Fuel Trims Crazy???

[swathdiver]

Ok, the new Magnaflow Y-Pipe is installed (new cats) and fuel trims were reset and engine was burning 93 octane fuel. Mileage still poor, no misfires, runs great. What does the data suggest?

 

[swathdiver]

@BlackBearPerf @badandyturbo @randeez @Rocket Man @iamdub @Galante @01ssreda4 @Scottydoggs @Doubeleive @Cattivo


The above run is saved in the Tech2 and can pull up other information if need be.

 

[Scottydoggs]

drive it for a few days, then re check the trims. if you reset them, then scanned them they have not learned yet. can take a few drive cycles for them to fully learn.

 

[swathdiver]

Scott, this was taken about 300 miles after they were reset and if memory serves, it was about all city driving. Right after this we filled up on E85 and now that tank is about exhausted and she's ready for more.

 

[Scottydoggs]

was that scan there on gas? or the e85?

 

[swathdiver]

was that scan there on gas? or the e85?

93 octane gasoline.

 

[Scottydoggs]

is there a separate reset for the content sensor?

the trims read the same when on the e85?

 

[swathdiver]

is there a separate reset for the content sensor?

the trims read the same when on the e85?

Yes, the content sensor is separate and was at 3% during this video.

No data logging has occured since switching over to E85 after the repair.

What prompted this repair was a P0430, the right side cat. Turns out this cat was not original either and the code would appear and be reset every time I drove the truck. About a week before the repair we got a P0420 code. LTFT were usually -1 or 2% on Bank 1 and -2 or -3% on Bank 2. Before the repair, I have no recollection if there was a difference in Fuel Trims between 93 and E85.

 

[Scottydoggs]

new cats are high flow i suppose right?

maybe the post cat o2's are not liking the new cats so much.

 

[swathdiver]

Can the Lower O2 Sensors affect the Trims? Hmm... I have new Upper Sensors sitting on my work bench and was putting off buying the Lowers unless I had a really really really good reason to buy them. Spent too much already.

Yes, the cats are quite large, Magnaflow 51578: https://www.magnaflow.com/products?partnumber=51578

 

[PG01]

Check this out james
http://www.easterncatalytic.com/education/tech-tips/fuel-trim-can-be-a-valuable-diagnostic-tool/

 

[Scottydoggs]

both up and down stream o2's talk to each other. the down stream one can set a cat code some times with high flow cats, not sure if thats a common thing on these engines tho. but it can mess with the fueling.

 

[Justin]

Can the Lower O2 Sensors affect the Trims? Hmm... I have new Upper Sensors sitting on my work bench and was putting off buying the Lowers unless I had a really really really good reason to buy them. Spent too much already.

Yes, the cats are quite large, Magnaflow 51578: https://www.magnaflow.com/products?partnumber=51578

Fuel trims are exclusively driven by the front O2 sensors.

Short trims don't really tell much, as they are a direct representation of the ECM's immediate compensation for O2 feedback. O2 reports rich, ECM responds with a short term trim negative and vice versa. Any average short term trim that is positive or negative will result in that average being shifted to the long term trim so that the short term averages out to zero.

As mentioned above, what is your ethanol content looking like, or commanded AFR? Do you have a cold air intake?

 

[swathdiver]

Fuel trims are exclusively driven by the front O2 sensors.

As mentioned above, what is your ethanol content looking like, or commanded AFR? Do you have a cold air intake?

That's what I thought. Ethanol content during that Snapshot was 3% and the motor was burning 93 octane gasoline. Stock airbox and newly installed stock paper high capacity AC Delco filter.

Have since switch over to E85 and was getting about 14-16 on the highway (instant) and the 11.4 on the AVG setting for all combined driving, mostly city and idling. The engine can more closely meet its mileage ratings on E85 than gasoline. Which is puzzling to me.

 

[Justin]

Got it. You have an AutoCal, right? Do you mind collecting a log file for us? Very negative trims at low airflow are not uncommon on 2007+ models due to MAF calibration in some cases, high fuel pressure in others.

 

[swathdiver]

Not at all Justin. Does it matter if the motor is burning gasoline or E85? It's nearing the end of a tank of E85.

Commanded and actual fuel pressure has always been 43.5 psi. At WOT to 70 mph on the night of the Snapshot the fuel pressure hit 42psi for an instant and remained at 43 psi at a 70% duty cycle.

Is there an easy explanation to explain why this gets normal fuel economy on E85 and reduced fuel economy on 93 octane gasoline in relation to the published ratings?

 

[Justin]

Not at all Justin. Does it matter if the motor is burning gasoline or E85? It's nearing the end of a tank of E85.

Commanded and actual fuel pressure has always been 43.5 psi. At WOT to 70 mph on the night of the Snapshot the fuel pressure hit 42psi for an instant and remained at 43 psi at a 70% duty cycle.

Is there an easy explanation for normal fuel economy on E85 and reduced fuel economy on 93 octane gasoline in relation to the published ratings?

Nope, it won't matter, I just need to know what fuel you're using so that I can take that into consideration.

Without data, I can't really comment on mileage being lower with 93 octane.

 

[swathdiver]

Ok, will try to get a log recorded tonight and send it through normal channels.

 

[Justin]

Ok, will try to get a log recorded tonight and send it through normal channels.

Sounds good.

 

[swathdiver]

Sent!