Vehicle is a1999 chevy blazer 4.3L v6 four door.
A couple of weeks back my blazer died on the side of the road - turned it off and couldn't restart it, but it did turn over. But I had no prime action from the pump.
no security light, no relevant engine codes.

now I'm going to fast forward a few weeks and list the tests ive done. I removed, inspected and repaired the entire electrical harness running from the fuse box to the tail lights, verified power at pump and at the relay, verified the relay works, verified the pump works, verified all fuses in both fuse boxes. I've swapped the ECM in and out with a spare to no avail. I've also replaced the NSS.

At this point I decided that it must be the ignition switch, the vehicle still wouldn't start, nore would it prime.

While replacing the ignition switch, I removed an old remote-start module installed previously. This required me to cut some wires from the remote start, which the model's manual identified as follows ;

Yellow - parking break lights + ( spliced into light blue wire from DRL cluster)
Red - 12v valet switch (ran to switch)
Orange - brake light (spliced into white wire leading to A1 pin, which is stop lamp)
white - N/A
Grey - N/A
violet - negative side Ignition coil (spliced to solid white wire on ignition coil)
black - ground (spliced to ground on harness)


Now after removing the remote start and installing the new ignition switch - I'm left with several unattached wires. The yellow one from the DRL parking light wire and the purple/ violet wire that runs to the starter. This shouldnt be relevant info, except after installing the new switch - It wouldn't crank, nore was the fuel pump priming (the issue the new switch was supposed to fix) - I verified that the ignition switch was in the correct position.

Today I tried just jumping the fuel pump and starter with some wires and it ran fine. After having it run for a moment and killing it again, I found the fuel pump prime sequence began working just fine (primes when key is turned) but I still can't crank. EDIT: fuel pump prime stopped again, jumped it into running again gave the fuel pump plug a wiggle while it was running and it died. I lost that plastic retaining pin for the saftey clip, thought the regular clips would hold it tight enough but I guess not - clearly a loose connection that needs to be fixed, can't verify the prime sequence is going off 100% until I fix this.

So that means the only standing issue now is whatever is going on in the ignition that is preventing me from cranking. Thus why that purple ignition coil wire makes me curious.
I'm also suspicious of the passlock system, but to my understanding doesnt it only cut fuel after the vehicle starts? I've also got no security light on, though I recall it being on all the time prior to breaking down (that means it's disabled right?) - I've attempted the relearn procedure regardless and haven't had any luck.

I've got the pin-out guide for the ignition harness, I've got the wiring guide for the remote start I removed, and ive got several circuit diagrams for the ignition- but I'm not certain how to proceed with diagnosis. To my understanding everything should be working right now.

I tried finding the circuit diagram for the Ignition Coil Control module so I could learn what that white wire is - but I didn't have much luck.

Would appreciate any advice or next steps anyone could offer.

 

I will be glad to help you but we need the year and model of your Blazer.

George

 

it's a 1999 chevy trailblazer.

 

Turn the ignition to the start position, hold it there and see if you have 12v coming into the crank fuse in the UHFB.


George

 

Measured the crank fuse and got nothing. Took the liberty to also measure a few more things while I was at it.

Measured the voltage between the red B1 battery output and the yellow d1 ignition switch output - finding 12v in all key positions.

Ive gone and tested the voltage between d3 magnetic rotation sensor and red B1 finding a value of 7-ish volts dropping 1.2-1.7 ish volts down to 6.5 when the key is rotated through

Measured the voltage between the red white d2 ignition switch output and the yellow d1 and found 12v through all positions of the key.

Measured the voltage between white c1 ignition switch output and red B1 finding 12v with the key off and 0v in the start position.

Also I ordered a new clip for the fuel pump plug, taped it in temporarily. Now the fuel pump prime sequence is firing just fine.

 

So I didn't think it was relevant- but after finding this schematic I want to be sure.... it shows part of the crank fuse circuit running to the transfercase.

I towed the vehicle home a with a friend about 6km, having disconnected thedrive shaft and leaving the vehicle in neutral in 2x mode.

I made the assumption that the transfer case wouldn't experience any movement, was I wrong?

 

“Measured the voltage between the red B1 battery output and the yellow d1 ignition switch output - finding 12v in all key positions. ”

All voltage measurements for now are between the test point and battery ground, not between two test points. So next put the ignition switch in the start position and measure the voltage on the yellow crank wire output in the ignition switch harness with the black meter lead on battery ground. I am going to assume that you have proper power coming into the ignition switch because you said when you turn the switch to the on position you get fuel pump priming. If you have 12 V on the yellow lead coming out of the ignition switch in the crank position then there’s a break in the circuit from that point to the yellow wire coming into the crank fuse in the under hood fuse block, which is what I suspect. your aftermarket box has a crank interupt loop so that wire was probably cut and needs to be reconnected properly. If you do not have 12 V on that yellow wire from the ignition switch and you’re confident that you have proper power into the ignition switch then the new ignition switch is faulty , we have to concentrate on this part of your problem because we can’t diagnose everything else until the truck will crank

 

Well I've just gone ahead and re-installed the old ignition switch and temporarily taped the remote start wires I cut back together. Now everything is working fine and the truck starts with no issue. Although, I still don't trust the old ignition switch. So tomorrow I will put the new one back in and continue with your recommendation.

During my initial work on this repair, I did find some damaged wires leading to the fuel pump. I repaired them and re-installed the harness, only to find I still wasn't getting any priming action. Ofcourse, now that I know just how loose that plug sits without the retaining pin - it could've just been been the plug not being seated while I ran all over testing things and came to the false conclusion that the only thing it could be was the ignition switch.

nonetheless tomorrow I will swap the new one back in and test things properly. I'm curious as to this interrupt loop you were talking about, what would I be looking for to identify it?


EDIT: on my way out the door here I just unplugged everything on the remote start box and gave it a go - sure enough it started up just fine. Clearly the wires I cut don't matter and there isn't a short, because with the remote start removed the old switch and the new switch should be identical....yeah just checked it, matches pin for pin.

Decent possibility of the new switch being dead as you mentioned.

 

The next time you don’t get any fuel pump prime crawl under the truck and look and see if you get two seconds of 12 V on the hot wire and the harness because if you do then it’s the connector or the pump if you don’t it’s got nothing to do with the connector of the pump And then we work our way backwards toward the ignition switch. It’s dealers choice. You can either do try gnostics with the parts cannon or we can use meters and logic to trace down where the fault is I’ll go whichever way you want.

George

 

14 gauge Violet and pin 11 on your starter loop.

George