fun with P2187

[Super Unique]

My 2008.5 speed 3 recently started throwing a P2187 check engine code, so I checked for leaks on my cobb sri intake, after finding nothing wrong I proceeded to clean my MAF sensor with appropriate spray cleaner I found that the light kept going back on after clearing it, I then took it into my local dealer for service. They found nothing wrong and returned the car to me. The next morning the light went off again and I returned it to the dealer. Then they said it was the high pressure fuel pump and proceeded to replace it. when these codes were thrown, I noticed my stft was running 25% and sometimes higher at idle. After the fuel pump replacement my STFT are now better but sometimes still return to 25% on idle. The LTFT is much better now, it was 22% and has since dropped to 12.5 and sometimes 11.3%. Here is the live data recorded from my drive home at the end where I let it idle some, take a look and give feedback
a/f R volts boost cat temp cool rpm fuel timing LTFT O2 STFT FT
14.59 17 14.2 -10.3 1265.2 199 748 431 2.5 12.5 0.14 23.4 20
14.59 17 14.1 -10.5 1264.1 199 747 425 1 12.5 0.145 21.9 20
14.59 17 14.3 -10.3 1262.8 199 744 431 3 12.5 0.15 21.1 20
14.59 17 14.3 -10.5 1261.8 199 746 431 3.5 12.5 0.15 20.3 20
14.59 17 14.2 -10.5 1260.5 199 742 425 3 12.5 0.155 19.5 20
14.59 17 14.2 -10.5 1259.1 199 742 428 3.5 12.5 0.155 18.7 20
14.59 17 14.3 -10.3 1257.8 199 744 432 3.5 12.5 0.16 18 20
14.59 17 14.3 -10.5 1256.7 199 738 428 3.5 12.5 0.16 18 20
14.59 17 14.3 -10.5 1255.6 199 732 428 5 12.5 0.165 18 20
14.59 17 14 -9.6 1254.4 199 751 431 6.5 12.5 0.165 20.3 20
14.59 17 14.4 -9.3 1253.3 199 781 431 4.5 12.5 0.17 25 20
14.59 17 14.2 -9.6 1252 199 772 431 7.5 12.5 0.05 25 20
14.59 17 14 -9.5 1251 199 764 432 8.5 12.5 0.05 25 20
14.59 17 14.2 -9.8 1249.9 199 759 425 8.5 12.5 0.055 25 20
14.59 17 14.3 -9.8 1248.6 199 743 428 10 12.5 0.055 25 20
14.59 17 14.2 -9.9 1247.5 199 794 428 -1.5 12.5 0.065 25 20
14.59 17 14.2 -9.9 1246.5 199 778 428 -1 12.5 0.06 25 20
14.59 17 14.2 -9.9 1245.2 199 774 435 -1 12.5 0.06 25 20
14.59 17 14.2 -10.1 1244.1 199 776 431 0 12.5 0.065 25 21
14.59 17 14.2 -10.2 1243 199 765 431 -0.5 12.5 0.065 25 21
14.59 17 14.2 -10.2 1242 199 759 424 0.5 12.5 0.06 25 21
14.59 17 14.1 -10.1 1240.9 199 750 431 1.5 12.5 0.06 25 21
14.59 17 14.1 -10.2 1239.8 199 752 431 1.5 12.5 0.06 25 21
14.59 17 14 -10.2 1238.7 199 748 425 2.5 12.5 0.06 25 22
14.59 17 14.2 -10.2 1237.5 199 755 432 1.5 12.5 0.06 25 22
14.59 17 14.1 -10.3 1236.4 199 740 432 3 12.5 0.07 25 22
14.59 17 14.2 -10.3 1234.9 199 753 428 2.5 12.5 0.075 25 22
14.59 17 14.1 -10.3 1233.9 199 753 431 3.5 12.5 0.095 25 22
14.59 17 14.1 -10.3 1232.8 199 744 431 2 12.5 0.105 25 22
14.59 17 14.2 -10.3 1231.7 199 749 431 2.5 12.5 0.12 25 22
14.59 17 14.1 -10.5 1230.6 199 749 431 3 12.5 0.13 25 22
14.59 17 14 -10.3 1229.5 199 749 431 2 12.5 0.14 24.2 22
14.59 17 14.1 -10.3 1228.5 199 743 431 3 12.5 0.145 23.4 22
14.66 17 14.1 -10.3 1227.4 199 743 432 4 12.5 0.15 23.4 22
14.66 17 13.9 -9.3 1226.5 199 785 431 2 12.5 0.08 25 22

 

[taf0422]

whoa...you need to post a better graph..such as an attachment instead of in the thread..can't read or line things up..

