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Jeep Wrangler (1992)

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Jeep XJ Cherokee 4WD Sport 4-door (1999)

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Added: 15 September 2013 - 01:16 PM


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Getting the OEM Air Intake Back Onto an 87 YJ


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#1 Pete H.

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Posted 17 April 2013 - 07:55 PM

Greetings, I have a 1987 wrangler YJ with the 4.2 straight six, and cold weather starts and performance are tough on the carburetor (ohio weather). As such, recently I had to invest in an oem offset air intake from ebay. The problem arises that I have a 77 Dodge truck BBD on the jeep, with a manual choke. My question is: is there anyone out there that can fill me in on which of the hoses I need to connect (and to where) to get the flaps in the intake to actuate? The intake came mostly complete, but looks like it is missing one of the vacuum hoses. Would I just be better of putting in a manual linkage switch?

Looking forward to others joining this forum!


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#2 Moses Ludel

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Posted 19 April 2013 - 10:59 AM

Hi, Pete...I understand your dilemma. First off, heat for the air intake is two-fold: Later CJs and the YJs with a 4.2L have an intake manifold "heater", electrically operated, directly below the carburetor area. This heats the intake manifold quickly to provide complete combustion. Make sure the manifold heater beneath the intake manifold receives voltage and heats up.

 

Secondly, as you note, there is the air intake flap that closes when cold and opens as the engine warms (thermal air cleaner). You can operate the air cleaner flap with a thermal vacuum switch (like the CTO on the Jeep engine) as a vacuum source. This vacuum switch simply keeps the door shut when the coolant temp is below the TVS setting (120-140 degrees F, approximately) and opens the flap when the engine coolant raises the temperature above this point. Whatever TVS you use, make sure it operates air cleaner vacuum when you need it, not the opposite mode! 

 

There is also the larger thermal air hose that goes from the exhaust manifold area to the air cleaner intake. This hose needs to be connected for the system to operate properly, as this is the warm intake air source. 

 

With the simpler BBD carburetor, it sounds like your Wrangler's engine has been stripped of some vacuum operated equipment. I've scanned details from a 4.2L 1989 factory vacuum schematic for your benefit. The later 4.2L inline sixes use an elaborate vacuum circuit that includes the spark timing, evaporative emissions system, air cleaner and more. For safety sake, make sure your evaporative emissions system works properly!...See the PDF attachment...Trust this helps...Moses

 

Attached File  4.2L Vacuum Details.pdf   2.13MB   4 downloads



#3 Pete H.

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Posted 23 April 2013 - 02:44 PM

Thank you for the heads up on the vacuum system. The more I dig into this, the less I am liking what the previous owner did and what I am saddled with fixing. I was able to mount the air cleaner, but the switches were non functioning on the trap door, and some of the other little parts to it were missing. The actuator arm came off in my hand (looked to have broken off inside of the intake) so I removed the actuated gates (plastic?). As of now, I have the heated air hose pointed down at the exhaust manifold heat riser, and the main spout pointed toward the radiator. I think with this set up it may require some warm up before driving, but should alleviate driving ice up. 

Looking at the evap system...HOLY SMOKES! I knew that the PO had removed the faulty 4wd actuator and put in a cable system (trusty thing, that...) but no evap canister on there, egr is hillbillied shut. I think I need to start a new thread here...Thanks again for your help!—Pete H.



#4 Moses Ludel

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Posted 23 April 2013 - 06:38 PM

Pete, the EVAP system and EGR each have useful functions, and these need to be addressed. The vacuum diagram I furnished will help here, especially for EVAP. I can provide EVAP fuel and vapor hose routings if you need them, too. There should be a junction point on your YJ Wrangler in the left side rear body well that ties with the fuel filler functions. Check hoses at the top of the fuel tank, too.

 

As for the EGR, this is a passive device that many condemn needlessly. In fact, the EGR does little to inhibit performance, and it's good side is a reduction in upper cylinder temperatures. Without EGR, an engine can ping (detonate) and even overheat piston material and valves.

 

The intent of the EGR is to reduce upper cylinder temps to below 2500-degrees F for reduction of NOx. EGR removed or disconnected on a non-EGR engine can create up to 4,600 degrees F upper cylinder temps—an oxy-acetylene torch cuts around 6000-degrees F. Spark advance can usually be increased with the use of an EGR valve.

 

When restoring the EGR function, follow the vacuum diagram I provided. The EGR valve works from ported vacuum through the CTO switch. This means it only operates when the engine coolant has warmed. The valve opens from ported, not manifold, vacuum. Ported vacuum starts with the throttle just opening and drops off at wider throttle openings.

 

If for no other reason than to reduce risk of ping and engine damage, to permit running lower octane fuel, and to increase spark advance, restore the EGR function. You're doing the atmosphere a service, too!—Moses



#5 Pete H.

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Posted 23 April 2013 - 07:52 PM

I sure appreciate the extra information on this. The fella who was teaching me the ins and outs of my jeep just got switched to a travel assignment, so I am trying to figure out just what I need to do to get her running safely. To make matters worse, we made a deal that he would teach me how to fix stuff on it but instead he went and started fixing stuff himself... (I'm grateful to him, but I'm kinda confused about what does what now.)

I had installed a new fuel tank, pump, filters, and lines recently, after the jeep came back from the shop with aluminum shavings in the tank, (I swore that was the last time I would trust a mechanic with my vehicle) and noted that the evap canister was weird...Well as I noted earlier, it really wasn't there (I pulled it apart and there were no innards to it.

Looking at my fuel lines... I have one coming from the tank to the fuel pump, one frome the pump to the filter, one from the filter to the carburetor, and one from the filter to the tank return. The gas tank is vented to the fake evap canister. Can I find those diagrams in the MR 279 and 280? A company in Ohio sells the FSM on disk for about $30.

I have nothing against the EGR, but it looked like the po had a serious vendetta against it. The valve itself was cut off and looks like the stub was soldered shut. Again, thanks for the diagram. Hopefully, I can take the jeep to that early 60's format we had discussed, and get her running more reliably.
Many thanks,
Pete H. 



#6 Moses Ludel

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Posted 24 April 2013 - 01:36 AM

Pete, the routing of the fuel supply lines and the return line sounds correct if the hoses are attached properly. The factory (AMC or Mopar, depending upon the YJ Wrangler model year) service manuals will be a valuable tool for working on this Jeep. Factory manuals contain the vacuum circuit diagrams, EVAP information and fuel line routings—plus anything else you might need.  My 1989 YJ Wrangler era books include Jeep Chassis/Engine/Body (including powertrain and axles, steering, etc.) and the Jeep Electrical book.  Verify that the CD version has the contents for both...If you plan on doing your own work from here out, AMC or Mopar service manuals for your year and model should be your first "tool" investment!  A CD is handy, this is PDF and allows for printing individual pages when you perform work.

 

Looking forward to your posts and trusting that others will jump in with helpful comments, too!...Moses




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