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It all started when my dad go stuck at the store. Car (2004 SantaFe 2.4) cranked but would not start. My buddy came out to help me diagnose but did not bring OBD reader so we were in the dark. He tried to jump the ECU relay to the fuel pump relay and got the terminals mixed up and something went wrong (fried something maybe? Not sure?). I got it back to the house put OBD on it and it told me that the cam shaft sensor was bad. Replaced that but still had issues starting the car. I jumped the fuelpump relay and the ECU relay. (the right way) The santafe started right up. The fuel pump would not run without being jumped. I decided to get a new ECU and that fixed the problem for about a month or two then I got the same problem car cranks but no start. No OBD codes so I found another ECU and replaced it the car ran fine for another 2 months and then died again. No codes. I thought **** I cant afford to keep buying ECUs so I did some reserch and found the crank position sensor could cause intermittent no start issues with no codes. So I decided to give that a try. I found the water pump was leaking a bit so I changed that and the timing belt while I was in there. Remember the car now has both cam and crank sensors replaced. Yesterday I tired to turn the car back on and same issue crank but the car does not run.

The only way I got this car to run is getting new ECUs form the junkyard but this only fixed the car for a moth or two and then it was back to the same no start issue. I am really lost here. I can understand the first ECU going bad if my buddy jumped the wrong terminals but I dont understand how two other ECUs worked fine for a month or two and then I was back to the same issue.

This is my parents only car and I have let them use mine while I am figuring this out but I am really getting frustrated and scratching my head trying to figure out what could be killing the ECUs or if there is another issue?

Please help I have tried everything I can think of.

Thanks

Victor
 

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Remove the battery, locate the negative terminal wire, remove the wire and clean the connections on the car body, then clean the ground wires on the engine
 

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Discussion Starter #3
Thank you Camper. I will do that tonight when I get home from work. I did not think the ground would be an issue. Car only has 60k miles. But at this point I will try everything and anything. I will clean the ground wires tonight.
 

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the ECU shares some of the starter motor and ignition current, so if the ECU grounding is bad, they gonna toast the ECU. That's why you should check the ground when ECU goes bad. The ECU should have 3 grounding wires, 2 on the top of the engine and 1 maybe under the air filter cover
 

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Are the old ECU's bad?
Did you throw them out?
If not then have you tried putting in an old one to see if it works?

Just thinking that the ECU should be sturdy and should be able to bounce back from a bad grounding issue
Never know.
So, I ask
 

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Discussion Starter #6
Hi camper. Thank you for the valuable information. I am checking the 3 grounding wires now. If I find an issue and fix it will I have to get a new ECU? Or will the old one start working?

avisitor I am not sure if the Old ECUs are bad. I know as soon as I put a new used one in from a junkyard the car magically stats working for a short time. The first ECU I got from Advance Auto (a local yard pulled it and sold it to them in partnership) and they wanted a $350 core charge for me to keep my OEM one. As much as I did not want to give them my nice one (with less then 60k on it) I was happy to bring it to them as I thought the issue was fixed. So the one that came with the car is gone. The next time it happened I went and found one myself at a yard. I have both of these ECUs that came from other Santafes and both now give me a crank but no start issue (after the month or two of use) when pug them in and try to use them. I have tired both numerous times with no luck. I hope that they can bounce back and start working if I correct the ground issue. Although its strange that they work for a short time with the bad ground? I am still scratching my head on that one. Advance only had the one in stock at the time and it took me months of searching the local yards to find one myself. Hyundai wants $1,500 for a new one and Advance charged me about half that for the used one. I dread to consider having to buy another let alone finding one. At the junk yards they only seam to have the V6 laying around and I almost never see the I4 2.4. I dont know if I will find one.
 

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He hasn't been here for 11 months and the thread is a yr and a half old.
 
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