Thread: timing jump problem- nissan data scan

I am having a hard time tracking the timing with my b13 sentra se-r. When I check the timing at the distributor I can get a a stable reading but when I look at Nissan data scan timing fluctuates all over the place between 3-17 degrees at idle. After 17 degrees the needle jumps strait to 26 degrees, everything above 26* is displayed correctly. What could be the problem? This program worked flawless on my b14 200sx.


Ok so here is the problem i am having I finally have a video of it.

The timing fluctuates at idle with TPS plugged in.

It looks completely normal to me.

Also, tracking the timing via ECU and via the timing light are two different things I think.

When we are checking timing via a light, that is the base idle ignition timing. The ECU readout you are getting from the Nissan Datascan is what the ECU is doing to adjust the timing for whatever conditions it wants.

why does it not display timing after 17* and jumps strait to 26*.... at the distributor the timing looks fine though. When I look at nissan data scan, timing jumps all over the place at idle or stays frozen at 15* it does not change according to my movements at the distributor even in base idle mode. This is a problem I noticed with my new b13..... my b14 had no problems everything was in sync.

The distributor position is ASSUMED by the ECU to be at 15deg. The timing you're seeing reported by consult is the ignition timing advance output by the ECU, not the timing being read from the crankshaft.

If you set the dizzy in base idle mode to display 20deg BTDC on the crank pulley, it will still only show 15deg in Datascan. Timing is like fuel pressure. The ECU ASSUMES you have correct fuel pressure, but if you don't, it will be unaware of it, just like advancing the timing.

I think for one, that your idle is a bit too low, and its falling out of the area that the ECU sees as being the normal idle area and the rpm is jumping around a lot so the ECU is trying to compensate by altering the timing to hit the target idle speed (its faster for the ECU to adjust the timing to raise/lower the rpm at idle than for it to adjust the AAC). Maybe the USDM stuff is set to idle lower, i'm not sure there as i have only played with JDM & AUDM ECUs & maps.

Light throttle application like you showed will give high timing readings because the load is low/none and is like to do with the map (even stock isn't smooth at zero load, there is a big jump). If you drive and rev the car slowly on low load to 5krpm, you might see 30-32deg timing until you add load when it will drop down a lot.

Question ...

What is your AAC valve value (will be something between 10 and 95) at warm idle (i.e when you took that video?).

If you use something like Nistune or TunerPro, while doing a map trace you would be able to see exactly where the ECU is for timing in the map.

Most maps have large jumps above and next to the Idle cells.

What I tend to do when setting timing is highlight all cells near idle or where the car thinks idle is and set the all to the desired base timing (15* in most cases) then move the dizzy until that # matches in the consult gauges. Its a easy way to lock & set timing.

You can do map tracing in datascan (depending on the version) if you have the map and the required addresses.

Of course your way for setting the timing works, but there is a perfectly good "base idle adjustment & timing mode" built into the ECU specifically for that purpose. Not only will it lock the timing to 15deg, but it will also lock the idle control so it won't try and compensate for the changes in RPM when setting the timing or adjusting the idle valve screw.

What these guys are saying is consistent with my experience as well. The ECU is changing the timing to control idle speed to spec. It stops doing this when you go into base timing mode.

NDS has an active test capability that allows you to enter base timing mode. Once you click into this mode, the dispayed timing should be steady at 15*. While in this mode is when you should set your physical location of your distributor to 15* with a timing light. Set your base idle also.

What you are seeing on your computer screen looks pretty normal to me as it is.

it seems normal to me...and i also agree with what the other guys said...they have explained it very well.

I have the same problem wit my B14 except the timing on datascan shows a solid 26*, my idle is also far from stable, and between 2-3k rpms it bucks and jerks like a wild horse.

Exactly.

The reason it jumps up to 26* or so when you give it gas is because it changes from the Idle Ignition timing table to the primary ignition timing table when you get off of closed throttle.

The reason it fluctuates that much is definitely to control idle speed, you can zero out the delta RPM idle ignition tables to keep this from happening.