Dave04

Hey Everyone,

Wanting to get some opinions on my misfire, I have gotten both P0302 and P0301 in the past. Engine is still being broke in, has around 650 miles on it so far. No starting issues cold or hot, no loss of power at any time. The only times this happens is under hard acceleration and high rpms. I collected some freeze frame when this most recently happened with P0302 this go around.

Said it was in "open loop due to engine load"
Calc load was 100%
Coolant temp was 203'
STFT was 0%
LTFT was 16.41% - seems high to me
RPM was 8161
ING timing was 24.5' adv
Intake air temp 114.8 F
Mass AFR was 26.29 lbs/min
Absolute Throttle position was 78.04%
Baro was 29.53inHg


I have cleared the code, idled the car in garage and currently getting these readings,

Mass AFR .6lb/min
O2 sensor Lambda Bank 1 sensor 1 1.02 - Not sure if this is volts?
02 sensor bank 1 sensor 1 0.09ma
02 sensor 2 0.69v
A/F ratio 15.1
Coolant temp 203.0
LTFT 12.5%
STFT 0.8%

Plugs, coils, wires have all been replaced recently, MAF has been cleaned. Any ideas? Also, what is the difference is the two readings on the 02 sensor bank 1's? My App is giving me both readings.

Thanks,

David

Loki

iTrader: (1)

Your LTFTs are very high indicating an excess of unmetered air - vacuum leak.

Open loop at full throttle is normal, most cars work this way.

Dave04

That's what I was thinking, I'm going to check everything today to see if I do have a vacuum leak. Could there be a chance that the front O2 is faulty? I do not see it switching from 1v at idle.

Thanks Loki

Dave04

Today I checked everything for any amount of a vacuum leak, no luck. I even went as far as taking the UIM off to check the solenoids and OMP injector hoses. All were tight, no cracks, confirmed with carb and choke cleaner everywhere possible for a leak.

Judging by the O2 readings and the AFR, the car is running lean. I also added another reading on the front 02 to my first post. Sort of confused on the difference on them too. Any help would be much appreciated. Thinking my MAF sensor is faulty or I could have a some lazy injectors???

Thanks,

Loki

iTrader: (1)

15 AFR is reasonable at idle. Actually your lambda sensor 1 (O2 sensor) is showing 1.02lambda (not volts) which is a hair above stoich (1 lambda). So it's not running lean in that data, but it's definitely getting some extra air somewhere, based on the LTFT.

If it leans out full throttle, that's another story. I know you checked everything, but the numbers don't lie. Have you checked the underside of the throttle body? there is a vacuum port for the VFAD which should be plugged if you have an aftermarket intake, or it should have a thin vacuum line going up to the stock airbox and a solenoid in that area. It's invisible and easy to overlook.

Possible you MAF is bad, but I doubt it. Perhaps it just needs a cleaning with the appropriate cleaner.

Dave04

Thanks for the clarification on the lambda reading. I know exactly which line your referring to under the throttle body. It is hooked up as it's supposed to be, that's one area I check for a vacuum leak today. I do have a stock intake.

Looking at the freeze data from the misfire, the LTFT was 16.41%, so I guess it does seem to be leaning out with full throttle.

TeamRX8

iTrader: (25)

LTFT is about closed loop part throttle. The system goes open loop under full throttle. So your thought about that is not correct.

Going back to your first post, fuel trim is an accumulated and stored value. It is not a live actual reading; i.e. at WOT it isn’t indicative to what is occurring for fuel ratio then. Only the AFR value matters then assuming it’s accurate. In open loop under full throttle the computer runs entirely off of pre-programmed tables to provide a certain level of fuel for the conditions it detects. It only adjusts fuel in an iterative scheme in the closed loop mode. It seems like you need to do some more reading and gain a better understanding on how the process works.




.

Dave04

TeamRx8 - I do understand at WOT it uses open loop, pre set parameters. On my last post I was just stating what the freeze frame was showing, didn't mean to confuse.

The big question is why the misfire.. Is there anything else I could look at other then the possibility of lazy/dirty injectors or a faulty MAF sensor? I did clean the MAF sensor again just for grins. Ruling out a vacuum leak, what else could it be?

Like loki said, the LTFT doesn't lie, its definitely adding additional fuel at all rpms. I just don't wan to throw parts at it and **** money down the drain lol

Thanks guys.

Loki

iTrader: (1)

Does the misfire only happen at full load and high rpm? Possible your cat is clogging?

I wouldn't rule out a vac leak. Your MAF reading at idle is a tad low, and fuel trim is high.. there aren't too many ways around that.

TeamRX8

iTrader: (25)

There are multiple LTFT storage values for different engine operating parameters. The two you need to be concerned about are closed loop operation at idle and closed loop operation during low low speed cruising (30 - 50 mph). I saw you posted the one for idle but not cruising. It can apply LTFT at WOT, but not because of WOT/open-loop conditions. I just didn’t want to confuse the situation by getting into those details because it’s not really relevant. Replacing parts is no guarantee they are operating properly. You need to start at ground zero and go through the system testing and eliminating the possibilities in a logical sequence.

Dave04

Loki - The Cat was replaced (new) when I put the engine in two months ago. Yes high RPM under heavy load is the ONLY time I will get a CEL flash.

TeamRx8 - I will get some readings at cruising speed tomorrow morning/afternoon. Which parameters would you like to see? I assume both 02s ST & LTFT, MAF. I did look at these readings yesterday while driving around 50mph, I can't remember what they were though. From what I remember both 02 readings were low even with the ECM switching Lean/rich.

