Hi,

I took another scan9495 today and was hoping for some help looking it over. The last scan was from Sept, 2019: Here

Before I was running rich, and was noted by Fred from that scan that the left bank (B1) is adding 18% fuel, and right bank (B2) is adding 12.5% extra fuel due to a perceived lean condition.

I've since replaced plugs and wires (OEM), exhaust manifold gaskets (after restoring the manifolds), and new AC Delco O2 sensors. I don't know how to extrapolate the data in the fuel trims cell to what percentage of fuel is being added, and therefore don't know if the fuel rich condition still exists (perceived lean). The dipstick still hints of gas after driving, but I suspect that's leftover before I sealed the exhaust manifold leaks and installed new O2 sensors and it hasn't evaporated, thus leaving my oil diluted.

I've been going at this problem because I've got the low oil pressure (check gauges) light when the car is hot and at idle. I've deleted the oil cooler, and changed the oil 200 miles ago, but should probably change it again since correcting the exhaust manifold leaks.

If anyone could explain to me how to take the numerical values in the FT cells to a percentage of fuel I would appreciate it. I'm still learning how to read these scan files. Today's scan is attached.

Thanks,

 

The fuel trims - long term and short term - are multipliers. The correct value for a neutral fuel trim is 128. Divide the fuel trim number by 128. Subtract 1 from the result. Multiply the remainder by 100 to get the % fuel adjustment.

If a fuel trim is 128:

128 / 128 = 1.000
1.000 - 1.000 = 0.000
0.000 x 100 = 0%


If a fuel trim is 140:

140 / 128 = 1.094
1.094 - 1.000 = 0.094
0.094 x 100 = +9.4% (added)


If a fuel trim is 115:

115 / 128 = 0.898
0.898 - 1.000 = -0.102
-0.102 x 100 = -10.2% (subtracted)

In the OBD-2 PCM they simplified it by reporting fuel trims as a positive or negative %

 

Thanks Fred, that helps a lot. It seems from the first scan in Sept. 2019 (B1) was averaging 151, and (B2) was 144. Now, after new plugs n wires, O2 sensors, and sealing up the manifolds (B1) hovers around 128, give or take bit, but (B2) averages 126, which is a bit leaner now. So it seems nominal, but could use yours or another's expert eye to confirm.

The more I drive it, the oil holds above 6 psi when I stop at a light or stop sign (or return home idling in the driveway), and doesn't trip the check gauges indicator as often. I've got a couple hundred more miles on the SPEC Stage 2 Clutch breaking in, then I'll probably change the oil. It's got Mobile One 10W-30 in it right now, and I'm stuck on going back to conventional oil at 10W-40, or go with Mobile One 10W-40.

Slowly getting there, one thing at a time. It's idling pretty nice, the 'tick' from the exhaust leak is gone and the whole engine seems smoother/quieter when at idle.

 

I didn’t get a chance to download the file yet. Too many distractions in my life. Try to get to it tomorrow l

 

Oh no worries, I appreciate your eye whenever you've the time and inclination. I've been looking over the data from the last scan and slowly learning it. I only know some of the nominal parameters of the sensor readings, so I've only been looking at trends in family.

B1 seems okay, stable. The right bank (B2 passenger?) seems a bit lean now. From engine start to somewhere around 206 seconds engine run time when it begins populating data on the long and short term fuel trims. B2 LTFT stays at 126 until I back out and go for a drive. It trends below 128 on the drive under different rpms. By the end of the drive idling at home it's at 120.

It has the original injectors and they've never been removed. It wouldn't surprise me if they could be clogged a little on that rail. Since it's only one bank, I'm guessing that should rule out the MAF, and anything between the fuel pump and FPR.

