89 BJ74 with BT13 not shutting down!

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Blueegg

Blueegg

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Went for a drive in my 89 BJ 74 and the engine is not shutting down. Turning ignition off turns the electrical off but not the engine. Fuel cut off not working correctly. Need real-time advice on what to do!
 
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I was able to shut it down by cutting off the air intake at the air filter.
 
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13B-T engines have a weird system to shut down.. A vacuum switching valve will apply vacuum to a diaphragm, which will pull a lever and close a butterfly valve that will shut off the engine.

Some good tech with pictures of the components of this system on this thread.
forum.ih8mud.com

BJ74 just died on highway

forum.ih8mud.com forum.ih8mud.com

So, any one of several things could be wrong... not enough vacuum, possibly due to bad vacuum pump, or a bad brake or clutch booster, a bad vacuum line, or leaky vacuum storage tank, etc. Or, a bad Vacuum Switching Valve. Or a bad diaphragm. Or bad electrical connections to the vacuum switching valve. Or something mechanically wrong with the shut down butterfly. So many possibilities.

You can shut down by engine by dumping the clutch in 5th with the brake on (my preferred method). If you have any automatic, you can let it run out of fuel, or if your ar in a hurry, I suppose you could manually activate the diaphragm arm to close the butterfly valve.

This system can cause novice 13B-T owners many problems, and utterly stump non-13BT mechanics. It can cause various issues such as yours (Can't shut down), or other issues like "can't start the engine". Or the really frustrating one... engine shuts down when merging onto freeway. All are symptoms of this goofy system. The problems can come and go seemingly at random, and right in the middle of an otherwise peaceful drive. I've never seen a system like this on any other engine.

On one of my BJ74's, the whole system was bypassed by the frustrated previous owner unable to diagnose the issue, and he put in a pull cable to manual actuate the shutdown butterfly with a pull-lever on the dash.

Why can't they just have a fuel cut-off solenoid like a normal truck? sigh...
 
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Wow, lots of possibilities. I’m going from zero knowledge about this situation to knowing the basics. Great info!
 
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Behemoth60 said:
13B-T engines have a weird system to shut down.. A vacuum switching valve will apply vacuum to a diaphragm, which will pull a lever and close a butterfly valve that will shut off the engine.

Some good tech with pictures of the components of this system on this thread.
forum.ih8mud.com

BJ74 just died on highway

forum.ih8mud.com forum.ih8mud.com

So, any one of several things could be wrong... not enough vacuum, possibly due to bad vacuum pump, or a bad brake or clutch booster, a bad vacuum line, or leaky vacuum storage tank, etc. Or, a bad Vacuum Switching Valve. Or a bad diaphragm. Or bad electrical connections to the vacuum switching valve. Or something mechanically wrong with the shut down butterfly. So many possibilities.

You can shut down by engine by dumping the clutch in 5th with the brake on (my preferred method). If you have any automatic, you can let it run out of fuel, or if your ar in a hurry, I suppose you could manually activate the diaphragm arm to close the butterfly valve.

This system can cause novice 13B-T owners many problems, and utterly stump non-13BT mechanics. It can cause various issues such as yours (Can't shut down), or other issues like "can't start the engine". Or the really frustrating one... engine shuts down when merging onto freeway. All are symptoms of this goofy system. The problems can come and go seemingly at random, and right in the middle of an otherwise peaceful drive. I've never seen a system like this on any other engine.

On one of my BJ74's, the whole system was bypassed by the frustrated previous owner unable to diagnose the issue, and he put in a pull cable to manual actuate the shutdown butterfly with a pull-lever on the dash.

Why can't they just have a fuel cut-off solenoid like a normal truck? sigh...
Click to expand...

I’m getting the “merging on the freeway” shutdown. Pretty sure it’s the shutdown butterfly and nothing else.

If I really get on it, she closes off and nearly stalls the engine for a few seconds, no power, lots of smoke then boom back like nothing.


Not sure if it’s just that dash pot being weak or what but it’s annoying.
 
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FJBen said:
I’m getting the “merging on the freeway” shutdown. Pretty sure it’s the shutdown butterfly and nothing else.

If I really get on it, she closes off and nearly stalls the engine for a few seconds, no power, lots of smoke then boom back like nothing.


Not sure if it’s just that dash pot being weak or what but it’s annoying.
Click to expand...
There are TWO sources of vacuum to the shut-down butterfly diaphram that will shut down the engine.

Source 1 is expected. Vacuum from the vacuum pump, triggered by the vacuum switching valve when you turn the key off. 80% of the time, this is works 100% of the time.

Source 2 is very unexpected and sometimes unwelcome. At other times, quite appreciated. There is a vacuum line that starts between the air filter and the turbo intake. That line snakes around the front of the engine and connects to that aforementioned vacuum switching valve. However, this particular vacuum line is actually open to the butterfly valve actuator diaphragm. All the time. It is never switched by the vacuum switching valve. If that line experiences low enough pressure to actuate the diaphragm and close the butterfly valve, your engine will shut off. low pressure between air filter and turbo intake = engine shuts off.

The clever engineers at Toyota built this on purpose. It's a Hydro-lock avoidance feature to protect your engine from deep water crossings that dip your intake below water. If your intake goes below water, and your air box fills up with water, this will cause such a low pressure situation, and your engine will shut down before it can pull water through your turbo and into your engine. Awesome. Those jerks with hydro-locked 3B's can suck it. We 13B-T drivers cross rivers with confidence. I can tell you, the new ford bronco sure doesn't have anything as cool like that.

