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Thread: WARNING: Fuel Pump Relay

  1. #1
    SoCalEvo.net Vendor



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    WARNING: Fuel Pump Relay

    I am writing this as a warning to those who own an Evo X. There has been a couple of threads on Evom about Evo Xs that are running lean on the stock tune at WOT. I have not encountered that until recently. I was baselining an Evo X for a tune and the car was running unusually lean. The car had an exhaust and an HKS drop-in filter. Here is the way the AFR looked on the stock tune:



    I have never seen such a lean AFR on the stock tune. The lean AFR and the advanced stock timing made the car register 10-14 counts of knock by redline. The owner and I surmised that this was a fuel related problem. The car was not getting the needed fuel during WOT operation.

    Luckily the owner of the car is an expert electrical trouble shooter. With the help of the service manual he discovered that:

    …the fuel delivery system on the Evo X has two voltage operation states. One state is at low load and it supplies the fuel pump with a low voltage that goes through a resistor circuit to drop the voltage prior to going to the fuel pump. The second fuel pump voltage state occurs at high load conditions, not necessarily WOT, but high load. I don't know what the various determinants the ECU uses or what strategy Mitsu used to initiate the high voltage state, but I do know that the ECM powers up fuel pump relay #1 during higher load running conditions.


    Using a multi-meter and a power source he tested the resistance on the fuel pump relay and he discovered that it was OL, which mean that it was Out of Limits, which mean the circuit stayed open. He then tested the horn relay (green trace on picture and same type as the fuel pump relay) and found that it was working fine. So he determined that it was a faulty fuel pump relay.

    A few days later he came to my place and we swapped the high beam lamp relay (blue trace in the picture) with the fuel pump relay; the high beam lamp relay being the same type as that of the fuel pump. Then we hooked up my logging equipment and went logging on the stock tune. The car ran pig rich. This is the first time I was happy to see an Evo X running rich Here are the stock runs with the functioning relay:



    I just want to warn everyone with an Evo X about this. This is very serious and can blow your engine. The relay that Mistu used for the fuel pump is weak and it is failing. This is my first encounter with this problem, but I am sure it is not going to be my last.



  2. #2

    Re: WARNING: Fuel Pump Relay

    WOW are you serious!!!! Ouch!!! Damn them

  3. #3

    Re: WARNING: Fuel Pump Relay

    wow that is no bueno

  4. #4

    Re: WARNING: Fuel Pump Relay

    so are you saying we should replace the existing relay with the one that is used for the high beams? or the car should go to the dealership to get this reported and corrected??

  5. #5
    Canyon Racer
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    Re: WARNING: Fuel Pump Relay

    Wow! Good find NJ!

  6. #6
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    Re: WARNING: Fuel Pump Relay

    Quote Originally Posted by bmguser
    so are you saying we should replace the existing relay with the one that is used for the high beams? or the car should go to the dealership to get this reported and corrected??
    First you need to find out if you have this problem on your car. Not all Evo Xs are doing this. This is the first time I encountered this.

    If you have a stock tune, then log the AFR. If it is rich, ie, in the low 10:1 ratio, then your car is fine. If it is lean, like this car, then you have to get the relay replaced. Just buy another relay from the dealer and replace yours, IF your Evo has this problem. The relay is cheap.

    I doubt that the dealer is going to replace the relay for you w/o giving you a song and dance routine about how you do not know what your talking about.

    Edit: One test that the owner and I conducted was to swap the fuel pump relay into the high beam relay and turn on the high beam. The high beam came on and then it SHUT down after a few seconds. That indicated that the fuel pump relay was failing.

    You can conduct the same test IF YOU KNOW WHAT YOU ARE DOING. If you do not know what you are doing, then leave the car alone.

  7. #7

    Re: WARNING: Fuel Pump Relay

    Good info. It sucks but it's good.

  8. #8

    Re: WARNING: Fuel Pump Relay

    Does anybody have a howto on how to test the relay with an multimeter? ¬*Additionally, anybody got a the part number for the stock relay and do they have aftermarket relays that one can just buy locally (eq. napa)?

  9. #9

    Re: WARNING: Fuel Pump Relay

    Quote Originally Posted by Looney Tuning
    I am writing this as a warning to those who own an Evo X. There has been a couple of threads on Evom about Evo Xs that are running lean on the stock tune at WOT. I have not encountered that until recently. I was baselining an Evo X for a tune and the car was running unusually lean. The car had an exhaust and an HKS drop-in filter. Here is the way the AFR looked on the stock tune:



    I have never seen such a lean AFR on the stock tune. The lean AFR and the advanced stock timing made the car register 10-14 counts of knock by redline. The owner and I surmised that this was a fuel related problem. The car was not getting the needed fuel during WOT operation.

    Luckily the owner of the car is an expert electrical trouble shooter. With the help of the service manual he discovered that:

    …the fuel delivery system on the Evo X has two voltage operation states. One state is at low load and it supplies the fuel pump with a low voltage that goes through a resistor circuit to drop the voltage prior to going to the fuel pump. The second fuel pump voltage state occurs at high load conditions, not necessarily WOT, but high load. I don't know what the various determinants the ECU uses or what strategy Mitsu used to initiate the high voltage state, but I do know that the ECM powers up fuel pump relay #1 during higher load running conditions.


