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1991 Chevy Silverado Engine remains running in off position

Tiny
GHOSLEY
  • MEMBER
  • 1991 CHEVROLET SILVERADO
Electrical problem
1991 Chevy Silverado V8 Four Wheel Drive Manual

Ok, this has been killing me all week. I am able to start the engine no issue the problem starts when I go to turn the engine off, all instruments are killed but the engine remains running. The ignition switch is completely functional (i have replaced it twice to ensure this!) The ECM/ECU has also been replaced prior to this problem. I tried pulling fuses under the dash to see if I can trace what is backfeeding the ignition and found that the ecm fuse is receiving power when engine is on and ignition is off, this pwoer is killed however when the engine is off. The only way to kill the engine is to pull this ecm fuse or to stall it out via clutch. I tried locating electrical diagrams to trace the ecm power supply but have come up empty handed. Does anyone have any advice! I'm running outta ideas. I have heard advice that there is a ignition diode of some sort to direct the flow of power to the coils and that this maybe backfeeding the engine as well. I have been unable to locate or support this advice.
Thanks!
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Sunday, November 1st, 2009 AT 3:45 PM

8 Replies

Tiny
IMPALASS
  • MECHANIC
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Hello -

To better assist you please be more specific on your model... Is it a C1500, or C2500 and what is the engine size in liter.
Also..... What was the reason you changed the ignition switch to start with... Because it would not shut off?
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Monday, November 2nd, 2009 AT 10:28 PM
Tiny
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Sorry about that! Should have beeen more descriptive. It is a k1500 z71 350/5.7
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Tuesday, November 3rd, 2009 AT 9:24 AM
Tiny
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Hello -

Not a problem. . .. . .thanks for the info. . .. . .. . ...

Okay. . .. . ...I searched through about 250 TSBs and didn't see anything in there that may relate.

The other item. . .. . .. . .you forgot to answer what was the reason you changed the ignition switch to start with. . .. . ...was it because it wouldn't shut off or another reason and now it won't shut off?

For now - the biggest thing we see for this is the linkage on the switch is out. . .. . .. . .you can test for sure by turning the key off and then moving the linkage. If it shuts off. . .. . ...then that is your problem.

I have attached the procedures for removal and installation and it does talk about ensuring the actuating rod is aligned with ignition switch.

IGNITION SWITCH

NOTE: It is not necessary to remove steering wheel. Ignition switch is mounted on top of steering column, near front of dash.

Removal

1. Remove steering column-to-dash panel bracket. Lower steering column. Remove ignition switch retaining screws. Place ignition switch lock cylinder in LOCK position.

2. If cylinder lock was removed, the actuating rod to the switch should be pulled up until there is a definite stop, then moved down one detent, which is the LOCK position. Disconnect electrical harness connectors. Remove ignition switch assembly. See Fig. 1.

NOTE: Use only specified screws. Using screws that are too long may prevent column from compressing under impact.

Fig. 1: Identifying Column Switches
Courtesy of GENERAL MOTORS CORP.


http://www.2carpros.com/forum/automotive_pictures/248015_1_187.jpg



Installation

Place ignition switch in LOCK position. See Fig. 2. Install ignition switch. Ensure actuating rod is aligned with ignition switch. To complete installation, reverse removal procedure.

Fig. 2: Identifying Ignition Switch LOCK Position
Courtesy of GENERAL MOTORS CORP.


http://www.2carpros.com/forum/automotive_pictures/248015_2_123.jpg


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Tuesday, November 3rd, 2009 AT 5:04 PM
Tiny
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Hello -

Also, it looks like you may have some recalls on your vehicle. The dealer may fix these for free. Please contact the dealer service department, give them the VIN number of your car and have them check on these to see if they apply to you.


http://www.2carpros.com/forum/automotive_pictures/248015_recalls_8.jpg


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Tuesday, November 3rd, 2009 AT 5:08 PM
Tiny
GHOSLEY
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Thanks for the info. I had previously replaced the ignition switch while attempting to pinpoint a failure with the fuel pump not running. After several replaced parts I figured out the problem was the oil pressure sending unit. That took place about a year ago. Since then I have been experiencing an issue with getting the engine to turn over that was getting progressivly worse until it finally wouldnt start at all. Last week I fixed this issue by replacing the ECM. But with the soultion of that problem came this one. I have made sure of the ignition linkage, even with the colmn apart and using a small punch to manipulate the ignition switch into the on/off/acc it will not shut off, there is a clear response to this however with the turning on and off of lights and AC. I was workin on it today again trying to pinpoint where the backflow of power is coming and im still at a loss.
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Tuesday, November 3rd, 2009 AT 8:53 PM
Tiny
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Hello -

Well... This may sound crazy but I have had one customer that the alternator was causing the problem. The diodes.........

I would certainly hate for you to spend the cash and swap it and still have the problem... But you are getting power feeding back....... That comes from the alternator/battery.....

Now I guess it could also be a relay stuck..... But my manual doesn't have info on the relays for some reason..... Or even a diagram of the fuses.......

See what you think about this..... Normally with the engine running if you disconnect the battery the engine should still run..... Because of the alternator. Now I have never done the other way..... But if the alternator was disconnected it should also still run from the battery. Now what if you disconnect the battery..... See if it still runs..... Then turn the ignition off and see if it shuts off. Then do the same with the alternator..... That is if it runs with the alternator disconnected..... Then you turn the key off and see if it shuts off. Your thoughts on this?

Also..... You could still go to Auto Zone and they can bring their tester out and check your battery and alternator for output.......

Again, your thoughts on this? If I need to I can contact another moderator for more input. What would you like
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Tuesday, November 3rd, 2009 AT 10:21 PM
Tiny
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I was finally able to give this a try. But unfortunately it just keeps on runnin. Only when I disconnected both the alt and battery does it shut off. Any other ideas? I'm going to see if I can find any wiring diagrams for it.
Thanks!
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Saturday, November 7th, 2009 AT 9:00 AM
Tiny
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Hello -

Here is the only info I have on this. . .. . ...the manual doesn't seem to give out too much on this vehicle for some reason.

My other thought is go to Auto Zone (AZ) or O'Reilly's (OR) and for FREE they can bring their tester out and check your battery and alternator. I am interested to see if your alternator is putting out anything odd.


http://www.2carpros.com/forum/automotive_pictures/248015_Picture1_98.jpg




http://www.2carpros.com/forum/automotive_pictures/248015_Picture2_63.jpg


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Saturday, November 7th, 2009 AT 8:45 PM

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