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I installed a new isa. I can manually run it out and back in. But it will not move on its own. I've done all the test's including closed idle and nothing. I checked and have continuity from plug to ecu and test switch and nothing appears shorted. It doe's nothing when I turn off key. Any thoughts 

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Do a voltage reading on the leads when you KEY OFF.  Check voltage with KEY ON.  Verify that you have a ground circuit that's working.

Turning off the key should have the ECU opening the ground circuit...Perform a ground continuity and ohms resistance test at the ECU ground and the ground feed to the ISA motor.   You can have continuity but high ground resistance that creates a voltage drop.

Check your grounds as we have discussed at the 2.5L TBI troubleshooting.  The ground near the dipstick to body/firewall is notorious for high resistance over time.  Clean up the ground connections and see whether that helps.

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Thanks for your reply, you seem to be the best resource for us home grown repair men.  I'll do some more checking on grounds and resistance between ecm connection and isa plug. Is there any wiring diagram available for the relay next to the battery and the solenoid  below the battery. I'd like to understand where to expect 12 volt and 5 volt. I have had to fix some corrosion below the battery before. Hope it's not ecm, don't think I'll find a replacement. Thanks again for your help!

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csmart...The Jeep YJ 2.5L TBI was a 1987-90 phenomenon.  You're in a limited cohort of Jeep owners, which prompted our extensive dialogue at the forum.  There has been a flood of discussion around this engine and chassis.  The 2.5L TBI was also a Cherokee/Comanche standard as well, so we've helped Jeep owners with those models as well.

There are two books in the Mopar/Jeep factory service manual series for your Jeep YJ.  The "Electrical" book contains all of the wiring diagrams for your model.  Perhaps you can find a print copy at eBay or an online PDF.  Try a wiring diagram search under your vehicle/engine type.

Moses

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So far grounds have no resistance,  while in still cleaning connections I thought I'd make sure I'm getting 12 volt to ecu, pin 3 ingnition is good, 4 battery good, 7 B+ latch good, should I have it on 19 system power B+, because it's no voltage. Not sure where it goes to

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5 volt at closed throttle + side key on throttle closed, run isa forward and it goes to 0 volts. No voltage on the reversing side of plug with key on or off and never loose the ground continuity at the plug. I'm stummped.

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Another update, after back and forth studying and searching I finally took ecm apart to get a visual inside as I traced out the pins for the forward and reversing of isa I seen this, 

20171216_183451.jpg

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That will do it, csmart!  Nice troubleshooting work!...I found this offering online:  https://www.partsgeek.com/gbproducts/DC/2222-05204754.html?utm_content=DN&utm_term=1987-1990+Jeep+Cherokee+Electronic+Control+Unit+A1+Cardone+79-4763+87-90+Jeep+Electronic+Control+Unit+1988+1989&fp=pp&gbm=a&utm_source=google&utm_medium=ff&utm_campaign=PartsGeek+Google+Base&gclid=EAIaIQobChMIx_Wu35ua2AIVkIJ-Ch0R1QaWEAQYASABEgLns_D_BwE&ad=47584901292

You might shop price or various sources for the A1 Cardone rebuilt ECU.  I recently (prior to SEMA Show) installed an A1 Cardone front driveshaft assembly in our 2005 Ram 3500 4x4.  I was skeptical but did so because the factory driveshaft is so poorly designed and seemed like a waste of time to rebuild.  I am pleased with the Cardone assembly and its balancing.

While at the SEMA Show, I took a day to visit the AAPEX Show.  I spoke with the staff at the Cardone booth and was impressed with the rebuilding strategies employed by this company.  They have a global market and generally an abundance of cores on hand.  I would consider this a reliable source, and the price seems reasonable, too.

Moses

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Thanks again for all the help Moses, I spent a good amount of time on this search this past Sunday. My findings are if you have one of these ecm's they are harder to get everyday, several online auto parts show it online but when you call they are no longer available. Local Napa store could send it off for rebuild (A1 Cardone) but one smaller parts store i use alot called and had 3 places with one on the shelf. It should be here today, hope I dont mess it up :) . Again thanks for your help and taking the time to find some information for me, Have a Merry Christmas and Happy New Year.

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csmart...Make sure the wire circuits use the factory relays and fuse protection via the OEM method.  Verify that wiring looks "original" and is routed accordingly...Try to eliminate the issues associated with blowing out elements of an ECU board.  Could have been a defective board or faulty components like the old ISA motor.

There are repair outlets that work with modules only.  I had success years ago with ModuleMaster out of Idaho (https://modulemaster.com/rebuilds/).  They rebuilt a G.M. Kelsey-Hayes ABS module and saved us $650 compared to the new OEM part cost.  An outfit like this might be able to rework and test a board like yours if you find a need in the future.  Let's be optimists about the rebuilt board that's on its way.

Again, you really did a thorough troubleshooting job here.  Good news is that you've already accessed the ECU and are ready for a quick install of the new unit...Keep us posted!

Moses

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I have not bypassed any fuses or relays and have not see any sign of that, I am a lineman by trade so I know how important it is for over current protection. The rebuilt ecm seems to be working just fine. If I run across another one for sale I think I'll grab it for a spare. I will do some searching for info to make sure all the fuses and relays are where they are suppose to be. Snow expected tomorrow and really cold temps after that so I want to make sure the jeep is in as good of shape as I can have it for now.

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csmart...Thanks for sharing your in-depth troubleshooting on this topic.  Most want the problem to be a simple parts replacement, preferably just the ISA.  You took troubleshooting to the next level. 

I've suggested the possible need for a new or rebuilt ECU/ECM in many discussions around Jeep 2.5L TBI models.  You graphically showed what the actual damage can be, these ECUs can be 30 years old!  (Does anyone have a PC motherboard that's lasted that long?  Amazing, really.)  You inspected the unit internally and actually pinpointed the burned out component on the board, very graphic in your photo!

The cold weather should be a test for both the ISA and the rebuilt ECU.  I'm guessing that you might have been able to replace the burned board component in a pinch, individual pieces can sometimes be found through computer/electronics suppliers.  The trick is removing and soldering the new piece onto the board.  Maybe this could be a spare board?

Be safe in your work, it's the "season" for power outages.  Thanks for your service to the community!

Moses

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Ok it's 3 degrees out with a wind chill of -10 other than the starter not wanting to work, the old dog started and ran just like it should. That is the result I hoped for. Now I can spend money on it and now I'm not completely wasting it.

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There is warm air coming from the vents but the amount of cold air entering around all the dried up seals (door mostly) keep it from getting real warm but its good enough to drive. It needs more air volume from the heater blower. -6 degrees this morning and again other than the jeep not wanting to turn over it finally did start and run. Got new starter to put on and see is that eliminates some of the drag on on the starting system. Here is a few pics of how it sat outside for a couple years until I rescued it. Not bad for $950

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Incredible buy for $950!  Suggestion:  I installed a Kat aftermarket block heater on our '99 4.0L six.  Easy to install if a freeze plug is accessible.  Cheap, reliable solution, our engine is ready to fire and does not have an oil drag issue.  We plug in when anticipating a sub-freezing morning.  The unit has worked through seven winters so far.

Good for the lower end engine bearings, the starter, heater and defroster, a win-win.  Does require 110V AC current handy, we have an extension cord designated for this task.

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