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-   -   VVT motor lean and die (https://www.miataturbo.net/engine-performance-56/vvt-motor-lean-die-97096/)

Leather_Belt 06-01-2018 03:03 AM


Originally Posted by SpartanSV (Post 1484826)
Shouldn't be battery. Are you using an NA alternator?

I would measure voltage at the battery and injectors to confirm it matches what the ecu is seeing.

Voltage differences can make a pretty significant change in fueling but AFAIK that shouldn't be an issue if the ecu is seeing the same voltage as the injectors and the injector dead times are set correctly.

Yes I'm using the same NA8 alternator I had before. I'll have to do that tomorrow then maybe. Does that point to a potential wiring issue? I could maybe see that being a possibility since I had to solder on a new connector to the harness to replace a broken one.

Is there any other weird reason the injectors wouldn't be getting the same voltage? I'm just assuming the dead times have been correct since it's not something that was changed since it started running poorly.

Leather_Belt 06-01-2018 03:04 AM


Originally Posted by SpartanSV (Post 1484828)
Bingo. Voltage drop caused an issue because someone fucked with the injector dead times. Compare your dead times to the DIY basemap.

Ok will do.

Leather_Belt 06-01-2018 03:30 AM

2 Attachment(s)
Eh bad news I guess? Injector dead time is the same across my tune and the MSPNP base map.

I feel like the drop in voltage could definitely be affecting the injectors though. But I don't know what would cause that. I guess this is where my knowledge ends and I try to learn from you guys and more research.

Skamba 06-01-2018 05:50 AM


Originally Posted by Leather_Belt (Post 1484831)
Eh bad news I guess? Injector dead time is the same across my tune and the MSPNP base map.

I feel like the drop in voltage could definitely be affecting the injectors though. But I don't know what would cause that. I guess this is where my knowledge ends and I try to learn from you guys and more research.

You are using curve 1 which is not really a curve at all. Also not all basemaps are equally good. If you want a good reference, take a look at Brain's basemaps. He uses these settings.

curly 06-01-2018 09:08 AM

Usually you see dead times more like 2-3-4

SpartanSV 06-01-2018 12:13 PM


Originally Posted by Leather_Belt (Post 1484831)
Eh bad news I guess? Injector dead time is the same across my tune and the MSPNP base map.

I feel like the drop in voltage could definitely be affecting the injectors though. But I don't know what would cause that. I guess this is where my knowledge ends and I try to learn from you guys and more research.

That is not the deadtime curve I saw in the DIYAutotune basemap for 94-95. MegaSquirtPNP by DIYAutoTune.com

I'm still pretty confident a totally flat deadtime curve will cause your issue. You still need to figure out why your voltage is sub 13 when running too.

Leather_Belt 06-01-2018 12:20 PM


Originally Posted by SpartanSV (Post 1484883)
That is not the deadtime curve I saw in the DIYAutotune basemap for 94-95. MegaSquirtPNP by DIYAutoTune.com

I'm still pretty confident a totally flat deadtime curve will cause your issue. You still need to figure out why your voltage is sub 13 when running too.

Ah yes well I'm using the base map appropriate for the 03 motor.

Could my alternator be going out? My battery is only a year old. I'll try and find more reasons I would suddenly have slightly lower voltage.

curly 06-01-2018 12:23 PM

Yes, afr is telling you that you have a charging issue. I'd go with the alternator being an issue.

SpartanSV 06-01-2018 12:27 PM


Originally Posted by Leather_Belt (Post 1484885)
Ah yes well I'm using the base map appropriate for the 03 motor.

Could my alternator be going out? My battery is only a year old. I'll try and find more reasons I would suddenly have slightly lower voltage.

Yeah don't do that. Inputs and outputs are potentially different as the harnesses are different. AFAIK you should be using the 94-95 basemap and making changes to that in order to run the vvt engine.

It's very possible your alternator is bad. As I said before it shouldn't be a battery issue. Since it's an NA alternator it's internally regulated so there isn't really anything outside of it that would cause lower charging voltage. Measure voltage at the battery while running to make sure it matches what TS shows.

Leather_Belt 06-01-2018 12:37 PM


Originally Posted by SpartanSV (Post 1484889)
Yeah don't do that. Inputs and outputs are potentially different as the harnesses are different. AFAIK you should be using the 94-95 basemap and making changes to that in order to run the vvt engine.

It's very possible your alternator is bad. As I said before it shouldn't be a battery issue. Since it's an NA alternator it's internally regulated so there isn't really anything outside of it that would cause lower charging voltage. Measure voltage at the battery while running to make sure it matches what TS shows.

Oh wow that's the first I'm hearing this. I figured since I wired in all the NB2 sensors and had NB2 injectors I should use the NB2 base map. I really have never heard this before.

I'll measure battery voltage while data logging today and see if they're the same.

Skamba 06-01-2018 01:48 PM


Originally Posted by Leather_Belt (Post 1484885)
Ah yes well I'm using the base map appropriate for the 03 motor.

Could my alternator be going out? My battery is only a year old. I'll try and find more reasons I would suddenly have slightly lower voltage.

There seems to be something wrong with the 01-05 basemap. In this thread, people also found out that the ignition table is crazy. Would not suggest to use that map at all.

Leather_Belt 06-07-2018 07:39 PM

Hey just wanted to update this thread in case someone else has this problem some day.

It did end up being the alternator. Got it replaced with an AC Delco reman and everything has been running much better.

Found out not only from you guys in the thread, but as I was looking over a couple other things, the battery was too low to start the car again. My roommate suggested jumping it for me to help me out. While the battery was connected to his, the car started and ran just like I wanted it to. Also when he parked it behind my car and shut the door, he habitually locked the door and left the keys in the ignition. So when the AAA guy showed up (because no spare key) my roommate asked if he could test my battery and alternator. Lo and behold, the alternator was NOT sufficiently charging the battery.

Thanks a lot for the help guys, especially Spartan for sticking around so long, lol.

As for using the base map appropriate for the motor and not the harness/chassis, I donno what to tell you guys. It started up really well the first time after the swap, and now my tune is built around it. Spark timing has been adjusted all over the map as well. I appreciate the notice though.

SpartanSV 06-07-2018 08:46 PM

The potential problem with using the 01-05 basemap is that the inputs and outputs are set up differently. If everything is working correctly then don't worry about it.

You need to fix your injector deadtime curve. That part of the basemap is definitely messed up.


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