Nistune Forums

Hello there guys in need of some advice regarding the starting of my rb25 and the immediate idle after start:

Symptons: engine runs at 12-13afr when started @air temp of 78C afrs don't drop until run for a few miles cold

My mapper has used the warm after start tables and they do not change the issue. This is also causing a rough first start/cold start. The engine will fire in to life fine but will be hesitant to hold revs and sounds almost missy for a few seconds and then will stable itself and then idle nicely but idle at 12/13 afr.

On a hot start it's perfect

My mapper can see this thread and has access to my account so can add info if I haven't quite put across everything

Mike

The fuel mixture isn't likely to be causing the rough cold idle.

post the bin and we can have a look. if you have a log of warm up it will help.

I should be able to get a log off the warmup tomorrow what parameters do you want me to monitor? And I'll also post up the bin for you guys

Hello guys as promised i have attached a log of a cold start and idle from this morning

Mike

And the bin file

Mike

I'm guessing it's either really cold where you are or
the cooling system thermostat is stuck open or missing, maybe an air pocket etc.

The ignition timing isn't advancing vs coolant temperature.

The log wasn't really long enough to see the engine get to operating temps.

What size/cc injectors are installed?

They are gtr 444cc injectors
England isn't the warmest place haha. But funnily enough it was quite sunny and warm when I ran that log. But the car is in the garage out of the sun. I noted the coolant temp was 20 degrees through the consult before starting her up

Mike

Was fortunate to see my mapper today and he thinks everything is ok with the car in terms of the weird start after I could explain properly what was happening. He thinks it could be the cold start valve that's causing the revs to not immediately reach target value on a cold start.

The main issue we are having at the moment is the afr. Using every table associated with the warmup and cold start we cannot get the fuel right. It basically runs to rich on a cold crank and start and we cannot pull any more fuel out of it. Once it's warm the afr is perfect

Mike

Surprised I haven't had a reply from Matt yet. Is he on holiday? Still looking for an answer on how to control or change fueling in the start up of the car and the immediate cold idle

Have you tested the signal and power to cold start valve?

Cold start is fine now buddy looking for answers regarding the afr situation on a cold start and initial idle

I wish I was on holidays!

Unfortunately there are no AFRs in the log file to see the actual mixtures

I've viewed the files and made small fixes. The gear map should be same as the main fuel map. But it wont matter since it isnt used (High gear coef = 0)

Doing resize on Z32 ECU from 370CC > 440CC should move K from stock 288 to about 242 (with Z32 MAF)

However your K is quite a bit higher at 310 which I would expect result in a richer mixture (which is what you are seeing, before the vehicle hits 50 degC coolant temp when close loop trims start)

With the O2 feedback, once that kicks in you may get a change in short term fuel trims. Currently your long term fuel trim is at 4% which is stored from the last vehicle run (extra 4% fuel added)

So trims dont get adjusted until 50 deg C (o2 feedback temp), but some ECUs (including Z32) however will adjust the trim gauges in consult for other things like cold start and throttle enrichment (which is why we are seeing this change at idle outside closed loop) so that can be quite confusing. Not sure why Nissan did this, but doesn't help with tuning!

As Simon mentioned, we need a log file (stream mode preferred) with AFRs included once over 50 degC on cruise to see the O2 corrections.

If they are correcting too much, then K will need dropping (based on I think it is too high) until it runs 14.7:1 on cruise and good also on boost (may need adjustment to fuel map).

The fuel maps in this tune show a richer adjustment, where normally for larger injectors it should result in a flatter fuel map. That part is confusing me since I thought K would need to be leaner too

Hello matt thanks for the changes you have done and the ideas you have shared with me. I will get my mapper to have a look over your suggestions and what you have said and I will get back to you

Mike