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Old 06-19-2011, 09:50 PM
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Question Not cranking: starter, alternator... how can I tell?

my car stopped in the middle of the freeway 4 days ago and has refused to crank/start since.
It emits one loud/healthy "thud" when I turn the ignition key, but doesn't turn over and when I hold the key down, the dashboard lights turn off.
It's a 91 S10 4x4 Blazer with the 4.3L V6 engine.

I'm now trying to find out what's at fault... is it the starter motor? Or is the alternator shot? (It happened during a multi-hour continuous drive).

Do you know of a way how I could isolate the problem?
I was able to turn the frontal flywheel by hand about 15 degrees, so I think it's not the engine itself that is stuck.
It must be either the alternator or the starter.

But which of them could cause my engine to go out in the middle of the road?

Any help welcome...
Old 06-20-2011, 09:28 PM
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almost sounds like the big power wire going to the starter broke or grounded out. when you turn the key the smaller wire is still attached to the solenoid causing the starter to engage the flywheel just not turn it. if all your lights are working then doubtful it would be the alternator as the truck would probably be totally dead by now.

it may be normal for the dash lights to shut off when trying to crank the engine.

now you get the most generic answer... crawl under there and have a look. see if the wire came off or is nasty. its possible it could be the starter itself but start with the positive wire, heck even clean and tighten your battery cables you may get lucky
Old 06-23-2011, 10:35 PM
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Can you turn the engine any more than 15 degrees? I can turn my motor over and over by hand if i do it slowly. I bad starter wont kill an engine as its going down the road. If you cant turn it by hand the motor may be toast.

Get a multimeter and check the battery. Is it charged? What does the battery voltage do when you engage the starter?

Do some more dectective work before you start spending money.

Good luck
Old 06-23-2011, 10:39 PM
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check your crank fuse then check that cable on your starter . if those are good get a small hammer and bang on your starter a bit then try to start it
Old 06-27-2011, 02:30 PM
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Hey, so yes, after I removed the starter, I turned the super large gear (I think that's what you call the "flywheel", right?) and I was able to turn it all the way around... it took some time and force but it felt smooth, so I guess the engine isn't seized... motor still ok..! yay!

The batter was also charged well. After the tests I did on the starter motor it went down a little though.
Old 06-27-2011, 02:42 PM
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Default it's the starter... somehow... ?

First.. thanks to all of you who replied, it does help a lot to hear the opinion of people who have had some more experience with their trucks than me.

This is the result of my tests:

Battery and engine both seem fine.
(Battery had enough charge, I was able to turn motor over manually all the way with the big flywheel on the car's belly.)

So, on to the starter:
I removed the starter motor from the car to do some tests on it:
the solenoid came on, moving the gear into the window, but the motor did not rotate.
I looked into the contact assembly of the switch and found a heavily worn contact for the motor's power.
I was able to fix that by turning the contact 180 degrees so that it exposed a non-worn side to the switch:
After reassembling, the motor seemed to work fine... yay!

But this is the situation now:
I put the motor back in half way, so that it doesn't actually crank anything, it just runs being electrically connected to all its proper cables with an added handmade negative contact:
Everything worked (both solenoid and motor)

When I put it back in all the way however (so that the starter gear will get in contact with the engine flywheel etc.), the solenoid continued to work, but the starter motor would not turn the engine at all but appear to get stuck instead.
The solenoid produces the "thud" sound I am talking about in my original post, but the motor doesn't turn.
I verified this by listening, unfortunately I couldn't watch what exactly happens when I turn the ignition key.
It definitely does not crank. There is a very silent winy sound after the solenoid click.
So, it seems that something is still wrong with my starter motor itself.

So here are my current questions:
In my repair manual it said that there are some parts that come loose when the starter motor is removed - some things that needed to be put back in sequence when it is reassembled.
Well, I didn't get anything like that:
All I had to do was loosen the 2 bolts that hold the starter to the chassis and remove the 2 nuts that hold the electrical wiring on the contacts (btw, which are a total pain to both remove and reattach, completely unreachable..), then it just dropped down/came out.

Could my starter be missing pieces, or is it just too "weak" to turn the engine despite running fine when I test it separately?

My next step is to take the starter and go to an auto parts store for testing.
I'm sure they'll love to sell me a new one

Thanks again for helping me! It's somewhat fun to climb around down there fixing it, but I hope it'll all lead up to a happy end...

