'89 YJ No Power to Choke....does this make sense?

[M.Johndrow]

So my friend who is really into the Jeeps came over today to check out my newly purchased Saraha and he quickly determined that the cause of my hard to start when cold engine is due to no power to the choke on the carb. So we checked fuses, tested relays and then opened the wiring harness and tested continuity between all wiring connections, searched for broken wires and after a few hours of doing that we came to a point where we think we found out why. But we do not understand why this is set up this way.

I will try to be clear as possible here. But we think the oil pressure switch is not energizing the wire through the relay to the choke. So on the side of the battery box you have the black connector with the two black relays. One relay has two orange wires that get power when the key is in the ON position. One of them at least feeds power to one side of the oil pressure switch / sensor from the gray connector. The other side of this connector has a blue wire with white stripe coming from it going up to the relay box. It is factory spliced one side going to the other relay which should energize it and the other side going to the choke. When we bypass that sesor and use a jumper wire on the gray connector we get power at the choke.

So the summary is we think when the key is turned ON power it is suppose to pass through the orange wires, through the relay and down to the gray connector on the oil pressure thing....jump across that to the second pin and back up the blue and white wire to the energize the relay and activate the choke. So we think I have a bad oil pressure sensor thing! Does that make sense or sound right? Power for the choke moves through this sensor? The oil pressure gauge is working BTW. There is continuity on all the wires.

I mean I could bypass this sensor and splice into the orange wire and get it to work like it should but I want to fix it right!
Matt

 

[SteelHeadz]

I've never heard of the choke circuit being spliced into the oil pressure sending unit. Is the relay good on the key on position?

 

[M.Johndrow]

Yep relays are all good. All splices in the harness are deffinetly factory made. It appears as if power goes to the first realy ( the one with the two orange wires) then down to the sending unit (two pronged with gray plug). The current appears to travel from the first relay down th orange wire on to the one side of the gray connector for the sending unit. The current travels through that to the other side of the connector with the blue and white wire and at the same will energize the second relay and activate the electric choke.

I tested the oil sending switch (or sensor) for continuity and there was none. I put 12 volt power to the orange wire side and a test light showed no voltage on the blue wire side.

But if you jump the gray connector pins with a wire and turn the key on everything works! Current is going to the choke and it works (though it does need adjusting)

Plug the connector back in to that sensor and you get nothing at the electric choke connection. I am going to go buy a new sensor tommorow I am pretty sure current is not moving properly because of it.

My friend who is a long time mechanic and really into these jeeps was in disbelief as well. He had never seen anything like that either. But that is what appears to be happening. Crazy stuff!

 

[HiHood]

I'ld spring for a manual choke conversion. That would be how I would fix that.

 

[glenn beck]

at a guess i would say the first relay is the acc which would supply power to all the gauge sensors- oil, temp, etc.......the second relay is most proberly controled by a thermal switch as theres no need for a choke on a hot engine. any chance what you think is the oil pressure switch is a thermal switch?

 

[M.Johndrow]

I am not sure. All I know is that if voltage does not get from one side of the gray connector to the other through this switch...or by using a jumper wire then there is no voltage to the choke. There will also be no power to the relay connection with the blue and white wire.

I will go to NAPA tommorow and get a new one. I will post with the results!

 

[Crazy4diesels]

I don't know about an 89 for sure but on all of the electric chokes I have worked on the electricity is there to turn the choke OFF (ie open it)faster than it would normally have gone off by the exhaust manifold heat exchanger tube. The lack of power there would tend to keep the choke closed ( "on" ) longer than the EPA would like it to be. If the Jeep is hard to start the choke is probably not closing when cold. With the Jeep cold and not running take off the air cleaner assy and push the throttle once to set the choke. It should snap closed completely. To check the unloader lever slowly push the pedal to the floor and the choke should open about a quarter inch or so. Start the Jeep like you normally do and once it's running look at the choke. The vacuum pull off should have opened it like about 3/8 of an inch or so. As the Jeep warms up the choke should open all the way. It's very common to have the parts get gummed up (and carboned up) and not work correctly. You might find that it needs to be dismantled and cleaned. Best of luck - John

 

[M.Johndrow]

Perhaps I am not right calling this part the oil sending unit. The guy at napa said it was called a "light switch" in his computer. But it deffinetly measures the oil in some way. It is round has two prongs for the gray plug and the other end is threaded and goes into another part on the block on the passenger side. Toward the back.

 

[Crazy4diesels]

Sounds like that IS an oil pressure switch. Maybe NAPA calls it a "light switch" because they think it turns on the oil "idiot" light. I don't know why they fed the choke through that switch... The only thing I can think of is that they didn't want the choke heater to "time out" unless the engine was acually running (oil pressure). Without this switch I guess you could leave the key on, the choke would heat up and open but the engine would be cold and so would not start.

Here's a little test you can do... Start out with the Jeep cold. Start the engine and quickly measure the voltage at the choke heater (from the heater to ground). Do this before anything heats up. You should see power at the heater until the engine warms up a little. At some point after the engine warms up, in theory, the heater will "time out" and the power will be disconnected (at least that's how I remember the older electric chokes to work).

Remember, the electric power does NOT "activate" the choke. The power just causes the choke to "deactivate" after the Jeep warms up. The choke should "activate" by itself when the engine is cold (upon depressing the accelerator) - as long as this set up is the same as the earlier ones. Best of luck and let us know what you find - John

 

[carnuck]

The computer at NAPA was programmed by non-mechanical people and a LOT of the parts have the wrong name. I know because I work there. The 2 prong switch puts power to the choke to open it when the motor is running. Otherwise the choke would open too soon. The choke may need adjusting however.

 

[M.Johndrow]

Ok that makes sense. I guess it just need a good adjusting! Time to put it all back to gether and get to work on that I suppose!