Hi guys,

I'm a total noob, please forgive me if I don't know the obvious. I'm the proud owner of a 1991 740 Wagon which I bought from a friend 8 months ago, and today I have my first real problem (apart from a flat a few weeks ago):
1. Lots of engine noise, kind of like when your muffler or the hose has a hole.
2. A hose that's clearly missing a section - see attached picture.

This hose seems to come from the cylinder exhaust, and appears to go back to the air intake (below the air filter). Is this the 'EGR' (Exhaust Gas Recirculation) system?
Do you guys know what kind of hose it is and if it's 'easy' to replace? Any problem going without it for a ride to the car parts shop?

Thanks for any advice, Stephan

 

That is the pre-heater hose. It basically is intended that in the winter it will provide warm air to the intake till the engine warms up. In the air box there is a flap valve that is supposed to turn off the warm air from the preheater and switch to cool air once the engine is warm.

Most people recommend that the preheater hose be removed. What happens is the flap valve in the air box goes bad and constantly provides hot air to the engine which ends up frying the mass air sensor.

Check the exhaust manifold down through the muffler for leaks. Most likely you have a hole or crack somewhere. If the noise is coming from the front of the car, check where the downpipe connects to exhaust manifold for leaks. If the noise is coming from the rear, check around the joints where the pipes connect to the mufflers. This is typically where they rot out.

 

Oh, thanks for the fast reply! That's a surprising answer, removing the hose is something I didn't expect. I'm living in Chicago, and would think that I'd need the pre-heating in winter time.
If I do remove it, don't I have to close the ports at the manifold and at the air box? Or would pinching the hose closed be the equivalent of removing it?

Is there a diagram of the various hoses and connectors of our engines anywhere on this site? I have a lot to learn...

 

"People recommend that the preheater hose be removed. What happens is the flap valve in the air box goes bad and constantly provides hot air to the engine which ends up frying the mass air sensor."

That may be, however in California for one, this is part of the emissions and as such if it's not there the car will fail the test...

 

I also live in the Chicago area and I have two Volvos - a '90 and a '91. One has it removed while the other has it. Haven't really seen much difference in the cold weather. Both start and run fine even down below zero. They don't smog test any cars in Illinois that doesn't have OBD II so removing isn't an issue.

If you do decide to keep it, just make sure that the valve in the air box is working.

 

OK, thanks again for your answers. I figured out that this pre-heat hose is just flowing air past the manifold, and that on the other end it's going through the air filter before getting into the inlet, so I guess it's really not necessary to close any ports if I choose to abandon the hose.
I also found the real source of the tractor noise - it's the connection from the pipe into the catalytic converter. It's totally loose (but not fallen off). I can't solder this myself, so I'll head to a muffler shop later to have them do it. Shouldn't be too expensive my buddy says ($50 maybe). I hope he's right.
Thanks again guys!

 

Problem solved by having the muffler shop weld the pipe back onto the catalytic converter. Wagon sounds rejuvenated. Cost $15.
Thanks for your help guys!