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The car in question is a 1999 Honda Accord LX+ABS Automatic. F23A1 engine. 250000km on the odometer.
I’ve owned the car since July 2007 with no issues. Originally I would always get anywhere from 9-10L/100km no questions asked. In 2009 during a long 400km trip the car threw a P0171 System Too Lean (Bank 1) code. When returning back home I took the car in to my (previous) mechanic and explained to him what had happened. When arriving to pick the car up I was told he diagnosed the rear o2 sensor (on the cat.converter) being bad/not working and he mentioned the front sensor was acting lazy. He had replaced both sensors with Bosch sensors. A couple of weeks after this my catalytic converter developed a rattle and its substrate was broken inside. I replaced the converter with an aftermarket one and after reading about bosch sensors and Honda not mixing together I replaced both front/back o2 sensors with denso first time fit sensors.
Not long after such fuel consumption kept getting worse and worse going to 11-11.5L/100km and now in 2012 is usually 12-13L/100km. After digging deeper I found out that the p0171 code could’ve been caused by a fault FPR as there is current a valid TSB out for my vehicle model. The fuel pressure regulator was changed with an aftermarket brand and the vacuum lines were rerouted as stated in the TSB. Following this I began getting a p0420 code for the cat.converter performing under threshold. After researching the issue I placed a spark plug non fouler on the o2 in the converter to slightly move it out of exhaust stream as it seems the issue is rather common with aftermarket converters. Since then I have ended up buying and owning almost a little mechanic shop of my own with respect to tools and gone through and checked and replaced the following to no success…
-Plug Wires with NGK HE73 wires
-Plugs with NGK Iridiums
-Cap/Rotor (Aftermarket from rockauto)
-PCV Valve (OEM)
-Both O2 sensors replaced with OEM Honda sensors
-K&N Air Filter(Has been cleaned)
-Tire pressure is kept at 32.5-33psi all around.
-Used fuel injector cleaner such as seafoam, bg44k, STP
-Changed the cat.converter again thinking the 1st aftermarket one was troublesome
-Throttle Body has been cleaned.
-Grounds have been checked and fortified with 0/1GA wire for the battery-chassis & engine-chassis & battery-transmission
-Battery is good and recently replaced
-Car does not burn oil (Oil changed every 3000-4000km)
-No vacuum leaks have been found
-Transmission fluid changed with honda oem fluid once a year
-All wheel bearings show no problems
-Rear drum brakes are not dragging(drums rotate freely about 1.5 turns when spun by hand)
-Compression test shows 210psi all across 4 cylinders when performed on a semi-warm engine(coolant was at about 60C and car had been sitting for about an hour after operating temp)-ECT is at about 88-95C when car is warm.
-Long Term Fuel Trim is at about -7%
-Short Term Fuel Trim at idle is usually discounting anywhere from -7% to -10%
-Ignition timing at idle is usually a variance between 11/12 degrees
-The car is warmed up in the morning no more then 2-3minutes until the coolant needle shows movement
-The car is driven where gear changing happens at no higher then 3000-3200rpm
-At idle(700rpm) the front o2 oscilliates from 0.3 to 0.8v rather slow and at times hangs either up or down. If increasing idle even to 800rpm the o2 then oscillates rather quickly from 0.3-0.8v. The rear o2 shows movement but at a much much smaller range.
-The car starts on the first try whether it be morning/afternoon/night with no hesitation at all.
-There is very very minimal valve tick in the morning on a cold start which disappears once the car is warmed up. Minimal to the point that you need the hood opened and your ear close by to notice it.The car has a SRI(short ram intake), magnaflow catback exhaust…otherwise the engine is stock as a bone.
Any ideas on what I can look for…
This has been an on-going issue for 3 years now and it’s really eating away at me that i cant figure out why.PS. Repair/maintenance history if it is relevant
-Oil changed every 3000-4000kms.
-Tranny fluid changed once a year.
