock.

--
3 Volvos, 2 presently

Congratulations on your purchase. 93 has the latest of the b230f engines, an "L" block so it has the piston cooloing oil squirters and as such is generally one of the quieter of it vintage. Two things come to mind. First I have noticed that if use certain oil filters(the orange Fram ones with the rubber grip crap on the end comes to mind) the engine seems almost starved of oil at idle and does make a knock as you describe. So try a "real" Mann oil filter, makes my 94 940 noticeably quieter. Second see this link to visualize
the line that comes out of the oil pump and the O-ring that can overtime become damaged/mis-seated. http://www.pbase.com/stealthfti/image/33091995
You may want to hook up a "real" oil pressure guage and see what you are getting..good luck.

Can you elaborate on the low knocking sound?

I would say engine mounts might be old and soggy and letting the engine rest on the crossmember. That could explain vibration, but I don't think that explains knocking. A thorough tuneup would be a good place to start and you should try to determine what's making the knocking - an engine misfire, a mechanical defect, an exhaust leak, Gremlins jumping up and down under your hood... ;)

The more info you can give us, the easier it is to help.
--
1990 740 Turbo, on its way to stock specs, maybe beyond

Since buying this car, I have replaced the timing belt and the exhaust system. My mechanic also had to undo wiring and add a relay. I have a receipt where the owner rep[laced the battery. My mechanic says is has a new alternator and starter, too. The previous owner left a bag of old parts inthe truck. Ih ave not idea what they are. Anyway, it just makes this thumping sound and adds like it wants to shake sometimes while I am aitin gofr the light.

I am getting ready to sell my 1994 850. Are there any interchangable parts?

Dear 85oflgirl,

Hope you're well. Few parts interchange between 850 and 9xx cars, chiefly because the former are front-wheel drive and the latter are rear-wheel drive.

The shaking likely is caused by fuel supply and/or electrical abnormalities, that disrupt the normal operating sequence of the engine. I'd look at:
(a) spark plugs, plug wires, and distributor
(b) fuel pressure (should be 43 psi [pounds/square inch]) and flow.
(c) the idle air control valve, mounted on a bracket, below and beside the intake manifold, may need cleaning
(d) the crank sensor could be on the way out: when the signal is lost, the fuel pumps shut-down.

A question: when the car shakes, does the tachometer show a drop in the number of revolutions/minute? Are there any trouble codes (see FAQs for how to read these codes).

The plug wires, if factory-original units, are well past the end of their working life. Time and heat degrade the rubber insulation. The same is true of the crank sensor.

If the fuel pump is failing, then one would expect these shaking episodes to become more frequent. Does the car have Rex-Regina or Bosch fuel management? The Rex-equipped cars have a square coil unit, on the driver's side strut tower (North American models). The Bosch-equipped models have a cylindrical coil mounted on the passenger-side strut tower brace. Rex-Regina models have a single in-tank fuel pump. Bosch models have an in-tank pre-pump and an externally-mounted main pump on the underside of the floor pan, just beneath the driver's seat. Fuel pumps usually last far more than 80,xxx miles.

Hope this helps.

Yours faithfully,

Spook

What weight oil are you using? Some recommend that "high mileage" (1) cars use a heavier weight, e.g. 15W-50. Until the engine is thoroughly heated up that 15W may not be flowing freely. My 960s are sensitive to that, so I run synthetic 5W-30 or 5W-40 in summer.

Another thing to check - at idle you might get an idea of the sound frequency by listening and watching the tachometer. One main bearing would knock at half the rpm. Count fast for 10 to 20 seconds, do a little multiplying. A main bearing knock is often deep and not too loud. Oil starvation might not be limited to just one bearing, you should be able to tell by the sound.

Also, the "right" filter is a Mann 917. I use that one on my 960's and 240's.

Good Luck,

Bob

:>)

(1) Usually mechanic types not familiar with Volvos.