Narrow-Band Air/Fuel Gauge Install - Failed O2 Sensor?

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Narrow-Band Air/Fuel Gauge Install - Failed O2 Sensor?

Post by DPDISXR4Ti »

After my debacle of trying to install a MerkMeter in a Scorpio, I opted to just go with the more conventional 2" round gauge - something you can find all day long on eBay for less than $20. I found that the yellow wire headed to the radio is a good supplier of switched 12V+, and it's conveniently located behind the right side of the instrument cluster. There's also a Gnd location conveniently nearby - I'll try to remember to take a pic next time I have the cluster out.

With the gauge hooked up, I went for a quick test run last night. Upon cold start-up, the gauge shows a solid 13.7:1, but before I could even get out of the garage it was pegged on 20 and stayed there for the duration of the trip, even with the engine fully warmed up.

I'm thinking I've diagnosed a bad O2 sensor. Would you agree? This would also be consistent with the drop in fuel mileage since installing the slightly larger fuel injectors, given that there is no closed-loop operation.
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Re: Narrow-Band Air/Fuel Gauge Install - Failed O2 Sensor?

Post by brokencase »

Maybe not such a good idea to install larger injectors on a MAP system?
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Re: Narrow-Band Air/Fuel Gauge Install - Failed O2 Sensor?

Post by Ed Lijewski »

(I'm scratching my head.)

Air ratio above 14.7 = lean mixture.

What was your reasoning for installing larger injectors? Which in any case would be expected to affect mileage?

YMMV
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Re: Narrow-Band Air/Fuel Gauge Install - Failed O2 Sensor?

Post by DPDISXR4Ti »

Ed Lijewski wrote: Sat Jan 23, 2021 12:40 pm Air ratio above 14.7 = lean mixture.
Correct. But the engine wouldn't even run at 20:1, so don't put too much faith into that number. I think it's essentially an error. I might believe it was a wiring or gauge issue if it weren't for the brief 13.7: reading when stone cold.

I did a whole write-up on the EV6 injector swap - here it is... http://forum.merkurclub.net/forum/viewt ... 29&t=36577
Typically you can go +/- 20% on injectors and closed-loop operation will readily clean things up. I hear about people going with 50%+ injectors and not having issues, though I don't agree with that approach at all.
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Re: Narrow-Band Air/Fuel Gauge Install - Failed O2 Sensor?

Post by Ed Lijewski »

Just one site from an A/F ratio search noting the ratio is okay up to 20:

"Air-fuel ratio, lambda and engine performance – x-engineer.org" https://x-engineer.org/automotive-engin ... chiometric.

YMMV
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Re: Narrow-Band Air/Fuel Gauge Install - Failed O2 Sensor?

Post by DPDISXR4Ti »

Ed Lijewski wrote: Sat Jan 23, 2021 3:38 pm Just one site from an A/F ratio search noting the ratio is okay up to 20:
But a NB O2 sensor can't even sense ratios that wide, only a WB can.

I doubt I'd see a difference from the gauge if I installed the EV6 14's, but I may do it any way. I was just hoping to see what the current setup was telling me before swapping.
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Re: Narrow-Band Air/Fuel Gauge Install - Failed O2 Sensor?

Post by my8950 »

Sounds like it to me, sensor is bad.
But, as also mentioned, a narrow band sensor can't go that high anyway. A narrow band sensor just switched from "high" to "low" constantly, if it sways more high, then the ratio is higher, if it sways low, then the ratio is lower.
Is the only way you have to read the sensor this gauge? I see you mention that it is a NB sensor, I guess I'm wondering what you're expecting of this system, or what you want it to do for you? If you want to see what the actual A/F is on the output, I'd suggest install a wide range sensor and a good way to monitor it. I personally have never been a fan of dash gauges that read A/F, not sure how to actually read them accurately. If it had a digital readout, or a way to record it, that would be more beneficial.
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Re: Narrow-Band Air/Fuel Gauge Install - Failed O2 Sensor?

