Same problem with my 2010 GMC Sierra 5.3. It all started with a misfire. That threw a po300. I hooked up my scan tool and showed a ton of misfires on cylinder 3. I switched the plug with cylinder 5 and the coil to cylinder 1. The misfire stayed on 3 so I switch wires with cylinder 2. Misfire moved to 2. I bought a brand new set of Delco Gold wires. Installed them. Then I started getting completely random misfires on random banks and cylinders. I figured it must be air or fuel to be able to just bound everywhere whenever. It’s always on misfire on a completely random cylinder. On a couple misfires within the first couple miles. Normally at lower RPM’s. I had Denso TT Iridium plugs installed at that time so I put my original worn plugs in. The misfires went down but still occasionally get a weird random wherever misfire. I was also battling with the virtual Flex fuel sensor miscalculating and creating a positive feedback loop that would screw up my fuel. I was angry enough, I used my HP Tuners to disable Flex Fuel. I went and filled up my truck with. Ethanol free gas so there would be no running wild virtual sensors. Still had stumbling problems and it really seemed like the o2 sensors were really slow. I bought replacements but haven’t put them in yet. I also did a Delco replacement fuel pump about 6k miles ago. I was seeing signs of a vacuum leak. I tried the spraying brake clean all over after a cold start up. Didn’t notice any changes. I assumed it much be the intake manifold so I replaced both banks. The valley cover was insanely loose. I 4-5 bolts were finger tight. I pulled the valley cover and cleaned it up. Gasket looked new so I put it back on and torqued it down to spec and in sequence. After starting and doing so runs around town, my trims settled into a new home. High LTFT and spot on STFT. When I rev the engine and hold the RPM’s. The LTFT will drop right down to 3-4. I bought all the injector gaskets so I can pull them and give them a deep cleaning, but it seems I more than likely have another vacuum leak. Time to get a transfer pump and a cigar. 😂😂😂
my ltft is at 15+ at idle. When i go to drive it drops to 7+. 2 different master techs told me my mass aiflow was bad and upstream was lazy. Replaced both with OEM and the trims are the same. I smoked the whole system and multiple people helped me look and we couldn’t find an intake leak. When I’m driving at highway speeds. The ltft is at 0. The stft is jumping in the -1 to -4 range.
@@zygi22 if you don’t see a code. Leave it. Not every engine runs perfectly. 14.7 to 1 is kinda overrated. Some engines idle lean like mine. It’s normal I would say
Thanks for this information. My issue with a Mazda 3 2012 its similar. The SHRTFT1 is aorund 0 to -1≈-4, normal, but the LONGFT is around +9 to +14 in idle. When i drive the car this drop to +3≈+4 and the scanner some times go to check engine with the P0171 code. My fuel consuption is OK buth the power engine seems to be lower compared with before. Also sometimes the start goes difficult in the first athemp but goes normaly after the second one. This still could be a possible vacum leak or a fuel pump/inyection problem?
A normal reading should be no more than +/-10%, you are still in normal range. Make sure to add long term and short term together in order to get your total fuel trims. Theoretically, anything above +/- 12.5% will trigger a check engine light.
Hello, I have a 2000 camry 2.2l with high postive long term fuel trim at 20% at idle, but at higher rpm it drops to 5%, but I cannot find a leak, would a exhaust manifold or intake manifold leak would cuase this? I also have do NOT have check engine light on.
Hey I have a scion tc ( 2.4L 2AZ toyota engine) that i Boosted and have a piggy back computer along the toyota ecu. At idle the wideband AEM air fuel ratio gauge shows lean and STFT is normal but the long one is at -29. We figued the the toyota ECU is over correcting so we tried to add more fuel but it needs SO much fuel that that car won't start again if i shut it off. Injectors were set to %65 duty cycle to idle around 14.7 afr. Normally it was set to %22 or 25. Maybe the trick is to take away a little bit of fuel so the toyota ecu doesn't see it as rich and trying to take away fuel? I checked for boost leak. If there is any its very minimal. I checked for vacuum leak with a propane tank and couldn't find a spot where the car revved up. Thanks fo the help in advance.