Dave04

- Sorry for the delayed update

So last week I installed a new set of OEM injectors (all 6). After 50 miles are so at idle my LTFT has dropped to 7% but I have seen it as low as 6.3%. My idle seems smoother and I have not seen my CEL flash since install.

Cruising in 6th around 55 mph, I am getting the following readings

02 bank 2 : 0.77v
STFT : -1.6%
LTFT : 4.7%
MAF : 25.70 g/s
Lambda bank 1 : 1.03

Before I purchased these I checked once more for vacuum leak via a smoke test. Everything proved to be sealed tight!

Question is do these readings seem normal for an engine that has aprox, 900 miles on it since a full rebuild? I'm still in the break in stage still so I haven't been hamming on it regularly to see if will flash, 90% of my driving I keep it under 5k. Since replacement of the injectors I have ran it up to 9k in 2nd then into 3rd at WOT twice with no flash and have done a handful of pulls up to 8K with no issues.

Maybe I'm being a little paranoid. I stuck a lot of money into the rebuild and just want to make sure she's A-Okay lol

Thanks guys!

Loki

iTrader: (1)

Glad it's improving. How is your fuel pressure or how old is the fuel pump? It's possible it's adding fuel trim to compensate for low fuel pressure.

Dave04

I checked it about two weeks ago, 58 psi with engine off. I don't have the equipment to check it with the engine running. I connected to the red disconnect under the hood on the drivers side where the metal line comes up the fire wall.

So your thinking 7% is still to high at idle? One point I have noticed, at idle I don't see the 02 reading lean/rich. Judging from the reading at idle the ECM is only switching when the car is cruising. Is this normal? From what I have read the ECM should be switching lean/rich at idle as well.

*side note*
During my rebuild I noticed the PO had installed one of those "universal" 02 sensors for the downstream. I've often wondered if he used the correct one... I ended up reusing it...

TeamRX8

iTrader: (25)

The rear O2 is only for cat converter efficiency. It doesn’t influence fuel control under normal circumstances. You do need to be sure you’re watching the correct O2 signal on your monitor though.

Those trims don’t see that unusual for a new engine. That’s what the control system is designed to do. The pump could be weak or the internal filter could be blocking up some.

Lets see the idle data. How about an idle vacuum reading?


.

Dave04

I doubled checked the 02 readings, they are the correct readings for each of the 2 sensors. Ill keep a watchful eye in the future though.

Post new injector idle data:

02 bank 2 : 0.67v
Lamba bank 1 : 1.04
MAF : 4.53 g/s
STFT : -0.8%
LTFT : 7%

Engine vacuum at idle (hot) : 15in with steady needle.

Previous reading was 13.5" last time I checked about 100 miles ago. This was with the old injectors but I don't think the new set would have much influence on the vacuum going up. I guess it's the apex and side seals seating in? Even with the old set I still had a steady needle @ 13.5"

From what I have read, it should be comparable to a stock piston engine once it's broke in (17-19). Is this true?

Dave04

Does anyone know what the "approximate" MAF reading should be at idle? Looks like I am getting 4.53g/s . I have looked all over and can't find anyone who has posted their readings at idle.

My LTFT is now around 4.7% and short term bounces around from low negatives to low positives. Misfires are gone except I still get a little blip now and then at idle. I'd like to see it with a little smoother idle.


I have looked everywhere and smoke tested for vacuum leaks. Wondering if my MAF is slightly out of calibration.


Thanks

Loki

iTrader: (1)

4.53g/sec sounds correct-ish for a warm 800rpm idle. It should be around 5, but temperature and altitude make a difference. Adding the 5% LTFT puts you at 4.78 actual. So either the MAF is a bit off as you say, or you're still pulling in air somewhere. But obviously thr computer is able to compensate, so I would guess your blips or misfires have another cause. Could be airflow to the MAFis unstable. Are the screens before it nice and undamaged?

Dave04

So I decided to take the rx8 to a friends shop last week who has an actual smoke tester instead of using the backyard method. We found zero leaks, we stuck the "nozzle" in the brake booster hose, then directly into the main oil injector hose and into the large intake hose that connects to the back of the lower intake via a metal pipe with a short piece of hose. No leaks anywhere....

I went ahead and picked up a new denso MAF, it did bump up my readings at idle to 5.29g/s but now my LTFT is 6.3% and I still have small blips at idle every 10 or seconds.

No misfires at driving or high rpms, starts right up hot and cold. Other then these little idle blips and fuel trims the car is perfect.

I'm completely stomped by this, if anyone could point me in the right direction or things to check I would greatly appreciate it. I also pulled the plugs to give them a glace, all looked really nice and tan.


Thanks

UnknownJinX

6.3% isn't really that bad. As long as STFT, LTFT and their sum are all within ±10%, it's fine.

Maybe the throttle body? Have you read the throttle percentage live data?

Dave04

I have not, but I can get some data this week.

2hit6

Following this topic. I have the same/similar issue where around 7-8k rpm my rebuilt engine throws a misfire under slow/pedalled acceleration.

2hit6

Just to circle back. Can-Saf, the shop my car was at, figured out the issue. Vacuum leak at high rpm. Stupidity on my part, when I installed an oil catch can I did not seal tightly the intake plug at the top. The smoke test didn't show this because under normal load/rpm, there is was no vacuum leak. Lesson learned here is always check the basics first.

Vacuum
Coils
Fuel