Back firing out exhaust

[Justin Fleming]

Guys I just took in this 1988 k5. So I don't completely know the history, all original, 5.7, fuel injected. The problem is that it is backfiring out the exhaust. So I brought it up on number 1 compression, the rotor is pointing just about right at the coil stub where the wire boot plugs on. So I checked base timing and set to 4 degrees with the spark advanced wire unplugged. unhooked battery, plugged in spark advanced wire, check timing and it is about 25 degrees, rev the motor and it goes to about 30 degrees. so all this seems well. Truck back fires out exhaust during free rev, tried to drive it and the truck falls on its face and back fires more. The odd thing is sitting idle the truck just purrs like a kitten.

 

[4X4HIGH]

Why not start by putting the timing back where it belongs, zero?

 

[Justin Fleming]

because that did not fix the issue. I was at zero at first. It acts as if it needs more timing...

 

[Justin Fleming]

Any other ideas.... the map sensor cause this type of issue?

 

[Justin Fleming]

So originally I was fitting a back fire issue. Just got the truck so I don't know the history. I had it running but had no power and back fire issue. So I went a head and put all new plugs, wires, cap and rotor so I know I am starting fresh. Now the truck will not even start. I checked for spark from the coil and that seems to be working, I am getting fuel from the injectors and it would even try to fire. I even sprayed a little either in to see if it would at least try to fire. So what ever the issue was I believe it has now failed 100%.

Usually, spark, compression and fuel source it should at lest fire for a second....

Any ideas guys I am going crazy

 

[4X4HIGH]

Did you replace the ignition wires one at a time or did you remove them all at once? Chances are you either have the firing order incorrect or they are installed one or more terminals off.

 

[dremu]

I'm with Scott (he's my guru.)

Start with the simple stuff. Sensors aren't like to magically go bad, so look at what's changed, and get it back to where it was (even if that's running crappy.)

Also, if you're as forgetful as me, only ever take off one plug wire at once. Been there, done that.

-- A