Last edited by lazer2000; 06-27-2011 at 03:18 PM.
Old 06-28-2011, 03:44 AM
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Glad to hear your getting your hands dirty! How did you verify the battery was good? Before you pull the starter again, I would make DARN sure the battery was fully charged. A bad alternator would allow the battery to go dead and cause the truck to die. Since the battery was dead the truck wont crank.

Did you try to jump start the truck or put a charger on the battery?

Good luck!
Old 06-28-2011, 04:05 AM
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I am having the EXACT same issue with my 94 blazer. I have not officially fixed the problem, however I was told that my engine could be hydro locked, Meaning that you could have a gasket that blew and allowed coolant to fill a cylinder. I had it occur after replacing my lower intake manifold. I was told to try removing the spark plugs then turn the motor over by hand to see if any liquid comes out of the spark plug hole(s) I have yet to pull my plugs as I am back to work for a few days. I will hopefully get to it on Wednesday and let you know what I find with mine, hopefully one of us can figure it out. * note * if you do get liquid out of the cylinder turn the motor over a few times to drain it all then put in new plugs and start the truck, if it starts turn it off and do an oil change before driving.
Old 06-29-2011, 01:05 AM
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@kristoph30 thanks for the encouragement and your input! I do appreciate it!
I admit I never ended up attaching a voltmeter to the battery.
I got another car attach cables jump-starting-style once and there was no difference at all, so I concluded the battery does not make a difference.... but that was before I turned the contact in the motor around, so I guess there is still a loophole how it all could be a problem of the battery and in turn the alternator.
So you're saying an alternator could kill the engine while it's running?
That would be a solution... everything else sounds like a weird coincidence of failures. (I was thinking e.g. starter motor+fuel filter or sth. like that).
There definitely was the contact problem in the starter, which is weird enough, but the motor definitely switches/spins the way it should.

I will try attaching another car's electricity to the truck again tomorrow morning.
Maybe it'll just crank... . .. finger's crossed, I'll keep you posted!

@lowrdsdime Thanks for sharing your experience!
I think "hydro-blocking" would not be out of the question for my engine either: Before my truck broke down, it did emit white smoke for about 1 second every time it got started up after being parked for a while: There was sometimes more of it, sometimes less, and sometimes none at all actually.
My theory about this was that there is indeed a bit of coolant leaking into one of the cylinders, the amount of smoke depending on how the machine comes to rest when it is turned off... how much space there is for coolant to accumulate.

But what makes me think that is not what stopped my engine and prevents the motor from cranking now is that I am able to turn it over manually without noticeable rough spots, and that the starter doesn't turn the machine over for some reason.
So I'm still keeping up hope the white smoke problem/coolant in cylinder is not the reason for the current failure.

Last edited by lazer2000; 06-29-2011 at 02:33 AM.
Old 06-29-2011, 09:18 AM
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Youre very welcome. I know a pat on the back feels good no matter who it comes from.

The one second of smoke you see each time on cold start-up is normal. A product of combustion is moisture. When you start the truck the exhaust system is cold and the moisture condenses. just like your breath on a cold morning. Once the exhaust system warms up the moisture stops condensing.

If your alternator failed, I wouldnt say it would "Kill" your motor. Technically you truck will run without it. BUT not long - just until the battery drained until there wasnt enough juice to run the fuel pump or fire the plugs. So a more accurate statement would be - The alternator will let your truck die - not kill it. Does that make sense? I hope so cuz Im still working on my first cup of coffee.

If your battery was weak, (They dont last forever) It may have been putting a higher than normal draw on the alternator. After a long time the alternator will fail from being overloaded. (If the alternator has been abused its life may have been shortened also.)

If your battery is weak it WILL activley KILL your starter! Following OHM's law (I will not try to explain it here - google it - still on first cup of coffee) Low voltage from the battery will result in high amperage in order to start the truck.
Voltage * ameperage = wattage (Work done)

In order for the same amount of work to get done, if the voltage drops the amperage goes up. High amperage kills motors by overheating the windings and causing excess arcing at the brushes and relay contacts. (Sound familiar?)

When you tested the starter out of the truck and it spun, it really wasnt doing much work. It was just spinning itself - not the motor.

Check the battery. Check it before you try to crank it, the check it while you try to crank the truck. It should drop a bit but not too much. I think 11 volts is the max it should drop to. if it drops below 10v, the battery is basically dead. If it doesnt drop at all, then you have a bad connections somewhere. Bad terminal, of cable or something along that line.

Grab your meter and have a great day. I really need another cup of coffee.
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