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I am a fairly new Evo 8 owner, just having the car over a year. It's a 2003 JDM Evo 8. As I understood, the car has been over many many hands since 2004 that was imported to Cyprus and each owner has put his hands on the car. I am having an issue, where I start up the car, AFRs are 15ish, and in about 5-10 mins they drop to low 11s - high 10s... When cruising they may go back to 14-15 for a while and then drop back to 11. At times, when I rev a little to park it, the AFRs are so rich that the engine almost stalls and black smoke comes from the exhaust. Replaced already 2 front oxygen sensors (no rear O2 on the JDM cars) and the issue is exactly the same. How come the car have normal AFR for some time and too rich at other times? MAF working perfectly, when removed the car can't rev over 2k RPM, no boost leaks, the car is throwing P0130 Heated Oxygen sensor circuit fault (front).
2 questions arise:
1. Is this simply a wiring issue from the sensor to the ECU? As I saw from the ECU sockets, some wires are cut and taped, meaning there may had been an aftermarket ECU at one point and something is messed up...
2. Is it worth the digging or shall I just throw everything in the bin and get an aftermarket ECU and a proper 2021 modern wiring loom from a race car electrician friend of mine?
Bellow my ECU periphery which shows front O2 as "0" value, does that mean the front O2 may be disabled?
Thanks in advance!
Last edited by graikas; Jul 11, 2021 at 07:01 AM.
Reason: Add pic
Check to make sure the heater circuit on your sensor has current flow. It should be about 1 amp of current flow. If the sensor heater isn't working it won't read accurately.
It sounds more like the tune to me. What if you flash it back to an oem map? And what other mods do you have on there?
As far as I understand my ECU is with stock tune. I have an HKS power filter, Evo 9 diverter valve, Mishimoto FMIC and straight pipe exhaust. Most probably i need a tune and sort out the O2 sensor either with the stock ECU or standalone.
Originally Posted by colo_evo
Are you by chance running pump gas on an e85 tune?
98 octane pump gas, we don't have E85 in Cyprus unless you buy racing fuel.
Originally Posted by Jp7
Check to make sure the heater circuit on your sensor has current flow. It should be about 1 amp of current flow. If the sensor heater isn't working it won't read accurately.
Will do, I will also check if the thing gets power at all.
Originally Posted by gsrboi80
Retune time
Most probably a LINK ECU is coming in September to solve all the problems which will read from my AEM wideband and ditch the stupid narrowband altogether
Originally Posted by hutch959
i would check wire continuity of O2 plug back to ecu.
I think there is no wire coming from the sensor to the ECU, as far as I checked the diagrams both from LINK ECU software and Evoscan (Merlin ECU tutorial). Most probably due to the cut and tape I mentioned in the OP.
Today I noticed that when i am at about 0.1bar boost or near 0 (so the DV is closed) the AFRs jump up to 14.3 which is normal cruising, and when i let off and the DV remains open due to vacuum they drop back to 10...
