Its me again. Continuation from MCU? Had some time to do some diagnosing. Have a 88 yj, 4.2 / 258, standard, 2 bbl Carter The Metering pins on the carb are in the aft position, when starting the engine and when its running. Disconnecting a vaccum line will not advance the pins. Metered the stepper motor and got on an average of 67 ohm testing all pins to bottom center pin of the electrical connector of the motor On the test plug by the battery using a digital meter, I got approx 13 v steady for stepper motor AØ and the same for BØ. Not sure if digital meter is not sensitive enough to register voltage changes. Not sure were to test O2 sensor voltage. Is there a electrical diagram for the stepper motor itself any where, like to be able to determine if it will move. If I do the nutter bypass I will need to move the pins and not sure I want to go through the expense of a new MCU and O2 snser and stepper motor just to adjust the pins. On second e-test failed 40km/h test, idle was ok.
The pins can be manually moved. I can rock the shaft with a mini screwdriver and they will rock to the next step usually.
The Nutter bypass to dump the computer only needs two new wires and about a half hour. I run two new wires twisted from the orange and purple down at the ignition module and hook them to the orange and purple at the distributor.
The timing then needs to be set, it will have jumped and then you just go for your best lean idle with the two screws down front. Once it purrs you then go 1/8 to 1/4 turn lean so it 'just' starts to rumble.
You need to get the stepper's air pins just so the shoulder of them is sticking out. The next notch tucks the edge in, then do the idle mix.
Mike
86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00 'New' frame in the works for '08. Some Canadian Bush Trip and Build Photos:
You need to get the stepper's air pins just so the shoulder of them is sticking out. The next notch tucks the edge in, then do the idle mix. IDLE MIX?
The timing then needs to be set, it will have jumped and then you just go for your best lean idle with the two screws down front. Once it purrs you then go 1/8 to 1/4 turn lean so it 'just' starts to rumble. TWO SCREWS DOWN FRONT?
I take it you have never manually set up a carburetor.... It can be manually set up to run well once you stabilize the stepper pins right. Where is the shoulder of the stepper pin sitting now? How far from the back wall of the carb?
That carb has two mix screws down front on the bottom plate of it. These adjust the idle mix and to a point the running mix.
Stock they have a metal plug over them so maybe you don't even have easy access to them. If this is the case, it is a larger job to get at them but possible. Check if you have access to them and if not are there two metal slugs down there or a tin cap with a cross or just screws with springs like you hope.
The Haynes manual has a great writeup on adjusting that carb, the exact instructions that come when you buy a carb kit. Canadian Tire sell carb kits for about $25.00. The CJ Haynes manual is a lot better for your engine bay than the YJ one.
To set a carb for best lean idle, (after the stepper pins are set) you really want the timing proper first. Yours is now set for the computer in the loop, so the carb sets that way.
You warm it up and set the idle at the proper 650 rpm or if it won't go there, as low as it wants to run.
You then shut it off and carefully turn each of these idle mix screws all the way in gently until they stop 'counting the turns' so you have your old base setting.
Then you screw them both out to 5 turns and start it back up. Get the idle close. Then 1/4 turn at a time on each screw you start closing them. Every time you do a 1/4 turn, you have to push the throttle to give it a rev so it sets. Keep closing the screws in 1/4 turn increments, lowering or raising the idle as needed to keep it close to
650, until you feel the engine start to stumble. You then back them out
1/4 turn which is called best lean idle. Mine will just purr set like that, not a ripple in a glass of beer on the air filter.
Unfortunately that purr is just 'slightly' too rich for the sniffer, so you need to turn each screw 1/8 to 1/4 back in 'just' until a little rumble happens.
Because the pins aren't working, that suggests the engine is in 'limp home' mode which does mess with the timing. I don't know that any carb setting will pass like that without putting the computer to sleep and manually setting the timing.
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