But the Toyota engineers of the 1980's were designing this strange system for a farmer navigating a flooded 2 track in the outback. Merging a vehicle that is essentially a glorified farm implement onto an interstate on-ramp was inconceivable. Yet here we are, 40 years later, and some of you have jacked up your turbo boost, and are unleashing your desperately rare and impossible-to-find-parts-for 13B-T into the hostile world of freeway traffic, and the antique engine is sucking as much air as it can through your dirty aftermarket air filter. If there is too much dirt, or your filter was never of a great quality to allow sufficient air flow in the first place, then you've got a low pressure situation between air filter and turbo, and off your engine switches, just before your shift into 4rd gear at the most inopportune time. Oh dear.

It saddens me somewhat that this is known as the "Freeway Problem", and not the 'Hydro-lock Avoidance Feature'. It tells me that to many of us are exposing such precious and collectable trucks to the indignity of freeway driving, rather than properly off roading through back country stream crossings where a BJ74 belongs. <Deep sigh>.
 
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Behemoth60 said:
There are TWO sources of vacuum to the shut-down butterfly diaphram that will shut down the engine.

Source 1 is expected. Vacuum from the vacuum pump, triggered by the vacuum switching valve when you turn the key off. 80% of the time, this is works 100% of the time.

Source 2 is very unexpected and sometimes unwelcome. At other times, quite appreciated. There is a vacuum line that starts between the air filter and the turbo intake. That line snakes around the front of the engine and connects to that aforementioned vacuum switching valve. However, this particular vacuum line is actually open to the butterfly valve actuator diaphragm. All the time. It is never switched by the vacuum switching valve. If that line experiences low enough pressure to actuate the diaphragm and close the butterfly valve, your engine will shut off. low pressure between air filter and turbo intake = engine shuts off.

The clever engineers at Toyota built this on purpose. It's a Hydro-lock avoidance feature to protect your engine from deep water crossings that dip your intake below water. If your intake goes below water, and your air box fills up with water, this will cause such a low pressure situation, and your engine will shut down before it can pull water through your turbo and into your engine. Awesome. Those jerks with hydro-locked 3B's can suck it. We 13B-T drivers cross rivers with confidence. I can tell you, the new ford bronco sure doesn't have anything as cool like that.

But the Toyota engineers of the 1980's were designing this strange system for a farmer navigating a flooded 2 track in the outback. Merging a vehicle that is essentially a glorified farm implement onto an interstate on-ramp was inconceivable. Yet here we are, 40 years later, and some of you have jacked up your turbo boost, and are unleashing your desperately rare and impossible-to-find-parts-for 13B-T into the hostile world of freeway traffic, and the antique engine is sucking as much air as it can through your dirty aftermarket air filter. If there is too much dirt, or your filter was never of a great quality to allow sufficient air flow in the first place, then you've got a low pressure situation between air filter and turbo, and off your engine switches, just before your shift into 4rd gear at the most inopportune time. Oh dear.

It saddens me somewhat that this is known as the "Freeway Problem", and not the 'Hydro-lock Avoidance Feature'. It tells me that to many of us are exposing such precious and collectable trucks to the indignity of freeway driving, rather than properly off roading through back country stream crossings where a BJ74 belongs. <Deep sigh>.
Click to expand...

Great info!

Thanks for making me feel guilty driving my rig… :flipoff2: I called it freeway, but really I live in The country and get on it for good measure occasionally. Shhhh, let’s keep my “interlanding” aka Starbucks runs secret…I’m really dragging bus loads of orphans over snowy mountain passes running away from guerrila forces that are trying to force them into the drug mule workforce.

So I have an OEM washable filter, should be very clean but I’ll clean it out anyway.

I do have that line, and it was disconnected when I changed turbos and intake to turbo piping and the issue didn’t happen.

Interestingly enough, this all started happening when I went to the OEM snorkel top. It didn’t do it with the safari ram top style. It also happened with the factory ct26 at 15psi.
This leads me to believe it’s a low pressure issue like you say. I’m only pushing max 18psi at the moment.

So if it can only be a low pressure issue, and not a bad valve so to say, then I need to get rid of the restriction OR unplug the vacuum line for now. I will plug it in next month when I’m delivering grains and tools to needy tribes and have to cross the Nile.
 
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i cut half of the cyclone fins out of the oem snokel top, too restrictive
(mildly off topic...)
 
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There is a vacuum solenoid switch on the LH side of the engine block just above the starter. Hard to see and reach. It takes vacuum in from a hard line running behind the firewall. It has two outputs - one that sends vacuum to the butterfly valve to shut the engine off and another that vents vacuum so that you can start the engine.

That said, my shot in the dark would be to check for leaks at the clutch booster (if you have one). They can leak without you noticing. The clutch operates just fine without the booster.

I would disconnect the vacuum line going to the booster at the firewall on the RH side, plug it, and see if your problem goes away.

If not, it is process of elimination. I would start at the 3 fittings on the pump and check for vacuum. Move forward from there.
 
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I haven’t seen this mentioned yet, you can shut the engine down by manually operating the fuel shut off leaver on the side of the pump.
 
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TreadingLight said:
I think it is a butterfly valve on the intake. LH side under the round diaphragm.
Click to expand...
Yeah, that’s the vacuum shut off. I always just reach in and shut the fuel off. It’s easier with my fat fingers.
 
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