MPG/Mileage gone to the dogs…but why

[Levin]

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 arm

2008-Thermoquiet Front Pads/Rotors
2008-2x Cabin Air Filters

2009-1x Front/Rear Denso O2 Sensor
2009-Dizzy Cap & Rotor & Gasket
2009-Wagner Thermoquiet Drums/Shoes

2010-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 Valve

2011-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 A

2012-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

Topic

[Lord Ihcalam]

if you still have it replace the short ram with the stock box and test mileage thru a tank of gas. sometimes short rams allow hot air in which will rob power and possibly mileage too.other than that youve done everything i can think of. unless you wanna go through your car and rip out everything that is heavy. have you added a stereo system or anything to it? subs and amps and boxes will add a couple hundred pounds to a car and reduce efficiency.

you could also try throwing an ecu at it see if anything changes. or get yours tuned.

[Levin]

I’ve already tried interchanging between my stock airbox and even a CAI(cold air intake) just for the sake of checking. I’ve used my live data scanner and recorded parameters and sensor outputs from my car and compared them to sensor outputs of another car of the same year/model. I have noticed nothing different

The issue was existent with my stock airbox before i changed onto a SRI.
In addition it was present with the stock catback exhaust(2.0″) and my current magnaflow exhaust(2.25″).

There is no sub/amp or any heavy system on the car. Pretty much everything that I kept in the trunk 5 years ago is still what i keep in the trunk now with no difference.

The issue has got me to a point of going crazy…

[Lord Ihcalam]

i dunno then. everything is in spec, you didnt flash the ecu at some point obviously, you might try to see if someone can tune it to a more economical parameter but other than age i dont know what to look at.

dont feel bad though, my car only gets 4.61km to 1 litre

[Lord Ihcalam]

actually did you have the ecu tuned to the short ram? someone told me you have to program changes into them for your car to use them properly. I suppose you cleaned your MAF if you have one too? did i miss that on the list?

i noticed on your pic you have after market wheels. are they heavier than stock or lighter or the same? did you lower the car at all or add side skirts and that?

[Levin]

I was under the impression a stock obd2 ecu was not able to be tuned/flashed unless running something such as AEM Engine Management System standalone(which many run for performance under boosted conditions not for economy lol)

Its just the fact that friends/coworkers/family who own the same model car (98-02 honda accord) with the exact same engine/transmission as me, close to the same mileage as me, and possibly not babied their vehicles as I much as I have…get anywhere from 9-10.5L/100km easily with no problem. & I did too and then it all went to hell.

—
The ECU was reset after the addition of the SRI and Catback exhaust allowing it to relearn any necessary parameters. In all honesty the only difference they both make is possibly minimal HP gains and if anything alter only the sound heard from the engine.

My car does not have a maf and only has a MAP sensor directly above the throttle body.

The aftermarket wheels are actually lighter than the steel wheels the car comes with OEM.

The car is lowered on Tein SS coilover suspension and has been corner balanced followed by an alignment every year.

It does have a WingsWest Lip Kit installed as of 6 months now which made no difference in MPG.

[Lord Ihcalam]

i thought all obd2 hondas could be tuned. my friend puts a conservative tune on his OBD2 car for highway driving, and then has a performance tune for track. Do you use the same gas as them? have you tried a higher octane? what oil do you both run? is your Auto trans possibly starting to slip? is their car garaged and yours not? do they put in any additives?

grasping at straws here, this is a real head stumper. just remember though, two cars of the same model make year with the same equipment and miles driven the exact same way can age different. but this is strange i wonder if running lean damaged something internally but not enough to trip a code.

[Levin]

I might be wrong about the tune on a stock ecu with no addition of a standalone ems and shall inquire with a local tuner on the possibility.

That being said…
We all use Shell 87 gas; i’ve tried 89 and 91 with no difference.
We all use 5w30 engine oil…some use dino/some use synthetic(i’ve used dino oil on it since i got it every 4000km)
I’ve considered the tranny being the culprit but it shifts smooth no matter if cold/hot, it never hangs on a gear to the point where it over-revs, it never has slipped etc. That being said the transmissions in the 98-02 accords are known to fail on a regular basis hence my yearly fluid changes versus the manual recommended every 2 years and me changing the 2nd and 3rd clutch solenoids as preventive maintenance.
My car does sit outside; some of theirs sit inside/some out.
The only additives tried by both me/them has been Seafoam, BG44k, STP Fuel Injector cleaner.

By “them” i’m referring to 4-5 individuals who all drive the same generation vehicle, as we all partake in a local city car club.

[Lord Ihcalam]

i forget did you ever try replacing the fuel injectors? if the dispersal is wrong it might be using too much gas. or they might be spraying to much.

