latency and idle control for S1 RB25 running Z32 ECU

[DeJi]

Hi! I've successfully transplanted a series 1 RB25 into my s13, using Nistune type2 in a Z32 ECU. I actually haven't had any major problems with it, but there are two things I want to ask about.

Firstly, I have RC Engineering SH4-750cc injectors, and according to a forumpost I found when googling for the latency, it's supposed to be 1400us at 13.7V. But I can't get the car to idle very good unless I set it to around 930-950. I get the occasional pop and misfire however I set it though. Tried everything from 650-1400us and I can't get the little misfires to stop. Running NGK BCPR7ES plugs and 0.6mm plug gap. Anyone got a suggestion? Should I leave it at 950? Seems strange that I can't get closer to the specified values.

Secondly, I can't get cold idle right. It doesn't seem to raise the revs, I have to keep blipping the throttle to prevent it from stalling until I get 35-40 degree engine temp.

[DeJi]

oh yeah, nistune triggers IDLE SW when throttle is closed

[PL]

I wouldn't be too concerned about making latency 950us. Just give it what it wants.

Popping could be the use of copper plugs. The platinums do seem to give smoother idle. No idea why!

High idle at cold start should be controlled mostly by the cold start valve. On Nissans this is just a simple thermostatic thing that opens an air passage when cold. Obviously the ECU then adds extra fuel and adjusts timing to support cold start too. But if the valve isn't opening to let the extra air in there's little the ECU can do.

PL

[DeJi]

alright, thanks for that. Will let the latency be then.

could try increasing the gap on the plugs a little bit. I had the exact same plugs on my 400hp CA18 and had no popping problems. Did have a tiny bit more electrode gap on those though. Maybe 0.6 is insufficient for a clean burn on idle.

I've actually removed the AAC valve under the plenum (not the IAC valve though), cause I have a GReddy style plenum instead of the stock one. I removed it on my old CA18DET aswell for basically the same reason and it idled fine anyway, even in the dead of winter. I think I can tweak it a little to make it run better, cause I realized this morning that it's running stupid rich on cold idle (~15* C). I had around 10AFR.

[DeJi]

been fiddling around with it a little now, and it seems that if I set latency to around 1150-1200, the car idles better. The popping/banging more or less goes away. But when I do, I get richer mixture on idle. So I then tweak the K konstant to get ~14.7 again, and go for a drive. I then get 19-22 afr everywhere else across the map. I can tweak that back by modifying the map, but then it gets really steep after the first 3 cells up and to the right. The first 3x3 cells are something like 5 (filtered values used), and everything else needs to be around 60.

The RC engineering injectors latency are specified at 13.7V, and of course differs with voltage. Nistune has a map/table to adjust latency after voltage, but what voltage am I entering the values for in the "injector latency" parameter?

I have also noticed that the unstable idle isn't really mixture related. I have 14-ish afr's when on cold idle, and it's really rough and if I leave the throttle alone, it will stall. I monitor the timing when it does it, and I have about 35 degrees. Is that normal for cold idle (~15* C)? I've been looking around and can't really find a map or table to tweak cold timing.. maybe I'm blind?

[PL]

Latency figures will be at the voltage that the std JECS injectors are specified at. Not sure exactly what this is - I reckon Matt knows. Might be worth doing a search of these forums cos it's been discussed before. I've always been able to get a good result by juggling latency, K constant and fuel map values.

It really sounds to me like it may be worth somehow fitting up your idle control system again! There are usually 3 parts to the system on most Nissan engines of this age. I'll use the terms that Nissan use in the R33 service manual.

1) Air Regulator. This is the really basic part that's just a thermostat that opens an orifice to bleed extra air into the manifold when cold. This gives your high idle when cold.

2) AAC valve. This bit is driven by the ECU. It's a solenoid valve that responds to a PWM signal from the ECU. The ratio of on time to off time determines how much air is bled into the manifold and hence idle speed. This is used for both cold start and during normal "at temperature" idle control. It has a limited range of control, so it can't do cold start on its own.

3) FICD. This is a simple solenoid that bleeds extra air into the manifold when the aircon compressor is operating.

You definitely need 1) and 2).

PL

[DeJi]

if the car runs ok at 950us (which means it's potentially injecting fuel before the valve has opened sufficiently), you reckon it'll be better to just leave it there? Will it affect fuel consumption? I don't think it will, but then again, why does AFR's change when changing latency?

I still have 2). Don't have aircon so 3) isn't needed. 1) won't be refitted any time soon. Blocked the port in the manifold that feeds it, and cut the wires I know it sounds like a stupid move, but I really don't want that valve anymore, and it was a b*tch to route the hose to it neatly (running a GReddy-style manifold). I asked on a Swedish skyline-forum before I removed it and the concensus was that it was alright to remove.

As said my old CA18DET idled just fine without one regardless of ambient temp. If the cold idle timing sounds about okay to you (does it? 35*?), then I'm gonna adjust the throttle plate a little to compensate for the extra air needed.

[DeJi]

I'm starting to think more and more that it's timing related.. can anyone confirm what cold idle timing should be? The car feels very jerky when driving on low speed when it's cold. Runs fine when water temp reaches 40-45 degrees. AFR's are around 10-11 on first startup, so it's getting too much fuel at first (at around 15 degrees water temp), but then climbs to 13 or so, which I would think is fine for cold idle, right?

can I change timing vs temp somewhere? Have checked all the tables I can think of, but maybe I missed something?

also, how can I lean the mixture on cold, if the corresponding cell on the "cold enrich" map is only 2? Can't lower it below 0 I think.. do I have to lower that whole table first, and then readjust K-constant?

[Torque]

can I change timing vs temp somewhere? Have checked all the tables I can think of, but maybe I missed something?

Yes -> Cold Idle Neutral Timing / Timing Adv / Warmup Timing / and so on.
As for these values just use the standard values from your old ECU.

Also do record a log (timing / rpm / temperature)


I have to go through your post again ..

[DeJi]

I think I've sorted it out. Will have to wait until tomorrow to see if she idles better, but my money is on it being fixed I remembered I noticed the CAS was quite a bit from being centred in the adjustments, and thought I'd double check the timing adjustment procedure in the manual. Stupid me assumed that, since the RB is a CA on steroids, that the timing marks should be the same. They are not. I'm used to setting timing on the second mark from the right on CA's, and on an RB that's 25* BTDC Hooked up the timing light and adjusted CAS to 15* instead (middle mark) and the slightly rough idle I've been having completely disappeared I'm betting cold idle is going to be a lot better aswell.

[DeJi]

thought I'd post back since I've solved the problems. Latency I've left at 950us, simply because the car runs better there.. which is funny, cause it's about half way between the info I found online (one said 630us or something, and the other said 1350us..).

The cold idle problem was partly due to the timing being 10* off. When I set it right, it ran alot better, and stopped stalling on cold, and stopped jerking on slow cruise, but the idle was very erratic and a little low (about 650rpm or so) until it warmed up. Remembered we had fiddled with the adjustment screw on the IAC valve when it didn't run smooth on first startup. We didn't unplug the IAC when we adjusted the screw, which is what you're supposed to do. So I did that now, and had to turn the screw out quite a bit, to get idle to about 950rpm. Then plugged the IAC connector back in and it idled just fine, and handles cold idle like a charm. So the auxilliary air valve that's underneath the plenum is definately not "needed". It probably helps a bit, but for a modified car like mine, that's not build for comfort, it's definately not a must-have.

[PL]

Thanks for letting us know the result - always good to know how a story ends.

PL