EXT idle project - JeepForum.com
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post #1 of 23 Old 02-16-2020, 01:46 PM Thread Starter
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EXT idle project

I have been reading about the EXT idle and how to wire it on here. Lots of threads but Ralph77's postings are what got me going. He made it work and look stock on his dash. I am not concerned with it looking that way, all I want is it to work.I figure it would cost me over a hundred dollars acquiring the parts on Ebay or elsewhere. If the correct parts find me then maybe. Instead I am going to use a simple toggle switch and place it in a hole I already have on my dash. There was once a problematic alarm system I disabled long ago but there is still a little red indicator light installed next to the gauge cluster and I can use that for the hole. First problem was locating and verifying the solid grey A-12 wire that is in the PCM harness connector #1. I opted to open the large wiring harness closer to the brake booster for room to grab the grey wire easily. You must be careful because there are several grey wires in that harness. Some have various tiny colored stripes and are hard to see. Then there is another solid grey wire that you MUST NOT get confused and cut. It is from the same connector #1 and position #7. By opening the wire harness where I did I was able to grab the grey wires and pull while looking to see if the A-12 wire at the connector moved. Once I verified the A-12 only then did I slice away a bit of the insulation to test it. I ran a wire with an alligator clip to a good ground and then touched the bare end to the A-12 grey wire while the engine was running. The idle jumped right up to 1000rpm. You guys were correct about that. Then I scrounged a length of double wire with a protective sleeve and cut what I needed from that. The ends I soldered to the grey A-12 wire and a black ground wire. The ground I attached with a ring terminal under one of the sheet metal screws that secures the PCM mounting bracket. Once I have sealed and shrink-wrapped the connections the rest of the wire can be fed through the fire wall through a grommeted hole someone already made for the alarm wiring. Then I can get a small toggle switch and solder the wires to that. For now I am sealing my solder connections with Liquid Electric tape. That is a neoprene sealing liquid I use on all my auto and boating wiring. It dries semi-hard and waterproof. Then shrink-wrap and electrical tape. Here I am so far:

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post #2 of 23 Old 02-16-2020, 02:01 PM
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Well you seem to have done that without a relay.
Which has me wondering why did they use a relay in that write up I linked.
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post #3 of 23 Old 02-16-2020, 03:34 PM Thread Starter
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You really got me started Ralph! Thanks. I looked at the schematic in the FSM and the A-12 wire went through the switch directly to a ground. No relay involved. The fog lights use relays but the EXT idle is merely a grounded wire. But that is why they say to use a relay if you use a fog light switch and the factory wiring/harness. It is positive switched while the EXT is negative switched. By using a simple toggle switch all I need to do is go to a good ground. I should have mentioned for those not up to speed that the A-12 wire at the PCM goes to a dash mounted switch. When that switch is grounded the PCM raises the idle to 1000rpm for better cooling and alternator output but only in P or N. Here is a shot of the #1 PCM connector with the cover unsnapped off. You can see the A-12 grey wire right at the front of the connector. That is the one. Don't worry about cutting the wire since without the police package it dead-ends at connector #7 back of the cylinder head. I then sealed and shrink-wrapped the soldered connections, re-sealed and wrapped with black electrical tape, then tucked it all back into the factory harness. Then I re-wrapped the harness with tape and tucked that back into the convoluted wiring cover, and taped that shut too. Now nothing can be seen and it all blends in. The coil of wire at the end will go into the passenger compartment.
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post #4 of 23 Old 02-17-2020, 12:43 AM
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See I thought it was cause a Ext Idle switch is just not an on/off switch.
Like I assume a fog light switch is. Or the toggle switch you are using.
Which is why they use the relay.
I don't understand why that write up goes through all that trouble with the relay then.

So if I understand you correctly you the toggle switch you used has 2 terminals?
You wired the gray A12 to one and grounded somewhere from the other?
So when you throw the switch the circuit is completed?
And it just still raises the idle in park and neutral?
One thing I thought about for wheeling is if you could set it up to operate in gear too.
For instance sometimes in my old CJ2A I used to turn up the idle a little.
If I was by myself and had to creep over some rocks and whatnot I could literally get out,
walk along side of it and steer over things.

