Why do I have high negative fuel trims?
 

Fuel trims, Around Negative 18. When the car is Idling it shows 6.2 Grams/sec Mass air flow at 770 RPM.

Positive fuel trims should add fuel, and negative should take it away. A big positive should indicate a Vaccum leak. Or low fuel pressure. Maybe bad injectors.

What would a large negative trim indicate? Sticking injectors, an overpressurized fuel system? Is there something else I am missing?

2005 6MT, Ported and polished, with 130 Miles on the rebuilt engine. Stock fuel system. Origional pump with 140,000 Miles

Maybe a bad O2 sensor, or bad Maf

Gotta run for lunch ... will stew on it for a bit

How about a disconnected fuel injector? Hahahaha ;)

But seriously..does it run poorly?

MAF most likely

Is it just an idle trim?
Could be a leaking injector...but would tend to be less of a problem at higher rpm's

Wideband o2 sensor was replaced and the MAF on the rebuild. It won't idle in closed loop. I unplug the MAF(open loop) it idles great. I made a map that goes into open loop at 200 RPM and it idles great.

All the injectors Were pluged in(they are getting cleaned and flow tested now). If one was unpluged then I should have missifre? I think! One rotor would not be getting fuel. It would be a positive fuel trim to add enough for the one not firing. Or I would be really lean.

The MAF is about correct. I had a Vac leak and it was reading 4 g/sec at idle with positive fuel trims, When I got it fixed and reflashed it came up to 6.2 g/sec at 770 RPM. I believe that is a good MAF reading.

I have seen it from Idle to 3500 RPM with 30+ grams/sec I dont have any logs to confirm higher rpm.

Fuel pressure is steady 57.5 to 58.2 PSI

So you are tuning it yourself and are wondering why it isn't working?

That's a whole different question than originally inferred

Maybe posting your map particulars will get better results

You also might want to confirm the WBO2 sensor is working correctly...are there any CEL's?

No I am not tuning It myself I would like to play but I'm learning and getting Mazdamaniac to build me a map. The only problem with that is he's available 3 hours a month and My work schedule doesn't work well with that.

He pointed out the Vac leak(jan 17)and since I've gotten that fixed I have not been able to have him work on it.

In the mean time I need it to work at least some what.

It acts the same with his base map, or with the AP uninstalled(I can't log that). He has not given me a custom map yet.

I currently have a stock map, With Dwell * 1.45(delco coils), and fans lowered to 195 and 190 with the cutoff at 175.

I had a 1687, but I adjusted the OMP sensor and it went away. No cels currently. with about 50 miles and 5 hot cold cycles on the current map.

Is the car coming up to temp normally?...ie does the temp sensor make sense?

If the temp is OK..then the most likely culprit is the O2 sensor if everything else is normal

Have you checked the wiring? All the other COBB parameters look normal?

How would I confirm that?

The temp sensor reads a little low compaired to my after market. On ap and my Multi function dash I get the same ECU water reading, but the MFD shows about 10 Degrees higher on it's sensor. When the car is cold. The Outside temp reads correct on MFD, and 10 Deg colder on the ECU, So I believe it's the ECU temp sensor.

It does come up Steadly, I can track the temp to when the idle changes at the correct tempetures, and it starts going crazy about 100 Deg F. Until then the idle is smooth. The cold idle is set at 11.08 but a/f shows 11.7-11.9 That's a little off but I didn't think it was too far. It's about 7%.

This one screen reads strange. to me it looks like 0 rpm and 500 Calculated load.

One way is to swap in one that works....but that is a PIA ;)

What does your O2 sensor readings in the AP look like? Do they make sense?
They should read right around 14.7 at idle ( or 1.0 Lamba that really works better)

Is there anyting strange about your motor?...

The idle is up and down bad for a few seconds then dies.

There isn't really anything out of the ordinary. I rebuilt it with atkins rotary parts. All seals, and bearings, new rotor housings. I increased the oil pressure, It Idles around 30 PSI and it maxes at 90-96 around 4500 RPM. I haven't been over 5000 RPM. Ported and Polished, with d 585 coils. I bought the wiring kit, then ohmed it to the pin outs I could find. I don't think that is a problem because it idles good in open loop. I don't know how to make the AP read lamba. It does go to 14.5 to 14.9. When I am in open loop, but my fuel trims read 0.16. It pulls 8.2 PSI vac when warming up, and it is too unstable ro read once the idle goes crazy.

Is there anyone around South ft worth that Has a good WB02 I could borrow? I am in alvarado.