Mine is doing the opposite. At idle they both are at 0 percent or jumping around -4 to 3 on STFT and my LTFT once warm is stable at 0 or 0.78. When I rev the engine the long term is going to around 14 but when I let off the accelerator it goes back to the 0. My short term is in range. What would this indicate? Still have a p0171 and will a p0741 make the lean code stay ?
Hi i see you have a lot of knowledge on this thing can you give me an idea on my issue got a check engine light with codes p0174 air/fuel mixture to lean bank 2 and bank 1 p0171 + p2197 short term fuel trim way 1 is very unstable 19% long term trim way 1 stays constant at 34.4% thanks i hope i will get a response from you i forgot to mention if car gets hot in hot weather it will not start until i let it cool down for half an hour or so driving a toyota...
It could be multiple things. Vacuum leak, restricted fuel injectors, dirty fuel filter or a fuel pump that can't deliver sufficient fuel pressure. I would try to attack a vacuum leak first. Best way, smoke test.
Fuel delivery such as dirty fuel filter, dirty fuel injectors, weak fuel pump or Air delivery such as dirty mass air flow sensor. Let's not forget, a slow response oxygen sensor or vacuum leak.
@@EliTheOBDTech how you doing? So I have 2005 accord ex 3.0 V6......at idle here are my fuel trims- bank 1-stft-14.8%/ ltft 8.6%.....bank 2 stft-14.8%/ ltft 7.8%.....when I keep it steady at 3000 rpm's, here are my fuel trims....bank 1- stft 11.7%/ ltft 8.6%......bank 2 - stft 9.4%/ ltft-8.6%........i had the heads replaced, all new valves, cylinder compression is good, intake and exhaust gaskets, fuel injectors, valve cover gaskets, pcv valve, map sensor, ect-sensor, egr valve, all vacuum hoses, ignition coils, sparkplugs....brand new.....timing is set top dead center.....and it's been smoke tested no vacuum leaks....!! Any ideas as to why these fuel trims are doing this?
I also notice when I rev and keep it steady at 3000 rpm's, so times short term fuel trim on bank 1 will rise about 2%, which tops it at about 14.3%.....and short term fuel trim on bank to will rise about 7% which tops it at about 21%
@@JamesAutoDude one easy test is to disconnect the evap canister hose to the purge valve along with harness connector, with the vehicle idling there should not be any vacuum coming from the purge valve evap port, lay your finger over the port to verify.
Was dealing with an integra today that sat for maybe 2 years before being started, fuel trims were reading high negative numbers on short term and when accelerating the numbers would go higher, but at idle came pretty close to 0, car also has issues stalling and bogs out, replaced injectors, have to check fuel Pump and fuel filter but just curious what do you think that is
Eli TheOBDTech i forgot to mention there’s no check engine light, I know i would get o2 codes or even evap codes i would think, but going to check the fuel pressure regulator tommorow
Eli TheOBDTech ugh I know, just figured after running the car and car stalling and having signs of misfires it would atleast throw a code, also whenever AC is turned on the car wants to stall out aswell
My 2003 Rav4 2.0L gas has bank 1 LTFT of 16-19. When I rev to 1500, it drops to 13 and stay there no matter what RPM. When I drop back to idle, LTFT goes back up to about 16. Is that drop enough to indicate a vacuum leak? --I replaced cracked PCV hose: no change. I checked the real time data, and the O2 sensors seem to be working, giving the same outputs. Also, it is only on bank 1. I would think that if it were a vacuum leak then both banks would have a high LTFT. No?
To rule out a vacuum leak, best thing to do, is to perform a smoke test. Toyota's are known for brakes boosters going bad and creating a vacuum leak. Don't rule out a bad intake manifold gasket. Last but not least, restricted/dirty injectors.
@@EliTheOBDTech I thought about the brake booster. I have a vacuum meter, but realistically probably wouldn't be good for a small leak. I forgot too that the O2 sensors are reading similarly; however, I replaced B1S2 a few months ago without issue. But, I'm thinking that B1S2 is WNL because the LTFT is high. If there was not corrected, lean condition, then the O2 sensor would likely read wrong. Does that make sense? Basically, the O2 readings are only normal because ECU is going + on LTFT. The O2 sensor is aftermarket. Maybe no good. Or maybe the wrong sensor.?
