Stuck choke/spark plug gap

[guitarfreak235]

Ive got 2 quick questions for yall. My choke keeps getting stuck whenever its plugged in (86 electric choke). The light stays on the whole time. With it unplugged it doesnt seem to do anything wrong. Why would the choke try to stay on all the time?

Since the choke has been stuck on im replacing my spark plugs. I think theyre fouled its not running right. What gap should i use? Ive been using .035 but recently read i should do .045 for hei vehicles and .035 for points ignition. Its a 73 350 from a one ton, running hei and the stock carb (86). Using accel shorty plugs. Thanks

 

[PrairieDrifter]

The choke linkage may be sticky. For a gap, .45 is good for hei

 

[chengny]

My choke keeps getting stuck whenever its plugged in (86 electric choke). The light stays on the whole time. With it unplugged it doesnt seem to do anything wrong. Why would the choke try to stay on all the time?


Are you sure the choke is sticking closed, or are you just going by the choke light to make that conclusion? The power to the choke heater is meant to assist in opening the choke - not keep it closed. When the engine is started (and oil pressure builds to about 10 psi), the oil pressure switch closes and sends power over to the choke heater to pull it open as quickly as possible.

I can see where unplugging the connector to the choke heater would increase the time it takes the choke plates to open.

But I can't imagine any situation where connecting the power supply would decrease the opening speed (or as you claim, prevent them from opening).

The truth is, the choke pull will open the plates soon enough - with or without electrical assist. If your choke is sticking closed after the engine is at operating temp, the problem isn't the electric choke assist. And having the power supply connected certainly won't cause that to happen.

I think that you are assuming that - because the choke light on the dash is illuminated - the choke isn't operating properly. Don't go by that lamp to determine choke function. It can actually be a warning for a far more serious condition - low oil pressure. If you unplug the connection to the choke heater, you are also disabling the choke light (and low oil pressure warning) by breaking it's ground connection.

I'm sure you have gauges and would know by now if you had dangerously low oil pressure. But in case you don't have an operational oil pressure gauge, and the choke light is staying on, it would be wise to investigate further.

Read this - especially the TROUBLESHOOTING part. Keep in mind that - on your truck - the CHOKE light is actually the OIL/ENGINE light and it's ground is provided through the choke heater:

Many trucks utilize a warning light on the instrument panel in place of the conventional dash indicating gauge to warn the driver when the oil pressure is dangerously low. The warning light is wired in series with the ignition switch and the engine unit--which is an oil pressure switch.
The oil pressure switch contains a diaphragm and a set of contacts. When the ignition switch is turned on, the warning light circuit is energized and the circuit is completed through the closed contacts in the pressure switch. When the engine is started, build-up of oil pressure compresses the diaphragm, opening the contacts, thereby breaking the circuit and putting out the light.

TROUBLESHOOTING
On some models, the oil pressure indicator light also serves as the electric choke defect indicator. If Oil or ENG. indicator light does not light, check to ensure electric choke is not disconnected at carburetor. Also check for defect in electric choke heater, blown gauge fuse or defect in lamp or wiring circuit. If indicator light stays on with engine running possible causes are: oil pressure is low, switch to indicator light wiring has an open circuit, oil pressure switch wire connector has disconnected or on some models, gauge or radio fuse has blown.
The oil pressure warning light should go on when the ignition is turned on. If it does not light, disconnect the wire from the engine unit and ground the wire to the frame or cylinder block. Then if the warning light still does not go on with the ignition switch on, replace the bulb.
If the warning light goes on when the wire is grounded to the frame or cylinder block, the engine unit should be checked for being loose or poorly grounded. If the unit is found to be tight and properly grounded, it should be removed and a new one installed. (The presence of sealing compound on the threads of the engine unit will cause a poor ground.)
If the warning light remains lit when it normally should be out, replace the engine unit before proceeding further to determine the cause for a low pressure indication.
The warning light will sometimes light up or flicker when the engine is idling, even though the oil pressure is adequate. However, the light should go out when the engine speed is increased.

 

[guitarfreak235]

My choke keeps getting stuck whenever its plugged in (86 electric choke). The light stays on the whole time. With it unplugged it doesnt seem to do anything wrong. Why would the choke try to stay on all the time?


Are you sure the choke is sticking closed, or are you just going by the choke light to make that conclusion? The power to the choke heater is meant to assist in opening the choke - not keep it closed. When the engine is started (and oil pressure builds to about 10 psi), the oil pressure switch closes and sends power over to the choke heater to pull it open as quickly as possible.

I can see where unplugging the connector to the choke heater would increase the time it takes the choke plates to open.

But I can't imagine any situation where connecting the power supply would decrease the opening speed (or as you claim, prevent them from opening).

The truth is, the choke pull will open the plates soon enough - with or without electrical assist. If your choke is sticking closed after the engine is at operating temp, the problem isn't the electric choke assist. And having the power supply connected certainly won't cause that to happen.

