Novice Tuning Question

[gwilkinson34]

Hi all, a hypothetical (learning about tuning):

if I was to drop 3-5% of the fuel out of the base map of an RB25 ie under 4k rpm and under '10' load (tuning in VE) in order to increase cruising and light load fuel efficiency, would I also need to drop an equivalent amount of timing from these areas to compensate for the lower air/fuel ratio?

Does anyone know any guides to this effect that compare the relationship of fuel / afr and timing maps?

Am I even thinking about this the correct way...?

Cheers!

Edited July 16, 2010 by gwilkinson34

[Crans]

Closed loop ecu? if so just change the closed loop target afr. At low rpm ou shouldnt need to adjust the timing at all

[gwilkinson34]

Closed loop ecu? if so just change the closed loop target afr. At low rpm ou shouldnt need to adjust the timing at all

Haltech P2000 - there's an AFR target table but in the docs it talks about dyno tuning and adjusting the fuel table to 'match' the desired AFR target... assuming this means it doesn't automatically adjust? Or does it automatically adjust just timing?

[gwilkinson34]

Ps I have no tuning experience and next to no automotive engineering experience - I do have a fair bit of general software knowledge and a working understanding of EFI / forced induction theory - essentially i'm a tuning / mechanic noob but very tech savvy so i reckon I can work it out...

[Moodles2]

I wouldn't be learning to how to tune on a expensive engine (NEO RB25DET), let alone messing with a professional tune (judging by power listed in car profile), really shouldn't be touching fuel at all without a wideband o2 sensor and long stretches of road in the middle of nowhere. Take it to your tuner and tell them your fuel economy goal get them to put it on the dyno and adjust the AFRs as safely to stoich as possible, it would probably be less than 1 hr dyno time.

[gwilkinson34]

I wouldn't be learning to how to tune on a expensive engine (NEO RB25DET), let alone messing with a professional tune (judging by power listed in car profile), really shouldn't be touching fuel at all without a wideband o2 sensor and long stretches of road in the middle of nowhere. Take it to your tuner and tell them your fuel economy goal get them to put it on the dyno and adjust the AFRs as safely to stoich as possible, it would probably be less than 1 hr dyno time.

Yeah I understand your point - but I'm not touching anything above 4,000rpm or half load so it's safe. I wont be mucking with WOT or high boost / load areas of the map (obviously without a dyno) so I don't really see how anything can be broken. Just fine tuning the fuel on idle and light load / cruising. It's the sort of thing that probably doesn't get enough attention on a 'professional tune' most of the time anyway...

I've got the original tune saved so really i'm just having a bit of a dip in the 'kiddy pool' area of the map - playing with idle control etc. Spent all this cash so I might as well learn what's going on!

Getting it tuned on E85 in a couple weeks so i'll be showing the changes I make to the map to my tuner and discussing it all with him then, while I watch him adjust everything for the ethanol.

(I'm the kind of guy that needs to know how everything works, obviously!)

[gwilkinson34]

Also on your "as close to stoich as possible" comment - surely that's not the most fuel efficient (across the whole map) way of tuning - leaning everything out a tad on deceleration would provide better fuel economy would it not...?

[wolverine]

Buying a wideband setup seems like the first step.

[Crans]

Any decent ecu on decel will totally cut fuel. Changing your afr target leaner that stoich will save fuel but you also have to watch combustion temps not that it will do any harm while cruizing but a sudden hit of boost my not like the extra heat

[Moodles2]

Check the injector duty cycle while cruising and idling, there's not a great deal of fuel going into the engine to begin with, and it's the O2 (lowband) sensors job to lean out the mixture while cruising at constant load or idle. A good point has been made, doing fuel map modifications yourself without a wideband sensor you could risk making the combustion temps skyrocket while cruising with a leaner mixture, and suddenly hitting boost might cause the engine to detonate.

[JonnoHR31]

1. buy a wideband

2. start reading and learning

3. save yourself shitloads of money by doing your own tuning, even for ethanol.

[The Mafia]

Buying a wideband setup seems like the first step.

1. buy a wideband

2. start reading and learning

3. save yourself shitloads of money by doing your own tuning, even for ethanol.

+1000 to both

[bradsm87]

the leaner u go past stoich, the more u'll have to open the throttle, adding more fuel anyway.

[rob82]

the leaner u go past stoich, the more u'll have to open the throttle, adding more fuel anyway.

Thats the whole premise behind lean cruise strategies they had in the late 90's. As your lean the mixture you need more throttle hence the pumping losses are reduced as the vacuum reduces as well.

The other thing most people dont realise is that the highest EGT's are around stoich ie 14.4-15 either side of this AFR the combustion chamber temps go down.

Advancing the timing 5-10degrees will help also. I would also look increasing your plug gap if you can. Also if you are tuning VE and your VE is correct then I would just change your desired AFR table to say 17:1. That is if the haltch software works properly.

[gwilkinson34]

Also if you are tuning VE and your VE is correct then I would just change your desired AFR table to say 17:1. That is if the haltch software works properly.

Does this actually do anything though? What I understand from reading up on the ECU software is that the desired AFR table is just that, a 'desired AFR' and then you tune the fuel map to reach this... ie changing the desired AFR doesn't automatically change anything tune wise... or have I got that wrong?

You would need a wideband plugged into the ECU to get it to know what AFR it was running wouldn't you? (which i will be organising next week...)

[JonnoHR31]

yes you need a wideband to do anything at all with AFR's

+1 for more timing. i added more than 20 degrees timing to my light load areas after a "professional" tune, it was a completely different car to drive after that. also improves fuel economy a lot

[gwilkinson34]

Check the injector duty cycle while cruising and idling

I can't for the life of me work out how to check the injector duty cycle in the Haltech software. The injectors should be wired up to an analogue voltage input shouldn't they? Can't seem to find it.

Anyone know anything about how to check this?

[Moodles2]

You will only see the injector duty cycle with the engine running

[gwilkinson34]

You will only see the injector duty cycle with the engine running

Yeah I had a quick look for it last night... perhaps I didn't have the correct views open.

Have another look today and log my drive down to get a haircut hehe.

[rob82]

Does this actually do anything though? What I understand from reading up on the ECU software is that the desired AFR table is just that, a 'desired AFR' and then you tune the fuel map to reach this... ie changing the desired AFR doesn't automatically change anything tune wise... or have I got that wrong?

You would need a wideband plugged into the ECU to get it to know what AFR it was running wouldn't you? (which i will be organising next week...)

The way a desired AFR map "should" work is to enrich the mixtures. ie 12:1 is an enrichment of around 22% over stoich. I haven't used the haltech software as I just dont like using them but if its anything like an autronic then changing the desired AFR map will result in a change of fuelling.