-Coolant/brake/power steering fluid changed every 2 years
-Engine Air filter changed/cleaned every 6months.2007-OEM TimingBelt/Waterpump
2007-NGK Plug Wires(HE73) and NGK Iridium Plugs
2007-PCV Valve
2007-Rear ParkingBrake Cables
2007-Driver tie-rod arm2008-Thermoquiet Front Pads/Rotors
2008-2x Cabin Air Filters2009-1x Front/Rear Denso O2 Sensor
2009-Dizzy Cap & Rotor & Gasket
2009-Wagner Thermoquiet Drums/Shoes2010-Fuel Pressure Regulator
2010-P/S and Alternator Belts
2010-1x Front/Rear OEM O2 Sensor
2010-Front Endlinks
2010-Catalytic Converter
2010-NGK G-Power Sparkplugs
2010-PCV Valve2011-OEM UCA+Ball Joint x2
2011-OEM TieRods x2
2011-1 OEM Stud on Front Driver Corner
2011-Distributor Cap/Rotor/Gasket
2011-Wagner Thermoquiet Pads/Rotors (Front) w. full brake bleeding
2011-OEM Timing Belt, WaterPump, Cam Seal, Crank Seal, Cam Retainer, Tensioner Pulleys & Springs
2011-OEM Clutch 2nd and 3rd switch
2011-Coolant Hose A2012-Upper Rad Hose
2012-Extend exhaust to clear rearlip
2012-Heater to engine inlet hose
2012-OEM Evap canister and shut-off valve
2012-OEM Oil Pressure Switch
2012-TYC KoyoRad Radiator
2012-Distributor inner oring
2012-Driver Side Axle Seal
2012-NGK G Power Spark Plugs
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Replies
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have you tried running the premium blend for a few tanks see if it changes your mileage? ethenol is horrible for cars. especially if they werent designed to use it. mileage on my saturn went from 38 to 32 just because of that ethenol crap.
[quote=”Lord Ihcalam” post=37912]have you tried running the premium blend for a few tanks see if it changes your mileage? ethenol is horrible for cars. especially if they werent designed to use it. mileage on my saturn went from 38 to 32 just because of that ethenol crap.[/quote]
Tried every grade with no luck, everything from 87, 89, 91 and even 94.
The only thing i noted and this was maybe a placebo effect and not really true but with the 94 the car felt somewhat peppier.Also tried something else tonight as one suggested that maybe the car is fine but the odometer is out of calibration, and to check that coolant and intake temps when the car was cold were equal soo…
With the engine cold(sitting for over 4hours) both Coolant Temp and Intake Temp show 12Celsius. Intake manifold shows 103.3 kPa which equivalent to the current kPa for my city as outlined in current weather reports.
It took about 2mins15sec for the ECU to switch from open loop to closed loop. I believe it happened when the coolant temp was at about 50Celsius. Once switched to closed loop STFT directly went to (negative) -10% from being at 0% during open loop.
I zeroed my trip B odometer and traveled from my residence to the closest Shell gas stations which is 1.5KM away (straight road). Upon arriving at the gas station the odometer showed exactly 1.5km. After filling up to the first click of the pump once again I ended up with 18.5MPG. I decided to test it a bit further at a larger range and got on the highway.
Upon driving to get on the highway, STFT when accelerating is at +3->+5%. If letting off the gas and coasting STFT drops to about (negative) -20% and then stays at about negative -10%. Throughout all this LTFT is at a steady -5% to -8%.Once on the highway speed was set at 100km/h with cruise control on. While at that speed I reset trip meter B and started a stopwatch. At the 30mins according to the odometer I had traveled 51.8km. At the 1 hour mark I had traveled 105.1km.
A 5km difference seems rather nothing as in a full tank it can only make a maximum difference of 20-30kms max.
I find the whole negative STFT and LTFT to be possibly weird but am not sure what to make of it. I’ve gone as far as taking out books from the local library and reading up on fuel trims but it hasnt helped much. Wish someone who knew what to make out of them would throw some insight…
I know for newer cars it’s actually a good idea to kill the KAM (Keep Alive Memory) that houses the trim information when noting reduced fuel economy or sometimes performance. This resets the computer back to 0 for LTFT, so it can then re-learn. Usually a fuse specific to this, but yanking the negative battery cable for like a minute will do the job.
FT’s are just a computer mapping of RPM at load, averaging out, trying to anticipate what is needed to get (what it thinks is) stoichiometric based on the values it’s getting and has gotten in the past from the 02 sensors.