@@EliTheOBDTech Oh. the intake manifold gasket Ya, smoke would be best for something like that. I pulled the plugs, and they all look normal, so I switched banks 1 and 2 just to see and no changes. I also replaced the PCV valve about 2 months ago. I wonder if the spring rate/compression is wrong, as it is aftermarket. I suppose I could just disconnect and clamp the hose and check for reading changes.
My short term zero % and long term 27%, but long term not go under 18% whatever RPM, if RPM like 3000 or more long term be 18%, you know if the vacuum leak or something else ?
@EliTheOBDTech actually has MAP sensor, I have P0068 code related to Map sensor, I replaced Map sensor with OEM and test sensor wires by multimeter and all Normal, Attached smoke test and no vacuum leaks at all, Also changed O2 sensor but still LTFT really high and not go less %18 even if 6000 RPM
How bout this: Short and long trim are fine during normal driving/idle. But when revved up to 2000, the long trim gradually climbs to over -25% in a few minutes and sets 175 (rich) code. Also, have a 0430 code (low cat eff.) for several months. What gives?
With negative fuel trims, you are running rich. Too much fuel to air ratio, so the computer is subtracting fuel. Potential problems: Leaking injectors, faulty fuel pressure regulator, contaminated/dirty MAF sensor, faulty/lazy oxygen sensors. A malfunctioning cat maybe causing this problem too.
Any engine codes? If there is no activity from the o2 sensor, most likely it's going to be a faulty o2 sensor, either in the sensing circuit or heater circuit. You can use a ohmmeter and ohm out the two colored wire the are same color and check resistance.
@@EliTheOBDTech LTFT AT IDLE AND AT ALL HIGHT RPM STAY 0% STFT AT IDLE -5% Until 7% AND AT 2500 AND 3000 RPM +12% UNTIL +18% .ORIGINALLY BEFORE I FIND LOW AIR LEAK Ι HAD STFT 0% AND LTFT +18 UNTIL +22% AT IDLE AND ALL HIGHEST RPM S.I WAS WAITING AFTER I HAD AN AIR LEAK THAT WHEN RAISING THE RPMS THE FUEL TRIMS DROP LOW !MAYBE I FINALLY HAVE TWO FAULTS WHY ARE THE STFTS AT 3000 RPM EVEN NOW GOING POSITIVE? WHAT IS YOUR OPINION?
@@EliTheOBDTech ALSO I BELIEVE IT IS A FUEL PROBLEM ISSUE MAF HAS NOT HAD MAP EGR PSV I TURNED IT OFF BUT SAW NO DIFFERENCE WHEN I LOOK AT FUEL .O2 SENSOR I DON'T THINK IT IS BECAUSE BOTH O2 SENSORS SHOW POOR CONDITION.AND I WILL LOOK FOR A CLOGGED EXHAUST AS WELL THOUGH I DON'T BELIEVE THAT.THANK YOU SO MUCH FOR ANSWERING MY QUESTION.THE AIR LEAK A FOUND TO FUEL PRESSURE REGULATOR IN THE PIPE
If so, if it goes from negative to positive fuel trims as you accelerate, you most likely have a dirty MAF sensor. Does your vehicle have a MAF sensor?
@@EliTheOBDTech Map... Only... 2000 camry 2.2 Thanks for answering. By the way on idle both values... Short and long term within range..... Plus and minus 3 or 4.
my van doesn't have a code. rough idle, lil smoke out tailpipe, running rich longft - 14 I'm thinking maybe stuck open injector. MAF, IAC, TPS, all seem normal range. O2's seem normal between 200/800
Do an ohm test to each injector and compare. You could also do a cylinder balance test by disconnecting each injector connector and watch for rpm drop.
With a turbo charged engine, you should have positive fuel trims at idle. Under boost mode, the vacuum leak will allow air to escape which causes the fuel trims to become negative during a boost situation.
@@miguelrodriguez2328If your o2 is really not doing any switching and is stuck in a lean condition, pcm will add more fuel due to a faulty sensor and you will get bad gas mileage.