And on a side note. Did you replace your front diff breather hose?
If not I never realized there was enough slack in it to pull it that far to above the brake booster.
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post #5 of 23 Old 02-17-2020, 09:07 AM Thread Starter
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The reason they use the relay is because they are using the factory fog light switch, harness, and connector. In that case you have positive 12 volts going in to the switch and positive 12 volts coming out. That normally goes to fog light relay #2 and actuates the fog lights. But the A-12 wire needs to be grounded to actuate the EXT idle. So instead the new relay gets the positive 12 volts from the fog light switch and the new relay grounds the A-12 wire. When I read all that in the threads I realized that it was a lot of expensive and unnecessary work to do a simple task. The factory EXT switch get 12 volts too but only to light the "ON" bulb and the dimmer dash light. Otherwise it is just an on/off switch to ground. I just wanted it to work so I tested the wire by grounding it and sure enough it worked. The idle jumped right up to 1000rpm. There is a guy on Ebay selling 3D printed 4 and 6 hole dash plates, others selling aftermarket rocker switches with various tags like "winch" , and another selling the 12v DC plugs because the factory plug can't be removed from the stock plate. Then add the cost of a relay and it gets to be way over $100 just to do what a simple $2 toggle switch can do. Unless you really need it to look stock, and there is merit to that, I just don't need it. Unfortunately getting it to work in gear is not in the cards at the moment. The PCM knows what gear you are in. It uses the same switch on the side of the transmission for the neutral safety switch. The only way to do it would be to figure out what wire tells the PCM it is in P/N or D and interrupt that wire. I am sure it is doable but further study is indicated. I would like that too just for summertime traffic with the AC running. My neutral safety switch is giving me problems and I had to add a dedicated starter momentary switch for when it doesn't want to work. The last time I tried to service it I could not get it off the shaft for some reason. So I may be investigating that sooner then I wanted. As for the vent hose as far as I know it is stock. I tied it up because it was flopping all over the place. It should be easy to extend as the cap on the end is just the standard 3/8" breather all the manual transmissions and rear axles use.

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post #6 of 23 Old 02-17-2020, 09:16 AM
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So if I am understanding you correctly you could still use a fog light switch without the relay?
Here is the wiring for the switch. So what would hook up where?
And I understand that the little green light, blue wire 12 volt run source, would not light.
At least I think that is what you are saying.
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post #7 of 23 Old 02-17-2020, 10:40 AM Thread Starter
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Is that the stock schematic or what you used? First off that schematic is incomplete. The violet wire at terminal #3 is 12v positive and comes from the fog lamp relay #1. That relay gets enabled only if the headlamps are on in the low beam function. High beam disables it. Then the light blue wire from terminal #2 is 12v positive and goes to fog lamp relay #2. That relay enables both fog lamps. You could use another fog lamp relay to ground the EXT idle circuit but the hot wire at terminal #30 would instead need to be a ground and terminal #87 would go to your A-12 wire. That is why they use a separate relay when using the stock fog lamp switch as the EXT switch. The fog lamp switch is positive switched and the EXT is negative switched. Don't feel bad. I also work on G-bodies. GM made a change from negative to positive switching in their wiper motor circuits around 1983. It confuses people to no end.

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post #8 of 23 Old 02-17-2020, 10:55 AM
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Think you are misunderstanding my question.
I only show that diagram so you would know what the wires on a fog light switch are for.
Forget the rest of the diagram. That is for wiring like aftermarket using an factory switch.
Can you use a fog light switch without a relay and wire like you did with the toggle switch?
If so what wire off the switch goes where?
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post #9 of 23 Old 02-17-2020, 10:55 AM Thread Starter
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No you can not do it that way and have the "ON" light work. But if you did not care about that, then yes. You just use it as a grounding switch. Terminal #3 would be the ground and terminal #2 would be the EXT. No positive could go in for the "ON" light but I think the dimmer light would still work. Ralph, while looking at the FSM pin-outs I noticed that on PCM connector #1, cavity #6, it is for " park/neutral position switch sense". There it is! I am not sure how the PCM uses that info besides enabling the starter solenoid and the EXT function. I am sure there are other functions that are dependent on the shifter position but I can't find any other shifter position inputs to the PCM. So perhaps it is possible to "fool" the PCM into thinking we are in P/N for the EXT to work while in gear. EDIT: As far as I can tell the transmission range selector is a ground that tells the PCM it is in P/N and enables the starter relay. If that is the case, and no other functions are involved, then we have a way to enable the EXT while in gear by artificially grounding that wire. It would require a single pole double throw switch that did two things. One would be to ground the wire gong to the PCM telling it we are in P/N. The other thing would be to disable the wire that enables the starter relay. Otherwise the starter would start when the switch was on. I actually have a switch like that among my boat parts. It is 3 positions: ON/OFF/ON. So I could use it to enable the EXT, be off completely, and enable the starter. That way it would do double duty as an anti-theft switch. Interesting, eh?

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post #10 of 23 Old 02-17-2020, 11:54 AM Thread Starter
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Update: I found the schematic for the range selector switch. I looks like the starter relay wire goes right through the switch to ground. All the other positions go to the transmission control module. Therefor I believe that for our purposes we can enable the EXT while at the same time disableing the starter with the right type switch. Stay tuned.

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post #11 of 23 Old 02-17-2020, 12:02 PM
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So terminal #2 is ground and terminal #3 is to the A12 wire.
Alright now I got it.

