EnduranceAuto

Fuel trims are an inferred value they are not derived from a single reading. The Trim is what the computer is requesting to bring the engine to stoichiometric operation...

When showing - it is requesting to add fuel to bring the engine to proper mixture thus the engine is actually running rich because it is adding fuel and cannot get the mixture to Stoic.

That being said you most likely have a vacuum leak. causing it if MAF is funcitioning as you say it is running correctly.

oldblue

a vacuum leak isn't the problem, the computer is trying to lean it out because its running rich. if the numbers were positive, then yes that would indicate a lean condition and would probably be the result of a vacuum leak. he already found that he wasn't getting good vacuum to the pressure regulator which was causing it to dump too much fuel. he supplied the regulator a proper vacuum source and this did bring the values down, but i agree -10 shows its still a little rich. ideally the short term values should switch between a low positive and low negative number, continuously changing. i'd like to know what the front o2's are doing at idle.

EnduranceAuto

Malfunction Indicator Light (MIL) is on. Rich code P0172. Long Term Fuel Trim (LTFT) is -18% at idle. Fuel pressure is good with no injector leak down. The front O2 sensor is cross counting and the rear O2 sensor reads ok as well. Replaced the spark plugs and cleaned the fuel injectors and performed an induction clean on the intake. Blocked off the Positive Crankcase Ventilation (PCV) system and no help. Tried an aftermarket Mass Air Flow Sensor and no help. Engine temperature is correct on the scan tool.







1. Check scan data for LTFT and Short Term Fuel Trim (STFT) while driving. Look for 0% plus or minus 10% to be normal. See if the fuel trims are far negative (meaning the Engine Control Module (ECM) is trying to take fuel away) at idle only, or while cruising down the road too.

2. If the fuel trims are far negative, check scan data for the Mass Air Flow Sensor grams/second and calculated load. With a warm engine at idle and the A/C off, the Mass Air Flow (MAF) Grams Per Second (GPS) should be 3.3 to 4.7 and the calculated engine load should read 15 to 21.4%.

3. If the GPS and the engine load are high and the idle speed is correct, verify the MAF sensor connection and grounds are good and check the voltages. The White/Blue wire at the Mass Air Flow Sensor should have battery voltage. The Brown/Black wire and the Black/White wire are grounds and should read 0.05 volts or less. The Mass Air Flow Sensor output voltage is on the Red/White wire and should read about 1.1 - 1.5 volts at warm idle.

4. Disable the canister purge solenoid in case of a flooded canister and see if the LTFT and STFT come down into the range of 0% plus or minus 10%.

EnduranceAuto

had the positive and negative trims backwards I do that when I try to do this without a car infront of me...

jjyoda_86

Ill have to let you know on Monday when I go back to the shop

davis10

Yea the rear o2 is for cat efficiency only. I don't even have mine plugged in and the motor is running well

jjyoda_86

checked my front o2 sensor/air fuel sensor and its reading 3.3v and it does range with throttle increase. Where is the canister purge solenoid plug you are talking about, and if the canister is flooded what do I do to fix the problem. I disconnected my canister purge solenoid cleared codes and fuel trims and my fuel trim went right back to -14%. tried disconnecting rear o2 to see if that would help and still no change. I have ran 87 octane last couple tanks since my fuel economy sucks right now and it still hasn't changed. I monitored the new maf gps and its right around 3.8 and engine load is at 18%. I even tried capping off the vacuum line that goes from intake to switching valve near evap canister and still no change.

MudHippy

It's because you're running 91 octane fuel. 100%, without a shadow of a doubt. Did you even stop for half a second to wonder why I asked that question?

So you can quit chasing your tail now. And disregard ALL the other speculation found in this thread.

