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help with 89 jimmy 4x4-computer/ECM
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alfagator
Novice
Feb 18, 2007, 1:16 AM
Post #1 of 6
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help with 89 jimmy 4x4-computer/ECM
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have 89 jimmy 4.3 throttle body which i just replaced the air idle control valve. Now, no matter what I've tried, it wont idle below 2000 rpm. I followed installation instructions exactly. Previously the "service engine soon " light quit working, so cant retrieve codes this way. Its the second iac valve I've tried so a faulty valve is unlikely. The valve pintle isnt seating inside, ( I blocked it off inside and it runs ok this way, but this is only bypassing the problem ) So now I suspect the computer ( ECM )
So the question is, is there any way to determine if the ecm is at fault by testing the connections to the iac valve with a digital/multi meter ? Or any way to just test the computer in general ?
I love to do things myself and most of you can imagine the cost of taking this to an electrical repair shop. All and any help and advice would be greatly appreciated, no matter how remote ...thanks in advance :)
(This post was edited by alfagator on Feb 18, 2007, 1:21 AM)
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steve01832
Veteran
Feb 18, 2007, 5:55 AM
Post #2 of 6
(1948 views)
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Re: help with 89 jimmy 4x4-computer/ECM
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You can get an IAC valve noid light at an auto parts store that will show you if the circuit is ok and if the ECM is commanding the IAC. Since the MIL is not working you may want to check out the fuses. There should be 2 fuses that read ECM1 and ECM2. If one of the fuses is blown then the ECM is not powered up and command functions will be disabled. If the fuses are ok then check the lamp driver circuit at the ECM. This is the wire that goes to the MIL from the computer. One side of the MIL (check engine light) is fed 12 volts through the dash cluster. The ECM completes the ground side to illuminate the light. With a test light, connect the alligator clip to battery positive. Touch the probe tip to the wire.(I take a paperclip and open it up. Slide the straight end gently into the connector from the backside of the wire. Push in until you feel it touch the terminal. Touch the test light to the paperclip). Turn key on engine off. This is bulb check. If the test light glows, ECM is working and the problem is either an open wire from the ECM to the cluster, a faulty cluster circuit board, or the lamp has burned out. If the test light does not glow, replace ECM. Make sure you also replace the PROM and CALPAC chips to ensure the latest software. Post back and let us know how you make out.
P.S. If you need a wiring diagram and ECM pinout chart you may want to check out www.eautorepair.net. It will cost you a little money but you will have all of the documentation that you will need to fix the truck.
One helpful hint: If the test light glows on this test leave it connected. Ground the ALDL connector and use the test light to retrieve any codes.
Steve
(This post was edited by steve01832 on Feb 18, 2007, 6:07 AM)
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mw1871
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Feb 18, 2007, 3:24 PM
Post #3 of 6
(1940 views)
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Re: help with 89 jimmy 4x4-computer/ECM
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mw1871
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Feb 18, 2007, 3:36 PM
Post #4 of 6
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Re: help with 89 jimmy 4x4-computer/ECM
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Try checking for vacume leaks esp. the pcv hose. Vacume leaks will cause a high idle on fuel injected cars. Good luck and keep us posted.
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alfagator
Novice
Feb 21, 2007, 2:04 AM
Post #5 of 6
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Re: help with 89 jimmy 4x4-computer/ECM
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Hey Steve,
Thanks for the awesome advice here, was hoping this reply would one of success. I've accessed the computer but gonna have to wait till I find a wiring diagram and pinout chart. Both fuses are ok, would you happen to know if an ECM from a 91 would work out ? Also, I'm not quite sure what a IAC noid light is. Also, I have one of those digital dashes and hard to trace the wire back to the MIL light, but am working on it. The bulb checks out ok tho. Currently this is my only vehicle, so have to keep putting everything back together every night. Am looking into the eautorepair site, seems like a worthy investment. I can see your very knowledgeable and will keep you posted.....thanks again :)
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alfagator
Novice
Feb 21, 2007, 2:12 AM
Post #6 of 6
(1923 views)
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Re: help with 89 jimmy 4x4-computer/ECM
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Hey mw1871,
I wish it was so easy as a vacuum leak, I can get it running fine by blocking off the inside of the throttle body where the IAC should seat ( Duct tape....every toolbox needs some ) But thank you very much for the reply........will keep you posted
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