97 Blazer No Crank No Start
 

97 Blazer 4wd, 211k, had it around 3 months, some rust on the chassis, body in ok shape, interior in good shape, has been driving and shifting great.

Step-son was pulling up the driveway and the car just died, he coasted the last few feet and stopped, when you turn the ignition key all the dash lights and dials come on, various relays click in the glovebox and I hear a whining noise, which I assuming is the fuel pump, when you turn the key to start/run everything goes out and there is nothing, no noises etc.

The battery, alternator are good, and I do not see and "Security" light.

I have the following codes, which were not there before this issue

P719
P740
P753
P758
P1860

Having read that this may indicate a faulty ignition switch (a very common fault) and also seeing that the wiring to the switched has already been "got at", where somebody, by the look of it, has already spliced in a new ignition switch, I replace it with a new one, complete with loom, no splicing in this time, however it has not fixed the issue.

Since replacing the ignition switch and wiring, clearing the codes, and turning the key multiple times, the fault codes have not reappeared.

Any help appreciated.

Ok, I pulled he starter relay and took a few voltage readings.

Red wire - constant 12v, when turning key to run, constant 12v
Purple wire to solenoid - no voltage when turning key to run, I believe I SHOULD have voltage here when turning he key to run
Yellow wire to ignition sw/neutral safety - no voltage when turning key to run, I believe I SHOULD have voltage here when turning he key to run

There is also a grey wire but I cannot find any info on this.

I was wondering if it is the neutral safety switch?

If I remember correctly, the yellow wire to the starter relay should only get power when the key is turned to the "start" position- not "run".

I believe the yellow wire signals the relay to give power to the purple wire- and the purple is the "signal" wire for the starter relay.

I would start by testing the yellow wire for power with the key turned all the way to start. If you do have power I would follow up by putting power directly to the purple wire, and seeing if your starter engages. If it does not you have isolated your issue, and know the problem is either in the purple wire or the starter/solenoid.

This is the electrical path for the starter circuit:

Energize:

Hot>20A fuse>orange>connector>red>ignition switch>start position, not run>yellow>crank fuse 10A>purple>park/neutral switch>purple/white>starter relay coil>black>ground

Starter power:

Battery>red>battery fuse 175A>red>ignition A fuse 40A>start relay contacts>purple (energize and start power)>starter/solenoid

George

I usually diagnose from the load back:

What is the voltage on the purple power wire at the starter with the ignition key turned to start?

What is the voltage on the relay coil (85)/purple/white wire with ign sw to start? what is the voltage at the power input to the start relay contacts (30)/red both before start command and during start command?

What is the voltage during start on the purple wire/input to park switch?

What is the voltage during srart at the yellow wire leaving the ign switch?

Voltage at the red wire into the ign sw before and during start?

Voltage on the orange wire leaving the ign fuse before and during start?

George

I've gone ahead and replaced the neutral safety switch, it looked in bad shape, covered in dirt, oil and rust, still have the same issue.

The relay has 4 wires, red, purple, yellow and grey.

Thanks for the tips, I took some voltage measurements at the yellow wire to the starter relay, even in start or run I get 0 volts.

What is the voltage on the purple power wire at the starter with the ignition key turned to start? Still getting to that one

What is the voltage on the relay coil (85)/purple/white wire with ign sw to start? what is the voltage at the power input to the start relay contacts (30)/red both before start command and during start command? Red wire at relay has 12V, there is no purple/white wire, but the solid purple has 0V.

What is the voltage during start on the purple wire/input to park switch? Still getting to that one

What is the voltage during srart at the yellow wire leaving the ign switch? 0V

Voltage at the red wire into the ign sw before and during start? 0V

Voltage on the orange wire leaving the ign fuse before and during start? Still getting to that one.

I'll up date the other voltages after I've got the car up on the stands


https://cimg0.ibsrv.net/gimg/blazerf...1ed2782ebc.jpg

97 Chevy Blazer starter relay

I would check voltage to both sides of the "crank" fuse as George suggested. Make sure both sides are getting full voltage- this way you rule out a faulty fuse. If you don't have voltage at either side- it would seem to me the issue is either behind the fuse panel or possibly a fault in the new ignition switch wiring. Another thing I would check is the ground wires that go to the back of the driver's side head. One of these is the ground for the starter circuit, and a bad connection would cause a no crank situation

Where is he 'crank' fuse located? Is it in the fuse box?

Ok, I found it, 10A labelled 'crank'!

0v at run, goes to 12v when trying to start.

both sides of the fuse are at 12v when trying to start?