Added dual A/F ratio sensors & meter today -

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Old December 5th, 2017, 08:22 PM   #1  
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Added dual A/F ratio sensors & meter today

I just added the Innovative Motorsports DLG1 dual O2 sensor A/F meter to my 98 convertible today. This was an interesting project which took maybe 8-9 hours to complete at a very casual pace.

Most people would add an A/F ratio sensor to provide feedback to an EFI system. In my case, I'm just trying to tune a quadrajet/qjet as well as possible. O.k. so maybe I'm being a bit extreme here.

I had my exhaust shop weld in O2 sensor bungs into my 2.5" exhaust. There are no headers (On a 98?). I just have factory dual 2.25" system feeding into 2.5" pipes & resonators. The bungs are about 6" down the 2.5 pipe, which seems far enough to give good A/F ratio signals.

Other than the welding, the Innovative kit is about as hard a wiring a modern stereo system. Connections are switched power, ground, 02 sensor connections and an interconnect between the gauge and an auxiliary unit which permits software logging of the A/F ratio.

Early returns: The Stochiometric A/F ratio goal is 14.7. That's probably a bit lean for the real world. My idle is a maybe a tick rich at 14.1- 14.3 AF ratio. The real news is part throttle cruise was in the 15 - 16 AF range. Too lean. I'd never have discovered that with a vacuum gauge. I haven't done any WOT testing yet, but that fun is yet to come.

Long & short of it is, an interesting product @$300 giving useful data for qjet tuning. If I were trying to economize, I'd go for single sensor gauge. There's not all that much difference between the two banks exhaust outputs. Other single 02 sensor units run about $200.

I'm not affiliated with Innovative Motorsports and have no idea how long this thing will live, but on Day1, it's working as advertised. Fun mixing modern and old.

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Old December 6th, 2017, 01:53 AM   #2  
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cf, the requirements for straight gas and 10% ethynol may be different. Beware of ideal numbers, they may not be what your engine wants. Call Cliff Ruggles if possible, he's an expert on qjet tuning. Got any pics of your 98 to post? Best of luck with your Olds.
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Old December 6th, 2017, 03:01 AM   #3  
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FWIW I set cars (Qjets) up similar to how you mentioned it. Usually shoot for 14.2-15 @ idle, 15-16 light load cruise, 12.5ish WOT. Seems to work well & owners always happy after dial in. They usually pick up mpg, response & run their best #'s if checked @ track. It is a trial & error process with a Qjet & takes a few (or more) "top pops" to get it.
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Old December 6th, 2017, 03:58 PM   #4  
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Why 15-16 a/f ratio at light cruise?

Iím new at this, but I know Ruggles book pretty well.

If 14.7 is the ideal air/fuel ratio, why is it a good idea to go 15-16 at part throttle cruise? Isnít that too lean? Richer WOT, I get, but why not shoot for 14.7 at part throttle cruise as well?

Havenít had time for WOT runs yet, but itís not like I use my 98 for racing.

Thanks for your insights in advance.

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Old December 6th, 2017, 07:21 PM   #5  
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Just a quick pic:

'66 Big Cars
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Old December 7th, 2017, 07:49 AM   #6  
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Love those!
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Old December 10th, 2017, 03:31 PM   #7  
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Just a quick update. The 98 convertible is running well, if just a tick rich at idle 14.1 AFR at 850 rpm. Part throttle cruise is running 15-16:1, WOT or heavy throttle in the 12:1 range. I still have some tuning to do, but the a/f gauge is really helping. It's like getting a new pair of glasses - suddenly everything is clearer.

Here's the latest recipe for 17058553 (late) qjet: 2 turns out at idle, only 1/2 turn out on APT screw. The primary side is 75 jets / 45 rods. The secondary side is a K hanger and CV secondary rods.

I'm not sure what % of ethanol NorCal gas is now or any other time of year. I'm leaving the car a bit rich on the theory that local fuel is not pure gasoline. Alcohol has a much lower stoichiometric ratio than gasoline so running it a bit rich may be a good idea.
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