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General Site Info => General Discussion => Topic started by: pullmyefinger on October 29, 2018, 11:53:38 am

Title: 1985 GMC S15 2.8 Engine won's shut off
Post by: pullmyefinger on October 29, 2018, 11:53:38 am
I have replaced the ignition switch on this truck and the engine will not shut off.  I have to put it in gear and stall it, then turn the key off.  Everything does shut off in LOCK position.

My mechanic and I are at the point where he thinks something is supplying current to some part in the engine and that is why it keeps running.
He said start the truck, put it in Neutral, shut it off with the key and then go out and disconnect the inline fuse to the radiator fan.  No luck with that.

He mentioned the distributor, the starter, relays, etc.  He has taught me alot but I don't always understand what he means.

He said it was definitely not the key switch on the column.

What else do I look for, what else might be causing this...??  I don't know what most of you know so please don't assume that I am a mechanic in your replies.  I have learned quite a bit but it does take me time to understand some things.

I have found no burnt wires under the dash, I just am looking for ideas for what to check next.  I can use a voltmeter but am not an electrician.  Any Ideas/Help would be appreciated, this is past the point of a nuisance..

Thank you all...

Title: Re: 1985 GMC S15 2.8 Engine won's shut off
Post by: bd on October 29, 2018, 01:23:58 pm
I have replaced the ignition switch on this truck and the engine will not shut off.  I have to put it in gear and stall it, then turn the key off.  Everything does shut off in LOCK position.

In order to assist you, tell us a little more about this ^^^^.

Standard transmission?  Tilt or standard steering column?

Did you replace the "ignition switch" on the topside of the steering column under the dash or the "key lock cylinder" on the right side of the steering column below the steering wheel?

Did the problem begin before or after replacing the ignition switch?

Have you tried "adjusting" the ignition switch?

---------------------

See if the symptoms go away when you unplug the two-wire connector from the rear side of the alternator.
Title: Re: 1985 GMC S15 2.8 Engine won's shut off
Post by: Rapid Roy on October 29, 2018, 03:25:46 pm
Welcome
Title: Re: 1985 GMC S15 2.8 Engine won's shut off
Post by: VileZambonie on October 29, 2018, 04:45:35 pm
did you try pulling your finger?

Gauges or idiot lights? What happens when you unplug the two wire connector at the alternator? Does it shut off?
Title: Re: 1985 GMC S15 2.8 Engine won's shut off
Post by: Irish_Alley on October 30, 2018, 07:52:48 am
did you try pulling your finger?

lol took me a minute to see the reason for this.




Title: Re: 1985 GMC S15 2.8 Engine won's shut off
Post by: pullmyefinger on October 30, 2018, 09:37:17 am
Fixed column steering wheel, standard shift. 

Problem started before installing a new switch topside, not the lock cylinder. 

Only problem now is that it doesn't seem like the switch because both switches give the same result (old and new).  I understand that the new switch could be bad but I am not looking at that right now.

From what I know the positions in the lock cylinder that correspond to the slider clicks are Accessory, Lock, Off/Unlocked, On and Start (spring loaded, returns to On/Run position.  These seem ok and the panel lights and all that crap Seem right, but...  They only other thing I noticed was when I shut the truck off the alternator gauge "dips" (moves toward 0v.) for a fraction of a second and then goes back to charging and the motor keeps running.  Lately though the alternator goes close to overcharging most of the time (a week or two before the truck quit shutting off).

I will try unplugging the Alternator 2-wire relay and get back to you.
Title: Re: 1985 GMC S15 2.8 Engine won's shut off
Post by: pullmyefinger on October 30, 2018, 10:17:44 am
Yes, the truck did shut off when I pulled the 2-wire lead from the ALT..
Title: Re: 1985 GMC S15 2.8 Engine won's shut off
Post by: pullmyefinger on October 30, 2018, 10:35:01 am
did you try pulling your finger?

Gauges or idiot lights? What happens when you unplug the two wire connector at the alternator? Does it shut off?

