85 900S Very Poor Acceleration (bucking)

Aug 15, 2003 2 Replies
85 900S 5 speed 190K

First noticed a hesitation (bucking) during a drive yesterday. The bucking would increase going up inclines and get much worse accelerating from a stop More like bucking then than a hesitation had to clutch to stop the bucking and coast a bit and very slowly accelerate. OK starting, at idle and at 55mph on a flat road or a slight decline.



Changed the fuel filter, plugs cap & rotor a few months ago. Wires Ok. Fueled the car the day before and drove several miles. No problems noted.



My first thoughts are the fuel pump is begining to fail, low fuel pressure or a failing ignition module causing a very weak spark. Any advice would be greatly appreciated in troubleshooting.



Jim


"W4murdza" wrote

I'd bet on the fuel pump myself, but check all your vacuum lines first.

Check your gas cap. When it's bucking, pull over and try openning the cap. If you hear a sucking sound, you need to replace the cap since you're pulling a vacuum on the tank (the charcoal canister is connected to the low pressure side of the throttle as well as the tank that's why high vacuum conditions like coming off of idle and going up hills makes it worse). I've run into it with Volvos, VWs and BMWs, wouldn't surprise me to see it on a Saab.

My $0.02 Bill

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