Timing a 93 sonoma

[grif44]

I have a 93 4.3L tbi Sonoma. I had it tuned up... but then my distributor went out. I put a new one in myself, but every time I re time it, my gas mileage goes down... I'm down to 13.8mpg... which is way lower than what I was at before (18-21mpg) I could use a little help with the process of timing my truck... like how to disable the auto advance and what all the marks mean. Thanks

[Fox_Rocks]

ok, where to start.....first off, you need to find out what your base timing is. look on the sticker under the hood, one of them will say something along the lines of "0 degrees, transmission in park" anyways once you find your base timing go into the truck on the passenger side and look down where your feet would normally go, there will be a brown or tan colored wire with a black tracer...you should se a plug on that wire....unplug it. (this is called a "spout" connector, it's how the computer advances your timing for you) ok now....hook up your timing light to the #1 cylinder and point it down at your harmonic balancer (the wheel on the front of your crankshaft) it will have two different notches in it, but you will only see one (sometimes a good idea to mark it with nailpolish or white-out) ok so now you will see what looks like a mountain range beside your notch (this is a steel plate with those marks on it you were asking about) the way these work is....the first mountain bottom is 0 degrees, the first mountain top is 2 degrees, and the second mountain bottom is 3 degrees, and so on all the way up to i think 10 degrees or so....ok so your base timing is likely 0 degrees so you want to turn your distributor until you get the notch beside the 0 degree mark (or whatever your timing is) now tighten your distributor down and re-check it to make sure it didn't move on ya....now go hook up your spout connector and start it up ( i forgot to mention that you should have the truck shut off when you either unhook or hook up the spout connector) You should be done now. Sometimes you can advance the timing a bit for performance but you will definitly know when you went to far, your truck will run like a bag 'o' crap. I hope this helped and your not asleep from my long winded answer, i tend to go into too much detail sometimes....ok let me know if that helped, e-mail me if you like....i'm normally in the Chevrolet S-10 area. Peace.