Help Troubleshooting Fuel Trims

[GregBunney]

I ran into a similar issue years back. Not the same but had high fuel trim issues. My long term trims were high after a 2+ hour road trip. After the MAF and MAP sensor replacement without changes, I found it to be a fuel pump issue. The previous owner had had the pump replaced but they didn't crimp the new electrical wires together. They twisted the ends together and taped them up. After the replacement and proper crimping of the wires, better trims and no issues since.
Again maybe not the same but just thinking it could be a pump issue.

Tested today, primed at 53-54 and ran at about 42-43. Fuel pump time probably?

 

[GregBunney]

Many auto parts stores will "rent" them for a credit card deposit that is refunded when the kit is returned.

Tested today and came back 53-54 at prime and 42ish running. Fuel pump time?

 

[mhaywoodcz]

I would say it can't hurt. I also had the MAF or MAP codes,(can't remember).
Fuel pump would at least eliminate that issue

 

[Fless]

I think you said this is a gas system, not Flex Fuel, so it shouldn't have an inline fuel filter (I think).

For fuel pressure, according to Haynes:
KOEO
Flex Fuel: 48-54 psi
Non-Flex: 55-62 psi

 

[West 1]

To see 25% on both banks you either have a large vacuum leak or something similar throwing off your data. What are your Bank 1 sensor 1 and bank 2 sensor 1 O2 sensors showing?

The fuel trim adjustments are driven by O2 sensor information from the before Cat O2 sensors.

The after cat sensors mostly tell you if the Cat is working properly the before Cat sensors feed tune information to your computer to adjust fuel trims.

I have repaired engines that had very high LTFT readings and the trims corrected right after the repair was completed. I have not seen the 25% #’s on both banks ever so I am curious what you end up finding as the cause.

Is your gas mileage terrible? Is the power weak? I would fix this quick before your cats are ruined.

 

[Marky Dissod]

If MpGs are down due to running rich, not only are the catalytic converters aging more quickly,
but you gotta change the motor oil more often too, 'cause more of that excess gas sneaks past the piston rings.

 

[GregBunney]

Well, better late than never I suppose, but I finally got around to working on my rig. Replaced the intake manifold gaskets and now my LTFT are looking way better and instantly getting better MPG. Did valve cover gaskets and put on the updated covers too, hopefully that took care of my oil leak/consumption issues. Now I’m going to start diving into my new, long crank cold start issue. it’s always gotta be something haha

 

[West 1]

Long crank start is usually caused by the Cam Sensor and Crank sensor signals. When the computer does not see a match from those two signals the computer does a reset while you crank and will finally start with a fail safe using the one sensor sending a signal. A good scan tool can allow a reset for the cam sensor / crank sensor in your ECM.

Maybe a bad sensor or bad wires to the sensor. Fix that and you should start fine again.

Your long term fuel trims should settle quickly down to less than 5% for both banks. Anything less than 10 on both banks is OK but less than 5 is running great. My 03 was typically less than 3% on both banks. Hwy MPG was usually 16-18 depending on how fast I was pushing it. 16 would be 75-80 mph. 18 mpg was more like 65-70 mph. Around town city stop and go might be 11-13 MPG. I had 3.73 gears in it and larger tires than stock.

 

[Fless]

As @West 1 indicated, a CASE relearn should be done to rule it out. Also, prior to a cold start, the fuel pressure should be monitored to determine if the fuel pump is doing its job.