Loaded up all the correct settings in Tuner Studio to get the car running, all of that went well and the car started and I was on my way testing it out on the road and everything felt pretty good. The only thing wrong I noticed was my AC was running constantly regardless of where the switch was On/Off. So, I took the harness off and fixed the bad solder joint, plugged the MS back in, and noticed the AC issue was fixed, but when I went to take the car out it started lurching and bucking uncontrollably. It seemed like whenever I gave the car gas the AFRs leaned way out. I built the MS3X myself and followed the whole guide on Trubokitty.com I have a feeling it is something with the IAC valve becoming stuck or not moving because everything was working before and I did not change anything to the tune on the car. I tested the Idle Valve in Tuner Studio and it seemed to work okay in there, but I have yet to take it out and look to see if the valve is actually doing something. Now when I try to run the engine, it will sometimes idle rich, around 11-12 AFR but it seems relatively stable with a few sort of pop sounds coming from the engine which I do not know what those could be. When I give the car gas it will give it fuel but the AFRs go lean and stay pegged around 18 until the car dies out. I am not sure what could cause this problem other than something mechanical.

Tune file and logs are below:

 

I wouldn't suspect the IAC too much if it runs at idle. Car dying when you open the throttle can't really be caused by the IAC.

What I think could be the problem is shown here in your log:


Just after starting, your AFR's seem to be at around 7.5 for 10 seconds, and then suddenly go up. I think what's happening here is that you are running insanely rich, so much that after 10 seconds or so one of the cylinders stops firing. As this cylinder no longer combusts, it lets all air through, leading the wideband sensor to think you are running much leaner than you actually are.

I'd try leaning out your fuel 30% across the board to see if it runs any better.

 

Normally the AFR being at 7.5 is the wide band warming up before it jumps to running and giving a good signal, not that it is dumping too much fuel.


Do not try to drive it right now, you need to first just free rev it and try to adjust your fuel values in the cells, and once you have those close, then start scaling other cells to that.

It running rich might be the warmup where it adds fuel.

You need to let it get up to temp and do your fuel map then, not try to do it as it is warming up, as you are trying to chase a moving target.

 

I saw some fluctuations in the AFR in the first 20s, but I guess they could be signal noise as well.

 

The 7.5 AFR is indeed the gauge just warming up. The only reason I suspect the IAC is because it was running completely fine on the same tune before. And now, I forgot to mention in the previous post, but I noticed a loud humming coming from the engine and I disconnected the IAC to see if that was it and it was the noise. I don't think the IAC is supposed to hum very loudly, but I could be wrong. Even then when I try to start the car sometimes it will idle for about a second and then die with very lean AFRs.

 

I will try to get the idle tuned once the car is warmed up as well and see what I can do from there. Hopefully, tomorrow and will report back with results. Just think this is a hardware problem and not a tuning problem, but I am asking here to get some insight, so thanks for the help so far

 

With what you are describing now, make sure you are getting spark.

An o2 sensor detects oxygen, so even if a cylinder is getting air/fuel but it is not ignited, it is reading that air, even though there is a ton of fuel too.

Has anything else happened that was not in the original post?

 

I just went outside and checked for spark on all cylinders, Cylinder one does not have spark. When I took out the spark plug wire the terminal came out of the boot. So I think that could have definitely caused it. It must have gotten spark every once in a while because it idled okay. I think I might have to order new spark plugs/wires.

 

Here is the spark plug wire that was broken in 3 pieces, figured it doesn't hurt to get new ngk spark plugs and wires since they aren't too expensive. Didn't have any so i will be installing them tomorrow

 

Unfortunately, the new wires/plugs did not fix the issue, but it is a maintenance item anyways. I let the car idle and finish WUE for warmup to temperature. I then adjusted Idle VE table so it would read more around 14.7 (close-ish). You can see that in the log with this picture.

This is when the car was idling and sounding pretty healthy, I then touched the gas. About 1% throttle and it almost immediately dies.
Log for this picture is "car idle, fix fuel then cuts after little gas.mlg"

 

Now, I got a log of the car running with a little throttle. It fluctuates a lot and is reading very lean AFRs


Any help would be greatly appreciated, Thank you!

This is the log I got and the file along with it "car with gas fluctuates.mlg"

 

Just to make sure, did you set the base timing?

 

At 166.5 seconds in the datalog from post #10 your fuel pulsewidth goes from 2.6 ms to 1.7 ms. The car was running at 14.0 AFR at 2.6 ms worth of pulsewidth. If you reduce that by ~35% it's not going to be happy. If you look at status 2 in the datalog at the same point you can see it go from 128 to 0. This is telling us that the megasquirt is leaving closed loop idle. If you look at your idle settings you'll see that you have idle ve on and you have much larger values in that table than you do in the same area on your main ve table.

It idles fine because it's using the larger VE numbers in your idle table. As soon as you give it throttle it uses your main VE table which has numbers far to low. I looked closer at your main ve table and started wondering why your numbers are so low pretty much everywhere, and I have absolutely no idea. As was pointed out earlier if you were misfiring it would have register as lean and VEAL would have been increasing your VE numbers, not reducing them. Did you manually adjust the main VE table when you thought the car was running to rich?

For now I would recommend importing the VE table from the trubokitty tune. That will at least get your main table much closer. I recommend not using idle VE. You can play around with it when you know what you're doing, but at this point it's only going to cause issues.

 

Yes I did

 

So, a weird thing happened. I got time to try and work on the Miata today and decided, what the heck I'll load it up and turn Idle VE off and play with the fuel tables. Did that and to no avail, nothing changed the problem still persisted. Now, I decided to reload Trubokitty tune from the website and the car started up fine, and when I gave it throttle it didn't die or go very lean right away. The tune isn't perfect but I decided since the car is running fine again for some unknown reason I took it out for a little test drive and I logged it.


Log here:
2020-06-20_17.40.10.mlg

 

did you reset base timing when you reloaded that tune, because that would have changed it again

 

I verified with a timing light that it reads 10 Degrees BTDC on fixed timing so it is set correctly with this Tune

 

Don't know what could have possibly fixed the issue other than an intermittent mechanical/electrical issue with the car. I was planning on putting the stock ECU back in to see if it was a problem with the engine/car and not the ECU but it weirdly fixed itself so I am unsure. Will take it out tomorrow to see if it is still running normally.

 

It's very obvious in that log that you didn't have enough fuel pulsewidth after you dropped out of closed loop idle. My suspicion is you didn't get settings adjusted properly or you didn't actually burn the changes. Without seeing another log after you made the changes I can't know for sure.

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​​​​​​Judging from that log you absolutely had a tune issue. Nothing mechanical was causing the stalling.

 

Good to know, I have attached the current tune Fuel Table. Here: