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RB26 Loves fuel at idle

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Hey, have noticed the same with my RB25 but it loves to be rich at idle.. at 14.7:1 it misses and stumbles, I can have a fairly decent idle at 14:1. at 13:1 its noticably smoother and revs higher same again at 12:1

Im just using the stock Injector firing angle from the haltech basemap but tried adjusting it and did not seem to make much difference..

Is this pretty normal?

What ECU and loom are you using? I had this once and it was because a plug and play loom wasn't firing an injector.

Pull the plugs to make sure they're all even, if not investigate why.

For a stock RB26 I'd say that isn't typical. It's not uncommon to find that an engine will idle a little better just a touch richer than stoich - Perhaps 0.90-0.95 but much richer than 0.90 will risk you fouling the spark plugs. I find that this is more prevalent on engines with low cylinder counts (4-6 cyl) where as a V8 will typically be much smoother and happier idling at 1.00 lambda. The need to idle richer becomes more prominent on engines with more aggressive cams but still I'd be reluctant to go much richer than about 0.90.

What injectors are you running? What's their history? Have they been cleaned/flow tested recently?

Haltech PNP

They are band new Siemens Deka Injectors but have not been flow tested at all.. Whats one way to test it out... just pull each injector plug and see that the rpm and or the o2 drop is equal for each injector... Im guessing ill have to disable the idle control so its not just trimming back to target.

i have not tried rb engines yet but i have had some uneven flow of siemens deka injectors,even though i have had better engine behaviour/more stable afr with bosch injectors than deka..flow test your injectors.

I did a cylinder drop test today... To try keep everything even I locked the timing at 20 degree's, disabled the o2 control, disabled the idle control, flattened the fuel map around idle area to the same numbers then let the car stabilize.

Removed number one injector plug, waited for abit.... replaced injector plug, waited for abit then onto number 2 and so on...

I wasn't watching the screen to make sure it had fully stabilized or timed how long I had the plugs on/off for so its not 100% consistant..

For some reason you can see as I progressed after replacing the injector plug of each injector it seemed to be getting leaner and leaner and actually getting quite erratic afr's by the end... Maybe I just didn't give it long enough to stabilize each time?

The RPM drop (seen in yellow) seemed to be pretty consistant with #6 maybe dropping a little more.

I might redo the test but wait longer between each point...

I watched the webinar for tuning AE with a haltech and on Andre's 350 (370z?) at idle the AFR was 14.6 and only changed up and down 0.1-0.2 points.

Where mine will swing from 14 - 15.5 for example... The richer I go the more stable it is.

Another possible cause/issue is my Wideband guage (which is actually about 8 years old) shows abit richer then the wideband in the tuning software (the gauge is run off the Haltechs wideband box) Since the haltech wideband is brand new and I was careful to free air calibrate it I figured the gauge was playing up.. Also when it was on the dyno the Dyno's sniffer pipe was agree'ing with the haltech software... so maybe its just the gauge, or maybe im actually richer or leaner then i think i am

Attached Files

is that engine otherwise stock? I've had an RB26 on the dyno about a month ago and had no problem idling it at lambda 1.00 with ID1000 though.

Cam's and idle relevant stuff was all stock.

This was on a PlugIn LinkECU.

Dekas are renowned in this part of the world for having crap spray pattern & non-linear delivery at low pulse widths, I'd suspect they are not all doing what you're expecting. Get some EV14s!

Yep starting to think thats the case... my idle pulsewidth is about 1.4ms and the datasheet shows they are only linear down to 1.5ms even then its quite uneven until about 3ms.

EV14's have been added to the shopping list

If you do change the injectors, I'd be interested to hear if this fixes your issues. I've had little to do with the Siemens injectors personally so can't add much here.

Will do, but will be awhile off, $720 or so for a set of ID1000's and is only a very minor problem, Above idle im tracking my targets pretty well...

Funny thing is in my limited experiance of tuning about 4 modified RB's they have all had Siemens injectors so I was thinking it was normal..

Will be interesting if changing the injectors does indeed smooth out AFR fluctuations across the range.

On a side note/very slightly off topic... I was doing abit of research on EV14's and there is choice of different spray angles.. Im guessing this choice is defined by your style of intake manifold/injector location... is the aim to get an unobstructed shot at the back of the valve?

Typically with the spray angle, yes it would be selected or defined by the manufacturer to reduce the amount of fuel wetting the port wall. In the aftermarket we're not so lucky though and often don't have a choice.

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