is it normal for a 940 non turbo to knock when using low or mid-octane fuel? my car seems to do this, especially when I'm only accelerating very lightly. I'm at sea level and the temperature is in the 60s, not too humid. It's recently had a tune up with new plugs, wires, rotor/cap, oil, fuel filter, etc. the engine seems to run strong other than this knocking, but it is quite noticeable. is it possible that there would be another sound that sounds similar to knocking that I'm mistaking this for? It certainly doesn't make it when I rev the engine in neutral, under no load. but it also doesn't do it under heavy acceleration, which is when my old 122s would knock, and with less sound insulation on that car it was much easier to distinguish the sound.

Hi,

My car also knocked on light acceleration, it was a bad rear fuel pump. My car would get exceptionally high gas mileage, in the 30's on the highway. I don't know what it gets now, but I have much more power, no pinging, and it runs on regular.

Gus

hi gus,
acutally what you say is interesting because I know that the front fuel pump is going bad. it makes a funny noise but the mechanic said didn't seem to think I needed to fix it, only to keep more than half a tank of gas in it. perhaps it isn't providing enough fuel pressure?

This is not normal especially since this car should have a knock sensor. It may be time for a new one; I have never had to change mine so I am not sure how you can test it. Others here may have to chime in at this point.

Andrew S.

As far as I kow only my 940 turbo wagon recommend premium gas. my NAs run great on reg 87 pump gas.

The fuel pump, and filter should be checked, The knock sensor is fairly robust and there is not a easy way to check it. However it is directly under a part of the head gasket that is prone to weep coolant with age but it very easy to R and R with a know good sensor from another car. Mind the torque,

Other issues could be carbon build up,. I found additives works well and an Italian tune up. Then a nice three hour drive to Palm Beach an back usually takes care of it.

well, my fuel pump is now fixed and doesn't make a loud noise. but the knocking sound that I've been after is still there. my dad listened to it and didn't think it was engine knocking, but suggested exhaust gaskets wearing out. its kind of a quiet tap tap tap that i hear upon acceleration, pretty faint actually. is the best way to check for exhaust gasket leaks using soapy water? and if the bolts are all rusty, should i pretty much expect for a stud to break when I take them off? there seemed to be pages and pages about this in the FAQ section.

thanks to everyone on this thread. i had thought the front the pump was bad because it was making noise, but as the FAQ file instructed I checked out the sender unit and found the problem to be there. it was dead. 90 bucks (pump, gasket, and sock filter from RPR) and a few hours of reaching my hands into that tiny hole over the gas tank later, i got the thing working.

getting the whole unit back into position, with the gasket, is harder than it sounds... it seems like it won't fit and you have to really jimmy the whole sender assembly around to just the right angle before you can get it all the way back in. there must be some sort of baffle in the tank that it fits into. at one point I thought for sure i was going to break the thing.

and by the way, only try to do this job when your tank is less than 3/4 full. I'm such a moron--I learned the hard way...

now the primary pump noise is more or less gone, and the car doesn't hesitate like it did before. it must have been a little starved for fuel with the sender unit not working. hopefully working overtime didn't damage the primary pump too much because i'd rather not have to replace that anytime soon. what with the tune up i gave it, the timing belt, radiator/hoses/water pump/ the suspension bushings, the wiper motor...i've spent a lot of $$ on this car this year...