I think that you are assuming that - because the choke light on the dash is illuminated - the choke isn't operating properly. Don't go by that lamp to determine choke function. It can actually be a warning for a far more serious condition - low oil pressure. If you unplug the connection to the choke heater, you are also disabling the choke light (and low oil pressure warning) by breaking it's ground connection.

I'm sure you have gauges and would know by now if you had dangerously low oil pressure. But in case you don't have an operational oil pressure gauge, and the choke light is staying on, it would be wise to investigate further.

Read this - especially the TROUBLESHOOTING part. Keep in mind that - on your truck - the CHOKE light is actually the OIL/ENGINE light and it's ground is provided through the choke heater:

Many trucks utilize a warning light on the instrument panel in place of the conventional dash indicating gauge to warn the driver when the oil pressure is dangerously low. The warning light is wired in series with the ignition switch and the engine unit--which is an oil pressure switch.
The oil pressure switch contains a diaphragm and a set of contacts. When the ignition switch is turned on, the warning light circuit is energized and the circuit is completed through the closed contacts in the pressure switch. When the engine is started, build-up of oil pressure compresses the diaphragm, opening the contacts, thereby breaking the circuit and putting out the light.

TROUBLESHOOTING
On some models, the oil pressure indicator light also serves as the electric choke defect indicator. If Oil or ENG. indicator light does not light, check to ensure electric choke is not disconnected at carburetor. Also check for defect in electric choke heater, blown gauge fuse or defect in lamp or wiring circuit. If indicator light stays on with engine running possible causes are: oil pressure is low, switch to indicator light wiring has an open circuit, oil pressure switch wire connector has disconnected or on some models, gauge or radio fuse has blown.
The oil pressure warning light should go on when the ignition is turned on. If it does not light, disconnect the wire from the engine unit and ground the wire to the frame or cylinder block. Then if the warning light still does not go on with the ignition switch on, replace the bulb.
If the warning light goes on when the wire is grounded to the frame or cylinder block, the engine unit should be checked for being loose or poorly grounded. If the unit is found to be tight and properly grounded, it should be removed and a new one installed. (The presence of sealing compound on the threads of the engine unit will cause a poor ground.)
If the warning light remains lit when it normally should be out, replace the engine unit before proceeding further to determine the cause for a low pressure indication.
The warning light will sometimes light up or flicker when the engine is idling, even though the oil pressure is adequate. However, the light should go out when the engine speed is increased.

Yes i was aware of the light being an indicator of low oil pressure, i have oil and the oil pressure gauge is functioning properly.

I think i was backwards on the way the choke functioned, being that the circuit opens the choke instead of closes it. I assumed the choke was stuck closed because of the light and it running poorly.

I will check the fuses along with the wiring to the engine unit. Thanks for the reply that was very informantive.

In the mean time, is there a way to keep the choke open if the circuit isnt functioning properly?

 

[chengny]

Yeah, first check the choke fuse - bottom fuse (20 amp) 3rd column from the left. It is kind of screwy, but without power, the choke light will remain illuminated.

If the fuse is good, go to the oil pressure switch, pull the connector and confirm 12 VDC at the pink/white lead:

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The pink/white goes to one side of the contacts and the dk blu & lt blu leads both go to the other side of the contacts. The blue leads look to go to different terminals but they are spliced inside the harness plug:

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The two female sides of the connector:

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if you have power at the pink/white lead, check the oil pressure switch for proper operation.

With the engine off, check continuity across the two switch terminals - you should read infinite resistance (i.e. an open circuit).

Start the engine and check continuity across the switch again. With oil pressure above 10 psi, the switch's contacts should be closed and now there should be no resistance.

If the switch closes and provides power to the blue wires, everything is okay so far. Check the wiring from the switch to the heater & warning lamp.

With the engine still running (and the oil pressure switch connected back to the harness), go over to the choke heater and pull the Lt Blu lead off the heater coil. Measure for 12 VDC between the Lt Blu lead and a good clean ground point. If you get that, the power supply circuit to the choke heater is operating properly.

The only other thing that would prevent the choke warning from turning off (when oil pressure is established) is a problem in the lead (the dark blue one) that goes from the oil pressure switch to the lamp. In order to check that - all the way to the lamp - would require removing the dash bezel and instrument panel to gain access to the IP harness plug.

If you go that far, it is the same as the power to the choke heater. With oil pressure established, there should be 12 VDC at the pin on the harness plug that connects to the dk blu lead. Should be the 4th tab down from the top, on the RH side (looking at the plug not the socket).

This shows the tab in the socket (4th from the top left hand side);

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[guitarfreak235]

Yeah, first check the choke fuse - bottom fuse (20 amp) 3rd column from the left. It is kind of screwy, but without power, the choke light will remain illuminated.

