83 K10 Cold Idle issues

[ThisOldK10]

When I start my truck in the morning I have to sit on the throttle for approx 8 minutes (half throttle) otherwise the truck will die. Any ideas on why this is happening?

 

[chengny]

Check that your choke begins opening up as soon as the truck is started. The choke heater may not be assisting as designed and the choke is only opening due to engine heat.

With a properly functioning choke assist, the plates should be wide open within about 3 minutes.

Make sure it's not stuck closed for 8 minutes and then all of a sudden popping wide open. Even without a choke heater, it shouldn't take 8 minutes. I know it can get cold in Nevada at night, but it's not the Arctic.

Have someone else man the gas pedal while you observe the operation. It should begin to slowly creep open right away.

When you very first start it, does it run okay for about 30 seconds or so?

 

[ThisOldK10]

Check that your choke begins opening up as soon as the truck is started. The choke heater may not be assisting as designed and the choke is only opening due to engine heat.

With a properly functioning choke assist, the plates should be wide open within about 3 minutes.

Make sure it's not stuck closed for 8 minutes and then all of a sudden popping wide open. Even without a choke heater, it shouldn't take 8 minutes. I know it can get cold in Nevada at night, but it's not the Arctic.

Have someone else man the gas pedal while you observe the operation. It should begin to slowly creep open right away.

When you very first start it, does it run okay for about 30 seconds or so?

Nope, immediately dies.

 

[chengny]

Maybe it's colder in your part of Nevada than I thought and maybe the problem is that the choke isn't closing - rather than that it isn't opening quickly enough.

What did you find out when you observed the operation of the choke in the morning?

After an extended shutdown - when the engine is completely cool - it is important that you fully depress the accelerator to the floor one time before you crank the engine up.

This action produces two results:

1. It releases the choke linkage and allows the choke spring to snap the butterfly fully closed

2. It operates the accelerator pump which injects a shot of gas directly into the throats of the venturis.

Or, as Hemmings explains it:

An automatic choke does not require driver intervention in order to set the proper air/fuel ratio. What it does need is the proper starting procedure to set the choke butterfly in the closed position.

An automatic choke closes against spring pressure. During engine crank, it then exposes almost full manifold vacuum to the carburetor venturi, drawing a large amount of fuel through the main metering system.

When the engine fires, the increased piston velocity partly blows the choke plate open against spring tension to allow a sufficient amount of air to lean the mixture by reducing the depression in the venturi.

As the engine warms up, the spring tension is reduced until the butterfly is completely open and has no impact on the signal the carburetor venturi (booster) is exposed to.


When a hot engine is shut off and starts to cool, the tension on the choke spring increases in lockstep with the drop in temperature. The choke plate and fast-idle cam are attached to the spring via the carburetor's throttle linkage.

This requires the throttle to be pressed slowly to the floor once to allow the choke plate to close, and needs to be done prior to cranking the engine over. When functioning properly, the full depression of the accelerator pedal will release the choke spring tension being held by the fast-idle cam and screw, while also providing a shot of fuel into the manifold by the accelerator pump. The accelerator pump shot works as a small prime pulse to provide a combustible mixture prior to the fuel being discharged by the venturi booster.

So one cold morning (before you attempt to start the truck), get in and press the gas pedal down to the floor one time. Get out and confirm that the choke butterfly plate is completely closed. Like this:

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If it is fully closed, that's good. But before you crank it up, you need to check one other thing - the accelerator pump operation. I wrote how to do it on these images:

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[Skweegle89]

Dumb question, but I have to ask. Does your choke light on your gauge panel stay on after you start the truck?


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[ThisOldK10]

Maybe it's colder in your part of Nevada than I thought and maybe the problem is that the choke isn't closing - rather than that it isn't opening quickly enough.

What did you find out when you observed the operation of the choke in the morning?

After an extended shutdown - when the engine is completely cool - it is important that you fully depress the accelerator to the floor one time before you crank the engine up.

I haven't looked yet but I will try this tomorrow morning! Thanks for the thorough explanation.

Dumb question, but I have to ask. Does your choke light on your gauge panel stay on after you start the truck?

