1985 CJ7 (Jeep) choke question


#1

The choke on my 85 CJ7 does not open when the car is warmed up. It runs great until it gets hot and then it dies. If I hold the choke open, it stays running. Any idea which sensor is sending the signal to the choke to tell it to open? I’ve traced the wire from the choke coil back to a harness. From there I’m lost as to where it goes.


#2

You’d need a manual. However, have you checked the output of the temp sensor? I’ll bet dollars to doughnuts it’s bad.


#3

I bet you’re right! I just don’t know where that temp sensor is.


#4

That’s why you’ll need a manual. I don’t either!


#5

Was Jeep a product of Chrysler at that time? Or Chrysler powered? I would doubt that the choke has anything to do with sensors. With the car off, spray some W-D40 on the linkage assembly and then work the choke plate back and forth, full range. If that doesn’t work save yourself the headache and have the choke calibrated at the most honest local shop. It will save time in the long run because the shop SHOULD have the proper (Professional) calibration gages.
Oh, I just remembered. If Chrysler powered then you may have what they use to call an ECM (Electronic control module) on the air cleaner. It looks like a black box on the air cleaner assembly. Unplug all the wires (At the harness)and see if that makes a difference. If so, get a new ECM. This is an old Ford trick that might work on your Jeep.


#6

Convert to manual choke?


#7

The choke is wired to heat up as soon as the engine is started. Often the oil pressure switch had 3 pins, 2 were connections to the choke switch. As soon as oil pressure was present the switch closed, sending current to the choke heater which heated the chokes bi-metal thermostat, causing it to pull the choke open. Sometimes relays were used in the system. Start at the choke (the black plastic cylinder on the side of the carburator) the wire to it should be live when the engine is started.


#8

Hold for a minute whole I pull my foot from my mouth!

As is obvious, I’m unfamiliar with the electrically heated choke T-stat setup. i’m assuming it was used as a method to choke off the engine when the key was turned off to prevent dieseling? Would it then be a solenoid instead, whereas a bimettalic coil would not allow the choking function? I’d truely curious.

Thanks Rod.


#9

The schematics show 2 completely different methods for powering up the choke heater based on the engine you have. The 4 is vastly different than the 6. Which one do you have?


#10

you CAN fix this automatic choke. it will take a couple hundred bucks (or so)

or you can go down to your local auto store and get a choke kit (with a cable, knob and a clamp) to eliminate the auto choke. this does take knowledge to learn how to operate, but it IS possible to learn (we drove cars for 70 years or so with manual chokes)

it only takes an hour or so to install a manual choke, you just have to figure out how to route it, and make it as direct as possible.


#11

I now think it’s the oil pressure switch


#12

it’s a 6


#13

I agree


#14

Further research leads me to believe that the oil pressure switch is bad. I will try replacing that.


#15

it’s a new carb. the choke is fine. I think there’s some sort of signal not getting to the coil thingy


#16

a common problem of this era engines is the (prehistoric) computer was easily confused.

i used to be regularly warned (beat up) about NOT touching the accelerator during initial start. the carb has a mechanical sensor (sorry i don’t know more about it) that depended on input from the engine to start and adjust the carburetor.

what i DID learn was that you can buy a manual choke to eliminate this automatic choke.

in later generations the EFI and computers eliminated the need (or possibility) for a choke. but on these '85 “cusp” vehicles there is a need for a manual choke, actuated by mechanical methods which depends on sensors.

on a different note, if you can move the choke plate lever (to keep the engine running) then at least the choke plate still works. i think the linkage, and the cables could be freed up to (at least try) to let the choke work as they were installed.


#17

I think what you are referring to is what Chrysler called the SMEC (Single Module Electronic Control) That was around 1988 Because its OBD1.


#18

Basics of choke. When closed it helps the engine run when the engine is cold. It makes the engine draw more fuel and less air.


#19

Here’a a link to a wiring schematic for the 6. Scroll down to No. 29 and look at the top right section of the choke heater wiring.
There is a 25 amp fuse in the circuit so make sure the fuse is good first. Use a test light to verify that power is provided to the choke switch and that power also passes through the choke switch. Do not be concerned with the manifold heater, heater relay, and heater switch as these have no influence on the choke heater itself.

I’m not a Jeep expert so I cannot tell you where the choke switch is located. One could assume that it is located on the intake manifold near the carburetor and should have a pair of red wires leading to it. Maybe someone more familiar with this particular switch can provide the exact location. Hope that helps. I don’t see this being a major repair though.


#20

Thanks! (where’s the link?)