    Using a multi-meter and a power source he tested the resistance on the fuel pump relay and he discovered that it was OL, which mean that it was Out of Limits, which mean the circuit stayed open. He then tested the horn relay (green trace on picture and same type as the fuel pump relay) and found that it was working fine. So he determined that it was a faulty fuel pump relay.

    A few days later he came to my place and we swapped the high beam lamp relay (blue trace in the picture) with the fuel pump relay; the high beam lamp relay being the same type as that of the fuel pump. Then we hooked up my logging equipment and went logging on the stock tune. The car ran pig rich. This is the first time I was happy to see an Evo X running rich Here are the stock runs with the functioning relay:



    I just want to warn everyone with an Evo X about this. This is very serious and can blow your engine. The relay that Mistu used for the fuel pump is weak and it is failing. This is my first encounter with this problem, but I am sure it is not going to be my last.


    Good job, Naji.
    John Mueller www.muellerized.com
    Expert service and suspension work, including insurance repairs professional competition driver coaching and chassis development, our engines and chassis have won in SCCA/NASA/IMSA/FIA road racing, SCORE Off Road, SCCA ProRally Shock dyno service, MIG/TIG welding, tube bending/fabrication, race engine configuration
    30 years experience

  10. #10

    Re: WARNING: Fuel Pump Relay

    Nice naji O0
    I forsee a recall TSB in the future
    Forum Nazi-mods blocked my PM box for no apparent reason, email me:<br />[email protected]<br /><br />My Blog<br /><br />&#039;official&#039; Fanboi of GM cars and LooneyReeseGSTdr.GRAYself tuning (or just tuning in general)

  11. #11

    Re: WARNING: Fuel Pump Relay

    Scary, but nice find Naji.

  12. #12

    Re: WARNING: Fuel Pump Relay

    if anyone needs help with this pm me and i'll be glad to help good info naji awesome heads up

  13. #13

    Re: WARNING: Fuel Pump Relay

    man naji after talking to you tuesday im getting a little worried.. i guess because my tunner is so far and very hard to log my car.. shit.. something else to think about.. :'(
    http://autotechinteriors.com

  14. #14
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    Re: WARNING: Fuel Pump Relay

    Here is a thread on Evom from April 09 about a X that had the same problem.

    http://forums.evolutionm.net/evo-x-e...under-wot.html

    Some interesting tid bits:

    Anyone that is having this problem needs to check the fuel relay in the relay box under the hood. SilverEvoX brought his X in last night and we discovered that the relay coil was weak. It wasn't clicking the switch over very well. We put in a new relay, and the problem went away. We concluded that the relay may get weak due to the number of actuations."

    "The relay seems to be quite inexpensive in nature and you could probably keep switching out relays until you burn them all out and then maybe you could get a bulk discount on them. The problem seems to be creeping up when you hit 20K miles or so. I guess it would also depend how often you make your fuel pump go into "High voltage mode."
    This car had 29,000 miles. So it seems that the higher the mileage, the more likely this could happen. These relays are weak and with use they start to fail.

  15. #15
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    Re: WARNING: Fuel Pump Relay

    Quote Originally Posted by DRJ1014
    Noob question but changing out the relay is just a temporary fix? Almost sounds like this problem will come back down the road after changing the relay out once ?
    I believe that you are correct. My hypothesis is that the more miles you put on the car, the more the relay will be used, and the more the relay is used, the more likely it is going to fail. It is not by accident that it happened on a car with 29,000 miles on the odometer.

    The horn relay and the high beam relay are less likely to fail than the fuel pump relay since you rarely use the other functions, but you do go into high load/WOT often.

    One preventive move that you can take is to test the relays when your car hit 20,000 miles. Simply swap the high beam relay with the fuel pump relay, turn the ignition, and turn the high beam on. If the high beam shuts down after a few seconds, then the relau is shot. That is the simplest and fastest test and requires no tools at all.

  16. #16

    Re: WARNING: Fuel Pump Relay

    One preventive move that you can take is to test the relays when your car hit 20,000 miles. Simply swap the high beam relay with the fuel pump relay, turn the ignition, and turn the high beam on. If the high beam shuts down after a few seconds, then the relau is shot. That is the simplest and fastest test and requires no tools at all.¬*
    genius! O0

  17. #17

    Re: WARNING: Fuel Pump Relay

    That is some great information, I don't own a X but I can appreciate good work. This is what the community should be all about :mitsu:
    www.muellerized.com<br />www.roadraceengineering.com

  18. #18
    Experienced kungfudevil's Avatar
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    Re: WARNING: Fuel Pump Relay

    http://www.amsracingblog.amsperforma...r-to-run-lean/


    Looks like AMS is confirming this problem.
    Do-Luck status

  19. #19

    Re: WARNING: Fuel Pump Relay

    Naji's way seems a lot more easier to test. GJ

  20. #20
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    Re: WARNING: Fuel Pump Relay

    Two more threads about failed Relays

    http://www.evoxforums.com/forums/showthread.php?t=18316
    http://www.evoxforums.com/forums/sho...t=18475&page=3

    This is spreading. I am very concerned about this happening on tuned Evo Xs. A lean AFR and higher boost will knock the 4b11 into oblivion.

    Please check your fuel pump relay as the car approachs 15,000 miles. Better yet change it with another one from the dealer it is only $35.

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