I don't care anymore about being able to up the idle while in gear, stopped thrashing around out there a long time ago, but thinking some guys might.
I know adjusting the idle on a carb did when I was.
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post #12 of 23 Old 02-17-2020, 12:12 PM
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And you could mostly likely have the symbol illuminate when you turn on the headlights cause you are not using terminals #1 and #4.

See this is what I discovered when I put fog lights in my '00 that did not come with them.
In a 2 slot bezel the fog light connector is behind the blank in what would be the third slot. And terminals #1 and #4 are hooked up even though the Jeep did not come with fog lights.
I know this cause when I plugged a fog light switch into that connector and turned on the headlights the symbol illuminated. So I asssumed the ground, #4, was hooked up otherwise that would not have happened.
Thing is #2 and #3 are not. While they are wired to a point they only go so far.
If you look in the PDC of a Jeep without fogs you will see the relays and fuse for the fog lights are not in there.
Not only that put the terminals the relays and fuse would plug into are not even there in the PDC.
Not to mention the connectors in the headlight harness for the fog lights.
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post #13 of 23 Old 02-17-2020, 03:36 PM Thread Starter
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Yes, I guess it was cost effective to wire the harneses for whatever accessory might be ordered, but not after certain connectors. Like A-12 ending at Connector #7. That is why you find various connectors behind the dash just sitting there not hooked into anything. And empty fuse/relay holders. So get this: I did some unscientific testing today. I looked at the wiring diagrams again. You are correct- the range selector just grounds the starter relay wire so the starter only starts in P/N. The wire also goes to the PCM so it knows the selector is in P/N. It is in Connector #1, cavity #6. So lets call it A-6. So I re-opened the harness I laboriously taped up yesterday, and found the black/white stripe A-6 wire that goes to the PCM from the range selector. Luckily it is the only wire that color in the harness. I started the Jeep, let it warm up, idle down, and then engaged the EXT idle. It revved right up to 1000rpm. I shifted to D and the idle dropped. All good so far. Then I chocked the wheels, put the hand brake on, put it in D with the EXT engaged, and went to the A-6 wire that I had stripped a bit. I touched a ground wire to the A-6 and the idle jumped right up to 1000rpm. In Drive! So there it is. Now the bad news is that by doing that you can start the car in any gear. That is unsafe. So I am trying to figure out how to enable the EXT, in gear, without enabling the starter. I think this 3 way switch I have may be the ticket. It is ON/OFF/ON. I am thinking that I run the A-6 wire to the center common spade, the range selector wire to an end spade, and a ground to the other end spade. That way I can ground the A-6 wire to enable the EXT, even in D, but at the same time disable the Range wire so the starter can't work. Then in the other position the starter can work and the range selector also tells the PCM it is in D/N as normal. That is important because the warm-up sequence is dependent on being in P/N. Make sense yet? I sure have a headache but I think it will work.
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post #14 of 23 Old 02-18-2020, 02:57 AM
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I have all those same schematics too.
There is no way that I could figure any of this out.
All what you have been doing is above my head.
But you have made much progress in figuring out if this is even possible.
Again I am just guessing here but thinking a lot of guys might be interested in this.
You run across guys wanting to install a hand throttle and one time I think I read a guy
wanted his cruise to work under 35, 45, whatever the lowest MPH is that you can actually use that is.
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post #15 of 23 Old 02-18-2020, 09:10 AM Thread Starter
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I think I have it now. The A-12 enables the EXT idle when it is grounded. The A-6 tells the PCM you are in P/N so that the EXT idle only works in P/N. If you just connect them together and ground them then the EXT idle will work at all times no matter what gear you are in. The problem is that if you connect both the A-6 and the A-12 to ground then the starter can also start in all gears. Because grounding the A-6 to RS wire also grounds the starter relay. You would be bypassing the Range Selector and lose the Neutral Start safety function. There is another way to do it but the wiring has to be interrupted way over at the Power Distribution Center. I want to keep it simple.You can't remove the Range Selector wire because the PCM uses that for the warm-up sequence in P/N. So the task is to connect both the A-6 and A-12 wires to ground while at the same time disconnecting the A-6 from the Range Selector and starter relay. I think a Double Pole Double Throw ON/ON toggle switch will do that. See the sloppy wiring diagram I drew. In one position the Range Selector is connected to the A-6 and everything functions as normal. The A-12 and ground are dead. In the other position the A-6 and A-12 are both grounded while the Range Selector to A-6 is dead. This way the EXT idle is enabled in all ranges but the starter is still dependent on the Range Selector for the Neutral Start function. This requires three wires (A-6, A-12, RS) to go to the dash mounted switch and a fourth wire will be grounded at the dash. Or send that ground back to the engine with a fourth wire. I think this is the answer. The EXT idle will work at all times and not interfere with the Neutral Safety switch. What do you think?
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