[Levin]

[quote=”Lord Ihcalam” post=37728]i forget did you ever try replacing the fuel injectors? if the dispersal is wrong it might be using too much gas. or they might be spraying to much.[/quote]

That I have not done, mainly because of the cost of brand new injectors and only because i’ve experienced no issues of injectors leaking etc.

In addition that changing the plugs last week all plugs looked normal to me… I actually still have all the plugs saved that i’ve used since i bought the car and shall take a quick snapshot showing condition.

Edit: Snapshot of plugs taken out last week wednesday.
[URL=http://img37.imageshack.us/i/img0156yw.jpg/][IMG]http://img37.imageshack.us/img37/6474/img0156yw.th.jpg[/IMG][/URL]
[URL=http://img195.imageshack.us/i/img0157jr.jpg/][IMG]http://img195.imageshack.us/img195/8700/img0157jr.th.jpg[/IMG][/URL]
[URL=http://img89.imageshack.us/i/img0158ddmucm.jpg/][IMG]http://img89.imageshack.us/img89/8762/img0158ddmucm.th.jpg[/IMG][/URL]

One thing that does have my mind boggling a bit is the fact that at idle even though LTFT is at -7/-8%…STFT is still pulling more fuel off at another -7/-8%.

[Lord Ihcalam]

maybe there’s nothing wrong with your car at all. maybe someone is stealing your gas.:silly: or there’s a leak, have you checked for leaks?

[Levin]

[quote=”Lord Ihcalam” post=37730]maybe there’s nothing wrong with your car at all. maybe someone is stealing your gas.:silly: or there’s a leak, have you checked for leaks?[/quote]

Now you might call me crazy after this but…
I actually have 2 security cameras in my property one looking at the front/one looking at the back of house where the car is parked. No weird creatures have been caught by the motion sensors stealing gas.

As for leaks all 3 gas lines(feed/return/vapor) from the tank to the engine are bone dry. The car has even been parked over cardboard for 1 month and nothing was seen.

[Lord Ihcalam]

not crazy. necessary. i have security features as well. Mine are a little different than a camera though.

If its not the injectors then i am completely out of ideas. i dont think a bad cap would let gas evaporate that fast. maybe someone else will have an idea.

[Levin]

[quote=”Lord Ihcalam” post=37732]not crazy. necessary. i have security features as well. Mine are a little different than a camera though.

If its not the injectors then i am completely out of ideas. i dont think a bad cap would let gas evaporate that fast. maybe someone else will have an idea.[/quote]

Wouldn’t the injectors show some sort of sign or symptom though if they were leaking or dumping too much fuel?
I have no misfiring(at least do not feel it or have any codes for it), no rough idling, no gas smell near the fuel rail when the car is running or when the car is off.

As for the Gas cap, i’ve tested an aftermarket one and switched caps with a buddy with no change to the issue.

PS. Thanks for brainstorming ideas even as much, greatly appreciated.

[Lord Ihcalam]

not necessarily. injectors can get clogged by dirt or varnish and operate but not efficiently. sounds like your car is still in factory spec, but we all know drivers know their cars better than engineers, and we KNOW when something isnt right. its just hard to find it when the computer says everything is in tolerance.

look up videos on youtube for cleaning the injectors you have. not with stuff yuou pour in your tank but actually removing them from the car. ive seen them but dont remember where.

btw when you seafoamed your car what vacuum port did you use?

[Levin]

[quote=”Lord Ihcalam” post=37772]not necessarily. injectors can get clogged by dirt or varnish and operate but not efficiently. sounds like your car is still in factory spec, but we all know drivers know their cars better than engineers, and we KNOW when something isnt right. its just hard to find it when the computer says everything is in tolerance.

look up videos on youtube for cleaning the injectors you have. not with stuff yuou pour in your tank but actually removing them from the car. ive seen them but dont remember where.

btw when you seafoamed your car what vacuum port did you use?[/quote]

I’ve usually done the seafoam twice a year. Once at the end of winter, once at end of summer. For the procedure i’ve used the vacuum hose from the pcv valve and only used it through the vacuum and gas tank method. I’m a tad weary of throwing it inside my crankcase even if it is for just 5 minutes. Once all seafoam has been sucked i’ll turn the car off and give it 15-20 minutes prior to starting it and going on a spirited highway drive.

I’ve been calling around today trying to find a shop that would clean, spray test, back flush injectors etc but pondering over cleaning the current ones or buying new ones even though they do not show any visible issues.

That being said, someone mentioned to me today that Honda shows its LTFT/STFT readings in opposite of all other makes:dry: Is this correct? ie. my car currently at idle shows LTFT at -8 and STFT usually around the -7% mark. According to what i was told today by this person, this would mean that this scenario means the engine is running lean and there is more oxygen versus the common sense that the engine is running rich and the ECU is compensating by pulling fuel away.

I find this rather unbelievable as its going against any mechanical manual i’ve ever read.

[Author]

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