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Unread 12-30-2014, 03:09 PM   #1
SMT73
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mc 2100 electric choke help

Tried searching this but I couldn't find anything.
I have a 4.2 with a mc 2100. The electric choke does what it is suppose to and jeep is properly tuned , no vac leaks or any of that stuff.
I've tested this with a circuit tester, so I know this is a problem. After about 10 min the electric current to the choke shuts off causing the choke to start closing. This causes the high idle to get stuck on the second step while driving...
any help is appreciated...

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Unread 12-30-2014, 03:26 PM   #2
Mark05059
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where is the electric choke wired to? It should be wired to the oil pressure sender I believe. I have TBI so Im not an expert by any means
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Unread 12-30-2014, 04:08 PM   #3
boduke5051
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Not sure if it would be any different with the MC, but my Webber is hooked to the oil pressure sensor. There's 2 separate sensors mounted right together over on the passenger side near the distributor. The top one that is cylindrical shaped is the sending unit for the gauge. That threads into the 2nd one which is more of just an on/off sensor, and that is the one that my choke is connected to. This 2nd sensor threads directly into the block.
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Unread 12-30-2014, 06:30 PM   #4
SMT73
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Ya..mine is wired from a relay that is also part of the oil pressure switch...I had thought maybe my pressure ( sometimes doesn't exist ) was triggering the relay and killing power to the choke, manifold heater etc....but today while using the test lite, I had pretty good pressure when the power to the choke coil went dead....
I can't imagine I'm the only one whose run into this issue.
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Unread 12-30-2014, 07:34 PM   #5
laybackman
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Quote:
Originally Posted by SMT73 View Post
Tried searching this but I couldn't find anything.
I have a 4.2 with a mc 2100. The electric choke does what it is suppose to and jeep is properly tuned , no vac leaks or any of that stuff.
I've tested this with a circuit tester, so I know this is a problem. After about 10 min the electric current to the choke shuts off causing the choke to start closing. This causes the high idle to get stuck on the second step while driving...
any help is appreciated...
Where is your source of the voltage for the choke? You could wire it to the + side of your coil. That gets constant voltage when the engine is running.
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Unread 12-31-2014, 08:20 AM   #6
boduke5051
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I'll double check mine when I have the time, but I don't think mine goes through a relay. I think my choke wire goes directly to the oil pressure sensor through the harness loom.
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Unread 12-31-2014, 08:55 AM   #7
Mike Romain
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Quote:
Originally Posted by SMT73 View Post
Ya..mine is wired from a relay that is also part of the oil pressure switch...I had thought maybe my pressure ( sometimes doesn't exist ) was triggering the relay and killing power to the choke, manifold heater etc....but today while using the test lite, I had pretty good pressure when the power to the choke coil went dead....
I can't imagine I'm the only one whose run into this issue.
You are the first one I have read of. I would figure either your oil pressure switch is going bad turning off the choke or your pressure is just too low or the connection is getting ratty. No relay in that circuit.
Do your backup lights and seat belt buzzer work right? Their fuse is the one feeding the oil pressure switch it's power.
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Unread 12-31-2014, 11:15 AM   #8
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Originally Posted by laybackman View Post
Where is your source of the voltage for the choke? You could wire it to the + side of your coil. That gets constant voltage when the engine is running.
Both the coil and the ICM run from the same power source
-> The resistor wire <-
This is where the electric choke should be wired to
Its a regulated power source

If you trace the wiring (which I've done a few times now) on these old carb'd setups, the resistor wire feeds these three items and also the original computer (for those that still have it) - you would have to trace the choke wire back thru the oil pressure switch

HTH
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Unread 12-31-2014, 07:33 PM   #9
SMT73
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My computer is long gone...my old school neighbor, who is usually pretty knowledgeable, mentioned that he doesn't think the electric choke is supposed to have constant power. He claims this is why on Ford's there is a heat tube that takes over after the initial electric shuts off.....
Does anyone run power constant on there electric choke...any issues ?
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Unread 12-31-2014, 11:46 PM   #10
Mike Romain
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Originally Posted by SMT73 View Post
My computer is long gone...my old school neighbor, who is usually pretty knowledgeable, mentioned that he doesn't think the electric choke is supposed to have constant power. He claims this is why on Ford's there is a heat tube that takes over after the initial electric shuts off.....
Does anyone run power constant on there electric choke...any issues ?
Heat tubes are old school. Yours has an electric bimetal coil on it that needs constant power to stay open. The power comes from the oil pressure switch. You have oil pressure, you have power. You have a ratty connection or a carb that isn't grounded well or something going on.

I would just take a multimeter and put it on the oil pressure switch wires to verify power in power out and go from there. A punky leg on the fuse could even be the issue which is why I asked if your reverse lights work well. Same fuse as far as I know. It is on the CJ, figure YJ uses the same fuse.
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Unread 01-01-2015, 05:20 AM   #11
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Quote:
Originally Posted by Mike Romain View Post
Heat tubes are old school. Yours has an electric bimetal coil on it that needs constant power to stay open. The power comes from the oil pressure switch. You have oil pressure, you have power. You have a ratty connection or a carb that isn't grounded well or something going on.

I would just take a multimeter and put it on the oil pressure switch wires to verify power in power out and go from there. A punky leg on the fuse could even be the issue which is why I asked if your reverse lights work well. Same fuse as far as I know. It is on the CJ, figure YJ uses the same fuse.
OP states there is a relay in the loop.... should be no relay for this correct?
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Unread 01-01-2015, 06:52 AM   #12
Mike Romain
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Originally Posted by Mark05059 View Post

OP states there is a relay in the loop.... should be no relay for this correct?
Well... The oil pressure switch turns on 2 things. First it has a direct electrical connection to the choke and second it feeds a relay trigger ( pin 86) to turn on the under carb heater via a thermostat in the rear of the intake manifold that grounds the trigger (pin 85). The relay pulls direct power from the fuse link (pin 30) on the starter relay for the heater off pin 87.

Now if the OP has his choke wired through the relay so it gets its power off pin 87, then the power to the choke will shut off when the thermostat in the intake opens.
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Unread 01-01-2015, 08:43 AM   #13
Mark05059
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I believe that is his issue
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Unread 01-01-2015, 09:08 AM   #14
Mike Romain
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Originally Posted by Mark05059 View Post
I believe that is his issue
Kinda sounds like it doesn't it.
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89 YJ Renegade. BBD Carbed 4.0 HO. Locked front and rear with 33x9.5 BFG AT's
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Unread 01-01-2015, 06:33 PM   #15
SMT73
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Thanks for the response to this....I will run out in the morning and try to trace some wires and clean some contacts
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