Headers with 1-wire o2 sensors

[Beezer]

Guys,

I have a Soarer v8 fitted with Rush headers. I decided to test my o2 sensors & they didn't appear to be working at all so I bought and fitted some new universal 1-wire units. After all, the original ones were over 150k miles old, so I figured it was time for replacement anyway. However, the new ones ALSO didn't appear to be working!! I checked & double checked that I was testing them properly but they still didn't appear to be putting out the voltages they were meant to!

I knew that the o2 sensors need to be hot to work but the car was up to full temperature. I decided to take the car for a quick thrash round the block to get it REALLY hot. When I got back, I quickly tested them again & this time they appeared to be working fine. However, as I stood there, the voltage tailed off to almost nothing as the car cooled.

After some research, I found some American modders who had similar issues on their cars after installing aftermarket headers. Apparently the o2 sensors were further away from the engine on a cooler part of the exhaust & hence didn't work properly. The solution, of course, is to use heated sensors instead. So, I ordered some universal 3-wire units & wired them in so that the heater circuits come on when the ignition was on.

To test their effectiveness, I connected my digital multimeter to the laptop & did a sample of the voltages whilst driving around the block (mixture of 30mph + brief 60mph section).

Without heaters:-


As you can see, without the heaters running, the o2 sensors barely ever even activated properly. I think that the ecu never even went into closed-loop mode. I think the o2 sensors just barely even registered what the ecu was doing in open-loop. Worse, as the sensors cooled, they registered weak mixture, so the ecu was injecting even more fuel - judging by the constant smell of fuel whilst in traffic.

With heaters:-


You can see here that the o2 sensors are working properly. The ecu is obviously running in closed loop mode. This reflects in the driving characteristics. The car feels MUCH more lively. Part throttle response is much better. Car is a joy to drive.

I've done this mod on friends car who also owns a 1991 Soarer with Rush headers + 1-wire o2 sensors. Here is what he has to say....

http://www.soarerworld.com/forum/showpost.php?p=239295&postcount=16

Of course, what I've found & done here is obvious really when you consider it. However, I've mentioned this here because people might not always think of checking this after they've fitted headers to their v8, especially if you've got 1-wire o2 sensors.

 

[Mat Grant]

Hi,

Thanks for this post - I'm fitting a 1UZ into a Lotus, I've got the loom that supports 1 wire O2 sensors, but no o2 sensors so need t buy some.

I always wondered why some are 1 wire and some have 3 or 4. Am I right in understanding what you're saying, that the three wire ones are two wires for a heater, and 1 wire for the signal.

And that the sensors are universal? The link has an ebay item number which is £18 in the UK, the toyota ones I see listed are always really expensive.

My car has the stock SC400 manifolds on the first half, but with the bottom cut off and a new section welded on for chassis clearance purposes. Does this mean I can buy the universal ones, and could run with or without the heater wires connected?

If so this will be a big help - from what you've said I'd try to get the heaters wired in anyway, but worth knowing.

Cheers, Mat.

Cheers, Mat.

 

[gloverman]

I always prefer to use heated sensors myself. Ive done the same tests myself as well with the same results.

Cheers

 

[JBrady]

Beezer, great post on a subject that most will not consider.

 

[Beezer]

I always wondered why some are 1 wire and some have 3 or 4. Am I right in understanding what you're saying, that the three wire ones are two wires for a heater, and 1 wire for the signal.

Exactly. The 1-wire units have a signal wire & ground through the body of the sensor itself. The 3 wire work in the same way but also have 2 wires (12v & ground) for the heater circuit. You can just wire this up to an ignition live + ground. The 4 wire units are also the same, except that the extra wire is signal ground.

And that the sensors are universal? The link has an ebay item number which is £18 in the UK, the toyota ones I see listed are always really expensive.

Yes, they are truly universal provided you get a zirconia sensor with 18mm thread (most common). I see some on ebay now for less than £15. Note, you'll have to chop the plugs off your old Toyota sensors & attach them to the universal ones. When you buy genuine Toyota parts, they are truly plug n play - but far more expensive.

My car has the stock SC400 manifolds on the first half, but with the bottom cut off and a new section welded on for chassis clearance purposes. Does this mean I can buy the universal ones, and could run with or without the heater wires connected?

You might find that 1-wire units are ok with stock manifolds. Test it with a digital meter (don't use analogue one). Test across the ox1 and ground and ox2 and ground on the engine bay diagnostics connector. You should see voltages swinging back and forth approx between 0.2 and 0.8.

Considering the cost though, I'd just do this mod anyway for peace of mind.