occasional stalling under decelleration

zrated · Post by **zrated** » Sun Nov 15, 2009 1:59 pm

Hi guys,

I'm having problems with my Z32 in terms of stalling under decelleration and some general idling issues.

In terms of modifications, it's fully built but has standard cams, turbos, etc. I'm running sard 800cc injectors and according to sardracing.com the 'dead time' is 1.6msec so i've resized the injectors using the nistune app then changed the injector latency to 1650uS

The idle seems OK but sometimes is a little erratic. I've had to add more fuel in the first time enrich to get the car to start when its warm. Other than that, i've trimmed a little fuel out of the main fuel map and also raised the fuel recover to 1900 between 70 and 100deg. This seems to have helped a lot with the stalling but it's still happening from time to time.

I'm currently trying to get the car registered and they've signed off on everything except 'stalling under decelleration'. It usually happens when you rev the engine up to around 5000rpm in 2nd gear, then put the clutch in.

Can you guys look over my tune and log attached and see what else may need to be changed to sort this issue out? I only managed to get it to stall once in the log, it's at the very end.

Thanks in advance!

zrated · Post by **zrated** » Sun Nov 15, 2009 2:01 pm

I forgot to mention i've removed the stock viscous fan and am running a thermo fan which is hooked into the Z32 A/C fan instead. It turns on at 82deg and i think it sucks a bit of battery juice!

Seank · Post by **Seank** » Mon Nov 16, 2009 6:24 am

Couple of Q's.

Are you running a dual maf/dual filter intake or single maf/single intake? Dual intakes seem more prone to air being forced into the maf resulting in erratic maf readings. A common remedy is to place some sort of partial block on the filter to prevent air from directly hitting the filter. Search for 'flower pot' mod on tt.net.

Have you checked for vacuum leaks? (not necessarily boost leaks since this happens under decel/vacuum conditions) Currently replacing the brake booster on mine to hopefully clear up idle/ AFR issues. Check your clutch booster/vacuum reservoirs (and brake booster while you're at it) for leaks.

zrated · Post by **zrated** » Mon Nov 16, 2009 10:12 am

I'm just running a single AFM setup at the moment.... It's located in the stock location and I think the intercooler may be pushing air directly into the AFM due to its shape.

I wouldn't have thought it would be AFM related as the voltage in the logs seem fine when coming off throttle.... or am I missing something?

Definitely no vacuum leaks either.

zrated · Post by **zrated** » Mon Nov 16, 2009 6:29 pm

anyone?

Matt · Post by **Matt** » Mon Nov 16, 2009 11:32 pm

some problems

i cant see valid TP or injection time in these logs. Also there is no AFR input so we cant see the mixtures either

so hard to diagnose from this when i only have RPM and MAF which doesnt indicate the outputs

normally likely air on decel is causing a MAF spike like at 1:07.392 would be due to air going backwards more than a tuning issue

zrated · Post by **zrated** » Mon Nov 16, 2009 11:56 pm

dont really understand....

1:07 @ 3920rpm?

im having problems trying to get logs working..... i go into stream mode, hit consult and hit record, but when i save and got back to playback mode, only RPM and MAF info appears.... ive had to just look at all the logs in excel....

Matt · Post by **Matt** » Tue Nov 17, 2009 12:39 am

1:07.392 that is the positionin the log file (end bit is seconds)

you will see here that AFM rises whilst RPM drops

zrated · Post by **zrated** » Tue Nov 17, 2009 11:29 am

I dont think its maf spike, it just doesn't spike that much. Is it possible that it's injecting too much fuel when starting to stall?

Matt · Post by **Matt** » Tue Nov 17, 2009 5:37 pm

what are your AFRs before stalling?

STATUS · Post by **STATUS** » Tue Nov 17, 2009 8:28 pm

unfortunately the z32 does not allow you to play with the timing in both neutral and in gear, usually this fixes it with S13's and R32 etc.

I have played with your inj and ign maps broadly to give you an idea of what to do to tackle the stalling, i don't have the time to check your logs but it is enough of a change to notice it in both your inj and ign maps. it is best to interpolate the bottom row up to the max figures i have put in to make it smoother.

In the INJ map when the car starts to stall (due to reversion thru maf) it will generally trace/bounce along the bottom row mid to 3/4s across to the right, the trick is to take all the fuel out which forces it back to where it should be.

In the IGN map you increase the timing along the same points as above to stop it stalling

zrated · Post by **zrated** » Wed Nov 18, 2009 12:13 am

Matt wrote:what are your AFRs before stalling?

to be honest it's hard to emulate this on the dyno, just on the road.... i don't think the sniffer up the tailpipe works well enough for checking the afr on decel.

zrated · Post by **zrated** » Wed Nov 18, 2009 12:15 am

STATUS wrote:I have played with your inj and ign maps broadly to give you an idea of what to do to tackle the stalling

thanks status, really appreciate your help. it gives me an idea on how to tackle this issue.

i've changed the injectors back to stockies so I can get the vehicle inspected and on the road.... ill be putting the sards back in next week so ill give it a try!