Oh the VFAD Is Disables, I accidentaly broke off the vac line fitting from the manifold. So I covered a small screw in RTV and screwed it into the hole. I'll get the tube removed when I have time to take off the front bumper, but that shouldn't affect ma any until high RPM. I am positive that it is not leaking. I cleaned it with brake cleaner before putting in the RTV, then covered the screw completely with RTV.

It is unlikely that it is going to idle for shit ported without a custom map

I know mine didn't....I altered the fuel and timing before it would idle correctly. It will like idling at about 900-950 better as well :)

If you have a new O2..I would likely assume it's working and work on the map if it isn't throwing a CEL for the O2 sensor

I appreciate the help maybe I'll try to bump up the idle. what did you think about table I posted? It looks like those two figures are backward to me.

Well on one note, I will never go to Lone star injector in FT worth, but that isn't here or there.

I got the car back togther and My fuel trims are around -15 on average. Since it was from 5 g/sec to 75 g/sec I don't think it is MY MAF. I Raised my Bank 1 Injector from 369 to 424. and raised Idle to 1000RPM

It Idles better but still dies. I have Idle LTFT of 2, at 9-20G/sec Trims of 1, and Cruise fuel trims of 5.

I am thinking of removing 1% fuel from Bank 1 then tweeking my MAF Calibration to account for the Idle and 20+ G/sec fuel trims.

Does this sound about right? Or should I not adjust my Fuel injector scaling that much. I did it because I thought removing 15% from My MAF across the board would lower it way too much

I see that Dan has been trying to help you ...
So apologize in advance to Dan if I step on his toes...

I think (read hope) that it's just labelled wrong. Meaning the RPM and Load values are in the correct spot just the x and y axis labels are incorrect.

I'm sorry .. don't take this the wrong way but I'm having a very difficult time trying to understand your terminology?

You say your fuel trims are around -15 ... are we to assume you mean you STFT (short term fuel trims)?
Because there is both LTFT and STFT fuel trims.

I don't understand the relevance to the 5 g/sec to 75 g/sec values?
Do you mean you were revving the engine? If so this would send the STFT's all over the place or did you do this a set intervals up the rpm range?
Like a 30 second cruise at 1000 rpm then another at 2000 rpm etc.


Here again ... these are both trim values.
LTFT means Long Term Fuel Trim and the ECU learns this values over time as well as there are different break points of LTFT through the Maf range.
So an LTFT of 2 at Idle is good with a STFT of 1 which is a total of 3

I would just try one thing at a time ... take 1% off the idle range in the Maf table.
However you mention 9-20 g/sec .. 20 seems pretty high to me for idle ... but I've not had any experience with ported rensis.

Doing a 15% cut across the entire maf table would be a very dangerous thing to do .. And most likely unnecessary
Like I mentioned there are different break points on the maf table ... basically a range for idle, cruise and WOT
You wouldn't necessarily want to make a whole sale change to the entire table and even if you did, I would recommend a much smaller increment like 3-5%

Furthermore these break points will maintain there own LTFT value as well. So you can and most likely will see a different LTFT value at idle than you will at cruise.

I tried to look back through the posts but couldn't find any mention of fuel injectors.
Sorry if I missed it but are you running or have exchanged the fuel injectors?
Are they a different size now?
If you've taken them out they might not have been seated correctly when you reinstalled them (just a thought) or you perhaps hooked the wiring back up incorrectly (another thought).

I've also found on my own setup (top mounted turbo) that a little bit of timing adjustments at idle can help things out. Have you tried this?

Dan has way more experience with this stuff than I do ... but maybe so of the things here might stir the juices on a solution.

Dan am I totally way out in left field?

edit: Just wanted to add this piece of info in case you didn't know .. the AP will read 0.16 STFT when the ECU is in OPEN LOOP

I took the time to actually re-read the thread

It might be worth checking that they were installed and hooked up correctly

Just another option for your dwell settings.
Oltmann deconstructed the dwell table using a hex editor.
You can find his work and a downloadable excel file to see the dwell settings here https://www.rx8club.com/engine-tunin...5/#post4260808

And here is basically what's in the excel table https://www.rx8club.com/engine-tunin...0/#post4366152

Didn't do anything for me in regards to idle but it sure made a halluva difference on the warm start.

