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Discussion Starter #1 (Edited)
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 SpunkySandoval's 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 SpunkySandoval 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 couple of 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. He then turned the high beams on with the fuel pump relay in place. A few seconds later, the high beams shut off, indicating that the fuel pump relay was faulty.

We kept the high beam relay in the fuel pump relay slot, 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.
 

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Awesome info. BTW what program are you using? I love tables like that when data logging.

My AFR's have just gotten extremely lean, maybe this could be one of the reasons why.
 

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Discussion Starter #7
Awesome info. BTW what program are you using? I love tables like that when data logging.
I log in Evoscan and I then use a Macro to move the data into a template that can be read by Logworks ver 2. Logworks is freeware from Innovate. It is used to read Innovate logs. It cannot read Evoscan logs w/o the macro template.
 

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If the stock relay is weak, is there any better ones out there that we can swap in so we dont have to worry about it failing?
 

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Discussion Starter #9
If the stock relay is weak, is there any better ones out there that we can swap in so we dont have to worry about it failing?
As SpunkySandoval explained it to me, Mitsu should have used a solid state relay (don't ask me what that means). I do not know if there are solid state relays that can work in place of the stock one.

Hopefully, SpunkySandoval will chime in one this.

I hope this gets to Mitsu's attention. While there have not been a lot of documented cases, it is entirely possible that some cars have this problem and the owners do not know about it. Afterall, how many owners have a wideband on their cars and actively log AFR???
 

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I hope this gets to Mitsu's attention. While there have not been a lot of documented cases, it is entirely possible that some cars have this problem and the owners do not know about it.
Good find...you're the man!

Afterall, how many owners have a wideband on their cars and actively log AFR???
As soon as I find a decent gauge pod, I for one will be buying a wideband gauge ASAP.
 

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we did this on rockstars car and it did not fix anything.....

he was leaning out under WOT..

he got a dealer reflash and was good to go.
 

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Thanks for the info...!!

Do you care to point me in the right direction for the macro.... I cannot read evoscan graphs
 

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You probably had a different problem than this one. But this has happened before to others.

sorry, i was not saying that what you did, did not fix it, because it did.

just that his car was doing the AFR's.. but it was running 15-16's under WOT.

We tried the relay, and once the fuelpump was tested, it was found that the pump was loosing voltage under WOT. almost fully. The dealer reflashed it and it now runs 11.s
 

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great info. almost makes me want to check mine, but I think the black-smoke-o-meter points to pig rich...
 

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Discussion Starter #20
sorry, i was not saying that what you did, did not fix it, because it did.

just that his car was doing the AFR's.. but it was running 15-16's under WOT.

We tried the relay, and once the fuelpump was tested, it was found that the pump was loosing voltage under WOT. almost fully. The dealer reflashed it and it now runs 11.s
Ok, now I get it. Yours was a complete failure of the relay while ours was on its way out. That is why yours leaned out to 15-16 while ours stayed in the mid 11.5:1
 
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