ibrakelate

Howdy,


About 3 weeks ago, I acquired what has been a headache of a Miata (NB2 2001). Only about a day after I bought the car, I found it would misfire when cold starting below 50 degrees. Cool. I didn't exactly sign up for a project, but the car was cheap and I've been bored anyway. I'll deal. While poking around the car looking for a solution, I discovered that the factory ECU was swapped with a MSPNP. To remove any extra variables that may interfere with my diagnosis I dropped the factory ECU in, reinstalled the factory O2 sensor, removed the vacuum line for the MS, and let it crank. No start. No tach, no fuel, no spark, no codes. With the factory ECU in place, I replaced the cam sensor and crank sensor, as they both appeared to be original. This changed nothing. I put the MS back in to see if it would still run, just to verify I hadn't missed a connector or broken a wire while taking things apart and putting them back together. It fired up without hesitation. I've since taken the factory ecu home to inspect. I know very little about circuit boards, so I'm not sure it's worth much to say that I don't see anything obviously wrong with the ECU. No funny smells, no burn marks, nothing is detached. I'm officially at a loss.


Aside from the MS, wideband O2 sensor, aluminum radiator, and replacement NGK wires, this Miata is completely stock. All factory wiring appears to be untouched.


I would like to see this car run properly with the factory ECU before I put the MS back in.


Could any of you help point me in the right direction to make this happen?


Thank you all!


Update: At this point, I figure i'll be closer to figuring my misfire out by leaving the MS in place and learning how to use the Megasquirt. I'll try to provide a datalog tomorrow.

Stoffl

Could be a dead immobilizer or swapped keys/locks without the matching ECU(same issue => immobilizer)
If the car is otherwise stock the previous owner might've just swapped in a cheap standalone to bypass he immobilizer ?

tfbmiata

I like th eimmobilizer idea. You have to pull a code to see it. I bet they had a dead system and used the mspnp as a replacement that is cheaper than the immboilzer.

Rrrracer

That's a pretty common "solution" to the immobilizer problem.

@ibrakelate post your tune and a log with the misfire when you get a chance please.

ibrakelate

I did think of the immobilizer, but I didn't get some of the symptoms that are commonly reported when it fails. I.e. with the original ECU plugged in, the light flashes in its normal operating sequence. I also frequently read that a faulty immobilizer would let the engine fire for a second or two before shutting the engine back down rather than only letting it crank, which is not something I experienced, so I put it in the far back of my mind. Oh well. The MS is completely connected to the car again anyway. It runs and drives fine, save for the cold start misfire and a new (ly discovered) stumble between at around 3k RPM.

I'm letting my laptop charge now so I can go take a log real quick.

ibrakelate

@Rrrracer
Here are the logs. One at idle and one driving with the stutter condition. If I did everything correctly when setting this MS back up, it should be running the 01-05 Miata base map from DIY.

Rrrracer

No AFR being recorded in the log so we can't really see what fuel is doing. Looks like you are triggering accel enrichment during cruise, and VE is jumping around a bit as well due to the engine lurching. Without having the tune, hard to say 100% what the cause is but you might try turning AE off to see if that solves it, and possibly flatten the VE table.

That's just tune related stuff... you could very well have a mechanical problem such as a bad coil pack, which is common enough with the NB2. That would not prevent the car from starting on the stock ECU though.



The DIY base map is just that... a base map to start with. It still needs to be tuned, which you will not be able to accomplish without a functioning WBo2.

ibrakelate

@Rrrracer I have another WBO2 sensor on order. I completely forgot that it wasn't functioning. I've mostly ignored the possibility of needing new coils since they have been replaced once already, but of course I have no way of knowing how long they've been installed or how long they should be expected to last. Thank you for your help so far.

Attached is the installed tune.

Rrrracer

I forgot how bad the DIY NB2 base map is LOL.

Take this one for a test drive. All I did was turn off injector trim and acceleration enrichment, smooth the VE table and raise the values to hopefully make sure you are not running lean. If it's no better, then we will probably need to wait until you get your WBo2 going.

ibrakelate

@Rrrracer Thanks a ton. From what I've been reading I bet you're spot on. Will update Monday when I have access to the car again.

Stoffl

I'd have my stock ecu modded to disable immobilizer instead - less headache and effort.

ibrakelate

@Rrrracer Just took it around the block with your changes. Seems to have fixed it! Does the fact that your changes worked point to any issue with the car? Should I have any need for injector trim and AE? Thank you!

Rrrracer

Only that it needs to be tuned LOL. No need for injector trim, but after you get your VE table dialed in, you will be able to turn on AE for smooth throttle transitions and taking off from a dead stop. Get your wideband going and LMK if you need help.

ibrakelate

Right. I'm not driving it around as a usable car just yet. When the WB arrives I'll start working to make it stable, which I'm excited to do now that I know nothing mechanical will be a hindrance.