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Appreciate any insight the group might have on the following problem with my ’95 Volvo 850 Turbo.

After purchasing/installing an OBX 3" exhaust system online, I had it professionally installed. My turbo is conical so I needed to re-weld the flange from my original exhaust to a down pipe in the kit. At first the exhaust was installed without a catalytic converter (straight pipe as supplied with the kit inclusive of the stock oxygen sensors). However, in NC a catalytic converter is required to pass a state inspection. So I returned to the muffler shop and they installed a new 3" catalytic converter (still with the original oxygen sensors).

Since adding the catalytic converter the car has run extremely poor. My volvo specialists pulled codes and it is reporting that it is running way too rich (dumping fuel and killing driveability). The car starts, idle runs to 1500 RPM, backs down to about 800 RPM and sometime cuts out. The shop has only offered the idea of using different oxygen sensors (an expensive proposition). There didn’t seem to be an issue with the straight pipe (with same oxygen sensors). The shop did re-tighten the downpipe flange to the turbo and it ran better for about a day and then back to the running bad. Not sure exactly why it was loose but I notice the enging rotates sharply when the car is shifted into reverse. Not so bad when the trans goes into drive. When shifted in reverse I can see a puff of exhaust at the turbo-downpipe connection. But it isn't always there...

Any of you heard of this kind of issue? What would you suggest as a corrective course of action to get the vehicle running better? Btw, have replaced spark plugs, wires, ignition coil, mass flow meter, vacuum tubing...

The following is what I purchased:
OBX Turbo Back Exhaust

Manufacturer: OBX Racing Sports
Part Number: EX11111


Thanks in advance for any ideas you can offer.
 

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If there's smoke coming from the turbo/downpipe area, It probably has something to do with the flange weld you did. That would probably affect back-pressure on the engine, but I don't know if that would cause it to run rich. Post your question over at matthews or volvoforums - they have a good collection of mechanics that seem to have all the answers.

When they added the cat, did they have to cut the pipes to install it, or just unbolt a section? Try swapping the cat with a straight pipe and see if the problem remains.


When you say the "engine rotates sharply", do you mean it wiggles in the engine bay?! I'd say your mounts may need replacement, or the trans is putting a lot of torque on the engine.
 
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