Still think I'm wrong? Run some 87 octane for awhile. Then watch as the LTFT% moves towards the positive.

jjyoda_86

so endurance auto I checked my maf voltages your wiring wasn't the same as mine so I looked up the wiring diagram and its wired as a 2000 cali. model, but this motor has no egr. anyways white/red source voltage,blk/blueand brn/black .0032v, yel/grn 5volt ref, and signal gry/red was at 1.529v .

vital22re

iTrader: (2)

Are the injectors correct to the ecu? I'm trying flamethrower injectors and noticed at idle my LTFT went from -14 to -18. Watching the AFRs as i drive, it runs a lot richer with these bigger injectors.

MudHippy

No you haven't. Or it would have changed. And your fuel economy would have gotten even worse too. Smart move...

But, by all means, don't listen to me. I'm just the only one who actually knows what's going on here.

BTW, nice try on editting that in there to make me look stupid. That's not going to work either. SORRY!!! +1 FAIL!!!

Really smart move there...

And you're still pretty sure you want more advice from the guy who says the following?
Ideal defined how? You do realize if the LTFT% is negative you'd be burning less fuel per mile right? No, I know you don't know that. Didn't expect you to. That was rhetorical. One more thing on that though. A better term for it is fuel efficiency. The word economy tends to denote a monetary value. But the difference in terminology isn't widely accepted, or regularly used. So I know what you and the OP are really talking about when you say that. To most folks they still mean the same thing, mpg.

Miles per gallon = fuel efficiency
Cost of the fuel burned per mile = fuel economy

And, no, there's no direct correlation between the two. One is the price you paid to go how far. The other is the volume of fuel it took to get you there.

Yeah, because the car would have corrected you on that right?



Dude obviously HAS NO CLUE!!!

I'm out. Can't justify wasting any more time on this one. See ya!

oldblue

What would a different octane rating have on fuel trims? not doubting you, but this is the first i have heard of this. higher octane fuel burns at a slower rate, maybe thats why, a little extra HC's left over after the burn? i really can't see it causing THAT much of a change in the fuel trims though. enlighten me (cliff note version)

MudHippy

You've got the general idea.

And yes, it will easily cause that much of a change to LTFT.

Why/how a bit more specifically? Simply put, LTFT 0%, or rather, the basic injection duration, is based on running the engine on 87 octane. Since the engine is not necessarily meant to run on higher(than 87) octane fuel(see your owners manual). Which isn't to say that you shouldn't, or that you can't. Because you can(and you should, in most cases). Since the ECU is programmed to adjust for fuel octane levels by changing the LTFT%(A/F ratio, or O2, sensor) and providing for more advanced ignition timing(knock sensor). Allowing for the engine to both increase its power output, and increase its fuel efficiency, when ran on higher(than 87) octane fuels. Why run higher(than 87) octane fuel in your EFI engine that will run just fine on 87? That's why.

Oh the untold wonders of EFI. Of course it isn't really so mysterious, and/or difficult to understand, at all. These facts are all very well documented. And very well known to the manufacturer, and those who truly get how it all works.

jjyoda_86

do you have a problem with me mud hippy. I know for a fact that I have a problem. no I don't know it all but I do know all vehicles f/t are supposed to be + or - 10% ideally around 0% like endurance auto specified. mine is at -18% I know that I have been running 87 octane like you suggested and fuel trims did not change and im getting maybe 9mpg now.
I am still running stock injectors.

dropzone

iTrader: (6)

OK folks, give it civil

vital22re

iTrader: (2)

Pull injectors and have them bench tested You are running rich. At idle i'm at -18 as well. But this was only after the higher flow injectors from Flamethrower. They LTFT drops closer to 0 when driving though. Keep in mind I run 9lbs of boost and my afr's are running richer in closed loop as well as open loop. Down to high 12s normal driving.

jjyoda_86

I disconnected my afr sensor and fuel trims went to +14% I then reconnected it and fuel trims went right back to -14%. think this could mean I have a faulty air fuel ratio sensor? i tried putting a good air/fuel ratio sensor and no change. some one told me that my wiring could be wrong and to check my voltages going to my o2 any ideas

twiztidditzwit

***My Cousin Vinnie moment for the WIN!!!***