Very unstable idle and AFR

Whacker · Post by **Whacker** » Fri May 08, 2009 10:46 pm

Hi!

I recently started doing this myself and I'm just trying to get the car running safe and good enough to pass the MOT on monday..

It's a 200sx s14a -98..

I have a gt2871r .86 turbo and the z32 AFM and currently I'm testing my modded stock injectors which now flow around 880cc..
They might be the problem but I'm not sure yet.. Can't afford to buy new ones so really have to make sure if they are the problem or not before I do anything else..

I've modded the k-konstant to around 21000 which the AFR seem to be closest to 14,7 AFR in idle but it's hard to get it stable.. It moves up and down from 14,0 up to 15,6 and every now and then the rpm falls down to 600 and the engine almost dies if I'm not ready with the throttle even though I've raised the idle to 950 rpm..

Also the fuel map is very strange.. All the cells on high load are at about 14,6 to make it a 12,6 AFR on full throttle.. If I raise the fuel in those cells the it gets overflooded at around 9 AFR.. And the rest of the cells at and before boost transtion area can be everywhere from 19 to 14 to get the result of 14 AFR and high 13 when on the throttle..

It's really hard to explain the problem though but I think you'll understand.. I spent 2 hours yesterday just to get it these way by editing the fuel map, before that it almost got flooded in neutral, just reving..

Another thing I can't seem to find the answers to in the manuals are:
Increase Fuel vs TPS.. It's millivolt on one side and RPM on the other but how exactly does this work?? When doea the engine increase fuel and where??

Also can't find what the Injector Response does??

Any help would be appreciated..
I don't know if it's the injectors, something else in the engine or my ignorance which does this and before I leave it to an expensive guy who know all this I want to make sure that it's running fine..
And I also want to learn =)

FHCRSky · Post by **FHCRSky** » Sat May 09, 2009 1:22 am

Read the mapping guide, ECU tuning basics PDF's on the main website under "Documentation".

I think that problem you are describing at higher rpm's with AFR, might be this problem -

viewtopic.php?t=996

Upgrade to latest version of software that Matt has posted -

viewtopic.php?t=1017

With the fluctuating A/F ratio around idle, turn of o2 sensor feedback. You can do this on Type 1/2 board via disconnecting o2 sensor or turning o2 sensor feedback temp to 200 degrees or click flags check box in bottom of fuel map window and 0? the cells that are highlighted. Type 3/4 should have a "feedback switch" window with 02 feedback check box. Turning o2 sensor feedback off forces ECU into open loop, where it ignores o2 sensor. Also you'll notice the 02 sensor voltage stays at one voltage (voltage doesn't fluctuate) when o2 sensor is disconnected.

Throttle enrichment helps to fine tune throttle response. These throttle enrichment tables should be adjusted after you have fine tuned the main fuel maps.

Whacker · Post by **Whacker** » Sat May 09, 2009 1:52 am

Thanks..

I've read all the documents many times =) And then many times again..

I'll try the new software though...

I switched 02 off first when I adjusted the K konstans.. But turned it back on when driving trying to adjust it not be overflooded when I touched the throttle..
Why do you 0 all the cells when o2 is switched back? As I have to replace them again with what it was when I'm driving..

Also, about the fluctuating AFR on idle.. Even when the RPM is stable as it is most of the time it's accesing the same cell all the time but still fluctuating.. So I'm thinking there has to be something else being the trouble..

Mads B (dk) · Post by **Mads B (dk)** » Sat May 09, 2009 5:06 am

have you triede to adjust the lantency ?

chris2712au · Post by **chris2712au** » Sat May 09, 2009 8:44 pm

my wideband is not that stable on idle.. depends on how you have installed it ? have you done the basic checks.. fuel pressure ? fuel flow ? are you injector seals leaking ? On the SR with the standard T/B it has a fast idle cam that helps the cold start..

Also when you start is the idle light coming up in the consult interface ?

Whacker · Post by **Whacker** » Sat May 09, 2009 9:54 pm

Mads B (dk) wrote:have you triede to adjust the lantency ?

I'm using modded standard injectors so the latency shouldn't be any problem.. I don't think there are any problem with the injectors either but of course I can't be sure..

chris2712au wrote:my wideband is not that stable on idle.. depends on how you have installed it ? have you done the basic checks.. fuel pressure ? fuel flow ? are you injector seals leaking ? On the SR with the standard T/B it has a fast idle cam that helps the cold start..

Also when you start is the idle light coming up in the consult interface ?

I've installed it according to the description that comes with it.. The right angle and not too close to the turbo..
Yes, Fuel Pressure ok, No leaks at all..
Have no idea about the T/B or what it means to e honest

And yes, the idle light is on

FHCRSky · Post by **FHCRSky** » Sat May 09, 2009 10:05 pm

Air leak???