Truck does shut off if i pull that connector..  Voltage regulator in alternator bad?
Title: Re: 1985 GMC S15 2.8 Engine won's shut off
Post by: bd on October 30, 2018, 01:15:54 pm
Replace the alternator.
Title: Re: 1985 GMC S15 2.8 Engine won's shut off
Post by: VileZambonie on October 30, 2018, 03:18:51 pm
Or if you're cheap https://www.ebay.com/itm/CHEVY-DELCO-ALTERNATOR-HARNESS-ANTI-FEEDBACK-DIODE-10SI-12SI-15SI-27SI-wire/201247906131?_trksid=p2047675.c100005.m1851&_trkparms=aid%3D222007%26algo%3DSIC.MBE%26ao%3D2%26asc%3D40778%26meid%3D871418155a3d4d3fa6c085ebfcf2233e%26pid%3D100005%26rk%3D1%26rkt%3D6%26sd%3D191103912421

Title: Re: 1985 GMC S15 2.8 Engine won's shut off
Post by: bd on October 30, 2018, 04:02:26 pm
The fact that there's an aftermarket patch harness available tells you how common the failure was....

For even less (~$1), install a 1N7007 or similar diode insulated with some heat shrink.  The only minor drawback introduced by the diode is it will prevent the red charge indicator from illuminating during a severe overvoltage event (runaway alternator) - a very uncommon type of failure.
Title: Re: 1985 GMC S15 2.8 Engine won's shut off
Post by: VileZambonie on October 30, 2018, 04:44:29 pm
Or if you're even cheaper than that!... Get out, unplug it and just tell people there's a special procedure needed to cool down the hyperdrive motivator.
Title: Re: 1985 GMC S15 2.8 Engine won's shut off
Post by: bd on October 30, 2018, 05:01:02 pm
Vile, you're forgetting that that works only if the positronic transducer is negatively engaged through the omichron mitigator.
Title: Re: 1985 GMC S15 2.8 Engine won's shut off
Post by: pullmyefinger on October 30, 2018, 05:51:09 pm
Y'inz are still using an omichron mitigator?  Those have been out of style since forever..lol

Thanks to BD, Zambonie and the rest of the group for your replies, I have to go fix the warp drive on my go cart..
Title: Re: 1985 GMC S15 2.8 Engine won's shut off
Post by: bd on October 30, 2018, 05:54:18 pm
 ;)
Title: Re: 1985 GMC S15 2.8 Engine won's shut off
Post by: pullmyefinger on October 30, 2018, 05:57:20 pm
Almost forgot, I pulled the 2-wire connector on the top of the alternator, not the charging line, etc on the back.  I don't know if that makes a difference or not.  my guess is the voltage regulator is kaput?
Title: Re: 1985 GMC S15 2.8 Engine won's shut off
Post by: pullmyefinger on November 01, 2018, 05:16:55 am
Does it make a difference if I pulled the black and red wire connector on the top of the alternator OR
the charging line in the back of the alternator???
Title: Re: 1985 GMC S15 2.8 Engine won's shut off
Post by: bd on November 01, 2018, 07:04:40 am
I pulled the 2-wire connector on the top of the alternator, not the charging line on the back.

Correct.
Title: Re: 1985 GMC S15 2.8 Engine won's shut off
Post by: JohnnyPopper on November 04, 2018, 06:30:33 pm
Ha! I think I heard Vile laugh all the way here!

So, I'm new here; is Vilezambonie always cranky?

BTW, What's an 'e' finger and why would you pull it?
Title: Re: 1985 GMC S15 2.8 Engine won's shut off
Post by: bd on November 04, 2018, 10:38:49 pm
Aaaahhhh!  The sound of cracking ice!

Actually, he's a very funny man and quite accomplished.  Where did you get the notion otherwise?   ???
Title: Re: 1985 GMC S15 2.8 Engine won's shut off
Post by: Irish_Alley on November 05, 2018, 02:38:18 am
also sarcasm is another one of our great gifts  ;)
(http://i.imgur.com/mHD1N0q.gif)
Title: Re: 1985 GMC S15 2.8 Engine won's shut off
Post by: JohnnyPopper on November 05, 2018, 03:39:39 pm
I can see he's quite accomplished and a valuable part of this brain trust.

Maybe just pull MY finger?  8)