02BlackOnBlackSS

iTrader: (11)

Hey guys,
I was trying to figure out how I would raise my cruise AFR to around 15.5 or so for fuel economy. I have a wideband to make sure I am not running too lean. I was wondering what table you would mess with to do this. It doesn't seem possible because the nbo2s only read a certain range and this would be outside of it. Is there something I am missing?

Also, how dangerous for my engine is it to do this? Will I suffer any longevity problems? I just have a bolt-on car, but I do a lot of highway driving and if I could squeeze 2 or 3 mpg out of the car it would be great.

One last question: Should the timing be retarded for the ranges where I am running lean?

Thanks guys.

Black02SS

iTrader: (36)

Short answer, don't think so. You can leave the car in open loop and just modify the open loop fuel air table to be alittle leaner at the desired RPM.

Bombguy99z28

Theoretically, I suppose you could alter your rich/lean switch points to skew it in one direction or the other (spend more time under .5mv than over), but I would be dubious as to how accurate that would be or even how much of an effect it would have.

cantdrv65

iTrader: (3)

Sure you can...With the innovate wideband's narrow band simulation feature. Just offset the narrow band value sent to the ECU....of course you run lean at your own risk. Youd probably need two wideband kits though....

dynocar

Hard on CATs if you still have them.

02BlackOnBlackSS

iTrader: (11)

I thought about this, but it just isn't too feasable for me to buy another wideband. That would be pretty cool though.

Ditched those a while back.

Thats what I was thinking. Thanks.

02BlackOnBlackSS

iTrader: (11)

How many people do an open loop tune? It seems like this is the only reasonable way around this. Any advice? Also, what is the leanest AFR to stay safe while cruising at highway speeds.

sgarnett

iTrader: (1)

Open-loop tuning is not and should not be done for fuel economy Running an open-loop tune on the lean side will be MUCH more expensive than buying another wideband or just buying a little more gas. If you get REALLY lucky, the block MIGHT be salvageable after the pistons grenade, but I wouldn't count on it.

If you're that concerned about fuel economy, learn to be very smooth and light on the throttle when you are not racing. Don't choose the gear that feels "best". The most economical cruising gear is the one that keep the engine running smooth but with the revs as low as possible. If the engine is not running rough, but there is basically no throttle response at all, you are in the most economical gear for cruising at constant speed (and maintaining a constant speed is important for fuel economy). On my car, that's around 1200 rpm. A lower gear may feel better, but don't kid yourself; it's still using more gas.

Dropping back to the stock Z28 245/50-16 tire size may help a little too.

Sure, none of those options sound like much fun, but it's up to you to decide how much fun to pay for. I can promise you that grenading your motor will be neither fun nor cheap (well, maybe fun if you have the budget to build a new motor).

sgarnett

iTrader: (1)

BTW, I'm not saying there is anything wrong with running open loop if it's properly tuned, but I sure wouldn't try to run it lean that way.

Yeah, a lot of cars ran lean and open loop (with carbs) in the 70s for fuel economy, but those engines had very low compression and were making a LOT less power (and were still less economical than what we have now).

dynocar

One reason that the manufacturers run 14.6:1 A/F ratio is for CAT effeciancy. Another reason is that leaner mixtures increase pollutants such as NOX. If it were not for these reasons we would see much leaner mixtures and better fuel econony from them. Beyond this, running in the 15-16:1 range if it can be done without missfires at light loads is not going to hurt anything if tuned properly.

ringram

If you run lean at low load you should be fine, Id certainly not do it under WOT, but I think you would have to be silly to do so anyway.

I think if you run 15.5:1 under 50kpa you shouldnt have any problems, its only detonation and lean missing that would hurt and 15.5:1 isnt that lean, 19:1 yeah maybe.

Ive run thousands of miles with mine set up this way with no issues with ECT heat or otherwise.

cantdrv65

iTrader: (3)

Ive never seen a lean mixture increase NOX emissions on any of our monitoring equipment....Rich defintely. I think you've got that one reversed. The only thing that keeps an engine from being able to run leaner is the increased heat that comes with a lean burning engine, not to mention detonation....

dynocar

If your NOX emmissions level is too high, every troubleshooting proceedure that I have come across has you check for too lean of an A/F ratio. One example, note chart at www.autoshop101.com/forms/h56.pdf. I don't think that I "got that one reversed". I have tuned many cars leaner then 14.6:1 without any negative affects before the days of emmissions concerns. Again, the only reason we are interested in 14.6:1 is for emmissions and CATs.

fast98

iTrader: (16)

your right lean creates nox. lean makes combustion temps hot. nitrogen starts bonding with oxygen real well at 2500 degrees. rich would be high hc's

white2001s10

iTrader: (4)

You can't do it running closed loop with a narrow-band O2, that's for sure. The narrow bands only work right for stoich and that's all.

Open loop here, and it does improve fuel economy.
Ran 16:1 AFR for years at a time with no damage to anything. The only time lean will hurt you is when you load the engine.
For example you can't hold a 16:1 AFR with a significant throttle opening, or a towing situation. You would notice surging or lean misfire before you'd have a chance to damage anything. It simply wouldn't run good enough for you not to adjust the AFR back some.

Lean will build up damaging heat, but that's at WOT, not at light cruise where the VE is very low.
If you're running the engine coolant hot while you're running lean, and you happen to notice signs of heat on the plugs, then just swap to a cooler plug.

cantdrv65

iTrader: (3)

I dont doubt ya, but in my industry say on an industrial cogeneration unit----add fuel = increased NOX emissions. Looking at the troubleshooting document you provided I can see why it behaves the way you describe on an engine. Good Info! Thanks. On that chart, when you get lean enough Nox drops like a rock, and HC actually increase... interesting.

ringram

You might be able to mess with your O2 switchpoints, maybe shift to 400mv or something, stoich is usually 450mv. Stock is normally from say 465 and up depending on engine airflow, which err's on the side of caution of course. So you could drop your low airflow switchpoints and leave the higher airflow (Closed loop mode) points as is.

Also I agree lean means more NOx which is why there is research with Urea injection, urea bonds with the NOx releasing O2. Merc has an engine that does this. Urea is a major component of urine, hence the name simularity. Soon pissing on a merc, or ford for that matter will be a required task.

Look for lean burning petrol engines with urea injection coming to a store near you.

cantdrv65

iTrader: (3)

LOL **** in the tank...a cheap way to pass emissions Besides urea, anhydrous ammonia works well. Cat **** has plenty of ammonia.

muncie21

iTrader: (14)

Hold on a second....are you saying that we are creating NO2 (nitrous oxide) Nozzz when we run lean? How cool is that

cantdrv65

iTrader: (3)

Nox is a term used to describe oxides of nitrogen. It can be many different compounds. N2O2, N2O(nitrous oxide ), NO.. ...etc Yep....