Does an 87 throw any codes? -
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post #1 of 5 Old 04-30-2013, 09:08 AM Thread Starter
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2015 JK Wrangler 
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Location: NW WA
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Does an 87 throw any codes?

Just wondering if a 87 4.2 will show any if I take it to a shop? I don't believe my stepper motor on the carb is working. I don't see it ever move when working the throttle. I assume the computer controls it, its running so its working I guess.
I ordered a reman stepper off of Ebay I figured I give it a try, before I take it somewhere. Just don't know if any of the shops are really able to troubleshoot these old rigs or have proper diagnostic equip to test these rigs. Everyone says ya bring it in we should be able to figure it out, I've thrown so much $$$ lately I just have to try & save a $$ if I can.
It has a very erratic idle when cold & poor throttle response on the hwy. Thanks for any ideas!

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post #2 of 5 Old 04-30-2013, 09:29 AM
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The '87 is ODB1, which means you have to turn the key on-off-on-off then watch for the flashes to read the codes.

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post #3 of 5 Old 04-30-2013, 09:34 AM
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You will not get codes off an 87. Its possible your O2 sensor is bad and that can be tested with a voltmeter.
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post #4 of 5 Old 04-30-2013, 10:10 AM
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The 4.2L is pre-OBD 1. The computer does not record or throw codes, it only sends real-time binary signals to the diagnostic ports located on the passenger side of the engine bay next to the battery. In order to read the signals you need a diagnostic reader. However, you will have to make your own reader, as nobody manufactures a reader for the 4.2L setup. Furthermore, you need to understand what the signals mean in order to be able to make any sense of the info. The signal is binary - either a light in on or it is off for a circuit.

Fortunately, that info is available in the following website: Adventures Under the Hood. That site is the best one to explain what does what in the factory setup for the 4.2L, and the various ways to go about testing bits and pieces without needing a diagnostic tool. I recommend you read the whole site. Good stuff that will help you figure out the 4.2L setup. If you plan on keeping the Carter BBD, I recommend building a diagnostic reader as it will give you quick and easy access to basic computer signals allowing you to verify computer related functions.

Note: I'm assuming here that the computer is connected and the Nutter bypass has not been done. The purpose of the Nutter bypass is to essentially disable the stepper motor, and the computer controlled timing adjustments (basically making it a non-feedback carb). If the stepper motor has never worked since you acquired the Jeep, check that the bypass has not been done, and that the computer is still connected.

If the bypass has not been done and you are running an unmodified factory setup, you'll need to start by verifying that the computer is taking over and that the stepper motor is getting signals. Tips and tricks on how to do this without a diagnostic tool can be found in the website mentioned above.
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post #5 of 5 Old 04-30-2013, 01:54 PM Thread Starter
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Thank you for such informative replys! Yes it is totally stock & unmodified. I had the "stepper motor" replaced probably about 12 yrs ago. Has run really well ever since until a month ago.
That's what I was wondering if the stepper was getting any signals. That's why I was going to try that reman unit off ebay. I will certainly check out the site regarding the 4.2 circuit. At this point I prefer to keep it stock as I have done so much in the last several months. I would just like to replace something & be able to drive it for a little while. Maybe later I will perform the Nutter Bypass.
At this point here in NW Wa they don't test for the EPA, but its coming. So I would like to maintain it so it could pass possibly, without spending the big bucks for the injection system. Thank again!
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