Engine knock

[duren03msp]

alright so I just recently pulled my MSP out of storage and noticed an engine knock after 2 days of driving it. sounds like a knock from the bottom end but cannot tell quite yet. now onto the weird part. it only knocks when the headlights are on. soon as a turn them off I cannot hear anything abnormal. yet as soon as I turn them back on, within a few seconds it comes back. I really hope it's not detrimental.

also when I turn the lights on the RPM drops to about 600 compared to 750 at warm idle with lights off. is this normal? along with that it seems that when I rev the engine while I am listening to the knock it seems to go away. any ideas???

 

[Pez]

how is the battery voltage and charging system? if you had the car stored for a while then you might be running on a tired battery. The engine rpm drop is probably due to the load put on the alternator from turning on the headlights. just a thought..

 

[duren03msp]

haven't checked voltage. it's the battery out of my winter daily driver. it's old but still works fine. I can see how that could drop RPM but why would that cause a knock? other than spark knock from too low voltage to the coils.

 

[duren03msp]

nobody else? I knew it was weird but I would've thought more than one person would have an idea lol

 

[ap123]

i dunno if itll do any help, but if i ever hear any strange knocking noise first thing i do is check the oil level and when/how many miles its been since it was last changed.

 

[duren03msp]

oil level is good and changed with AMSOIL the day I put it into storage.

 

[hornsfan10609]

I would test the alternator and battery to start.

 

[duren03msp]

ya that was my first plan of action as soon as the snow quits here in Minnesota where I can get it to my work without getting a nice coating of salt on it. I started it up and got it to full operating temp and tried to recreate the noise and search for it with my stethoscope. couldn't replicate it. which IMO is very good but still frustrating. at least I know it's not any internal engine component.

 

[duren03msp]

alright fellas the knock is back. narrowing it down a bit to try to get best responses. I only hear it after a long spirited drive when the engine is nice and hot. I also noticed it sounds like it is coming from the rear main/ transmission area. once again It can only be heard when the headlights are on. unfortunately no more updates as of that considering I have only heard it twice and both times is in my dark garage with no flashlight to see anything.

also it seems to make an estimated 1 knock per 1 engine rotation.

thanks ahead of time for any and all ideas.

 

[Pez]

i am at a loss for words. i really haven't heard of a knock only when the headlights are on that match engine revolutions. lol. i'm sorry i couldn't help more.