Tune-up

I drive a '90 3/4 ton chevrolet pickup. A couple of weeks ago I had trouble with my truck wanting to die (particularly at low rpm's). First, it seemed to do it after a lengthy two hour drive I make every other weekend home from school. Pull up to a stop light after getting of the highway at it would want to fall on its face. That went away for a while then it constistently would do it during its warm-up cycle in the morning. The truck would crank longer than usual to start. It would run fine for 15 to 20 seconds and then want to fall on its face. The computer at times sounded like it was trying to pick it up but would eventually die unless I feather the gas pedal and fought threw it. I would take off and the problem would mysteriously disappear. The other morning it acted up a little on the highway. There was a sudden loss of power which tripped an O2 sensor code. This lasted about 30 seconds. The darn thing took off again and the "service engine soon" light went off. Later that night I was stranded at work. It would start but I could keep it running when put in gear. Idles very rough and will back fire through the exhaust as well as the throttle body ocassionally. The fuel filter, distributer cap and rotor, ignition coil, plug and wires have all been replaced recently.
My dad and I believe the problem to be timing. I removed the serpentine belt to get a good feel of any backlash in the timing chain. While watching the rotor for movement I calculated about 6 to 8 degrees worth of back lash in the chain. The questions are...Does 6 to 8 degrees represent a problem? Can the computer compensate for this? Does this seem consistent with the problems that I have had in the past couple weeks?

I am not able to answer your exact questions, but I am able to give you a bit of advice. I was have VERY similar problems, replaced everything you did. Finally took my truck to a certified mechanic and he stripped everything. All my problems revolve around my computer. I replaced that that night. Unfortuneately I am still hurting some by having to replace all parts that my computer "infected." My advice is to get that checked while you are at it. It is better than being sorry later for not checking it earlier, like I am. Sorry I could not help you answer the questions that you had though.

It sounds like a fuel pump problem to me. with the long crank time, a bad pump will cause it to back fire also. need to have a pressure test done on it. hope this helps

6 to 8 degrees is a lot. you need a new timing chain and gear or gears. you didn't say how many miles you have on it, but i bet its a lot. after you fix timing chain. check your computer and make sure you don't have a code for your map sensor.