Intermittent rough running and hard starting?

Tiny
RICKEYBOBBY494
  • MEMBER
  • 2004 HYUNDAI SANTA FE
  • 2.7L
  • V6
  • 2WD
  • 200,000 MILES
Two times in the last couple of weeks it has conked out on me, and I got it started back and it was running really rough like it was missing on one cylinder then after a few minutes of high idle and revving it up the miss went away it started idling smoothly and running good. Now it's happened again after about 2 or 3 weeks. So, I'm wondering if it is a computer or spark or stuck injector? The OBD will not give codes to a reader, and it doesn't look like there's a fuse for the OBD. Any help would be much appreciated.
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Monday, February 28th, 2022 AT 1:06 PM

19 Replies

Tiny
RICKEYBOBBY494
  • MEMBER
By the way it just started running rough again this time two times in one day it hasn't gone back to smooth running at this time.
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Monday, February 28th, 2022 AT 1:07 PM
Tiny
RICKEYBOBBY494
  • MEMBER
How do I make a donation?
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Monday, February 28th, 2022 AT 1:54 PM
Tiny
WENDY W
  • EXPERT
Hello again!

Thank you so much for posting your question in a new thread.

I've attached the schematic for the OBD II connector. Since your OBD II scanner doesn't seem to be communicating with the vehicle you might want to start by checking fuse 14 in the passenger compartment fuse block.

This video guide gives some repair tips for when the OBD II port isn't working:
https://youtu.be/6Tlg3JmgNSQ

If you are able to pull any codes, you can follow this link for more information on code definitions:
https://www.2carpros.com/trouble_codes/obd2

Please let us know if this works!

Thanks! Wendy W.
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Tuesday, March 1st, 2022 AT 11:04 AM
Tiny
WENDY W
  • EXPERT
Thank you for asking about making a donation. If you could just tell a friend about us, that would be great!

Thanks! Wendy W.
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Tuesday, March 1st, 2022 AT 4:00 PM
Tiny
RICKEYBOBBY494
  • MEMBER
I plugged in the OBD, it powered right up. Checked all fuses, found two 40-amp large square fuses blown. Labeled ECU. I replaced those fuses. Still no communication to OBD.
** Now the engine starts just fine when it's cold, then 5 minutes later it starts acting up. Like I'm losing one or two cylinders. Today I'm checking the coils for signal and spark. Getting frustrated. Can't find resistance values for MAP sensor or Crank positioning sensor to ohm them out. Thank you for your responses. I'm open for suggestions!
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Wednesday, March 2nd, 2022 AT 3:00 AM
Tiny
WENDY W
  • EXPERT
Hello,

I'm sorry you're still having trouble with the vehicle, but it sounds like you're making some headway. It's possible that the MAP or crank position sensors have failed, but maybe we should investigate the blown ECU fuses a little further.

I've attached the schematic for the engine controls (below). I see three ECU fuses (circled in red on page 2A). Do you know which two were blown? Did they blow again after you replaced them? If we can track down what's happening there, it may solve some of the drivability issues as well.

I have seen the insulation on the crank sensor wiring harness get old and brittle, leaving exposed wires intermittently touching the bell housing. This could cause ECU fuse 3 to blow. Do you see any evidence of brittle insulation on the wiring harnesses anywhere else on the vehicle?

I hope this helps, and please let me know what you find.

Thanks! Wendy W.
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Wednesday, March 2nd, 2022 AT 5:23 AM
Tiny
RICKEYBOBBY494
  • MEMBER
Below is the fuses and cover.
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Wednesday, March 2nd, 2022 AT 5:33 AM
Tiny
RICKEYBOBBY494
  • MEMBER
The 40-amp fuse that was blown on the right side of the fuse box says blr the other one I replace says rad fan.
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Wednesday, March 2nd, 2022 AT 5:34 AM
Tiny
RICKEYBOBBY494
  • MEMBER
As far as I can tell, there is no brittle or shorted wiring. This morning it is not starting easily like usual. Whatever the problem is it is not going away anymore. I'm going to try and check the coils and hope that is my problem.
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Wednesday, March 2nd, 2022 AT 5:42 AM
Tiny
WENDY W
  • EXPERT
Thank you so much for sending the video, that's very helpful. To verify, it seems like the fuses that were blown were for the radiator fan and the blower relay. Did the vehicle overheat recently before the drivability issues began?

I'm attaching the ignition coil test parameters and schematic for you; in case you need them.

Thanks! Wendy W.
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Wednesday, March 2nd, 2022 AT 5:53 AM
Tiny
RICKEYBOBBY494
  • MEMBER
Thank you for the parameters. I'll get back to you!
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Wednesday, March 2nd, 2022 AT 7:13 AM
Tiny
RICKEYBOBBY494
  • MEMBER
Well, I tested my coils and they all owned out at 12.6 k. So, I'm giving up and taking it to a mechanic, but thank you for all your help.
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Wednesday, March 2nd, 2022 AT 12:44 PM
Tiny
WENDY W
  • EXPERT
We're always happy to help. If you have an opportunity later, please let us know what the final diagnosis was.

Thanks! Wendy W.
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Wednesday, March 2nd, 2022 AT 4:40 PM
Tiny
RICKEYBOBBY494
  • MEMBER
Hi Wendy. After the mechanics diagnosed the PCM, it has been an ordeal to find another one. The part was discontinued. I found one three states away and now I have it. I'm going to install it myself. I don't even know where it is located on the car. If you have any tips or guidance, I could sure use it. I'm not sure the car is even worth the money time and effort, but I'm going to keep trying with your help. Thank you.
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Tuesday, March 29th, 2022 AT 1:41 PM
Tiny
WENDY W
  • EXPERT
Hello!

Thank you very much for keeping us posted about the PCM diagnosis. On this vehicle, the electronic control unit should be located directly to the right of the accelerator pedal, behind a panel that's held on with 3 screws.

Once that panel is off, you should see two modules, one on top of the other. The bottom module should be your electronic control unit. Typically there's a small black tab that needs to be pressed down, then the white part of the connector rotates around to release from the control unit. If you need any further clarification on locating the unit or removing the connectors, please upload some photos of the driver side footwell of your vehicle and I should be able to point you in the right direction.

I've also attached several pages of notes regarding the control unit replacement. It's possible you may need to use a GDS (Global Diagnostic System) scanner in order to reprogram the unit unless it was pre-programmed when you purchased it.

I hope this helps! Wendy W.
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Wednesday, March 30th, 2022 AT 5:48 AM
Tiny
RICKEYBOBBY494
  • MEMBER
Well, for what it's worth, the only one that I could find since they were discontinued was a used one with the same part number that mine had. I will let you know how it plays out and thank you very much for all those diagrams.
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Friday, April 1st, 2022 AT 11:23 AM
Tiny
WENDY W
  • EXPERT
You're very welcome. If there's anything else we can help with, please let us know. I hope the new ECU works out well for you.

Please keep us posted!
Wendy W.
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Friday, April 1st, 2022 AT 5:24 PM
Tiny
RICKEYBOBBY494
  • MEMBER
Hi Wendy. I am going to install the ECU myself. I have heard, but not verified, that my 2002 ECU may not need to be flashed (reprogrammed). Where or how would I verify whether or not this is true?
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Friday, August 5th, 2022 AT 9:56 AM
Tiny
KEN L
  • ADMIN
Yes, this is true, it is done with the VIN number of the car so have it ready, you can look on Ebay or Google for a service that will do this, there are many. Please let us know how it goes.
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Monday, August 8th, 2022 AT 10:10 AM

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