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brucepick 03-31-2009 04:50 PM

Lean Burn all the way!
Ever since acquiring my SG my main effort with the HX has been to keep it in Lean Burn as much as possible when on the highway (I mostly drive on limited access roads, usually 50-60 mi each way to work).

Today with temps around 60 and the wai pulling intake air around 85-87 deg. F, it drove like a champ. Lean Burn all the way.

Went into lean burn promptly after about 1.5-2 miles of highway cruise, and stayed in LB as long as I didn't go past its usual throttle position limit of 32 TPS on the SG (which takes it into open loop operation). Even after exceeding TPS 32 or after a downhill idling coast, it went right back into LB when asked to. Also went right back into LB after a couple nearly-full-throttle accelerations to 75 in 3rd gear. It has tall gearing.

I expect 50 mpg and better in the near future.

I currently have the drivers side grill fully blocked; that's where the cat converter and a/c condenser are. I'm pretty sure that keeping the cat warm counts for a lot on this car. I've gotten occasional CEL's ref. cat, and LB status does seem to respond to heating up the cat with fuel and/or grill block.

Passenger side has the radiator; it's maybe 30% blocked at these outside temps. It seems to kick out of LB if coolant goes to 186 so I can't choke off the radiator's air flow.

Daox 03-31-2009 04:55 PM

Great news. I've always really wondered what an HX can do. It seems like a lot of owners get high 30s but I know the car can do so much more.

MetroMPG 04-01-2009 08:25 AM

Sounds like a good commute. Remind me again how you're monitoring lean burn?

How long to the next fill-up? Please post back here so we know the actual outcome.

brucepick 04-01-2009 09:38 AM


Originally Posted by MetroMPG (Post 95120)
Sounds like a good commute. Remind me again how you're monitoring lean burn?

How long to the next fill-up? Please post back here so we know the actual outcome.

I have another approx. 200 miles left on this tank. I'm also temporarily off work awaiting a contract extension and also a new contract, so it could be a while to the next fillup.

I monitor Lean Burn status on the ScanGauge. Here's how to program it. Of course the procedure makes no sense if you don't have a SG or you don't have it's manual that gives you the basics of programming its X-Gauge options. Given those basics, one can do this.

TXD: 686AF10115
RXF: 044105150000
RXD: 2808
MTH: 000100020000

and save.

If the value for LBN = 0 you are in lean burn.

here's what I monitor on the SG
Coolant Temp - - - - - - - - - - - - Throttle Position
(due to grill block) - - - - - - - - -(LB kicks out at 32 TPS)

MPG or Intake Temp - - - - - - - - Lean Burn Status
(cold intake kills LB)

Vince-HX 04-02-2009 09:22 PM

Def cool how you programed the SG to read lean burn :thumbup:

brucepick 04-04-2009 12:00 AM


Originally Posted by Vince-HX (Post 95476)
Def cool how you programed the SG to read lean burn :thumbup:

Thanks but I can only take credit for following the written notes. They're from a post by a MrChoi on another message board.

SVOboy 04-04-2009 12:12 AM


Lean burn power FTW

theunchosen 04-06-2009 02:26 PM

I'm really not familiar with the SG at all, is there anyway you can actually measure you Burn ratio(stoich 14.7 what is your getting?)? I guess if you coudl measure the air flow and the fuel injected you could. . .?

I just keep tabs at fillups

rkcarguy 04-13-2009 04:11 PM

I have a wideband O2 sensor and display that I bought for tuning purposes, it displays 10:1 up to 20:1 AFR's.
You have to have an extra O2 bung welded into your exhaust, the display can just plug into the cigarette lighter.
Expect to spend ~$200 though unless you get lucky and find a used one.
You can also tap into the right wires at the ecu and get a voltage readout at the stock sensor that you should be able to convert to approx AFR if you do some research.
There 02 sensor should have a heater wire, ground, + constant, and + variable(O2 reading).

brucepick 06-06-2009 10:30 PM

RPMs Requirement: 2400+ (for Lean Burn)
Eureka. HX Lean Burn apparently requires 2400+ RPM

Sometimes I miss the most obvious things... In this case, in my search to learn the requirements for lean burn in the HX, I missed rpms.

2400 rpm and higher, to be specific. Just over 2500 on my dash tach but 2400+ on the ScanGauge. Or, in fifth gear, over 65 mph (on dash speedo). I've seen LB in lower gears so road speed isn't the requirement, it's rpms.

Below those levels, lean burn is iffy at best. I'm sure I've seen LB below 2400 rpm but at least in tonight's conditions that was the requirement.

Tonight, in conditions apparently perfect for Lean Burn, my '97 HX would not stay in lean burn and would go in only when it's "mind of it's own" decided to. Having noticed that increased speed sometimes helps, I brought it up over 65, and voila! Lean Burn. Next, I carefully monitored rpms and road speed to deduce what I wrote above.

OK, the other things I've written in the past still hold (notes below). But it seems they have an additional requirement, namely, 2400 rpm or better. Of course, attempting to go into LB at say 2410 rpm is probably a losing proposition because if you accelerate up to 2410, as soon as you let up on the throttle for the necessary TPS 20 or less, you'll lose rpm and will be below 2400, so no LB. Aside from that caveat, I seem pretty confident in this.

The other requirements:
TPS (throttle position) of 20 or less (as shown on SG) to enter LB. TPS over 31-32 will end LB. No air blowing on the cat converter - my grill is thoroughly blocked aside from the four segments in passenger side lower grill opening. Wet weather seems to reduce possibility of lean burn, but maybe that's due to the fact that I rarely drive over 65 if it's raining!

One other caveat. YMMV. I suspect my cat converter may not be functioning optimally, as I occasionally get a CEL with a code that references cat function. So it's possible that with a perfectly functioning cat the requirements for lean burn might be more lenient.

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