99nb overcharging
 

Hey folks, in need of some help. I just recently rebuilt my bp4w in my 99 10ae in prep for boost, and I’m taking it soon to get tuned. I’d like to have it completely mechanically sound before I get there so I don’t have to waste his time and my money. I currently have just over 1k miles on the engine. I’m using a mtx-L wideband that I can’t keep from burning up sensors. I’ve read numerous posts stating the heater circuits don’t like over 14.5v, I’ve checked both at the alternator and at the battery as well as my reference volt gauge in the car, and on average, my car charges at around 15v. I’m still on the factory ecu, but plan to use my rev built str class ms3. This is the third alternator I’ve had on the car since 2017. The original failed and I replaced it with a used alternator. And right before I tore it down for the build, the light came on again. So when I put it back together, again I used a confirmed to be good Mazda remaned unit. I’ve seen rev and brain recommend replacing the iat sensor for undercharging( which was my problem before) but can it also cause overcharging? I know the ms3 can control the alternator output and I’m also switching to a GM iat sensor. So I guess my question is, what can I do in the meantime to prevent from burning up o2 sensors?
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Have you measured voltage on the heater circuit? If the sensor is being controlled the way Bosch intended for it to be controlled then voltage should be varied by the controller. It shouldn't be a simple on off with it being fed whatever the battery voltage is.

No I haven’t. Will it allow me to measure it with the sensor unplugged? As of right now, it immediately throws either an e2 or e8 code upon start up.

If you want to try a different ECU, I will send mine from 1999 for cost of shipping. I’m saying if you think it is possibly something wrong with your ECU that is driving the voltage high.

You could put in an NA alternator that does not use external control. I don’t have details on this.

Are you sure it is voltage, and not position of the sensor that is causing the failures? There are instructions available for making heat sinks for the sensors.

All my random thoughts.

DNM

I will consider your offer. But in regards to the location of the sensor, I know it’s in the correct location because I fabricated the exhaust. Even with my old exhaust that placed the sensor in the midpipe, I still had the issue of burning up sensors in 3-4weeks. I’ve been wanting to switch to an aem system anyway but upon doing research on them, they have issues too.
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Old setup
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New setup

Check the ground on the intake manifold

I know it’s connected but I’ll try and clean it up.

Also have a look at the main relay in the engine bay.

Apparently they can oxidise or something, which changes resistance, and make the ecu etc think the alternator needs to output more (or something like that, i'm more an electrical fire kind of guy than an electrical knowledge guy)

Thanks for the info. I’ll look into it!