How to tell if ECU is bad - Defender Source
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Old December 17th, 2012, 09:10 PM
wantone
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Rick Thompson
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How to tell if ECU is bad

I have had wired stalling as posted before. The truck would cut out or miss really bad & sometimes die but would always come around & run. I changed the fuel filter. Silver relays. Then though the ignition amp was bad so i changed that. Then changed the stepper for the heck of it. Then i thought the alt was bad so i just put on a reman bosch unit (remaned by bosch). What is odd is after i would change something it would run well for a day or two, then the problems come back but in a different form. After i put the alt on, the idle was high, typical od the ECU resetting the idle with the stepper. Then when coming to a stop it would sometimes drop to 200 rpm & thren go up to 600-800rpm. Twice pulling out from a stop light it would shut off for a second, not miss but off, and then take off & run fine. Then just now coming home i let off the gas & pressed the clutch to see what would happen & the rpms dropped to 0. But then started right up & ran & idled. So what could be left? Has new cap & rotor. 150k miles. So could it be the ECU? I am so ready to just carb the damn thing....
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  #2  
Old December 17th, 2012, 10:09 PM
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Jason England
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If it works its not bad.

------ Follow up post added December 17th, 2012 10:10 PM ------

Where are you? I have an ECU testor or you can try rover gauge to figure out what's going on.
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Old December 17th, 2012, 10:21 PM
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Rick Thompson
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Omaha nebraska. So if the ECU is bad it wont run at all? Could the VSS be bad? I did replace the ignition module before the alternator, if the alternator was bad, which i am pretty sure of, could it ruin the new one within a couple thousand miles?
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Old December 17th, 2012, 11:43 PM
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I have had similar symptoms on three occasions, with three different causes. Two were my fault and one was maintenance issue.

The ground cable to the transfer case was corroded an needed replacing. I had also found and replaced a broken ignition switch which didnt fix it.

Cleaned the MAF hotwire after contaminating it with excess oil from the K&N filter. Just unclipped the MAF from the air filter an hose and flushed out the hotwire port with a can of MAF Cleaner.

Power washed the engine bay and loosened the connector to the inertia switch. Only located it after I couldnt hear the fuel pump run for its 10 seconds before running the starter motor. Nope havnt powerwashed the bay since then. Also zip tied the connector on...
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Old December 18th, 2012, 06:05 AM
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During a cold start, will it maintain idle without adding gas? Meaning it will start fine, but instantly drop to 200 rpm then shut off. To overcome this, a little right foot is required to maintain idle until the issue goes away in 30 seconds on it's own.
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Old December 18th, 2012, 07:01 AM
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Jason England
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Are you throwing any codes?

Does your code reader work?

VSS issues could contribute to what you describe. But my VSS is currently not working and it doesn't cause rough idle ... Maybe the occasional stall.

Did you check your air hoses with carb cleaner?
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Soapy water / KY jelly, etc. is is basically a must. Yes, good idea to remove trim panels - only takes 5 more minutes to do so.
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Old December 18th, 2012, 08:54 AM
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Rick Thompson
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No codes, but how do you check if it works? When i turn the key over it flashes a dim "00" or so it seems. Whatosition does the key need to be to show a code? Could the old alternator ruin the new ignition module? & if so would that produce the current symptoms? Thanks alot for the help.

It starts cold fine & idles fine. The dropping of idle i talked about is sporadic, so it the sudden short loss of power
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Old December 18th, 2012, 09:25 AM
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When you remove the battery and reconnect it ... you should see a code 02. The codes are clear and bright ... if they are dim ... that's not a good sign. check your engine ground straps ... easiest way is to run a starter cable from negative battery to the engine block to see if this improves it.

Investigate roverguage ... it will tell you a lot of info ... like the actual voltage read by the ECU ... this is important because the alternator may be good but the grounds are sucking the voltage.
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Soapy water / KY jelly, etc. is is basically a must. Yes, good idea to remove trim panels - only takes 5 more minutes to do so.
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Old December 18th, 2012, 09:34 AM
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ok, thanks so much. i will run the ground from the battery to the engine block just for good measure, or can i run it to the gearbox? when you reconnect the battery and the code should say 02, is that with the key on, truck running, or will it just flash that number for a brief period of time?
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Old December 18th, 2012, 09:42 AM
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Just to mention tractor supply has braded ground straps.
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Old December 18th, 2012, 10:54 AM
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i also forgot, my radio would intermittantly turn on and off randomly, but my heater fan and lights never did go out. a bad ground could do this couldnt it?
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  #12  
Old December 18th, 2012, 11:03 AM
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yes it could!
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Old December 18th, 2012, 11:17 AM
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so all my wierd intermittant stall, sputtering, stop idling etc. could be the simple ground? so what is the absolute best way to ground the damn thing? ground the battery to the block like suggested earlier and then replace the braided strap from the gear box to the frame?
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Old December 18th, 2012, 11:23 AM
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pretty much...its the whole trouble shooting game. Go to A, if not go to B...and so on. Not fun.
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Old December 18th, 2012, 11:30 AM
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what do you think is the best way to go about grounding it? simply replace the factory stuff or is a different route that may be better?
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Old December 18th, 2012, 09:16 PM
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Replaced the neg grounf with a new one from napa. Bolted it to the cross member & a short one from the block to the frame. It worked!
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Old February 7th, 2013, 09:24 PM
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Rick Mabus
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I am now having something similar. I did this take care of your long term issues?
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