Average AFR numbers from Rev3 3SGTE?

[yokomomr4bx]

Hi guys, for a couple of years I've been suspecting fuelling may be an issue (be it pump/resistor pack/ecu) and so got hold of a Innovate AFR ratio gauge to better understand what what may be happening.

I've been running it for around a month now and wondered what numbers people are seeing at a few points:

1) Cold start idle
2) Warm idle
3) Cruise (2500 - 3000rpm)
4) Accelerating (not WOT)
5) WOT up to 6/7k

I've noticed that (as you might expect) the ratio 'switches' on the trigger of the stock narrow band correcting and tuning the mixture rich/lean. However on occasion while under light acceleration I've noticed the ratio push up to mid 16s...which to me seems a little lean? Under these conditions any further throttle movement seems to make the engine feel like it's starved of air and struggling to make positive boost...? Under WOT I'm generally fine - around 11.8 to 12.5 depending on what side of the bed it wakes up on!

This (I suspect fuelling) issue has been evading me for years because it's so intermittent and nuanced - but ultimately I'm fairly sure I'm losing efficiency and by association power and reliability from this problem persisting.

I appreciate this is all a bit specific and everyone's engine will be churning and burning in it's own special way which is fine, but just as a ball park what are we looking at?

Cheers!

[jimGTS]

If you're on stock ecu, then afrs should be deep into the low 10s by redline. They do run pretty rich on boost. By 3-5-4k (wot) should be into 11s at least and into 10s past 4.5-5k ish.
Pretty much any time out of boost should be around 14.4-14.7 area.

I'd be looking at checking your fuel pressure, worth cleaning fuel injectors also, not difficult to swap in/out..

[jon]

When I dynoed my MR2 whilst it was stock, under WOT the AFR was 13.5:1 until 4000 rpm and then rapidly dropped to 10:1 by 6000 rpm.

Under light acceleration I'd expect the ECU to still be running closed-loop, so AFRs should be fluctuating around 14.7. If you're seeing 16:1 then either the ECU is running open loop or the there's a fuelling issue.

When I imported my MR2 17 years ago, it never ran that great under light acceleration. As far I could tell it hadn't been modified. I took the injectors out to be cleaned and found a few of the injector seals hadn't been centred correctly. After cleaning the injectors and new seals it ran much better.

As Jim say's check the fuelling, get the injectors cleaned and check / renew the seals.

[yokomomr4bx]

Thanks guys that's an incredibly helpful frame of reference! I'm sure the engine used to feel better under light acceleration years ago, but with issues like this it's hard to notice changes when they're gradual. Definitely time to dig out the fuel pressure gauge. Good call on the injectors, I haven't looked around there closely for a long time

[MR2TRD8]

Cold start mine is rich starts around 11
Idle is around 14 when warmed up
Holding revs and normal driving it's around 14.6 if I ease off it goes lean and the gauge shows nothing again if I accelerate it drops down.
On full boost I'm in 10s low 11s.
My maps very safe and I'm not really running any boost 1.1 bar

It's worth remembering afr gauges aren't really that accurate and are just an indication of what's going on.

[yokomomr4bx]

Just to resolve this thread for any poor soul looking at this in the future (probably me), wondering what the problem with my high AF ratios were. Turns out the O2 sensor was old and crap. I bought a new one in 2024 and didn't get round to fitting it until this evening. AFRs are holding steady in the mid to high 14s at idle and light load. Shoot up to 18 when lifting off momentarily and then back to 10s then back to 22.4 when decelerating in gear.

Moral here, do the simple stuff first. Replace the old unknown O2 sensor with a new one.