reactone

Wierd.
Thats good to know for the future, my motor is bored 20 over, I wonder if that small amount of displacement change will make a difference.

Slo_crx1

Actually it tends to make life easier and gives you a "buffer zone" type of safeguard. Think about it...battery voltage at idle is normally around 12.5~ volts which causes a "slight" delay in how fast the injector can open. This adds to the hell of tuning idle, which I'll go over below.
Scaling from a 240cc injector to say a 450 or 560cc size only changes the injector times to the "enlarged" ratio, not an adjusted ratio. Going from a 240cc to a 560cc is over double the fuel charge, so naturally if you put in the new injector size value as "560cc" it will cut your injector open times in half (and a hair more) for the entire map. Add in the latency of a much larger injector than stock, and you can see where it becomes hell to tune. The injector pulse is so fast that the injector has almost no time to open due to it's large latency "lag time", and the lower battery voltage at idle continues to hinder it. In the higher rpm range, voltage increases slightly and can open the injectors a bit faster. Therefore, if you set the injector size lower than what it's rated at (say 510cc instead of 560) it allows for a slightly longer injector pulse signal due to less of a ratio percentage applied against your fuel tables. The longer it's open at idle, the more fuel will come out of the injector in regards to it's inherent latency time. It makes tuning your idle much easier and keeps your your times to a semi-normal rate, and through the rest of the map you will end up cutting out a small amount of fuel time instead of normally adding to it. It allows for nice rich basemaps and easy control over fuel when fine tuning. Also, it adds the benefit of never running over a certain duty cycle if you keep your maps under 100% DC. Typically, injectors aren't really meant to hold times of over 85%DC, and this way adds a small bit of buffer just in case you do end up a little above the DC time you want.
More than likely Chris did the injector sizing this way to help you get up and on your way without having the typical idle latency issues normally associated with larger injectors.

brettsb16a2

Well my idle sucks, as in it idles up and down sometimes and sometimes its sits perfect at around 800rpms. I am running a P30 codebase and Chris let me know to try a p72 base. I did try that map with the 450 cc injectors in high altitude i think from denver or something and it was tuned with 450 in the fuel multiplier. My car ran extreamly rich and it set a check engine light right away. I didn't check what code it was but if i remember correctly it may have idle'ed better but i just went back to what i started with. I think i will just leave it with 353cc cause it runs awesome other then at idle.

zebvaj

why not just fix the idle your self? play with the idle iacv slider bar and try to get the car idling stock, shouldn't be that hard.

Oscar

If your car idles fine with a stock ecu, then messing with the slider won't do anything.

If the idle is surging, you're probably too lean. If it were too rich, the motor would die.

brettsb16a2

Oh no, i have it around 14.5-14.7 at idle. I will idle perfect sometimes and it will surge up and down sometimes. It will surge right after the rpms increase with my foot....then i let off and it idle surges for like 30 seconds to a couple minutes and then it just smooths out to a perfect idle between 750-800rpms.... then as soon as i touch the gas it will do it again. It could be my iac, i did pull it and cleaned it out real good with brake clean but maybe its still crapped out.... its the original one with 80,000 miles. It did the same thing the first time i started it up when i was runnig a SAFCII and the 450s after the turbo was installed but after those first initial start ups it never did it again while i had the afc. Now my car sat for a couple months with the transition of the afc to obd1. I have messed with the fuel maps alot, rich and lean and stoich but never fixed it. I think it may have done it in open loop, i don't remember for sure, SO if it did it in open loop, then it could be the IAC? When i pulled it the screens were nice and clean and the pintle moved freely, but i cleaned it anyways. Dang i wish i had a test one so i don't have to shell out some money for a new one if its not the problem. AS i read through what i wrote..... it sounds like i need to replace the IAC. what do you think

marcj

Have you checked all over for a vacuum leak? I'm using an obd0 head & intake manifold on a newer block, and I have caps on a few nipples from the obd0 setup.. awhile ago one came off and my idle would surge a few times after i let off the gas and then sit nicely at idle.. I thought it was something wrong with my crome basemap but i ended up finding one of the caps fell off a nipple and was leaking pressure. just a suggestion.

brettsb16a2

I will spray some brake clean around the intake and vaccuum lines tomorrow, i visually looked and didn't see anything and i cant hear anything but we both know that it could still have a leak. I hope i find it. Thanks for the advice cause i really havent tried that yet.

Oscar

To rule out the iacv, bypass the coolant lines.

zebvaj

I would just adjust the iavc slider. I had seen a couple of cars idle fine on stock ecu but can't idle without surging on crome. We usually just adjust the iavc slider and get it close to stock. But to each his own. GL