I have a lot of different sounds in my -89 6.2 Chevy with motorhome chassi:rolleyes:

The problem:
When I turn the key to glowplug warming on startup I can hear a sound that is like knocking from under the inner hood, somewhere nearby intake.
And i think that the sound is still on when the engine is in idle but im not sure, have to take the hood off or what is it called to be sure.

Can mention that sometimes when the truck has been standing for a few days I can hear no sound and the glowplug lamp will not lighten up until I make a few more tries with the key to on and off.

Open to all kind of ideas!
Keep this forum alive because its worth more than anything for me since I got to be the camper with greasy hands (and beercans) all the time....

Today I was under the truck to recognise where the sound comes from and it seems as it comes somewhere from the fuel tank in the back.
So my question is now is there also a fuelpump in the tank or what can it be?
Is it broken then? But the truck works good.

Some ideas would be great!

Thanks!

In my 93 1/2 ton there is an electric fuel pump that is mounted on the frame by the fuel tank. When I turn on the key to warm the glow plugs it usually clicks for a few seconds until it builds up supply pressure. Not sure if yours has electric or mechanical but if it is mechanical you will see it on the passenger side front of block vary much like on an older gasser. If it is not there you likely have an electric that could vary well be making the noise you describe.
As far as glow plugs not coming on if it has sat for a few days you may have a glow plug controller acting up. They are prone to it.

what he said is right on the money.

well personally i like to call them the el cheapo shake and bake filters they are a reciprocating electromechanical type filter look like this

http://www.partsamerica.com/ProductDetail.aspx?MfrCode=CTR&MfrPartNumber=P74019&CategoryCode=3339K

or this

http://www.jcwhitney.com/webapp/wcs/stores/servlet/Product?storeId=10101&Pr=p_Product.CATENTRY_ID%3A2005671&TID=100&TID=100&productId=2005671&catalogId=10101

they are ok imo but just not quiet what i like as far as capacity of fuel flow but they will get the job done for a stock 6.2

you will notice that the slight knocking goes away after a few minutes as fuel line pressure builds it is perfectly normal for these pumps and not a alarmable condition its when you dont here this tapping on start up that you may have a problem