1993 Volvo 940 Acceleration Noise (Card in Bicycle Spoke)


Recently I have noticed my 1993 Volvo 940 makes a noise
while driving, that sounds as best I can describe as a card in a bicycle spoke;
or kind of like the putt-putt sound, you hear from a large truck idling next to
you. I hear it while driving, whenever
stepping on the gas pedal, but not while idling, or when the car is in park or natural. The faster I accelerate the louder the noise
is. I want to try to trouble shoot this but I do not
know where to even begin looking into this. Maybe there’s a leak somewhere.
Any suggestions are appreciated. Please and thank you.

See if you can determine if it is related to engine rpm or vehicle speed. For example, does it stop making that noise if you put the transmission in neutral and coast? If the noise continues, that means it has something to do with the wheel speed, not the engine speed. And if the noise stops, visa versa.

fwiw, I’ve had similar noises on various vehicles over the years, found to be due to

  • deterioration of the belt that drives the water pump pulley
  • small exhaust system leaks
  • failing u-joint
  • CV joint rubber boot has split and flopping around

I don’t think it’s related to rpms, because I hear it anytime I gas it regardless of rpm level. I do not hear it while in neutral. I do not hear it while coasting. I think it may be related to vehicle speed because the faster the car accelerates, the louder the sound is.

Good to know. That eliminates most of the engine related problems, like exhaust leaks. Does your Volvo have a drive shaft with rear wheel drive? If so, ask your shop to check the u-joints in the drive shaft for play or in need of lube. If front wheel drive, ask your shop to check the CV joints for play, and the rubber boots are intact. It is a good idea to check the transmission fluid level and if equipped with a rear differential, the differential fluid level.

I would jack up each wheel, one at a time, and turn it by hand. You might be able to re-create the noise and being so close to the wheel identify the offending part, brake, axle, CV, wheel bearing.

My boots are torn and I wouldn’t doubt the other parts that go with them need to be replaced, and the transition fluid level is fine, but when you mentioned an exhaust leak i found this video that sounds a lot like what i have. https://www.youtube.com/watch?v=CtK75-HWeHE

I think this may be it.

start lightening up a cigar ( a cheap one) and start blowing smoke up the exhaust. See where it comes out…or not. Covering up the exhaust pipe with a potato or old rag might also work.

My friend thought it might be the exhaust manifold valves. I tried to find a leak with soapy water but couldn’t find any, and took it to a shop. They said I’ve got a bolt broken off on the exhaust manifold and that’s what’s causing the leak. they’d need to remove the turbo and the manifold to drill it out and put a new one in. Is that really what’s making such a ruckus?!

An exhaust leak could indeed make such a noise. You could try a little experiment. You say you can’t hear it at idle, right? Try idling the car in the driveway, and confirm that you can’t hear it. Now put a piece of board, say 1 x 4 lumber, and partially block the exhaust pipe. Not completely, but a partial obstruction. If there’s an exhaust leak upstream, that should make it louder. Does doing that make the sound loud enough to hear? Try it both when the engine is cold, and when at normal operating temperature. Easy enough to do anyway, and might provide a clue.

Apparently the vehicle is at a repair shop. Just go and have them show you what they have found and you will have your answer. You have to sign off on repairs anyway.

This sounds like an exhaust manifold leak. When you examined the exhaust manifold for leaks did you remove the manifold heat shields?