Refuses to go into decel....any thoughts?

[s14unimog]

I've posted on this problem before, but I've done some work since then, and the problem still alludes me. What I've got here is an S13 SR20 that refuses to go into decel. More precisely, the A/F's float around 9:1, 10:1, under engine decel. I noticed the problem when it seemed to be flooding out at an intersection. I can drive the car fine, meaning it runs a good A/F mix (14.5-14.8 cruising) under any load, responds to throttle fairly well and is quite quick out of boost. I remember before the rich condition happened, the A/F's would hold 21:1, on the wideband, under engine decel. To give a little back ground on the car, I recently rebuilt/built an s14 bottom end, utilizing stock pistons and a built s13SR head. I've got the whole engine ready for 400+ WHP; no need for a unnecessary mod list. To start with, the car ran great immediately after the build up and I was on my way to 500 miles (clutch break in, as well as a conservative engine break in), when at mile 300, or so, this all got started. So far I've checked quite a few things...

-Replaced wideband sensor (narrow band is not in use)
-checked/verified TPS voltage
-verified throttle cable tension
-replaced ignitor (just for kicks)
-BKR7ES-11's re-gaped to .028"
-checked/ verified MAFS voltage
-pressure tested charge system, fixing ALL leaks
-replaced PCV valve.
-brand new IACV
-checked/verified correct fuel pressure.
-checked/verified FPR responds to vacuum correctly
-Primed fuel rail off manifold to check for leaks
-Replaced ECU coolant temp sensor
-BOV is disconnected from vacuum but I made a block plate to insure it wasn't leaking, it wasn't
-checked/verified base timing
-fairly new 300zx fuel filter


I have a Nistune system and can monitor all sensors and codes. The system did detect a knock sensor fault so I first tried clearing the code (no difference) and then tried disabling the sensor with Nistune, and it didn't help the symptoms either. No codes otherwise; maybe I should replace that as well. I did a compression check, just for kicks, and she looks really healthy; there is no reason to believe otherwise though. If any of you guys have heard of this or could maybe shed some light, it would really help. I'm at my wits ends here.:smash:

The Build Thread (http://zilvia.net/f/chat/221815-96-zenki-slight-overhaul.html)

[s14unimog]

So it has been brought to my attention that the closed throttle voltage of 0.5v can sometimes not be true closed throttle if the ECU doesn't recognize it... Have any of you heard of this coming up? A friend of friend had an idle issue with an SR and lowering the voltage to 0.3v did the trick to cured the issue. If this is true, this would have also affected the decel maps...

[4x4le]

yes man, Just check to see if the closed throttle light is coming on, if its on then there should be no need to adjust the voltage lower, but at least check it out man.

[s14unimog]

FIXED; it was exactly it! Apparently my TPS needed to be set a little lower in order for the ECU to see "TPS idle" (closed throttle). This is just another reason I LOVE Nistune, although it was right in front of me the whole time, You can visually see the moment the ECU recognizes "closed throttle." For a more detailed explination, my TPS closed throttle voltage was fluctuating between 0.44v and 0.46v. I lowered it to a steady 0.40v; all verified by Nistune.

I hate that it took me this long to figure out but at least I know and if someone comes across this thread in the future, keep this in mind; if the symptoms are similar.

[4x4le]

once again, I dont know how people live without nistune or nissan datascan and a consult cable. I really thought I may have mentioed a closed throttle signal to you in the past, but who knows, I talke to so many people with problems with their cars that I end up thinking I went over stuff with someone when I really went over it with someone else visa versa.

I cant wait to be able to get my hands on this car now.

[s14unimog]

^haha I hear ya. I think we spoke of this in the past but never actually covered a possibility that it needed to go lower. Plus, lets not forget that the car did this all of the sudden. Thanks again for your help Brandon, I hope to have the car ready to tune in a matter of a week or so.

[s14unimog]

Just in case anyone stumbles across this thread in the future. The reason why my car wouldn't go into decel was b/c the TPS's base voltage was above 0.45V. I have since then lowered it to 0.40V and it has cured the issue.