Post by DPDISXR4Ti »

my8950 wrote: Sat Jan 23, 2021 9:19 pm I guess I'm wondering what you're expecting of this system, or what you want it to do for you?
One of the things a NB A/F gauge can do is exactly what I believe it is doing - tell me if the O2 sensor is working!

Another thing it can do is tell me at what RPM the PCM's strategy switches over to open loop operation. I have my reasons.

You can gather useful info from these, if you know what to look for. Much of it come from transient throttle application.
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Re: Narrow-Band Air/Fuel Gauge Install - Failed O2 Sensor?

Post by DPDISXR4Ti »

Couple questions as I stroll through the EVTM...

1) Where is this C1132 connector w/ 15A fuse for the HEGO? It says "RH DASH Behind Instrument Panel" (Page 40 of the 1988 EVTM)
2) Where is the connector for the HEGO, which then goes to the C1132? Looks to be over by the EEC Diagnostic connector, yes?
3) From the pictures I'm seeing, it looks like the HEGO used on the Scorpio is the typical Ford 3-wire version, same as the one used on USA cars, not something "Euro oddball", yes?
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Re: Narrow-Band Air/Fuel Gauge Install - Failed O2 Sensor?

Post by brokencase »

Have you plugged in a code reader recently? I would think that the EECIV will tell you if the O2 sensor is bad.

So what have we got...if the so called meter is indicating super lean then that would imply the voltage is very low coming from the sensor - correct?
Like maybe the sense wire to the meter is grounded somehow?

Or the sensor could be bad. Pull codes to see what the computer thinks..
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Re: Narrow-Band Air/Fuel Gauge Install - Failed O2 Sensor?

Post by Ed Lijewski »

HEGO fuse is in the auxiliary fuse panel accessed via the open glove compartment.

HEGO harness connector is near the battery.

scorpio HEGO unit may be same for other Ford three wire units but the connector may be different (thus Scorpio HEGO PN doesn't transfer to other Fords from what I've found).

YMMV

Edit: To what color O2 wire did you connect the sensor?
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Re: Narrow-Band Air/Fuel Gauge Install - Failed O2 Sensor?

Post by DPDISXR4Ti »

Ed Lijewski wrote: Sun Jan 24, 2021 10:45 am Edit: To what color O2 wire did you connect the sensor?
#29, Blue w/ wht stripe.

I will pull codes. Or maybe I don't even need to bother, as I see now from a post last year that I've already gotten this....

41 System was lean for 15 seconds or more (no HO2S switching)
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Re: Narrow-Band Air/Fuel Gauge Install - Failed O2 Sensor?

Post by DPDISXR4Ti »

I got the car up in the air today and crawled under armed with my 22mm wrench, ready to do battle with the O2 sensor. As I touched the wiring harness for the sensor, to my amazement the whole sensor moved. What!? It was not even finger-tight. I didn't see that coming!

So rather than remove it I tightened it into the bung and will take it for a test drive in the next day or two.

Stand by for an update.
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Re: Narrow-Band Air/Fuel Gauge Install - Failed O2 Sensor?

Post by DPDISXR4Ti »

Went for a 20-mile drive today and the O2 sensor is working. I never expected a A/F gauge to tell me that my O2 sensor wasn't screwed in, but that's exactly what it did!

It does however appear that the PCM is having trouble going into closed-loop operation - it stays on the rich side and doesn't ping-pong back & fourth as it should. And yes, the engine was fully warmed up.

So out will come the 16 pph injectors and in will go the EV6 14's. You may recall that I had tried 13.5 injectors and they felt like they were running a little lean. In the mean time I acquired some 14's.
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Re: Narrow-Band Air/Fuel Gauge Install - Failed O2 Sensor?

Post by brokencase »

I could be wrong - but I thought the EECIV only goes into closed loop when everything is warmed up and you are cruising along at a fairly consistent speed for a while, like while cruising on the highway.

You're not going to see closed loop in any around town driving. So I hope your 20 mile ride incorporated a long stretch of road.

Also - might it be wise to clear any pre-existing fault codes before doing that test? You're EECIV hasn't seen that O2 sensor work properly for a while.
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