If the fuse is good, go to the oil pressure switch, pull the connector and confirm 12 VDC at the pink/white lead:

You must be registered for see images attach

The pink/white goes to one side of the contacts and the dk blu & lt blu leads both go to the other side of the contacts. The blue leads look to go to different terminals but they are spliced inside the harness plug:

You must be registered for see images attach

The two female sides of the connector:

You must be registered for see images attach

if you have power at the pink/white lead, check the oil pressure switch for proper operation.

With the engine off, check continuity across the two switch terminals - you should read infinite resistance (i.e. an open circuit).

Start the engine and check continuity across the switch again. With oil pressure above 10 psi, the switch's contacts should be closed and now there should be no resistance.

If the switch closes and provides power to the blue wires, everything is okay so far. Check the wiring from the switch to the heater & warning lamp.

With the engine still running (and the oil pressure switch connected back to the harness), go over to the choke heater and pull the Lt Blu lead off the heater coil. Measure for 12 VDC between the Lt Blu lead and a good clean ground point. If you get that, the power supply circuit to the choke heater is operating properly.

The only other thing that would prevent the choke warning from turning off (when oil pressure is established) is a problem in the lead (the dark blue one) that goes from the oil pressure switch to the lamp. In order to check that - all the way to the lamp - would require removing the dash bezel and instrument panel to gain access to the IP harness plug.

If you go that far, it is the same as the power to the choke heater. With oil pressure established, there should be 12 VDC at the pin on the harness plug that connects to the dk blu lead. Should be the 4th tab down from the top, on the RH side (looking at the plug not the socket).

This shows the tab in the socket (4th from the top left hand side);

You must be registered for see images attach

Ok today I'll finally be able to get out and check the issue. I'll check the circuits as per your example. However, after rereading your first post thoroughly, you said the choke circuit only ASSISTS in opening the choke, and with time it'll open on its own correct? I'll take it for a spin and double check if the choke opens on its own, but im pretty sure the choke plate (thats what it's called right?) stays closed even after a long drive (It doesn't seem to run any better after a drive). I think this may be why it's running poorly. If i get on the gas really quick it stumbles for a second (doubly rich condition with choke plus accelerator pump...?), then runs smoother. If I floor it to WOT same. stumbles/skips for a second then kicks in smother. Even after the momentary stumble stops it just doesn't run like it used to. i'd say it gets 75% of max power at the most. Regardless of what may be wrong with the circuits, and choke light, Im pretty positive the running issues are due to the choke being physically closed. (whether its just physically stuck/worn out, or the potential electrical problems). THE DRIVABILITY ISSUES AND CHOKE LIGHT STAYING ON HAPPENED AT THE SAME TIME, so im pretty sure they are related. Additionally, I replaced the spark plugs thinking they were fouled. Yes, they definitely were. dark black looking so appears to be rich condition right? with the new plugs it ran better but didn't fix it. So all issues seem to be pointing at the choke.

You really are very helpful (well everyone here really). I recently purchased a 97 vw gti to drive while I work on the truck since its gotten into disrepair (this choke issue, auto locking hubs starting to bang, etc.). I've joined literally 4 different vw/gti forums and got less response as a noob there than I did when i first joined this forum. So again thanks for the help, I didn't realize how great a forum we truly have here. You'll be getting rep points from me for sure.

I'm about to go out and check the issue. I'll check back in shortly.
Wish me luck

 

[guitarfreak235]

well, I feel stupid. Turned out its just the fuse. I guess I was assuming that since the choke light was showing, that the circuit couldn't have been broken. Youre right it is kinda screwy but definitely a learning experience. I was checking everything but the fuse, but atleast I learned a bunch about the choke system. Thanks for the help regardless, it was worth it just to learn for the future. I will die with this truck, so i'll likely run into the issue at some point!

 

[chengny]

I know you didn't ask - and I don't know how much you care about this subject, but someone might.

Anyway, attached below are some drawings that attempt to explain the operation and relationship between the choke heater/ oil pressure switch/ choke warning light. When I first started working on these trucks about 10 years ago, the whole system mystified me. I was interested in how it worked, but not too much. It was only a couple of years ago that I took the time to sit down and figure it out.

I think this set-up is unique to GM and was only used for a relatively short time. In the mid eighties, when engines started to be computer controlled, it was abandoned. The EPA was demanding that the choke plates started to open immediately after the engine was started. The primary reason for this design was that it was an easy/cheap way to provide power to the choke heater coil - by using the oil pressure switch. Sounds great in theory, but the CHOKE light was then actually a low oil pressure light. I have to wonder how many engines were ruined because - if a driver saw the CHOKE light on, he just shrugged his shoulders and continued driving. Who really cares if the choke malfunctions after the engine is warm.

Engine running/oil pressure established, CHOKE lamp out:

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Current flow in the engine compartment components:

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Engine off/loss of oil pressure - CHOKE lamp illuminated:

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