Topic: Jeep Doesn't shut off when I turn the key to off

[BigCountry]

i mistyped. was reading a build on another site and had tbi running through my head. it's a 4.0l throttle body.

 

i'd guess it's a relay that's not disengaging (if it's not the ignition contact) from what you describe but it's a bit strange since you're saying that your gauges are active while doing this.

i also thought '91 was MPFI btw.

and the gauges are only active when they should be. when i turn the key to shut off, the gauges shut off while the engine continues to run.

[VA_YJ]

A few thoughts - I don't think it's the switch.  The switch is operated a metal rod that goes from the key cylinder to the switch.  The switch is spring loaded and will go to "off" if there is no pressure from the rod.  The timing between the key cylinder and switch can get out, but that would not explain the 15 second delay.  The springs in the switch could be weak, but I don't think that's likely.  The switch can be disassembled, cleaned, greased, and reassembled, but it requires "dash board diving".

I would check the ASD (automatic shut down) relay first.  If your horn works properly, you can swap these two relays and see what happens.  The ASD is designed to cut off the fuel and spark if you have a wreck, based no engine rotation (Crank Position Sensor input).  If you have a fuel pressure gauge, hook it up to the fuel rail and monitor pressure after you shut off the switch.  If the fuel pressure drops throughout the 15 second period, then you know the ignition circuit is causing the run on (power to the pump is being turned off).  Try this and let us know what you find.

[sharpxmen]

i am thinking on the same lines but he's got a TBI so not sure on the ASD (if he's got one).
With an MPFI 91-95 even if the ASD is stuck the engine would still shut off since the switched 12v line to the PCM (pin 9 on the connector, white/yellow wire) would turn off and there would be no spark or injector command from it (if the key contact is functioning properly). ASD is controlled by the PCM via pin 51 and would provide 12v to ignition coil and Fuel Injectors but the command for for spark is still controlled by the PCM via pin 19 as well as the injectors (pins 13 to 16) - once the ignition is turned off these pins would be inactive - but again, this is for MPFI so not sure if that is similar to the TBI he has.

good point on the fuel pressure, I would also put a light bulb on the ignition switched 12v from the key contact and see if that remains on after turning the key in the off position.

[VA_YJ]

Sharp is correct.  The ASD normally only comes into play once the engine stops spinning.  It is the only relay in the MPFI ignition circuit and easy to check.  When the ASD trips, the ECU kills the spark by interrupting the power to the coil.

I am ASSUMING that we are talking about a 1991 MPFI set up - hopefully that won't make an a$$ out of U and Me!  Big Country, please verify that you have four injectors in your intake manifold.

Did the problem start right after the electric fan install?  If yes, then check that wiring very carefully.

As far as reading the codes, make sure you have a scanner that is OBD I compatible.  This issue could also indicate a computer or wire harness problem.

Another thing to check is the 60 pin connector to the ECU (computer).  Make sure none of the pins are bent, touching or corroded.  Torque the connector bolt to 35 INCH pounds.  It is possible that you have a computer problem, but I would not investigate that possibility until you go over the circuits very carefully.

[sharpxmen]

Sharp is correct.  The ASD normally only comes into play once the engine stops spinning.  It is the only relay in the MPFI ignition circuit and easy to check.  When the ASD trips, the ECU kills the spark by interrupting the power to the coil.

I am ASSUMING that we are talking about a 1991 MPFI set up - hopefully that won't make an a$$ out of U and Me!  Big Country, please verify that you have four injectors in your intake manifold.

Did the problem start right after the electric fan install?  If yes, then check that wiring very carefully.

As far as reading the codes, make sure you have a scanner that is OBD I compatible.  This issue could also indicate a computer or wire harness problem.

Another thing to check is the 60 pin connector to the ECU (computer).  Make sure none of the pins are bent, touching or corroded.  Torque the connector bolt to 35 INCH pounds.  It is possible that you have a computer problem, but I would not investigate that possibility until you go over the circuits very carefully.

It's a TBI but a mistery why that's a '91 (page 1 of the thread)

nope. 91 is TBI. and the engine idles just like normal for like 15 seconds and then finally the rpms drop and it cuts off. when i shut it off, all my gauges cut off at the appropriate time of me turning the key. my voltmeter, tach and everything except the clock go to sleep.

[chardrc]

It's a TBI but a mistery why that's a '91 (page 1 of the thread)

per page 2

i mistyped. was reading a build on another site and had tbi running through my head. it's a 4.0l throttle body.

[sharpxmen]

per page 2

oops, i missed that  

EDIT: @BigCountry check if you have 12v on the white/yellow wire going to pin 9 of the PCM when turning the key off and the engine still running, if you do then that's your problem - report back - that is circuit G50 18ga white/yellow wire and is called "Fused Ignition Switch output" - this circuit also provides power to the ASD and Fuel pump relay on the coil side so that is another place you can check at to see if there is still voltage after turning the key off. this circuit comes from fuse 5 (another place you can check for voltage) and that is connected to the ignition switch on the other side, so there's no relay between the 2 circuits, just a fuse.

[BigCountry]

This is some good info guys. tomorrow i'll dive into it and see if it works. the problems did start immediately after the e-fan install. shop did it, i picked it up, when i got home and went to shut it off, had the issues. i was told by one shop they had to re-ground the computer, but that was after the problems started. it also broke off the firewall mount so it's dangling right now, held to the wall with 100mph tape.

[sharpxmen]

This is some good info guys. tomorrow i'll dive into it and see if it works. the problems did start immediately after the e-fan install. shop did it, i picked it up, when i got home and went to shut it off, had the issues. i was told by one shop they had to re-ground the computer, but that was after the problems started. it also broke off the firewall mount so it's dangling right now, held to the wall with 100mph tape.

hmm, i would look at how they wired the relay - sounds like somehow you're sending some voltage to the 12v "run" circuit (thinking what can be related to the e-fan install) although if that's the case i would ask for the money back from the shop that did the install