My choke light never lights up. I should probably check that out lol

 

[Skweegle89]

Lol I would. I didn't read chengnys whole post, but he can explain why that's important. Long story short, it's wired through the oil pressure switch, so the choke light also serves as a low oil pressure warning light.


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[chengny]

My choke light never lights up. I should probably check that out lol

The only time you should see the choke light illuminated is for that brief moment that your key is passing through the RUN position on it's way to START. As soon as the engine begins cranking, it quickly goes out. Unless you are actively watching for it, you most likely wouldn't be aware that it is working.

It will also illuminate in two other circumstances:

1. If, for whatever reason, you turn the key just to RUN (and leave there - without moving it to START), or if you stall out (and don't move the key back to OFF) the CHOKE light should come on.

2. If, while the engine is running, oil pressure drops below 5 psi - it will come on (or usually it just starts flickering on and off).

In this case; STOP THE ENGINE. If you continue to operate it (and the CHOKE light is telling you the truth - that oil pressure is dangerously low) - the engine may be suffer major damage.

So, and this is serious, the next time you go to start the truck, take a second to stop the key in the RUN position - before moving it to START. Look down and note whether the CHOKE light is on.

I bet it is- and that is a good thing. It means that it is functional and it should go out as soon as oil pressure is established.

Why they ever decided to label that warning lamp "CHOKE" instead of what it really indicates - something far more critical - i.e. the loss of engine oil pressure, is beyond me.

Really, if you think about it, do you really care if your choke heater is energized? And even if it isn't; does that merit a big red warning light prominently displayed on the dashboard!

These trucks are the only vehicles I have ever seen with that indication. Oil pressure gauges are very nice, but they are mostly useful as diagnostic tools - and not very useful as warning devices. As with any other gauge, it can only alert you to a critical situation if you constantly glance down at it.

WHY, during the design process, didn't someone speak up and say something like;

"You know since this new "CHOKE" light that we are adding to the instrument panel is activated by a loss of engine oil pressure, wouldn't it make more sense to just change the lettering to "OIL PRESSURE". That way, you know... if the lamp lights up, the driver might be more inclined to stop the engine before it incurs a catastrophic failure - as opposed to when he sees it, he thinks his choke might not open as quickly the next cold morning?"

IDK, maybe "OIL PRESSURE" was too long to fit on the lens. Or maybe the "CHOKE" ones had already been printed out and no one wanted to get in trouble for ordering millions of new ones.

Sorry about the diatribe (or what do the kids call it these days - a rant?) - but this is one of the few things about these trucks that bugs me. I am now stepping down off my soapbox.

 

[Skweegle89]

My choke light never lights up. I should probably check that out lol

The only time you should see the choke light illuminated is for that brief moment that your key is passing through the RUN position on it's way to START. As soon as the engine begins cranking, it quickly goes out. Unless you are actively watching for it, you most likely wouldn't be aware that it is working.

It will also illuminate in two other circumstances:

1. If, for whatever reason, you turn the key just to RUN (and leave there - without moving it to START), or if you stall out (and don't move the key back to OFF) the CHOKE light should come on.

2. If, while the engine is running, oil pressure drops below 5 psi - it will come on (or usually it just starts flickering on and off).

In this case; STOP THE ENGINE. If you continue to operate it (and the CHOKE light is telling you the truth - that oil pressure is dangerously low) - the engine may be suffer major damage.

So, and this is serious, the next time you go to start the truck, take a second to stop the key in the RUN position - before moving it to START. Look down and note whether the CHOKE light is on.

I bet it is- and that is a good thing. It means that it is functional and it should go out as soon as oil pressure is established.

Why they ever decided to label that warning lamp "CHOKE" instead of what it really indicates - something far more critical - i.e. the loss of engine oil pressure, is beyond me.

Really, if you think about it, do you really care if your choke heater is energized? And even if it isn't; does that merit a big red warning light prominently displayed on the dashboard!

These trucks are the only vehicles I have ever seen with that indication. Oil pressure gauges are very nice, but they are mostly useful as diagnostic tools - and not very useful as warning devices. As with any other gauge, it can only alert you to a critical situation if you constantly glance down at it.

