Hello and welcome to Just answer.com, Super mechanic here. About your vehicle.
Here is a picture of the marks.
The data base doesn't really show any 3.4 DOHC in 1999 for cars sold in the USA
However, here is what I have for the 3.4 DOHC from a 1998 GM yours should be just like it. Let me know if it's not, thanks
NOTE: GM does not provide a timing mark diagram for belt installation without using the special tool(s) listed below. For proper cam timing the use of tool J-38613-A is needed.
OH.....Let me get that for ya.
I will have to send you all the timing chain instructions for it. Might take a minute or two.
Revised Timing Chain, Sprocket, and Tensioner Removal Procedure Note: GM does not provide timing chain timing marks, or information to perform timing chain service without the special tools shown in this procedure. Tools Required:
Caution: Refer to Battery Disconnect Caution in Service Precautions.
Notice: Do NOT attempt to pry the sprocket off the camshaft or damage to the sprocket or chain housing could occur.
Important: The timing chain and the crankshaft sprocket must be marked prior to removal. If the chain or the crankshaft sprocket is installed with the wear pattern in the opposite direction, noise and increased wear may occur.
Notice: Use the correct fastener in the correct location. Replacement fasteners must be the correct part number for that application. Fasteners requiring replacement or fasteners requiring the use of thread locking compound or sealant are identified in the service procedure. Do not use paints, lubricants, or corrosion inhibitors on fasteners or fastener joint surfaces unless specified. These coatings affect fastener torque and joint clamping force and may damage the fastener. Use the correct tightening sequence and specifications when installing fasteners in order to avoid damage to parts and systems.
Important: Ensure that the camshaft sprocket alignment pins are in the cylinder block and the timing chain housing, prior to installing the timing chain housing. The camshaft sprocket alignment pins ensure proper chain housing and front cover location for correct front oil seat to crankshaft alignment.
Notice: Do NOT rotate the crankshaft clockwise to TDC. Valve or piston damage could occur.Important: The timing chain and crankshaft sprocket must be put in a specific direction for chain noise and wear considerations. The surfaces that were marked during removal should be showing when the chain and crankshaft sprocket are installed.
Important: Use the following steps in order to reset the timing chain tensioner assembly to the zero position:
Check the plunger to make sure that the plunger is out of the cylinder at the correct dimension. The correct dimension for the plunger to extend out of the cylinder is 1.7 mm ( 0.07 in ) maximum.
Notice: If the timing chain tensioner plunger is not released from the installation position, engine damage will occur when the engine is started.
Important: If the timing chain tensioner plunger cannot be depressed, the plunger is not properly reset and the procedure for resetting the timing chain tensioner should be repeated.
Notice: The timing chain on the engine is different from the chain found on earlier versions of this engine, and is not to be replaced with a timing chain from earlier model year engines. The timing sprockets were also changed and the shape of the chain links matches the sprockets. Engine damage may result if the wrong timing chain is used. The timing chain and the crankshaft sprocket must be marked so that they are reinstalled in the same side facing out at the time of assembly.