Hi lads am new to this ive just bought a new subaru impreza 1993 wrx saloon the thing is every time i start it up from cold it some times make a loud knock sound and then goes away it only last a 2 secs the most it drives spot on after that i bought if of a guy who had it stood for a year ive gave it a full service but it only dose it on a cold start once it warmed up and i tunit off and leave it for a bit when i come back and start it up fires up with out the knocking sound only does it on a cold start is this some thing to worry about
thanks lads.

 

could possibly be piston slap, does seem to happen on some cars, must admit though I havent heard of it on a 93. Possibly a noisy starter motor as well. Something you could try is when you turn the ignition on and you can usually hear the fuel pump for a few seconds, wait until that noise stops and then start it. I have an apexi ecu and a commander and sometimes if I just start straight away I can get a high knock count

 

Mild piston slap from cold is normally audible for more than just a couple of seconds, while things heat up and expand etc, then it tends to die down. If it goes away completely that quickly my uneducated opinion would be that you can rule that out. Could be wrong but I don't think so in this instance.

 

just to add, it will have hydraulic lifters, if its been stood for a year then they could be gummed up and taking a few seconds to presurize

 

My 1993 WRX sometimes will knock from cold. Only for 2 or 3 cranks of the engine, then it goes.

 

thanks lads is it some thing to worry about or is it normal, i turned the ignition on waited for the fuel pump noise to stop and when i crank the car i get 1 loud knock sound for a sec and then the car starts up i dont know if thats normal but runs fine after that.

 

i wouldn't worry too much about it, maybe check your oil level though. If it were knocking for a lot longer or all the time then I'd be worrying.

 

As you crank the engine and it fires, watch the oil pressure light on the dash. I'll bet the oil warning light stays on for exactly the same length of time it knocks.

 

thanks alot guys much appreciated