My dad has a 1997 (N) Saab 900 2.0. No turbo, just standard. He recently had the exhaust replaced at a saab garage and ever since then its not been quite right.

1. Ruffling exhaust noise at low and high revs in neutral. He initially thought it was caused by a poor fitting of the exhaust - but he had a look and it seems fine.

2. Loss of accelaration / loss of power

3. Car is not happy pulling away, but is fine once it gets going - like on the motorway. Symptoms return once car slows to 15mph or so, so its not something thats fixed by running the engine.

He thought it may have been the lambda probe (oxygen probe), but he replaced this last night, and there is only a small improvement. Obvious things like spark plugs etc have been checked.

Any ideas?

back pressure?

Check the wires to O2 sensor they might of damaged one. Or a joint is out restricting exhaust other wise i have no idea.

Or take it back and jump up and down and shout

Possibly they have damaged the probe and the brain needs reset to get it out of a limp home mode

It could just be coincidence that changing the exhaust did this. Its a brand new probe just fitted last night by us, but i'll go check wires etc.

Could it be that the 02 sensor needs to be calibrated or the cars computer needs to be reset or something?

This may not be the case but check the spark plug wires themselves. I have an eclipse that had the same problem you describe. I could not for the life of me figure out what was wroung. Everyone I talked to said to check/replace something else. Check the spark plugs, check the exaust.... no one ever said check the wires... I finally checked the wires for some reason and one of them was shot. Replaced them and instantly it was like driving a new car. And it only cost like $30 for a set with a lifetime warranty.

-Greg

Oh, God, please, somebody rewrite this thread in "Tom and Ray" style.

I'd do it myself, but I have to leave in a few minutes to go buy some bigger disk drives...

LOL...

The way to check for pipe leaks is to start the car and while at tickover, put the palm of your hand over the exhaust pipe and push hard.

If there is a leak, then you will hear a "whooshing" noise from somewhere up the pipe: it's useful to have someone listen to work out where the noise is coming from.

If there is no leak, the pressure on your hand will build up a lot, and the engine may well stall.

Exhaust pipe leaks lead to pops and bangs in the pipe on the over-run, but shouldn't really affect the running of the engine at tickover. If it's a 97, then it will be injection/catalyst. I don't know whether you had the catalyst replaced (it would have been pretty expensive) but it may be that they have fitted the wrong one.

If the engine fluffs and doesn't pull at low speed, then it's more likely to be something on the inlet side such as a blocked inlet filter. When was the car last serviced, and the filter changed? How about the fuel filter?

Clean all the spark plug leads with petrol/white spirit to get all the muck off them, including the centre lead. Check they are all seated properly at the coil end, the distributor end (this might not be the case if it is multi-coil) and the plug end. Push them all home hard and check they are not loose/sloppy. Start the engine at night, and with very little ambient lighting, see if there is any sign of "flash over" on the leads (pale blue glow or flashes to earth/body/engine).

I'd get the car to a SAAB dealer and ask them to run a diagnostic on the injection system as well: they should also check for inlet manifold air leaks (if the exhaust manifold was disturbed, then it may have also affected the inlet if they are twinned manifolds).

Start the engine at night, and with very little ambient lighting, see if there is any sign of "flash over" on the leads (pale blue glow or flashes to earth/body/engine).

Improve on this, make it a "torture test" by taking a spray bottle of water and lightly misting the plug wires, distributor, etc. while the engine is running. You should not get any arcing or misfiring when you do this. If you do, replace plug wires, distributor cap and rotor (assuming the car is equipped with a distributor and not some fancy multiple coil system driven by a crankshaft sensor.)

tanstaafl.