I've had a 2001 s60 n/a since late last year. It has approximately 130k on the clock, and I've really been enjoying it. A few months ago the car developed a vibration/rattle precisely at 1500 rpm (not there above or below). Soon after, the exhaust started clanging over bumps. My local mechanic checked it out and found that the exhaust was separating at the resonator. I had the resonator replaced with straight pipe to save several hundred $$$ and the clanging was fixed; however the vibration/rattle was still there. I recently had it to the dealer for a software update and asked them to check it out. The dealer is saying that the cat is bad - but the car is running well and not throwing any codes. My local mechanic also did not raise the cat as the issue, so I am suspicious. Is there a way for me to tell if the cat is bad? If it is bad, are there any cheap replacement alternatives? If not, what else could I check as the source of this noise? It's something I can live with, but it is loud - and much louder inside the car than outside. Thanks!

 

Try tapping the cat with a rubber mallet to hear if there is loose material inside of the unit. You can also get a back flow test done to see if your cat is the problem, check all your mounts too though as the rattle could be attributed to a bad motor / trans mount.

 

Thanks much for the reply. Had a muffler shop look at it for kicks and they say the flexpipe is worn but the cat is okay. Also noticed on the written dealer estimate they noted the torque mount needs to be replaced, but no one at the shop discussed it with me. I'll probably start with the mount and then move to the flexpipe if necessary.

 

A rattling catalytic converter on the Volvo 740? Most probably the platinum black (very poisonous) perforated castings have broken up inside despite their asbestos wrap-around supports. All good stuff for your health – if you go for a run with a new car going past with one of these, and they all have them now – the platinum black really knocks the breath out of you. But of course we need to reduce the greenhouse gases (nobody measures for platinum black). Depending on your local regulations, one method of fixing a cat is to remove if from the car, and use a bit of rio, or rebar, with a hammer to knock it all out from the flange side. It breaks up quite readily without damaging the container and pipe. Use a mask while doing it. Collect it and keep it in a plastic bag – apparently car recyclers get about $200 for the platinum.

Another rattle cause can be the front brake shoes. The holding clip is a bit weak on the 740 and you might have to bend the sides to hold the brake pads in place so they don’t rattle. Insert them and see if there is any play. The callipers have to be taken off to do that of course.

The centre tailshaft support mount is almost always loose in these cars. You’ve either got to get a new mount or somehow firm up the support with rubber strips etc. That’s my next project – the universal is actually hitting the chassis in low gear. And of course the rear trannie bearing and seal always go. There used to be a garage that did nothing but replace those. I got a few left-over spares from them – they fit all 240’s and 740’s (don’t know about 940’s).

These are all nuisance rattles, but you need to get rid of them to hear the potentially serious ones, like rack ends and tie rod ends and so on. I’ve seen a 240 on a roundabout with the front wheels pointing outwards on both sides! That roundabout might have been a lifesaver for the driver.

Apart from all that there are still nuts like me who believe the Swedish government-produced 240’s and 740’s remain the best cars in the world. What other cars (en masse) have good fuel efficiency, have lasted 30-odd years and are still on the road?

 

Volvo 740 electronics. I’ve just spent a week getting one of these old clunkers back on the road – after it hit a bump and stopped dead in its tracks due to no spark. So I handed my solicitor friend, who was enjoying the ride up a steep dirt track strewn with boulders, the fuse from the really accessible (NOT) fuse box, the fuse I thought was the ECU (Engine Control Unit) fuse, i.e. fuse No. 1. He checked it, I checked it – not blown. So. What next? Well we had tried a spark plug in one of the leads – no spark. So OK what about distributor problems? We connected the spark plug to the HT (High Tension) end of the coil – still nothing.

I then checked the resistance of the HT end of the coil which was 7.38MΩ (Mega Ohm) – that seemed a bit high for a copper winding even for HT. But it was actually almost identical to the HT terminal resistance of another coil in a working 740. Also by shorting the negative coil terminal intermittently we got a bit of a spark – you wouldn’t expect a proper spark because there’s no capacitor. Cranking the engine produced no significant pulse on the negative terminal of the coil – less than 0.2Vp-p (Volts high peak to low peak) . It should be around 12Vp-p.

Clearly the ECU, which in the 740 Volvo (1980 model) also incorporates the CDI (Capacitor Discharge Ignition), did not function. It seemed highly unlikely, however, that a bump in the road, even a boulder hitting the chassis, would damage the electronics of the ECU. We thought it HAD to be a connection problem of some sort. Next step – ECU critical inputs. The ECU won’t work without a crank angle sensor that works. So I pulled that really accessible unit (again, NOT) out and got a replacement. The replacement turned out to be the wrong length because I bought it on model No. etc. Anyway by this time I had taken the precaution of bringing all my electronic test equipment to the place in the sticks where the beautiful Volvo decided to take a nap. I even brought a ‘spark box,’ which the road service people used to carry. Well maybe spark box is exaggerating – it was the guts of an old colour TV set. Still, it put out a lovely 30,000V spark on the HT – about 3/8” long. Of course without the ECU working you don’t get no gas either, because it needs a 10Hz pulse or so to run that non-serviceable system. We did, however, get the engine to tick over by spraying StartYouBastard into the intake. So, progress! The next thing I checked was the crank angle sensor by running a couple of phone wires into the connection (no easy task). The plug actually doesn’t have to be connected to the socket – it puts out a pulse generated by the magnet/coil combination.

That pulse when cranking was about 1.2Vp-p on the scope, triangular wave, at about 160Hz, with a short flat spot where one or two teeth have been omitted on the toothed disk to identify TDC (Top Dead Centre) for the ECU. I’ve never seen this toothed disk but at about a 4Hz cranking speed I’m guessing it’s got about 40 teeth. Maybe someone could correct me.

So, no nothing despite a bit of a cough and splutter. Next step, new ECU. Picked one up for about $100 – has to have same Bosch number apparently. I put that in, no change. So what else is new? By this time my mate had actually bought me a Commodore V6 car for about $700 capable of laying rubber. I was just about the give the Volvo away as a boat anchor, when the last thing on my list, which I hadn’t done, was check ALL the fuses. Useless of course, because we had already checked the only relevant fuse – the ECU fuse, or so I thought. I pulled out the first fuse on the top left, and guess what – it was blown. I then re-checked the exquisite numbering system in the Volvo’s Pandora’s box and – hey – it was actually numbered numero uno. One! The fuse for the ECU. Previously I had assumed that the fuse BELOW the numbers were it. Now the moral of that story is, as my mate correctly pointed out, when you check any fuses in any car, check ALL the fuses. Still, about a week and hundreds of bucks down the drain, it was a learning experience. Needless to say with a new fuse – borrowed from the wipers – the horsy perked up with a neigh and purred down the highway beautifully, even with the old ECU.

Shows you that those ECU’s are slightly indestructible: they can even handle a short circuit on the output – of the ignition at least. I’ve yet to try shorting out the fuel system output – I’ll leave that for when I’ve got a few weeks to spare. It WAS actually a short circuit on the output of the ECU where it runs to the negative terminal of the coil. That shorted out when I hit the bump. It shorted out because I had cut that wire and put a kill switch in series, and the soldered blob had worn its way through the insulation and touched the chassis. So: if there’s no problems with your old Volvo you can always create interesting ones yourself!

PS: Borrowed a BMW while all the above was happening, and getting back into the Volvo was like going on a boat cruise! That’s OK, I don’t mind if it handles like a boat, just plan your corners. The bikies appreciate that.