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Unread 11-25-2015, 02:17 PM   #1
mark1305
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Simple Questions That I Failed to Find Answers For

I've been hitchhiking/hijacking on a couple of other threads with questions that kind of fit in so I didn't want to create a new thread to repeat some of the stuff.

But now I'm down to a few questions that have probably been answered, but escaped my searches.

89 4.2L; nuttered; BBD had rebuild kit installed within last 2 years and still working well; no EGR thanks to a PO and the manifold bung welded up so that's a long way off before restoring.

Past few days finished removing the under dash ICM and all the wiring I could identify as part of it. Located tach lead and good choice switchable 12V for upcoming CRT distributor install very soon now.

Latest research tells me I can remove the 4"/10" vacuum switches and associated wiring from the firewall. Correct?

If the ICM and soon the ECU are gone, will I be able to remove the yellow capped diagnostic plugs and associated wiring next to the passenger side hood hinge?

I also have the two relays outboard of the battery and hood hinge which are usually described as fuel pump relay (N/A for me) and b-latch which probably isn't functional since most of the plumbing to the carb has been removed or disconnected and capped off. I need to do a repeat test to verify the motor will crank and run either of them removed. One had no effect, but the other I wasn't sure. Right now I'm waiting for one eye to get un-dilated after a post surgery follow up today - hint: even though you have a spare eye, if you get used to focusing with two it sucks having one act funny on you. Just like it sucks getting old enough to have eye problems to begin with. But with all the stupid stuff I've done to injure mine over the years, this Thanksgiving I guess I'll be thankful to still have two that work more or less properly.

Edit: Couldn't wait so I tested start and run functions with both of those relays by the hinge hood removed and no difference. Might get to a road test later, but I think at this point they are excess or will be for sure after the CRT distributor goes in.

So biggest curiousity remains the yellow diagnostic plugs and the 4"/10" vacuum switches which seem to be gone for sure.

Happy Thanksgiving to all !

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Unread 11-25-2015, 03:01 PM   #2
Mike Romain
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The yellow capped plugs are diagnostic plugs for all the emissions stuff that no longer works, so are the vacuum switches. Relay on firewall might be for the carb manifold heater, you might want to keep that.
This link has a section on what to keep for a good runner as far as vacuum goes. Not all of it is junk. http://www.jeepforum.com/forum/f8/ho.../522262?page=1
Also how to set the carb up best is in there.
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Unread 11-25-2015, 04:48 PM   #3
Drednot
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Agreed...
You can lose the 4 and 10 switches
You can lose the diagnostic connectors
The relays function depends on whether you have the carbed 4.2L or TBI 2.5L
You don't need the lower one for sure, and being in florida, you don't necessarily need the manifold heater, either. It was primarily for cold startup emissions, but it doesn't hurt to have it. just make sure you don't disable its switch down by the oil pressure port

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Unread 11-25-2015, 06:09 PM   #4
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Cool. Thanks! Pretty much what I had surmised from previous research. I've unplugged the manifold heater for now just because of the average temps down here. With another El Nino season, it shouldn't be needed for another year.
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Unread 11-26-2015, 01:44 PM   #5
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Quote:
Originally Posted by Drednot View Post
Agreed...
You can lose the 4 and 10 switches
You can lose the diagnostic connectors
The relays function depends on whether you have the carbed 4.2L or TBI 2.5L
You don't need the lower one for sure, and being in florida, you don't necessarily need the manifold heater, either. It was primarily for cold startup emissions, but it doesn't hurt to have it. just make sure you don't disable its switch down by the oil pressure port

Drednot, I know the oil pressure switch that feeds the ECU system will prevent starting if oil pressure doesn't come up while cranking. But after I've switched to my HEI distributor that runs off just one switched 12V wire, does that safety feature go out the window as well, especially since I doubt I'll ever need the manifold heater function. Although looking at that compound oil pressure switch combo, that would be one of the last items I'd look to remove just for appearances sake.
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Unread 11-26-2015, 02:44 PM   #6
Drednot
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I'm almost certain the oil pressure switch only provides power to the electric choke coil, and power to the manifold heater relay coil. The manifold temperature switch will then provide a ground for the relay coil when cold to energize the relay. You want to keep the oil switch for electric choke operation.
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Unread 11-26-2015, 02:49 PM   #7
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Makes sense. I had forgotten that tidbit about the choke feed. Thanks much. BTW, in addition to thanks for all the help, Happy Thanksgiving!
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Unread 01-02-2016, 07:09 AM   #8
yellowdream
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I have a manual choke manifold heater deleted on my 1990 wrangler with 4.2 and installing a DUI distributor andam in the process of removing the ECM and all of the wiring associated with it. Can I completely remove those relays and wire to them? motorcraft 2100 carb
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Unread 01-02-2016, 07:20 AM   #9
Mike Romain
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Quote:
Originally Posted by yellowdream View Post
I have a manual choke manifold heater deleted on my 1990 wrangler with 4.2 and installing a DUI distributor andam in the process of removing the ECM and all of the wiring associated with it. Can I completely remove those relays and wire to them? motorcraft 2100 carb
Yes.
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86/00 CJ7 Laredo, 33x9.5 BFG AT's, 'glass nose to tail in '00, 'New' frame,wires and plumbing in '09. Carter BBD Carbed 4.0 HO in '10.
89 YJ Renegade. BBD Carbed 4.0 HO. Locked front and rear with 33x9.5 BFG AT's
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Unread 01-02-2016, 10:23 AM   #10
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Yes +1.

Just finished tracing each wire one at the time and removing them a couple of days ago. Deleted the manifold heater but kept the electric choke heater off the oil pressure switch for now. HEI distributor still sitting on the bench while I start to recover from a bout of Bell's Palsy. As soon as I can clean off the side of the engine without risk of getting spray or anything in my affected eye (can't close it tightly all the way yet and it has no blink response yet to protect itself) the HEI goes on and the few remaining wires running the Nuttered ECU and old distributor/coil go bye bye.

Oh yeah, on my 89 there is a red and red/white pair with a connecter that just form a loop below those relays you can remove. When I unplugged the connecter it cut power to the clock. So I kept that circuit. Don't know if the 90 model has the same circuit or not.

One of the side benefits of meticulously tracing each wire and disconnecting/reconnecting all connectors and checking that the Jeep would start and the gauges continued to work was that after pulling and installing the connector for the oil pressure gauge from the sensor a few times, what was an intermittent pressure gauge now seems to be working full time.
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Unread 01-03-2016, 08:06 AM   #11
yellowdream
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thanks Mike and Mark been reading articles on this forum since I bought the jeep over a year now but have had all my questions answered without actually posting up until now. and mark I was wondering what that loop was thanks again
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Unread 01-03-2016, 02:36 PM   #12
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Cool! This forum is a great repository of info on just about every topic. And Mike is a great help to lots of folks including me.

And welcome aboard!
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