if i could join in...
i too have had a new development of high negative stft's. On cold start it is -25 with a/f's in the 11's.
Warm start it is in the negative 16 range.
This is a sudden change for my tune. Its a BIG change--usually warm stft's are in the minus 5-10 range. I do idle at 1.2K ( supercharger).
LTFT's are at 1. Once past the break point of 2K rpms stft's go normal for me.
One thing I found out in trying to figure why this happened, is my car's ( 2004 built in 2003) wiring harness is not getting any younger. I recheck/cleaned grounds, maf connector and terminals and found that did improve my rich idle condition just a little---although the maf volts didnt change!
I also found out that the placement of the maf relevant to the TB position had to be exactly on!
By that i mean the top part of the maf sensor had to be inline with the TB valve as in oem config. If it is rotated a little it can throw it off. I do not run a maf screen.
I also think my maf ( 92K miles) may need replacing in order to get it exactly right. Idle sensitivity seems to be off a little. My voltage at idle of 1.2K can vary by 0.10V.
I hope this little stuff can help you or maybe someone else.

I hope the same thing, When I try to change those values, the one that is 500 will only let me change it to a max value of 10, and the one that reads 0 will let me change it up all the way to 10,000. I'll attach a clip.

No I didn't write it very well. I was trying not to make too long of a post.

When I first started this thread I was using combined fuel trims. I Had negative LTFT of -15 after driving about 50 miles. The referance of 5 g/sec to 75 G/sec is just to show that I am having high negative fuel trims across the board not just in a small range.

I would just try one thing at a time ... take 1% off the idle range in the Maf table.
However you mention 9-20 g/sec .. 20 seems pretty high to me for idle ... but I've not had any experience with ported rensis.[/QUOTE]

I am seeing 3 different points where my car is developing LTFT
8 g/sec and below
9-20 g/sec
21+ g/sec

But they were all -15 in the long term collum. They developed at different rates but settled at the same number. That's what made me believe it was something more then MAF scaling.

I agree, The fuel injectors are stock with 138,000 Miles, Cleaned and back flowed.

I could not see reducing the MAF across the board. I decided to increase the Fuel injector rating 5% at a time and see what that did. After 3 Adjustments I Have settled on Bank one injector size of 424. Now I am finally seeing some LTFT's that are not the same at every Range.

Currently with bank one injector scaled up to 424 I see
8 g/sec and less, LTFT is 2
9-20 g/sec, LTFT is 1
21+ g/sec LTFT is 5




So I am thinking if I remove 1% from my injectors I will have this
8 g/sec and less, LTFT is 1
9-20 g/sec, LTFT is 0
21+ g/sec LTFT is 4

If I get it there, I will drive it a while and adjust the MAF to see if I can get them any lower.



I think they are wired correctly. When installing them I checked the wiring. Then I started the car with only the red injectors plugged in. It didn't run without the UIM on, but It would fire for a second or two Multiple times. So I am pretty sure the reds are plugged in correctly.

I think the yellows are plugged in correct also, but They shouldn't affect anything below 20 g/sec at all. I guess I need to pull my manifold and check them again. Damn that's a lot of work and I've done it at least 5 times hunting vac leaks, and other things.

My Maf is 5 g/sec when I drive the car at 700-800 RPM, and it is 6 at 1000 RPM Idle. So I do not think I Have a Vac leak. I have sprayed a ton of either around looking for a rpm increase and nothing. I have also drenched it in water thinking it might stall with water at low RPM and nothing.

I think If I had a Vac leak I would have Positive fuel trims adding fuel to account for the unmeasured air. Does that sound right?

No I am not brave enough to try that on my own yet, any suggections?

I rebuilt it, and have very few miles since then. I unwrapped the whole engine wiring harness and inspected it well, including using lectraclean(SP) on all the contacts. Then I redid the wire loom and wrapped the whole thing in new electric tape. I hope it is all good,

But that gives me a Idea to check, I'll pull the ECU and OHM out the injectors through the wiring harness.

Oh well it will have to happen in a week or so I just got called out at work and have to drive up to Oklahoma for a few days.

Do you think the MAF placement might make a difference in a stock air box?

If it was me....at this point I would go back to a stock map and see what is happenning.

I think you have changed so many things that you are chasing your tail trying to get it to run.....

And quit playing with the auxillary tables....just change the MAF, injector, timing and fuel tables to start with..unless you are sure what you are doing will not have further consequences someplace else

By auxillary tables do you Mean, Idle, Fans and dwell?

Right not All that I have changed from cobb stock is

Fans 1a 190F with 10F Hyst and fan 1b 195F with 15F Hyst
Dwell* 1.45
Max rpm 5000

All Idle tables below 1000 were raised to 1000 RPM This was based on you saying your car liked 900-950RPM
Bank one Injectors from 369 to 424.