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:
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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:
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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
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Here are the stock runs with the functioning relay:
![Image]()
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.
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:
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
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.
