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Discussion Starter #1
Ok, I know I should be able to figure this one out, but if the O2 sensor is not getting enough flow, will your engine run rich or lean?

This is on a friends 89 Alfa with L-Jetronic injection...


Thanks,
Ed
 

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1966-2013
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Enough flow?

You mean a restricted exhaust?

That usually forces a rich condition, which presumably the O2 sensor would pick up and signal to the ECU, in turn the ECU would try to correct for that condition by leaning out the mixture.

As an EFI system, (not a single sensor), that's more or less what it should be doing anyway.

Whether it can accomplish it within it's range of adjustment and depending on this flow problem would be the bigger question.
 

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Discussion Starter #3
Actually he relocated the O2 sensor and it is now not exposed to as much of the exhaust flow... So my guess would be that its running rich, in which case ill check the plugs and see if they are black...
 

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Relocated where though? (if it's anywhere in the exhaust, and said exhaust doesn't leak, then it's getting a full sample. Temperature would be more the issue)

Usual aftermarket installation (relocating from stock = aftermarket :) ) on any car ideally has it within 3 feet of the head, and should be in a spot where it can sample all 4 cylinders, w/the 4 cyl sample superceding the 3 foot thing in importance.

If it's too far away it'll likely not run hot enough (unless it's a heated element) to give accurate results. If it can't sample all 4 cylinders, that's kinda obvious too.
 

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Discussion Starter #5
It is now in a bung at the front side of the cat/converter. Its actually in the converter. I would say its right under the drivers seat. It does get pretty hot down there, but its no longer in the direct path of the exhaust gases, so its not exposed to as much gas vapor.
 

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It is now in a bung at the front side of the cat/converter. Its actually in the converter. I would say its right under the drivers seat. It does get pretty hot down there, but its no longer in the direct path of the exhaust gases, so its not exposed to as much gas vapor.
The response will be slower, but it will still read correctly, assuming the sensor is properly heated. Masking the sensor isn't all that bad- you still see the gross mixture, but some of the subtleties will be missed (which isn't a big deal).

Eric
 

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I concur.

Even if it reads 'fast' and picks up everything, it's still lagging behind what's actually going on in the engine by a bit more time than you'd imagine.

A/F gauges continuously whip back and forth during closed loop from rich to lean onnaconna the delay between O2 signal and ECU reaction going from (almost) one extreme to the other.

Actually, that might be something to consider if there's concern about the mixture: a small A/F gauge so your bud can actually watch what's going on rather than making estimations by plug readings and such.

If the gauge reads correctly, then things are doing what they are supposed to.

Now granted, not everyone would want to hang one in thier car or make provisions to mount one permanantly, but as a diagnostic assistance thing, (for sure it'll show mixture changes going on during closed loop, what the engine does in open loop, and can show false air leaks by showing over lean mixture in almost real time) there's nothing saying one can't be temporarily connected.

A pricey thing to just leave on the shelf when not in use, but no more expensive than a timing light or fuel pressure gauge that would sit right next to it in the toolbox. :shrug:
 

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Almost anywhere they sell aftermarket gauges actually. (Advance, Napa, AutoZone, etc. all carry some version or another. I'm a bit more fond of the Autometer ones as opposed to all the others with names I never heard of til the ricer revolution)

Several styles are available from around $50 up to well over $100.

If it's going to be used as a test tool rather than an installed gauge, the only criteria that really needs to be met is that it's for a narrowband O2 sensor, which will work with L-jet and Motronic. (any vehicle with a narrowband O2 sensor actually)

See this page at IAP for a bit of info on reading one. (if it matters, the gauge shown on that page is what I have installed, but with a black bezel ring)
 

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The A/F gauge I installed last winter was by far the best modification I have done sense the rebuild.

With an A/F gauge you know exactly what's going on inside your engine and you can see in real time how different driving styles effects the A/F ratios.

Before I got the A/F gauge I thought that I needed to keep the rev's up to be good on my engine but after the A/F gauge was installed I saw that was causing the engine to run richer and with every touch of the throttle the A/F would jump around alot more

But when I shifted into a higher gear (4th crusing @ 3,000 to 3,500 rpm) around town and using (5th crusing @ 3,000 to 3,500 rpm) on the hyw's my A/F was rock steady at 14.7 to 14.9 A/F. Before I was trying to cruise around 4,000 rpm range and my A/F was in the mid to high 13's causing my tail pipe to be black now my tail pipe stays crystal clean with the new driving style.

I also installed an A/F monitor that I have tied into my ecu to log the A/F readings.

 

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Well I have an aftermarket ecu (Autronic SM-2) I'll let others answer on the possibility of tieing it into the L-Jet but I would think you could just add another bung to the exhaust system to install the O2 sensor that runs the gauge or monitor.

They also sell a tail pipe clamp that you can use with the LM-1 monitor? This way you can use it when you want to check the A/F then when your done put it away till the next time you want to check the A/F.

This was what I was going to do but having a gauge is nice that you can see in real time what is happening instead of reviewing the data logs.

When my fuel pressure regulator was crapping out on me the A/F gauge brought it to my attention right away. When I was adjusting the new fuel pressure regulator you could watch the a/f change ..................it's pretty cool tool.
 

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A narrow band A/F meter will pop right into an L-jet setup with the only compramise being a splice in the O2 sensor to ECU wire to get to the gauge.

As for Murray, he's on aftermarket wide band which is a whole 'nother animal AFA readouts and O2 sensor voltages. (stock Motronic would be a heated narrow band. As in, the same thing L-jet uses, but with a element to get and keep it up to operating temperature quicker and longer)

Narrow band A/F gauges don't read in numbers, just lean, stoich (in closed loop the lights will constantly bounce from rich to lean and back as the ECU tries to keep a corrected mixture) and rich, but you can still use it as a 'training aid' when driving by playing the 'how long can I keep it in X range' or 'how smooth do I have to be on the pedal to get the best mileage without jumping out of closed loop'.

Now before one gets all carried away thinking that you can run a narrow band O2 sensor for the ECU and a wide band O2 sensor with A/F gauge for a trick dash panel, look at the price of a wide band and wideband gauge.

Yes, that combination as described would indeed work, but not a lot of folks are gonna wanna spend the literally hundreds of dollars just to get another sensor and gauge that do little more than light up when it's getting a sensor signal.

The L-jet nor Motronic ECU can be made to work with the wide band O2 sensor.
 

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Sorry, Darren maybe I'm got carried away with un-necessary advice and was off base in the poster's question.

But the LM-1 monitor can be had for $270 and no you don't need the gauge and the light show that's agreed.

IMO it's a great tool to check the tune.
 

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No, my bad not yours.

In your system the wide band is pretty much a neccesity and the addition of the gauge a wise investment unless you want to try reading your current on-the-fly A/F ratios while driving and looking at a laptop simultaniously or putting it up on a dyno. And the better accuracy it offers is certainly a good thing when dialing on the maps.

I was trying to imply that wide band would be little more than a frivolous novelty that quite literally would serve no purpose other than personal amusement or to give a 'hey look what I got' factor when used with the L-Jet or Motronic sytems.

You know, kinda like racing stripes on a white car. They may help it look just a little bit better, but does absolutely nothing for actual performance.
 

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Discussion Starter #18
For some reason, I didn't think any piggy back or adjustments could be made to an L-Jet system because it was analog. The only thing I thought you could do is put a variable resistor on the air-flow meter to fool the ECU.

Ed
 
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