 

[Super Unique]

here is a pic of the log file

 

[Super Unique]

It's now back at the dealership. threw another P2187 code this morning. I saw them letting it idle in the shop and logging it on a laptop. He had removed the intercooler shroud, appears to be looking for any vacuum leaks and checking the purge valve for issues.

 

[Super Unique]

ok, they just called and now they are throwing an o2 sensor at it. LOL, the saga never ends.

 

[Super Unique]

Fixed right this time!

They appear to have it fixed correctly this time. considering they shot gunned it with parts......

Fuel trim at idle now hovers closely around 0%

 

[ReNaToMS3]

And what was the exact problem?

 

[Super Unique]

well, after a ton of parts, it turned out to be a bad o2 sensor.

 

[lynnriderm6]

now i have this same code....but my readings at ltft at like 20 and my stft i believe are between 0-4 ...i only get it when i flash stage 1 on that car though...do you think its a bad 02 sensor?

 

[coyfish]

If you only get it when you flash your tune then its the tune lol. I drive around with the CEL as well. In the process of getting custom tuned.

 

[MS3 GT]

i got this code too, i removed my intake, bov and inlet. CEL still on, but the rpm is acting normal. i believe the CEL its for my cattless dp/rp. I will get that check when i get a chance hopefully dont turned out a bad 02sensor...(im out of warranty).

 

[Super Unique]

all P2187 is, is lean at idle. It doesn't tell you WHY it is lean at idle. deductive reasoning would tell you that it is

1. Truly lean at idle, which would indicate air being ingested that is not being metered by the MAF = vacuum leak

a. Bad / leaking or stuck purge valve
b. clamp or connector loose somewhere on intake tract, would also account for boost not holding​

2. NOT truly lean at idle =

a. Air is not being metered properly.

1. Air straightener missing in aftermarket intake
2. Dirty MAF sensor
3. MAF sensor faulty​

b. A/F ratio not being measured properly = Bad o2 sensor​

I think this logic about covers it, anyone else got some input to my little chart here?

 

[ReNaToMS3]

Well, if you had a bad o2 sensor, wouldn't your AFR's look weird? From the log you posted, it seems your AFR were okay, just the trims are way off?

Weird.

 

[Super Unique]

Well, if you had a bad o2 sensor, wouldn't your AFR's look weird? From the log you posted, it seems your AFR were okay, just the trims are way off?

Weird.

Here is my take on it, however I am NOT a certified mazda tech by any means.

You have to step back from the problem a bit to fully understand why and how the o2 sensor can be sending incorrect data, even when the log indicates a steady a/f ratio. Remember P2187 means lean at idle, this is why my car was 25%+ adding fuel trim at idle. This is adding fuel to achieve the desired metered a/f ratio, which means the car was idling very lean at the default map fuel rate. but not so fast, if the o2 sensor reading is incorrect, now my car was adding fuel beyond the actual desired stoichiometric ratio of 14.59:1

Think of the old saying about computers, garbage in garbage out. The entire closed loop process depends on the reading from the o2 sensor. from this data it determines the current a/f ratio, then taking this and comparing it with the fuel table to see if it needs to add or remove fuel to keep the a/f ratio at the desired amount. This is accomplished with our TRIM variables, either adding or removing fuel to get the correct actual ratio, this happens in a constant loop, constantly adjusting to get the perfect ratio. Now, if your sensor data is not correct, everything else is moot. The MAF sensor also plays a role in this, in that it measures the amount of air coming in, this combined with rpm, throttle position etc.. determines the fuel table cell that is used to compute the amount of fuel to inject. If the MAF sensor data is incorrect, it can be due to a vacuum leak, turbulent air hitting the maf sensor, or a dirty/not correctly reading MAF sensor.

All these factors work together to get a correctly running engine. The difficulty lies in what steps a mechanic can take to trace down the ACTUAL cause of the problem. Simply throwing parts at a code will SELDOM fix it right the first time.

 

[lynnriderm6]

hmmm...cause i mean im just using the ots maps the cobb gives...i used the cobb in the ms3 and it was fine but for this its telling me its lean at idle...but even with it out its still kindof high but not high enough to have a cel go on

 

[Super Unique]

I spoke too soon on the dealers fix LOL....

I ran a whole tank through it, as the tank got emptier, the lean at idle w/ 25%+ short trims came right back, then when I filled the tank, and started the car after filling it, it sputtered like hell and barely ran for about a minute or so, then the p2187 code came right back. In the shop again for another purge valve replacement.......


I have the car back now, and seems fine, we shall see when I run another tank through it.

 

[Super Unique]

that last visit with the purge valve definitely fixed it correctly now.

Car is running just like it did when new.