# Bad ECU code



## timidev (Aug 31, 2017)

1986 d21 v6 MT. The guy I got it from jumped it backwards and it hasn't ran since. fusible link replaced, new battery. The ecu was just giving me a code for a bad ECU. replaced ECU with a junkyard matching ECU (G001), it gave me a temp sender code and a bad ecu code. Replaced the temp sender, just gave me a bad ECU code again. Turns over but wont fire. 

I'm thinking about ordering a remanufactured ECU instead of a junk yard pull, because maybe the replacement ECU was simply bad/fried as well?

Any suggested direction here would be much appreciated. I read on a different thread here someone had the same truck and same dumb friend jumping the truck issue, he replaced the link and ecu and was good to go, I was hoping it'd be that easy for me as well.


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## timidev (Aug 31, 2017)

update - got another ECU from a different junkyard. This one looked refurb as it's painted black. Came off same year same motor same trans, but it was 4x4. No markings to tell me a part code but the guy there said the truck ran with that ECU in it. Just swapped it out and no go. Same starting issue. This ECU also has the code light indicator blacked out, so I cant use it to test for any other codes. I figured it was worth a try to fix the problem for $70 because a refurb ECU online is $250. I figure this is worth mentioning.


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## jp2code (Jun 2, 2011)

You can find these on eBay sometimes. Just make sure to find the right part number, like you showed earlier.

I know they seem like a gamble, too, but most of them come with 14-day money back guarantees. Sounds like you now how to swap them out fast enough, so if it doesn't work you are only out the time for the replacement ECU to get to you.

This Search Result shows a mix of prices ranging from $60 up to over $300.

https://www.ebay.com/sch/i.html?_fr...ECU+G001.TRS0&_nkw=1986+d21+ECU+G001&_sacat=0


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## timidev (Aug 31, 2017)

Thanks JP. I've seen your posts around here and you seem like a helpful and active member of this community. Once I learn more about the truck I hope to do the same. 

I'm thinking about testing one other avenue before heading down the buy another ECU path. I know I'm getting spark but it may be a fuel pressure issue. I hear the pump prime when the key goes to the 'on' position, so i don't think the pump or relay went bad. Maybe the fuel filter is clogging the system? I'm going to check that I'm getting fuel pressure, and if I am, then go back down the ECU route. I've found my spec ECU on ebay at $260 refurb or $210 junk yard pull (I'm the G001).


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## rogoman (Dec 16, 2004)

An easy way to test the fuel pump and filter is to disconnect the fuel hose from the fuel filter and Tee-in a long length of spare hose with the other end draped over the fender going into a catch can placed on the ground. Now turn the ignition key to the run position but DO NOT TRY TO START THE ENGINE. You should see fuel going into the can at a good rate for several seconds.

Tee-in a temporary fuel pressure gauge between the fuel block and fuel filter. If the engine is unable to start, turn the ignition key to the run position but DO NOT TRY TO START THE ENGINE. The fuel pressure reading should be around 36 psi which would be a static reading.

The fuel injector may not be firing. This can be tested with a "NOID" light probe.


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## timidev (Aug 31, 2017)

Rogoman - All good suggestions, and I'll get on them when I'm done writing this. One question I have so far, I looked up how to use a noid light probe it looks pretty simple, but they started the motor to test it (it idles rough as it takes a cylinder out of the equation but works). Since I can't get the motor started, would it still light up while I'm turning it over?


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## rogoman (Dec 16, 2004)

Yes, the noid light should light up during start-up.


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## timidev (Aug 31, 2017)

I replaced the fuel filter and checked to see if the fuel pump was working while I had the hose disconnected. I'm getting fuel at a decent pressure when I turn the ignition to the run position, while the pump is priming the system. I did not hook up a pressure gauge to see if it's at 36 psi. 

Next up is the noid light probe. I'll let you know how that goes.


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