How do you set the timing on a 1991 Nissan pickup truck 2.4 L 4cyclinder D 21

There is no capacitor on that electric motor. They are not well made and have to be replaced. http://www.autopartswarehouse.com/shop_years/nissan-d21-blower-motor-1991.html

Try this site: http://www.2carpros.com/diagrams/nissan/pickup/1991

It is definitely mechanical - you are going to need to open up engine until you find a problem - focus on the timing chain

1991 Nissan/Datsun Truck D21 Truck 2WD 3.0L FI 6cyl

The Ignition Timing
15 Degrees Before top dead center*Warm idle speed 750 RPM*Transmission in neutral (Parking brake engaged)*All accessories off.

1991 Nissan/Datsun Truck D21 Truck 2WD 2.4L FI 4cyl

The Ignition Timing
10 Degrees Before top dead center*Warm idle speed 800 RPM*Transmission in neutral (Parking brake engaged)*All accessories off.

Your best bet,is to search the local junk yards.

it would have a belt

Here's a link on timing.http://www.autozone.com/autozone/repairinfo/repairguide/repairGuideContent.jsp?pageId=0900c1528018ceab

steering box, steering rack and pinion set

your stater is out

sounds like you have loose tapits or maybe a loose or worn timing chain