Thread: Idle drop when fans kick in, SA with Map

Having issues with idle dropping when the fans kick in. Wasnt a issue previously, so dont know if i have changed something or what.

What normally controls the idle up when fans kick in? I only have the idle speed stepper connected, not the other purple plug solenoid on the IACV connected, but its always been wired like this and hasnt had issues in the past.

Ive just gone from Nismo 550cc injectors to Sard 850s, and its been a massive retune given the small change in injectors, have had to retune just about everything, interesting tho, the 550s were maxed out, and the 850s are only at 55 duty.

Also, found a Accel map, labeled dTPS TPS Factor Table. No idea what it does, but in the base map i started with the numbers on the left side of the table were very high, but in a screen shot of the table that John posted the other day, the numbers are a lot lower, so i copied them, and finally got the car to not go super rich everytime i go close to the gas pedal.

Trying to work out overrun fuel too, so it doesnt go to 10:1 afr everytime i change gear or backoff, ive lowered the fuel map numbers on the far left column, which has helped a bit, but on very light load, ie while rolling down a hill with the gas pedal just very lightly open, the car now stutters and surges as its running super lean, like 19:1. Im sure there must be something in the tab marked deccel that is designed to control this, but ive yet to work out what table it is, or what parameter needs to be changed.

Idle AFR has been a challenge all day, changing one number up or down in 1 or 2 zones around where its idling can cause afr to go from 16.5:1 to 13.5:1, ive tried using latency as a idle trim, but not a lot of luck, and it will be perfect around 15:1 at one moment, then lean again the next time i stop.


Been a very busy day tuning, with a lot of changes, a lot of things learnt too i think.

There is no set "idle up" function for when the fans kick in, that is simply current draw which is sometimes related to battery offset issues for the injector. The other items you can look into are the idle error parameters and log the idle valve duty when you kick the fans on.




That is good to hear, which map did you see that had these values?

The dTPS TPS Factor Table is simply a multiplier for the final acceleration enrichment. The higher the values the higher the multiplier and the more fuel will be added.



If this is only when letting off the throttle then you likely wouldn't have to actually change the fuel map, only the decel factors. The higher the decel factors the more the injector pulsewidth will be reduced, so start with raising those decel factor tables and see if this helps you out. @OnTheChip might be able to help you further.



This is likely because your SD factor is set too high and the smallest little changes you are making to the fuel map will result in larger changes to the final injector pulsewidth. I would suggest trying to get your SD factor lower .. something in the 170-180 range and then rescale your injectors to make up the difference in fueling, since lowering the SD factor will reduce the injector pulsewidth per fuel map value.

If you send me your TCD I can assist you in doing this.

Tried some more tuning tonight, the car is dumping so much fuel on changes its popping out the exhaust with a thump.

I've tried massive changes to the deccel tables with no effect, and I'm talking about adding 50 to each of the tables, testing, removing and then trying the next table. It's very frustrating to have all these things we can tune, and no idea what they do, or any result to a issue with the tune.

My sd factor was about 170, I've lowered it and bumped the injector size to get afr correct again, this hasn't made any difference to the overrun fuel.

I'm getting a lean spot coming onto boost when I give it some gas, I've got a lot of this which I'll post when I get home. Clearly there will be a table in accel to control this, but so far the hit and miss approach to working out which one hasn't given any results.

The idle issue when fans come on is really bad, car is going super lean all of a sudden, and there is nothing I can do to keep the car running, it will stall despite pumping the gas to keep revs up, and restarting can take a few minutes where it will start for a few seconds, then just die. Repeated attempts will eventually just start like normal and idle like nothing has happened. Not so good when fans come on at the traffic lights. I've tried adding massive amounts to the latency at lower voltages, as the voltage does seem to drop for some reason, but I don't know if it's the alternator loosing efficiency due to low rpm or what.

It's still not amazing on gas, but sorting the drivable issues is primary. When my kids ask me why my car does this oscillating idle issue then dies is bad enough, hate to have a Gf and take her out in it.

Once you go to a larger injector, like the 850 and if they are an older style injector this can start to become more of an issue of the injectors being slow to react when letting off the throttle.



This wouldn't make any difference to the overrun fuel cut, it would simply give you more resolution in your idle portions of the fuel table.



After looking at your logs the lean spot coming onto boost IS NOT an accel fuel problem, it is a FUEL TABLE problem. You don't have enough fuel in the lower boost columns and that is what is causing the car to lean out. Accel fuel will only be active when load or throttle is being changed. If you are WOT then you wouldn't be tuning the accel tables, you want to address and add fuel to the actual FUEL table.




Have you tried checking over your engine and chassis grounds? The voltage should take a little hit when the fans initially turn on and then it should settle back out. This is almost always a battery offset issue in combination with idle error. You can try reducing the update timers in the idle error section to speed up how quickly the idle valve error will be applied to help catch the idle. It would also be a good idea to bump your idle speed up, if you haven't already to around 1000 rpm with that size injector to help this situation.

One other thing I noticed in your latest TCD you sent me was the cranking table seemed like it had a good bit of cranking fuel for higher ECT (around operating temperature) .. this might be some of the issue behind the hard starting when it stalls.

Here is a quick video that I made that addresses your issues with the idle and the fan coming on.

http://www.sr20-forum.com/nismotronic/71681-nismotronicsa-idle-tuning.html