LTFT -20.3%

Just purchased a 55k mi. 2004 MSM Miata. Came with FM's little enchilada kit. Stock ecu.

Been having an issue tracking down why my fuel trims are reading rich. If anyone can help me get on the right path that would be great.

O2 sensor pegs at .9 volts at idle, (Meaning it is reading rich obviously) then it will eventually fluctuate normally at idle. I think the problem is a shot O2, I am replacing it tmrw to eliminate that possibility.

MAF sensor was cleaned throughly and intake temp sensor was replaced.

I should add that my car threw a P0420
code for the cat converter. Cat is probably shot from running too rich.

Purge valve vacuum hoses were disconnect and plugged but fuel trims stayed the same.

Ordered injectors and they should be coming in next week.

Anyone is welcomed to chime in.

I will keep the thread updated!

 

Install a new cat and o2 sensor at the same time. Hook purge valve back up properly. You want to get the car as back to close to stock as possible to get rid of the codes. Then you install a MSPNP-Pro and have a good running car.

 

O2 sensor comes in today. Going to replace it and then going to the muffler shop to check the condition of the cat. If the cat is bad I'll just get a new one there at the muffler shop.

As in "close to stock as possible" do you mean I have to remove the FM little enchilada and put the stock mazdaspeed parts?

 

O2 sensor replaced. Fluctuates as should and car runs a lot better now. O2 sensor was definitely going out

Though I am still running rich at idle, going to replaced injectors to eliminate possibility of leaking injectors.

Going to the muffler shop tmrw to found out the condition of the cat.

 

Removed cat, new o2, still running rich at idle

LTFT at -20.3%

P2188
P2178

Found an old thread created on Aug 2016 on the Miata forums stating they have the same issue.

Turns out I have that same exact Miata and I have the carfax to prove it. This problem has been going on for 5 years with no resolution.. Going to try to solve it.

 

Quite amusing that you found the original thread, care to share it? Might provide some insight.

My guess is that this is an EGR issue. Too much recirculation = not enough O2.

I'd be surprised if this was a fuel system issue causing excessive fuel. Have you gotten the injectors out yet?

 

https://forum.miata.net/vb/showthrea...=619339&page=2

I'm replacing injectors today.

I called a Miata wizard, his shop is called rspeed in Georgia. He said to smoke test for possible vacuum leak that certain vacuum leaks can cause rich conditions instead of lean.

I could block off the egr system to see if the fuel trims change.

 

I replaced my injectors with a 01-05 Refurbished injectors from ebay. As I was replacing them I noticed I had DEKA injectors which are not OEM.

I put the new oem refurbished injectors in and started her up. Car started but struggles to stay on and dies. Tried to look over my work but nope everything was correct. I took out the new injectors and put the old ones in and started the car. Car ran like normal.

Either the new injectors are faulty or I have my ecu tuned for the current DEKA injectors which I am assuming are higher CC's. (But I have a stock ECU so is that even possible??)

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Now here is another side of the story. When I bought the car, it came with an ECU chip. Below are the photos of the chip.

The ECU in the photos is from my old 99 NB Miata. The chip I am holding is next to a similar chip on my old ECU. I am guessing the ECU's in my 04 MSM and the 99 miata are similar. I'm not sure if this chip has been swapped out in my current ECU and is affecting my fueling. I am sorta lost at this point.

 

Reading through the forums and I am seeing that BEGI used to reflash ECU's? You send them your ECU and they swap it out with another chip and send you back the ECU and original tip?? Any insight on this?

 

It sounds like there are three possible scenarios here:

1. Your ECU has been modified in some way to require larger injectors

2. Something other than the ECU has been modified, and was intended to be matched with larger aftermarket injectors

3. Something has gone wrong, and a previous owner has put in larger injectors to mitigate the symptoms.

I'm betting on #1 being the culprit, and #3 seems unlikely. This is all assuming your new injectors are not faulty.

 

I am leaning towards a modified ECU...

Found the injectors I have in my car

550 cc injectors

I am willing to bet my rich condition issue is because of the modified ecu and tune..