Whacker · Post by **Whacker** » Sun May 10, 2009 1:02 am

FHCRSky wrote:Air leak???

At first I thought so too but the Greddy Profec B is very stable and except for when it suddenly wants to die the idle is stable too.. Runs real smooth but the AFR is still fluctuating...

FHCRSky · Post by **FHCRSky** » Sun May 10, 2009 9:53 am

I was thinking about your problem, then I remember it was mentioned in FAQ under question 19 "higher flowing items will have less control resolution." That could be the problem if they are 880cc, as 800cc seems to be the limit for stock ECU. Although, one workshop has run 850cc injectors with a RB20DET ECU.

At idle on a RB engine, if you look at idle stabilisation table, ECU constantly switches between 4 and 0 degrees timing, which can be seen when adjusting base timing (CAS) and MAF/AFM voltage fluctuates on the gauge, which could explan the fluctuations in A/F ratio. RPM needle looks stable on dash, but rpm's fluctuate in NIStune software.

Also are they high independance or low independance injectors??? Low independance injectors supposedly react quicker to changes.

chris2712au · Post by **chris2712au** » Sun May 10, 2009 12:33 pm

t/b throttle body..

Whacker · Post by **Whacker** » Mon May 11, 2009 6:11 pm

FHCRSky wrote:I was thinking about your problem, then I remember it was mentioned in FAQ under question 19 "higher flowing items will have less control resolution." That could be the problem if they are 880cc, as 800cc seems to be the limit for stock ECU. Although, one workshop has run 850cc injectors with a RB20DET ECU.

At idle on a RB engine, if you look at idle stabilisation table, ECU constantly switches between 4 and 0 degrees timing, which can be seen when adjusting base timing (CAS) and MAF/AFM voltage fluctuates on the gauge, which could explan the fluctuations in A/F ratio. RPM needle looks stable on dash, but rpm's fluctuate in NIStune software.

Also are they high independance or low independance injectors??? Low independance injectors supposedly react quicker to changes.

Hmm, could be that.. But then there's nothing I can do to make it go away except getting smaller injectors??

Hmm, never watched the idle stabilization table that carefullt but I am pretty sure that MSF signal is pretty stable..

However I just noticed that there might be a very very small exhaust leak before the wideband lambda sensor.. Could a thing like this cause it to fluctuate??

Bernardd · Post by **Bernardd** » Mon May 11, 2009 11:34 pm

If the actual afr's on the higher load area of the fuel map are richer than the commanded afr's the k value is too large.

chris2712au · Post by **chris2712au** » Tue May 12, 2009 6:15 pm

you can disable the idle stablisation on the sr by unplugging the throttle position sensor as part of the base timing adjustment just a thought to try it out may work differently on other ecu's but atleast you have a fixed firing angle.. for testing alternative youmay be able to enter all the same values to get it stable or just keep raising the idle..

XR Pilot · Post by **XR Pilot** » Tue May 12, 2009 11:38 pm

Whacker wrote:[I'm using modded standard injectors so the latency shouldn't be any problem.. I don't think there are any problem with the injectors either but of course I can't be sure..

I know of other people who have removed the pintle cap off the injector (assuming that is how you modded your injectors to 880cc) and they have had similar problems. Spray pattern is critical with a small displacement motor and large injectors, I would say that is what is causing your idle problems.

As a comparison, the local workshop's S14 SR20DET powered drifter idles dead stable at 750-800rpm with 800cc injectors and a set of mild cams, but the owner spent spent a while chasing injectors with good spray pattern.

Playing around with latency might help.

Whacker · Post by **Whacker** » Wed May 13, 2009 8:37 pm

Bernardd wrote:If the actual afr's on the higher load area of the fuel map are richer than the commanded afr's the k value is too large.

I adjusted the k value 'til it was about right on idle but perhaps it's better to have a closer target AFR on high loads and then just change it on low load area until it seems fine?

XR Pilot wrote:
Whacker wrote:[I'm using modded standard injectors so the latency shouldn't be any problem.. I don't think there are any problem with the injectors either but of course I can't be sure..
I know of other people who have removed the pintle cap off the injector (assuming that is how you modded your injectors to 880cc) and they have had similar problems. Spray pattern is critical with a small displacement motor and large injectors, I would say that is what is causing your idle problems.

As a comparison, the local workshop's S14 SR20DET powered drifter idles dead stable at 750-800rpm with 800cc injectors and a set of mild cams, but the owner spent spent a while chasing injectors with good spray pattern.

Playing around with latency might help.

Yes I took that off but I replaced it with a new cap..
I got in a video here:
http://www.vimeo.com/4247698

It's actually the last purple injector I'm using but I took the cap that you can see on the first four red ones so I got the same 2 beam spray pattern on the ones I use...