Need some directional help. 94 Full size Blazer, 4WD 5.7L FI OH V8. Drove for 20 minutes at 75mph, slowed down to 40 mph and started to backfired for 45 to 60 seconds. when pressing down on accelerator, no power and would back fire. What are the next steps to diagnose and what do i work on first?
Thanks

 

Is it igniting out the exhaust or backwards up the intake?

George

 

out the exhaust

 

That is usually associated with a rich condition: poor fuel delivery (carb/injectors) or unburned fuel (plugs, wires, distr, coil, ...). A backfire up the intake is usually timing.

I would start by looking at spark at the plugs (1" of strong blue regular spark) and then some spark plugs to see if they are fouled. Do you smell unburned gas? An exhaust restriction can also cause the loss of power.

George

 

Thank you for your help with this.
Do not smell unburned gas.
What do you recommend for Spark Plug - Brand - Part number?

 

I am not very familiar with your engine but most of our trucks do well with standard issue AC Delco ignition components, incl spark plugs. Sometimes if you try to get fancy the truck is not as happy.

George

 

Thank you George.

If anyone has a recommendation, please let me know.
Thanks
.