Tuning for fuel economy - 5SFE and EFI in general

[Slasher]

Hi guys, this seems like the best place in the net to ask tech questions related to fuel economy. The US boards contain a lot of speculation on average. Most are also looking to push massive power out of the camry motor for whatever reason. Must seem easier than an engine swap.

I just purchased another 2nd gen MR2, SW21 here, and am needing to set it up for daily driving - long highway commute. The only maintenance issue so far is that it needs a new clutch.

From what I gather so far, the earlier years like mine have batch fire injection and no knock control. Maybe someone here can straighten me out on the injection scheme and if there are split "banks" involved. Any tips on atomization would be appreciated - the only plan so far is just a new drop in filter for the inlet side. Maybe ream out any obvious restrictions on the airbox.
I purchased an ebay header because the cat is almost integral with the stock mani; Wanted to remove that lump and find a good place to mount a wideband o2. If the runners are excessively large in diameter as with my 2jzge turbo manifold, anti reversion cones may be welded in at some point..

Basically I'm looking to use a spare AFC and my DIY WB 1.5 to lean out the mixtures, both open and closed loop. Shooting for around 17:1 closed loop with the narrowband output stoic adjustment and 13:1 WOT, if these aren't unreasonable. The newer 5S with knock control and better injection runs near 13:1 WOT based on at least one stock dyno run posted online. I will be listening for knock, of course, as well as reading the plugs periodically. Which brings me to the next point-

One area of confusion for me is spark plug efficiency. Would colder plugs and a leaner mixture likely result in better mileage or maybe the opposite for a more efficient burn? Also not totally set on timing, but I don't plan on advancing base ign timing for sure, and there don't appear to be many options for the cam timing. I'm not even sure what the cam timing specs are for this US spec 5S-FE. I'm not against moving a tooth one way or another if there is good reason.

Thanks for reading and I appreciate any clarification or advice.

[mattysshop]

have you looked into changing the 4 hole injectors to somthing a little more modern? (99% sure last time i pulled one down they had 4 hole's)

i did this in my 3.5 v6 mitsubishi (diamantae you call them over there), 4 hole units, in favour of the newer 3.8L v6 12 hole versions, same cc, same impedence, but helped particularly part throttle/curise economy..

were the later version 5sfe injectors any better? we had the 5sfe here untill about 02' in camry's.. i don't know wheather or not they had revised any versions of them..

[Slasher]

Great suggestion, I didn't even think about the injectors! Will see about finding some newer ones to compare.

[pandaah]

i think youd definetly want a colder plug for a leaner mix... you dont want a hot plug in there with lean mixtures cos you may possibly have pre-ignition or pinging issues, also id think maybe on leaner mix youd wanna retard the timing slightly to keep things safe, you could try advancing it more if your gunna study the knock controllers and find the balance of advancement of timing / stoic ratio

[Slasher]

Probably will try factory heat range coppers to start. It may be a slow process on the plugs and to see whether less timing and very lean or stock timing and not quite as lean will burn better.

[MWP]

Timing plays a big part in fuel efficiency.
Getting peak cyl pressure to occur at the right time increases power output, which then means less throttle & fuel need to be used.

Tune for fuel first, but make sure you do also spend as much time tuning your ignition.
Also remember that "advance to just before pinging" is not optimal.

[briney]

probably as a start to looking for fuel economy is making sure everything is ok. is the ignition timing spot on ? plugs/leads/dizzy cap ok ? oxygen sensor working ? fuel/air filters clean ? the car generally runs smoothly ? tyres pumped up ?

if you have this stuff under control, feel free to ignore. otherwise, i'd cover the basics before making too many changes.

[1JZ-Rolla]

What is your target of 17:1 closed loop (assumed high vacuum/cruise) based on?

Whilst your engine 'may' seem happy running at these lean AFR's on a flat road/cruise situation, you might find that its not actually returning best economy if its not at peak efficiency, in the same way that MWP mentioned tuning ignition for peak cylinder pressures at the appropriate point of the cycle (minimum advance - best torque), not maximum advance possible before detonation.

Cheers
Phil

[TRD184]

with my ST184 i changed form the early injectors to the later model ones, and there was basically no difference, they both had 2 holes

[Slasher]

Good suggestions,

Will be comparing fuel economy from baseline once all the maintenance is taken care of. I suspect lean burn will have an advantage over stoich, being that cars like the Honda HX take advantage of a leaner burn with stock wideband sensors. That's hard to say, being that the HX combustion chambers are said to be specially designed, as well as the timing and other factors. There's not a lot else to do with ign timing here, realistically, due to the cost and complexity involved. Dyno runs to adjust base timing would be nice.

Most likely this will involve tuning short of knock under load and averaging gas mileage a week between each change in tune. Plugs will also be read, cleaned, or replaced after load testing.

All the injectors I've check on thus far have been 2 hole units. Still working on finding some made conclusively after the 5S EFI updates. Or some other compatible injectors with a better spray pattern.