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Old 12-20-2015, 11:58 PM   #1 (permalink)
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Question Maintaining Speed in Lean Burn

When I'm driving sometimes I can see on the instant fuel economy bar graph that the car is going into lean burn. I want to hold it there, but it seems as though the power the car outputs while in lean burn is just a little too weak and so I can't "cruise" in LB. The car will slowly decelerate and then I have to hit the gas to get back to whatever speed I was going at.

There are a number of factors working against the car right now, so maybe y'all can identify which are the biggest issues?

- No IMA right now, my cousin and I are reconditioning a bunch of sticks, It'll probably be done in a couple weeks. We're doing his car's IMA pack first.
- It's cold outside. ( Canada )
- Missing three aerodynamic pieces under the front of the car. I'm on the wait list for one of those custom aluminum pans, that will replace all missing panels. I still have the big panels in the middle of the car and the strakes so that's good.
- I don't have LRR tires because winter. However, I did switch to Civic VX rims so at least the wheels are very light.

The IMA and missing aero components are just waiting-game type issues that will be resolved in the future. But I'm looking for solutions I can implement sooner than that. For example, I'm considering making an aerodynamic upper grill block.

The car is a 2001 and it has about 130K miles on it. I cleaned the EGR valve and changed the transmission fluid and oil about 1000 miles ago, but are there possibly other maintenance issues that I could look at to improve power in LB or at least let it cruise in LB? I can *barely* maintain 45 mph on a flat surface in LB.

Last edited by Natalya; 12-21-2015 at 12:01 AM.
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Old 12-21-2015, 03:27 AM   #2 (permalink)
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hmm, something sounds amiss - you should be able to maintain lean burn pretty easily at say 60-65 mph cruising on the highway... IMA won't have any bearing on your situation.

First would be the tires - depending on what you've got, it could be a huge difference or it could be a ... difference. I wouldn't think the same sized tires, just not LRR, would make too much of a difference; if you have over-sized winter tires - that could be the difference between say being able to lean burn at 65 mph vs. 55 mph (I'm kind of just making these numbers up, seems reasonable to me though).

The aero panels might be a couple mph difference...

I don't think cold weather would make much of a difference once the car's warmed up and you're cruising, but I'm not an expert on that... In general, cold weather does make it harder to lean burn, and I suppose that margin, teetering on the edge, even if you're cruising, can lower the speed you're able to maintain - so I guess I'd put that at a couple mph, too...

I'll leave it up to the experts to add anything else...
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Old 12-21-2015, 05:13 AM   #3 (permalink)
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You've mentioned 3 fairly strong contributors to increased resistance to 'gliding' through air: cold (cold here too), tires, and aero panels. But as eq mentioned, you should be able to hold lean burn, maybe not at the high mpg you'd normally get in better weather. Any snow or ice on the road is just more resistance to fight.

If you have an obdiic&c, you could monitor 'load', throttle position, or 'fuel injector duration' (I watch the last one). After getting into burn, VERY gently ease more into the throttle, but not so aggressively as to kick out of burn. I've learned to see and feel where the max engine load is before it wants to kick out of burn. I watch the fcd drop off too and 'settle for mid 70's or so on mpg.

If you don't have the obd, you could kind of 'feel' where the car wants to kick out of burn and stay under that threshold.

You may also consider airing up the tires a bit. A tough balance there with snow and ice on the roads.

fwiw: I was missing the 3 front aero panels under my mt. After installing Scotts' belly pan I saw an increase of 5% on the mpg.
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Old 12-21-2015, 07:56 AM   #4 (permalink)
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I find the same thing...

I can get into LB, and know I'm there since it'll "burp" when it should. If I'm doing 60, the car will gradually loose speed, and I have to hit the gas to increase speed, and fall out of LB. I've been wondering if there's something wrong w/ the car or with the driver

<== no ima and missing strakes and the passenger side under engine peice.
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Old 12-21-2015, 08:37 AM   #5 (permalink)
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When did you notice the poor lean burn performance? That might be a clue.

My vote for the elephant in the room is the winter tires. Nothing beats the RE92 LLR by a wide margin.

In addition to the factors mentioned, the constant cold intake air temperature is a negative. Also the density of cold air. All-in-all you have everything working against you.

I personally think that the car is normally challenged to maintain LB at 65mph under the conditions you mention.
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Old 12-21-2015, 08:51 AM   #6 (permalink)
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Quote:
Originally Posted by jime View Post
I personally think that the car is normally challenged to maintain LB at 65mph under the conditions you mention.
Tall gearing, but if you drop to 55mph its even harder. Maybe 4th gear would actually raise mileage at that speed?
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Old 12-21-2015, 03:35 PM   #7 (permalink)
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at 45 mph are you trying to use 4 fourth or fifth gear?
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Old 12-21-2015, 03:48 PM   #8 (permalink)
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No IMA you say? What IMA codes do you have? Some IMA codes will disable lean burn, and make it impossible to even enter LB mode.
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Old 12-21-2015, 08:50 PM   #9 (permalink)
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@Balto:
Not sure what code, I forget, but it does enter lean burn. It just can't maintain it. I'm in Canada so I use metric settings, the FCD instant fuel economy will drop to about 2 L/100km which indicates lean burn to me and yeah there is a small range of throttle available, but if you push too hard then the fuel economy goes back to a normal 4 L/100km situation and the engine sounds different. I am like 95% certain it is going into LB.

Weather right now has been slightly above freezing. I've been trying to stay in LB at speeds of about 45mph typically in 5th gear but it just can't hold it. I'm not attempting this in precipitation, I'm talking about clear days sun out, nothing on the road, mostly flat driving.
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Old 12-23-2015, 02:49 AM   #10 (permalink)
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Have you tried 45 mph in 4th gear? Perhaps the engine load in 5th gear is too high.
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