 

Also wanted to add I still suspect a contaminated fuel tank from it sitting for 5yrs. When it gets low on fuel it runs poorly, no throttle response, hiccups etc. I pour 93% in, immediately clears up. Varnished fuel could've gotten into the injectors. Next job is pulling the tank, clean and pressure test it, R&R pump and sender, some evap lines and anything else I find wrong 😄

 

I changed the oil and filter today. It was a bit dirty, not black - no shinies or debris. I put in mobil one 10W-40 full synthetic for high milage (up from Mobil One 10W-30), AC Delco PF454 filter, and have about an hour run time on it. The check gauges light hasn't illuminated when idling hot. Indicating about 8 to 10psi oil pressure.

After running it some more I'll see how it does, and make sure I don't have a leaking injector still causing a rich condition, although I think that would be noted in my scan, and I'm actually a bit lean in the Bank 2 now.

I must have had some gas in my oil pan, and it's taken(ing) awhile to evaporate/burn off.

 

I actually downloaded the file, set it up, and started going through it. But got sidetracked again. Tomorrow maybe. Sorry about that.

 

Initial thoughts:

- Engine seems to be running very well. Idle speed is extremely stable (less than +/- 25 RPM from target idle), intake vacuum at idle is stable and high (20.9"Hg).

Things that look "normal"
- went into closed loop at 206 seconds, by the book. See my scanning guide.
- idle IAC counts are good at 26 (range of 20-40 is OK)
- coolant temp is OK, creeping up at the end, but still near 200-degF
- system voltage good
- Barometer rational
- closed TPS volts OK
- MAF at idle in normal range
- injector pulse width at idle in normal range

Questions/comments:
- is the IAT value of 83-deg close to the ambient temp when the log was made?
- fuel trims at idle (cell 16) are OK on Bank 1 (128), but pulling out a bit of fuel on Bank 2 (120).
- on the low load cells (2, 3) it's pulling out a bit of fuel fuel on both sides.
- stepping up to the next level of load, only cell 6 shows a problem on bank 2
- up another level of engine load, and it starts adding fuel on Bank 1, with no issues on Bank 2
- you didn't drive it at the max engine load levels.

The "good/bad" rating is based on the fuel trims staying within +/- 5% of 128. You do not have a severe problem, but the situation seems to sw3itch from "pulling out a bit of fuel" to "adding a bit of fuel" as load increases. I'll keep looking at the "driving" portion of the log to see if anything stands out. I'll attach a graphic of your fuel trims vs. engine load (MAP) and RPM.

 

Yes
I still don't quite have 500 miles on the new SPEC Stage 2+ clutch I put in it, so I've only taken it recently to a max around 4000 rpm. First few hundred miles I didn't go above 3000. Soon I'll start doing a few slow pulls above 5000. Still chatters like crazy, real grabby in 1st and reverse. It'll take awhile to break in.

Would it help if I ran a scan under a specific driving/load profile? I could take it out to one of my back roads and start recording there, rather than a full engine start, warm up, drive, and park. Log gets pretty big. I'm about to download your attachment and study it.

I'm curious why Bank 2 went from 12.5% rich to approximately 5% lean after R&Ring the manifold gaskets and O² sensors.

 

This is the old 1LE you've been helping me with 😄

 

Revisiting this because I haven't done much but drive the vehicle on days off and enjoy it..

I decided to run another scan from cold start, and of course the Bank 2 lean condition persists. All other engine sensors are performing nominally still, but Bank 2 LTFTs are 124, and STFTs all bouncing 1-4 points under 128.

For a suspect condition I'm leaning toward fuel injectors being clogged, or otherwise not functioning correctly. They're the original injectors, so replacing them couldn't hurt with the vehicle having 128K miles.

I can't think of anything else that would cause only one bank to be a bit lean. It appears to be compensating under load, and adding more fuel to Bank 1 as throttle demand increases. If that's in line what what Fred was saying. I'm probably wrong and the PCM doesn't adjust fuel flow to different banks if the other is lean/rich.

Anything I could check before R&Ring the injectors?