This is the difference for LT and ST fuel trims. LT is long-term, for example if it sees needing 5% less fuel at 1200RPMs and 30% Load a few times, the LTFT gets set to -5% the consecutive times until triggered to do differently by the programming. Short term is what it is currently seeing needed to get stoich with LTFT being at that set value. STFT should bounce from slightly rich to slightly lean at a set rpm/load.
Most times it’s a mechanical/electrical issue, but don’t underestimate programming fails or it simply learning via your lead-foot moments in stop and go traffic and never adjusting back. In some cases it can actually be the reverse. As in they might keep resetting those tables every few weeks, expecting it to magically get them their missing MPGs from when they replaced their battery 6 months ago; never giving the computer enough time to re-learn more aggressively leaning(in both senses of the word) trim values.
The strategies are vehicle/manufacturer dependent, usually written in C, and often have issues, hence them having revisions to the PCM/ECU regarding this. Usually best to yank the battery cable, then clean as much as you can (TB, IAC, MAF/P, etc), let the computer get the most out of the initial readings efficiency wise.
The ECU has been reset more than once with no change to the issue. I fully understand what fuel trims are and the distinguishment between LTFT and STFT.
What I was hoping was someone interpreting/making sense of the fuel trim parameters posted on the videos a couple of posts above…
[quote=”Wayne613″ post=37994]I know for newer cars it’s actually a good idea to kill the KAM (Keep Alive Memory) that houses the trim information when noting reduced fuel economy or sometimes performance. This resets the computer back to 0 for LTFT, so it can then re-learn. Usually a fuse specific to this, but yanking the negative battery cable for like a minute will do the job.
FT’s are just a computer mapping of RPM at load, averaging out, trying to anticipate what is needed to get (what it thinks is) stoichiometric based on the values it’s getting and has gotten in the past from the 02 sensors.
This is the difference for LT and ST fuel trims. LT is long-term, for example if it sees needing 5% less fuel at 1200RPMs and 30% Load a few times, the LTFT gets set to -5% the consecutive times until triggered to do differently by the programming. Short term is what it is currently seeing needed to get stoich with LTFT being at that set value. STFT should bounce from slightly rich to slightly lean at a set rpm/load.
Most times it’s a mechanical/electrical issue, but don’t underestimate programming fails or it simply learning via your lead-foot moments in stop and go traffic and never adjusting back. In some cases it can actually be the reverse. As in they might keep resetting those tables every few weeks, expecting it to magically get them their missing MPGs from when they replaced their battery 6 months ago; never giving the computer enough time to re-learn more aggressively leaning(in both senses of the word) trim values.
The strategies are vehicle/manufacturer dependent, usually written in C, and often have issues, hence them having revisions to the PCM/ECU regarding this. Usually best to yank the battery cable, then clean as much as you can (TB, IAC, MAF/P, etc), let the computer get the most out of the initial readings efficiency wise.[/quote]
I’m stumped, damn new fangled cars. I can’t think of anything that would cut mileage dramatically but not power….have you had your car checked for gremlins?
[quote=”001stunna” post=38042]The ECU has been reset more than once with no change to the issue. I fully understand what fuel trims are and the distinguishment between LTFT and STFT.
What I was hoping was someone interpreting/making sense of the fuel trim parameters posted on the videos a couple of posts above…[/quote]
No expert, but seemed fine from the short view I gave them before (currently at work where I can’t view). Changing to a less viscous oil, a change that direction in diff/trans fluids, bearings, having added more weight to the car, or the tires having an issue are about all I can think of otherwise, all of which I think has already been mentioned. Other minor things it could otherwise be would be noticed I think (sticking caliper, etc).
