89 Silverado timing problems???

My friend has an 89 Silverado, 2 WD, Automatic. It was running rough and she took it to a mech(friend)...he replaced the distributor and it ran worse. I changed the plugs, wires, cap, rotor, all filters and fluids then retimed it, no difference. I got ahold of a scan tool and it threw some codes, everything from the O2 sensor, TPS you name it I have almost replaced it. Changed the timing chain and the coil. Scanned it again and it still reads O2 sensor. It is also throwing a Anit lock brakes code saying it is the vehicle speed sensor. It won't stay running on it's own, have to pump the gas, takes about 15 trys to start it, when it's cold it sounds like the engine is hunting rmp up and down...Can anyone help me with this, I would appeciate it.

is there a chance that the firing order is messed up? also could the cap be on backwards? was the distributor replaced in the correct place...that all effects timing too....sorry if you have checked all of that.

is there a chance that the firing order is messed up? also could the cap be on backwards? was the distributor replaced in the correct place...that all effects timing too....sorry if you have checked all of that.


I know what you mean, I thought the same things, I pulled the plug wires off, the cap and it only goes one way, the firing order is listed under the hood and the cylinder numbers are stamped on the manifold.

I even started from complete scratch by taking the No. 1 plug out and putting it to TDC and lining the rotor up with the coil contact.

Also tried putting the wires one contact point off on the cap. I am wondering if it might be the Fuel Pressure Regulator or the intake manifold gasket? I might be digging around in the wrong yard. I don't want to throw in the towel just yet.

Thanks for your reply.