Any idea what's going on with my fuel trims here?

[mkee87]

Engine was bucking pulling up to stop light so I pulled a quick log. Any ideas of the culprit?

datalog2.csv

[MTBwrench]

I notice two things:

 

1) You have negative A/F learning when the engine is under full vacuum. That's definitely not normal... As that would mean the ECU is seeming less air coming out of the exhaust that what's being pulled in. That's not really possible under vacuum unless you've got a leaky injector or bad MAF, causing things to run rich. The AF ratio looks decent though. If you're getting close to, or have more than, 100,000 miles you may want to replace the front O2 sensor. Log A/F learning a,b,c,d and post it up. That'll give more info as to what's going on. Also, are you on the stock tune? Any mods?

 

2) At times the OCV's are almost 4° apart, that's not good either. I've never seen mine vary more than about 1°. This can cause all kinds of drivability issues as cylinders 1&3 will be seeing a different running condition than cylinders 2&4. Take a short cruise log and look to see how they behave.

 

I don't know much about this stuff, but that would be my plan of action.

[mkee87]

I was thinking it was a sticky fuel injector myself. The ocv I already know about and have a new one on order. I'll log the full a/f learning values on my way to work tonight and post them in the morning.

[mkee87]

Here's more logs with full a/f learning

parking lot.csv

freeway cruise.csv

idle after drive.csv

[MTBwrench]

Hmmm, its really pulling a ton of fuel. All the ranges(A,B,C,D) are in the negative, which technically shouldn't be possible. Just for reference, heres a little description of them:

 

A/F Learning 1A: Idle

A/F Learning 1B: A very small range between idle and cruise... I rarely log it unless told to.

A/F Learning 1C: Cruising speeds (i.e.- doing 45mph under vacuum)

A/F Learning 1D: Pretty much all WOT/lots of boost operation

 

How does it run? I assume not very healthy? With that much fuel being pulled something is definitely up. From what I've learned/read/expereinced theres a few possibilities:

 

1- A bad front O2 sensor. They go bad all the time without throwing codes, and at your mileage it's very possible.

2- Fueling issue such as sticky injector. This can be serious as the ECU will pull fuel to compensate for the overly rich cylinder and make the others run much too lean. That leads to cracked ringlands, burnt valves... Are your fuel injectors making any weird noises as of late?

3- A bad MAF. This means the ECU is being told the engine is sucking in a different amount of air than it actually is. It can lead to all kinds of driveability problems. Pull out your MAF and clean it with some CRC Mass Airflow cleaner aerosol.

 

And, saving the worse for last...

 

4- A cracked ringland or burnt valve can cause incomplete combustion and blow un-burned fuel through the exhaust. The ECU reads it as running rich and pulls fuel to compensate. I would honestly go to Autozone or something and rent a compression tester. It'll give you a good idea as to how healthy your engine is anyways!

[mkee87]

I replaced my front O2 sensor 2 weeks ago, and my MAf less than a year ago. I put in a set of new(refurb) injectors today and so far they seem to be doing the trick. I did a long data log and my fueling trims are back within spec across the board with trim A still being a tad high.

datalog13.1.csv

[MTBwrench]

Looks much better! However the negative correction in the A range still seems odd to me. I would drive it for say 100 miles (gently) and see how everything settles in. Did you reset the ECU when you installed the new injectors?

[fahr_side]

Hmmm, its really pulling a ton of fuel. All the ranges(A,B,C,D) are in the negative, which technically shouldn't be possible. Just for reference, heres a little description of them:

 

A/F Learning 1A: Idle

A/F Learning 1B: A very small range between idle and cruise... I rarely log it unless told to.

A/F Learning 1C: Cruising speeds (i.e.- doing 45mph under vacuum)

A/F Learning 1D: Pretty much all WOT/lots of boost operation

 

Not quite. Negative fuel trims, like down to -5 or so, are quite normal with the stock hardware and MAF scaling. This just means the stock MAF is set a little high, which causes the injectors to spray just a little more fuel than is needed to hit stoich, and the AF correction and long-term trims to pull a little fuel to fix that. OEM thinking is that it's a little better to start slightly rich and then pull fuel to fix that.

 

AF Learning range D in most ROMs covers an AF range from 50g/s up to the switch to open loop. All operation at WOT or under boost should be in open loop, which does not come under the scrutiny of the closed loop correction system at all. Learning range D is usually only reached in fast highway cruising or slightly slower cruising uphill where throttle angle and rpm do not quite kick the ECU into open loop operation.

Correction learned in range D are however applied to injector pulse width in open loop operation, so large trim values here are still undesirable.

[MTBwrench]

Mkee87, listen to this guy!^

 

As you can see, he knows A LOT more than me, so he's probably a better source for advice.

 

 

Sent from my iPhone using Tapatalk

[fahr_side]

I would drive it for say 100 miles (gently) and see how everything settles in. Did you reset the ECU when you installed the new injectors?

 

 

This is also what I'd do. No need to reset, the trims will shift to a stable range pretty soon.

 

 

Sent from some electronic device.

[mkee87]

I did reset my ecu after installing the injectors. I'll check again in 100 miles and see how everything is looking.