I have a 97 Blazer 4X4 with a 4.3. when I turn the key to the on position the #5 fuse(ENG-1) blows and then I get a P0340.
Now, to let you all know I had to replace my ignition switch 2 days ago, I took the ignition switch out of my 95 Jimmy and they were identical. prier to switching out the ignition switches this never happened. does any one know I can start look. I have all ready checked the ignition switch harness and it seems to be tight (the one with the center screw)

 

There are differences in the schematics as well as the inner workings of the switch. It looks like the ENG fuse is not really wired any differently though, but the TRANS fuse is different according to the schematics I have which has the PNK/WHT wire at location C1 from the ignition switch being powered only in RUN on the '97 ignition switch while the '95 switch has this pin location as a WHT wire powered in RUN, BULB TEST, and START.

Since the ENG fuse is after the switch, I wouldn't think that a problem with the switch would cause the fuse to blow...

 

would you be able to post the schematics so i could see what is going on.

would there be any way to cut and splice the wires to make this work, my wife needs the truck for work and with Christmas here i don't have the money right now for a new switch.

 

The difference is inside the switch, not in the wiring. The switch itself is a set of contacts that are open/closed based on the position of a cam disc with different ramps on it. The ramps raise/lower pins that move the arms that the contacts are fixed to. You can see this in the pictures located in the ignition switch link in my signature.

I'm not sure that this is the source of your problem, but you could try opening up the old switch and cleaning the contacts, then reinstalling it.

As far as the schematics go... I just pulled them up to look at them and didn't save them. I do not currently have the time to get at them again, but may later.

 

OK i put my old ignition switch back in after cleaning all the connects inside and out and it's working but I'm still blowing the #5(ENG-1) fuse and I'm going to assume that's is why I'm getting the p0340 code. can someone please help me with this, I'm at my wits end and don't know what to do now.

 

You now have to find out why the ENG fuse is blowing. Electrical faults are rarely easy to find and take patience to diagnose.

The ENG fuse powers the following items:

• EVAP Vent Solenoid
• EVAP Purge Solenoid
• MAF (mass air flow) Sensor
• PCM (powertrain control module)
• B1S1, B2S1, B1S2, & B1S3 Heated O2 Sensors
• CMP (camshaft position) Sensor
• EGR (exhaust gas recirculation) Valve

There could be a fault in any one of those items as well as any of the wiring between the fuse and each item.

Everything branches off of one main splice pack S107 which is in the engine harness near the right rear of the engine compartment near the evaporator housing for the HVAC. The B2S1, B1S2, & B1S3 HO2 sensors branch off again at the splice pack S317 which is near the right frame rail and I believe it is accessible from under the truck.

 

your diagrams are just amazing, very easy to understand, thank god.
the next question just might tick you off a bit, but, what am i looking for? if the fuse is blown i can't check for power(not even sure if there supposed to be power). I've never track down an a electrical problem before and not to sure how to do it, and what to look for, needless for say some of the parts you mentioned.

 

Basic troubleshooting (without getting too in depth or using a multimeter) starts by disconnecting everything on that circuit and then putting in a new properly sized fuse. If the fuse still blows, you know you have a short in the wiring. If it doesn't you can measure the amperage across the fuse location with a multimeter. If you have zero amp draw, then the circuits are intact and it is one or more of the components on the circuit that is causing the excessive draw.

A short in the wiring is a bad thing to have as it will be VERY difficult to narrow down short of putting a larger fuse into the fuse block and looking for the smoke!

 

OK I'll try what have said. if i have a short then does that mean i have a bare wire somewhere touching metal

 

touching a ground point of sorts but simple answer is yes.

IF you manage to find the wire short it's not too difficult to repair atleast - splice in a new piece and use soldier & heat shrink wire wrap/tubing to protect the exposed wire from shorting and moisture.