I have a 99 civic that I replaced the cat on with an aftermarket cat and two bosch o2 sensors and haven’t had any problems with fuel economy. I would check the entire exhaust for restriction (since you had a rattle in your cat). I would remove the fouler in the o2 sensor and place it back the way it was supposed to. Also re-check the vaccum lines. Check fuel filter. Check the fuel pressure and inspect all fuel lines to make sure there is no restriction. Also consider the fuel pressure regulator since it is aftermarket. Also check the timing and inspect for voltage leaks.
thisisbuod…if by gremlins we are referring to a parasite current draw, animals fawking around, humans stealing gas, rusted/broke wiring, worn vacuum hoses, leaking fuel lines…all have been checked and no signs shown.
twiggy02919…the speedometer test was done a couple of days ago as mentioned a couple of posts above. Keeping in mind possible minor timing issues with me pressing a stopwatch I concluded that the car traveled 105.1km according to odometer when it should’ve done only 100. 5.1Km being nearly neglible.
Wayne613…i tried 5w20 vs the usual 5w30 for 4000km with no difference. Transmission fluid is OEM honda ATF. Wheel bearings havent been changed all around since i got the car but neither show any issue. I did try emptying my trunk fully yesterday and testing out the mileage for this ongoing week and looking for any change. I’ve been using the same summer/winter tires for the past 3 years now alternating with season changes. Assuming a sticking caliper would cause excessive heat, i’ve used an IR thermometer to measure rotor temperature directly after a highway run consisting of a lot of brake usage. The front rotors were at the same temp, with the rear drums being colder but at the same temp respectively to each other.
mckrishes…the entire exhaust was changed from the 2″ stock exhaust to a 2.25″ aftermarket magnaflow exhaust about a year and half ago. the rattle occurred 3 years ago with the oem converter and was due to a broken substrate on the oem converter. the fouler is only pulling the o2 about 1cm away from exhaust stream. FPR does not show to have a leaky diaphragm after playing with it yesterday. Vacuum lines have all been tested with a vacuum gauge off the car and all hold vacuum with no leaks. Fuel filter is inside the gas tank along with the pump on the accord unfortunately. Ignition timing at idle is at about 11-12degrees.
Something else i did last night…
I got together with a couple of friends whom all have the same accord. I tested their 4 cars and here were the results
Car#1 – gets great mileage at about 600/tank
Stft -15%
Ltft -17%Car#2 – same mileage as #1
stft +5%
ltlft +3%Car#3 – same mileage as #1
stft +6
ltlft +7%Car#4 – same mileage as #1
stft -12
ltlft -5Their fuel trims are all over the place but their mileage is unaffected. All other parameters between mine and their cars are the same. This thing has got me going crazy…
Unless you go through their complete tables to compare and average out, it’s not going to tell you much of squat.
Vast differences would alert you to a leak, restriction or the like, but they will vary RPM@Load from car to car. Even as the same year, make, and model.
[quote=”Wayne613″ post=38103]Unless you go through their complete tables to compare and average out, it’s not going to tell you much of squat.
Vast differences would alert you to a leak, restriction or the like, but they will vary RPM@Load from car to car. Even as the same year, make, and model.[/quote]
The comparisons were all done at idle after we all traveled the same distance from a wings restaurant to another restaurant.
What i’m trying to get that is the fact that their LTFT(long term average of what STFT has been doing somewhat) is different from each other and me. However their fuel mileage is pretty much the same in a tank of gas.try doing a power balance test with your scanner hooked
up.see what happens with fuel trims when you disconnect
each injector. also check that your egr is not leaking.Well i attempted a power balance test with pulling the spark plugs(much easier than even getting to the injector plugs as it seems for me to even get my hands or even some pliers in there i’d have to remove the cables/wiring and/or fuel rail). The change in engine tone/rpm was the same throughout all four cylinders.
When either sparkplug/cylinder was unhooked/disabled, the o2 went in voltages below 0.45v (lean) as i’m assuming unused oxygen was getting in the exhaust stream as nothing was firing/burning in one cylinder. STFT moved a bit towards the positive range, however I didn’t allow the engine to run in this state for too long as I had raw fuel dumping away.
I ended up pulling the trigger on a set of 4 OEM injectors from someone who swapped their f23a1 to an h22. Planning on taking his injectors to get cleaned/backflushed/flow tested and swap them in and hopefully look for a change. This way I do not have to undergo any downtime by taking off my current injectors and waiting for the cleaning process to be done.
[quote=”college man” post=38107]try doing a power balance test with your scanner hooked
up.see what happens with fuel trims when you disconnect
each injector. also check that your egr is not leaking.
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