intermittent backfiring (I'm a dumbass!) FIXED!!

[Hubnut]

I am experiencing intermittent backfiring in my 1991 K5 with TBI 350. One minute I have great throttle response and can spin the tires on a dime, the next it spits and sputters. Comes and goes on each trip. I've changed the coil, ignition module, injectors (runs smoother now at idle), and the IAC. No vacuum leaks. Wires, rotor button and cap look okay. Could it be something as simple as a bad wire or cap?? Please HELP!

Figured out the problem. After changing the MAP sensor, IAP, injectors and coil, the popping/"backfiring" problem was old wires allowing arcing! What a dumbass. I could have saved about $250, time and aggravation I didn't need if I had started with the simple stuff first. Truck runs great but I can't clear the 33 code for the MAP sensor by disconnecting the battery. Suggestions?

 

[Stomis]

Fuel pressure regulator?

 

[dhcomp]

and can spin the tires on a dime

I call BS

But when does this happen? Off of idle? Under throttle? under large load? When warm, When cold?

 

[Hubnut]

Okay, bark the tires. Any time, but yes, more so under load. Backfiring sounds like it's happening in the intake manifold. Hard to tell. Kind of a POP, then it catches, then it POPS again. New problem.

 

[dhcomp]

Ignition is an easy place to start. I'd check cap (is it loose, mine was ), wires (old, crusty, broken?) , plugs (all wires attached?) .

Check the condition of the inside of your cap and rotor too.

 

[Hubnut]

Just went out to run it and the check engine light came on. Idle is variable now. Wonderful.

 

[4xcrazy]

sounds like the fuel pump is dying to me, sounds very similar to what mine did before it got worse, which it sounds like yours is, and then finally just wouldn't run right, threw an engine code, don't remember the code number, but it was the o2 sensor saying it was a lean burn condition.

 

[Hubnut]

Just checked the codes. It is showing 33 (MAP low voltage or low vacuum). Would this cause backfire like problems?