1996 GMC sierra 1500. It backfires when....

SOURCE: runs rough too rich replaced oxy. sencer

That may help. Also check for fouled plugs. Also check the fuel pressure regulator on fuel rail, check for vacuum at the regulator.

SOURCE: Please Help Its All We Havw. 1996 GMC sierra 1500. It backfires when....

First, check your firing order. Then check the routing of the plug wires. Those that are twisted around each other need to be untwisted. You may have a condition of cross fire which can have a couple sources. The wires that run parallel to each other for any distance must cross once only. Also make sure plug boots are fully seated on plugs, and the distributor connenctions are fully down.

At night, start the vehicle up and in the dark using care around the fan, look for arcing at the plugs, at the wires themselves and across towers on the distributor. Even new wires can be leaky to high voltage. Watch for glow in the vicinity of any corner or edge.

If vavle train is noisy, resetting valve lash will quiet it down some and may alleviate some of the backfiring too. it entails warming up the engine, removing the valve covers/rocker covers, covering the push rod ends with foil, and with engine operating, backing the nut on each each rocker one at a time, until a clatter is heard, then in 1//4 turn increments, pausing at each increment to let engine stabilize, until the nut is 1 turn tight past clatter.

If the issue of backfiring is a bent valve or burned valve this may help isolate that valve as well as any popping at idle will coincide with the clatter of that particular valve.

If you have the air pump, don't ovelook that as a source of the noise too. Look to see if the back side of the valve at the back of the engine on the distribution piping has rusted out.