WHY, during the design process, didn't someone speak up and say something like;

"You know since this new "CHOKE" light that we are adding to the instrument panel is activated by a loss of engine oil pressure, wouldn't it make more sense to just change the lettering to "OIL PRESSURE". That way, you know... if the lamp lights up, the driver might be more inclined to stop the engine before it incurs a catastrophic failure - as opposed to when he sees it, he thinks his choke might not open as quickly the next cold morning?"

IDK, maybe "OIL PRESSURE" was too long to fit on the lens. Or maybe the "CHOKE" ones had already been printed out and no one wanted to get in trouble for ordering millions of new ones.

Sorry about the diatribe (or what do the kids call it these days - a rant?) - but this is one of the few things about these trucks that bugs me. I am now stepping down off my soapbox.

To my knowledge, I have never met anybody outside this forum that knew about the choke light/oil pressure warning. I only learned because my choke light was constantly on as a result of a bad oil pressure switch. I bet a lot of sbc's got smoked as a result of that setup.


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[ThisOldK10]

My choke light never lights up. I should probably check that out lol

The only time you should see the choke light illuminated is for that brief moment that your key is passing through the RUN position on it's way to START. As soon as the engine begins cranking, it quickly goes out. Unless you are actively watching for it, you most likely wouldn't be aware that it is working.

It will also illuminate in two other circumstances:

1. If, for whatever reason, you turn the key just to RUN (and leave there - without moving it to START), or if you stall out (and don't move the key back to OFF) the CHOKE light should come on.

2. If, while the engine is running, oil pressure drops below 5 psi - it will come on (or usually it just starts flickering on and off).

In this case; STOP THE ENGINE. If you continue to operate it (and the CHOKE light is telling you the truth - that oil pressure is dangerously low) - the engine may be suffer major damage.

So, and this is serious, the next time you go to start the truck, take a second to stop the key in the RUN position - before moving it to START. Look down and note whether the CHOKE light is on.

I bet it is- and that is a good thing. It means that it is functional and it should go out as soon as oil pressure is established.

Why they ever decided to label that warning lamp "CHOKE" instead of what it really indicates - something far more critical - i.e. the loss of engine oil pressure, is beyond me.

Really, if you think about it, do you really care if your choke heater is energized? And even if it isn't; does that merit a big red warning light prominently displayed on the dashboard!

These trucks are the only vehicles I have ever seen with that indication. Oil pressure gauges are very nice, but they are mostly useful as diagnostic tools - and not very useful as warning devices. As with any other gauge, it can only alert you to a critical situation if you constantly glance down at it.

WHY, during the design process, didn't someone speak up and say something like;

"You know since this new "CHOKE" light that we are adding to the instrument panel is activated by a loss of engine oil pressure, wouldn't it make more sense to just change the lettering to "OIL PRESSURE". That way, you know... if the lamp lights up, the driver might be more inclined to stop the engine before it incurs a catastrophic failure - as opposed to when he sees it, he thinks his choke might not open as quickly the next cold morning?"

IDK, maybe "OIL PRESSURE" was too long to fit on the lens. Or maybe the "CHOKE" ones had already been printed out and no one wanted to get in trouble for ordering millions of new ones.

Sorry about the diatribe (or what do the kids call it these days - a rant?) - but this is one of the few things about these trucks that bugs me. I am now stepping down off my soapbox.

When the ignition is in RUN I have no choke light. Also, mine has the image of oil/choke on the light with no words.

 

[GTME94]

Good info as usual Jerry! To be honest whenever I see a cold start thread I look at the age of the poster and start to think of explaining proper cold start procedure for a carbureted engine. Not to offend any younger people but if they've never driven a carb'd vehicle before they don't know how to set a choke.

 

[rich weyand]

Good info as usual Jerry! To be honest whenever I see a cold start thread I look at the age of the poster and start to think of explaining proper cold start procedure for a carbureted engine. Not to offend any younger people but if they've never driven a carb'd vehicle before they don't know how to set a choke.

That's a good point, so let's elaborate. A carbureted engine with an automatic choke (as opposed to a cable/manual choke) needs the throttle pedal depressed all the way to the floor once, then released, to allow the choke linkage to reset before starting.