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  • I4 Weber set-up

    I am installing a Weber on my '85 -2.5L.

    Why should I bypass the MCU (computer), and disconnect the EGR as the instructions say.

    This is my logic- please advise if flawed:

    In original configuration, the MCU receives inputs from various sensors and used the data to primarily control the carb. The MCU also receives info from the knock sensor and engine speed info from the distributor which it uses to advance or retard the timing. It seems to me that the MCU should remain in the system for timing purposes. The Weber does not require the carb outputs therefore those connections can be abandoned. The MCU also controls the pulse-air system from the 4" and 10" vacuum switch inputs which reduces emissions (without reducing power). The EGR system can be reattached minus the thermal vacuum switch that was in the air cleaner. It will still operate when the engine is warm because it is routed through the coolant temperature override. Finally, the vapor canister should be retained in the original configuration, ported vaccum from CTO as the signal, manifold vacuum from purge line and the bowl and tank vents.

    Am I missing some critical piece of basic understanding? It seems that MCU is so limited in function that it should be retained for timing and pulse-air operations, and the smog systems don't adversely effect engine performance so they should remain as well.

  • #2
    Weber installation success

    I submitted a thread asking for help with my Weber installation on an '85 CJ7 with an I4. Many read the question but I got no replys. I assume that my question was very rare as most people (I included) would just swap the engine and therefore there is little experience.

    For anyone contemplating a Weber swap I would advise that it is worth the money and effort. I would caution that the instructions advise the removal of emissions controls and plugging the EGR valve.

    My opinion is that since the emissions control system (without the carb) does not reduce engine power, one would be enviornmentally responsible to retain them. It is also an advantage to have a vehicle pass emissions testing in required areas.

    My Jeep now sports the Weber, has working emission controls, EGR system, the original computer controlled timing, fuel vapor collection, and more economy and power than stock. If anyone is interested in doing this modification I have several suggestions and materials that would certainly help.


    • #3

      Almost always if you get no response Dagan, it's because everyone is scratching their head going, 'I dunno.'

      You might consider a write up for future searches of the same type trouble.


      • #4
        I would of been one of those head scratchers. I've put a lot of Webers on a lot of cars but I usually have the engine in front of me.




        • #5
          Hey Daganscj7, I have the same jeep you do and have recently torn off my carb, emissions, and cylinder head. Could you send me some info on your weber, or are you concidering the mpi modification? Thanks.


          • #6
            Hey guys, here the skinny on the Weber computer question. The electronic controlled carbs on Jeeps up to the F/I years in 1987 used a Ford type fuel feedback system. This was tied to the distributor but did not electronically control timing. They did not start using that style system until the F/I required it. When the carb is removed you basically disarm the system because it no longer has a carb to control. You can just unplug carb and leave stuff hang and it will work fine. If you want to clean up engine compartment you can remove the whole computer harness, but it is a power feed for ignition system(this is where people are confused on operation of system) and some wiring has to be rerouted. I ran the Weber on a 1985 XJ with 4 cyl and had great luck. Better fuel economy and driveability all around.


            • #7
              Sorry for the delay. I am currently in Iraq and won't be home for awhile. Depending on your timeline I plan to sell the drivetrain forward of the transfer case. The motor has 29,000 miles, the Weber, and completely new cooling system. I plan to install a FI 350 and SM465.

              As for the MPI I also purchased some components like the intake with rail with injectors and the distributer, if you want them I can have the wife ship. I got it for about $75.00. I needed the thing for a daily driver for a few months so I did the Weber thing. The FI research I did with CUSTOM FI looked promising but it was still a 4 banger and a T-4. If you are just going the Weber route I highly recommed it. The only PITA is the adapter for the carb to manifold. I remember that the space was quite tight and wrenches only fit in specific orientations. Take the time to dry fit the entire assembly and snug up the bolts to get the sequence. Then disassemble it, add the sealant and reassemble. The throttle cable and choke plug right in, but you'll need to buy a return spring and fab a bracket to attach it to. I didn't tune it very well, but it runs much better than the stock setup. If you have any other questions I'll try to remember what I did, otherwise good luck.


              • #8
                Well when you put the Weber carb on you pretty much make it so you cannot pass emmisions. You have to have original type, Weber does not cover that part.
                So I agree with leaving the EGR valve connected as it help with the ecology, but as for the bypass, as woody said it doesn't matter any more so you might as well remove it.
                Now the FI conversion is really going to help with passing emmisions, you will like that.