Hello. I have a 2004 chevy blazer with the 4.3l vortec v6. It has a strange and quite annoying problem that ive been trying to research and find a solution for, all in vain as nothing has been able to fix it. The problem is that it sometimes doesn't start, and ill explain it. Sometimes, ill turn the key, and all of the electronics turn on and everything works, but the starter does not crank over, like its not getting power, and this is annoying because there seems to be 0 indication and 0 reason as to when it will or will not start. When it does start and crank over perfectly, nothing seems to be wrong with the vehicle.

I have replaced the battery, alternator, starter, neutral safety switch, ignition control module, the wire leads to the starter, the ignition lock cylinder. I've looked into the security systems on the vehicle. I've checked all of the fuses and relays I can find on the vehicle. I've taken out the BCM and looked at it, and all of the contacts looked absolutely pristine with no indication of corrosion. I've checked every single possible thing I can think of that it can be.

The only real pattern I can see with it is sometimes when its colder outside, it will start, and when its fairly warm or hot outside, it won't start. But its completely random and it could be just coincidence. Sometimes when it does start and ill let it run for 10 or 15 minutes and shut it off, it won't start back up right after running. It's very frustrating and ive tried almost every solution I can think of and find online. So im posting here for answers and solutions. Hopefully theres someone smarter than me on here that can maybe provide something I haven't tried yet or a solution to all of this.

 

You have two choices. Either travel with a digital test meter and be prepared to find the break in the circuit or use the parts cannon some more. The challenge with a no crank diagnosis is that you either need to have two people available or get creative on hooking up the meter so that you can see the reading while in the truck turning the ignition key to the start position. The problem with the parts cannon is unnecessary expense and it could be wiring and not parts at all. I’ll give you 2 options:

A proper diagnosis is my jam. The next time this happens, remove the crank fuse and measure the voltage of each open contact with reference to battery ground while the ignition switch is in the start position. If you have 12v then the ignition switch is probably ok. I say probably because that voltage may not hold up under the load of the relay coil due to wiring or a marginal ignition switch. Well save that for later if we need to. Depending on the result then we measure more voltage points.

You have not yet replaced the ignition switch assembly or the start relay. If trynostics is your thing then I would start with the start relay because it’s cheaper and easier. Also, this sounds heat related and I’m betting on the relay over the ignition switch since it’s in the engine compartment. Again, parts swapping will not find a wiring problem

Which ever route you go, inspect the large black power cable from the battery to the starter.

Report back and we’ll get you fixed up.


George

 

Ok update. I actually had it towed off to a friend who’s a mechanic. Together we tracked the starter and ground cables and replaced both of them. We also did the ignition switch, and the relay tested normal. However, we didn’t check the contacts as you recently asked me to try, which might be the next thing looked at, as it is still having the same issue.

 

It looks like you prefer parts swapping and that's cool but I try to answer these to help you and others who search and find these threads. There are 5 circuit elements that need to be in good shape to get your truck to crank:

• Battery. You need to be charged up to 12.6v, all connections clean and tight, good ground cable at the battery. If you suspect the battery, have it load tested to make sure it can hold the required voltage under the 100 amp load of the starter. Alternatively you can monitor the battery voltage during a start attempt to see how far it drops. Minimum is 9.7v but usually on these trucks its 10.5+V unless its really cold outside.
• Circuit C: That's the big fat black cable from the battery to the starter, make sure it clean and tight at both ends and not damaged
• Circuit A: This is the switching circuit that energizes the whole process. Battery power is routed through the Ign C fuse, then the ign switch, then the crank fuse, then the clutch or part/neutral switch then the start relay energizing coil then ground. It doesn't matter where you start to confirm 12v during a call for crank but I usually suggest pulling the crank fuse first because its easy to get to and you don't have to decipher relay pinouts or crawl under the truck. This tells you if its the ign switch/wiring/fuse or down the line. If 12v here then keep going.
• Circuit B: This is the power path for the voltage that is switched by the relay to energize the starter solenoid and bendix. Battery power through the mega fuse then Ign A fuse then the relay contacts then the ppl terminal on the starter. This also a reasonable place to start because if you have 12v on the starter ppl wire then circuits A and B are probably good. If not then test at each point for voltage: Ign A fuse, relay. Of course if there is no voltage on the starter ppl wire whith a call for crank then it can also be Circuit A in the section above
• Starter: If everything else checks out then its most likely the starter. You can have it tested or replace it.

If parts swapping is your thing then the order I would go is:

• Wiring inspection
• Fuses
• Battery
• Start relay
• Park/clutch switch
• Ignition switch
• Starter

George

 

Ok. I'm back after a while. Sorry for the super super late response, but I kind of figured it out, kind of didn't, but I can get it to start. For people looking for a quick solution, I have one thing you could try. What we did was locate the relay specific to the starter, and we actually took the cap off of the relay and pinched it together after the key was put in and turned, and it would turn over the starter and start the vehicle, every single time. The simple fix for me then was to just bypass whatever part was bad and run a push button starter and it seems to do the trick. As for what part was bad, I still don't know to be honest. But for now, this seems to do the trick and fix the issue. Definitely learned that relay trick and it seems to be very useful.

 

Glad your back on the road.


George