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

[college man]

I was hoping the short fuel trim would go to positive
as it did when the injector was unplugged.If the stft
would have stayed negative.That would indicate a leaky
injector.If all were the same as you stated.then I don’t
see a leaky injector.did you check the egr?

[Levin]

[quote=”college man” post=38342]I was hoping the short fuel trim would go to positive
as it did when the injector was unplugged.If the stft
would have stayed negative.That would indicate a leaky
injector.If all were the same as you stated.then I don’t
see a leaky injector.did you check the egr?[/quote]

I took off the egr valve and tested it with a vacuum pump. Replaced its gasket even though it showed no issues but why not.
Ended up cleaning the valve off with some brake cleaner and did a little picking inside the egr port with a shopvac and a tiny metal wire. The passageway was NOT clogged in any way but there was crud to scrape off nonetheless.

[EricTheCarGuy]

What kind of tires are you running? It’s not just tire pressure that’s important it’s also the rolling resistance of the tire itself. Honda’s run best on Michelins, if you’re running something else this could be a factor in your fuel milage.

Also don’t rule out a transmission problem. Say if the torque converter wasn’t locking up this could cause a drop in fuel mileage, also if you run in D3 instead of D4. On the same token if you have brakes that aren’t releasing properly they could hang up and cause a loss of fuel economy. Lastly, driving habits, if you have a heavy foot or you live in an area where there are a lot of hills or stop and go traffic this can also effect fuel mileage.

[Levin]

In the non-winter season i use 205-50-17 Falken Ziex ZE-912 on 17″ Enkei EV5. During the winter i use 195-65-15 on General Altimax Arctics on steelies.

That being said are we really saying that rolling resistance on a properly inflated tire can account for a 4-6MPG drop???

The car is always ran on D4. Its driven in a means where it changes gears at about 2-3000rpm and no more. It has never hung on a gear and never over revved or slipped a gear no matter if driven the usual granny style or pushed.

I’ve lived in my area and done the same trip/roads ever since i bought the car. Calipers have been checked more than once and show no issues. The temp on the front rotors has been checked and is roughly the same after a 1hr drive showing both calipers are working about the same, the same applies for the rear drums. Drums spin about 1.5-2 revolutions prior to stopping when spun by hand with the wheel off.

[EricTheCarGuy]

Yea I am saying that tires can account for that much of a difference especially if you can’t find an engine performance issue or transmission problem. Rolling resistance is everything when it comes to fuel milage. To be honest you might benefit from some better tires. Honda’s are VERY picky about the tires you run on them, I’ve seen it more times than I can count, poor wear, crappy handling, and fuel milage all suffer with the wrong tires. Tires really do make the car. I was glad to read that you had already considered the brakes as a possible contributor well done.

[Levin]

[quote=”EricTheCarGuy” post=39554]Yea I am saying that tires can account for that much of a difference especially if you can’t find an engine performance issue or transmission problem. Rolling resistance is everything when it comes to fuel milage. To be honest you might benefit from some better tires. Honda’s are VERY picky about the tires you run on them, I’ve seen it more times than I can count, poor wear, crappy handling, and fuel milage all suffer with the wrong tires. Tires really do make the car. I was glad to read that you had already considered the brakes as a possible contributor well done.[/quote]

As mentioned a few posts above i partake in a local car club. With that in mind both me and 3 other individuals with 98,99,00 accords(same engine, all kept up with the same maintenance) all use the same combination of tires for summer/winter. They can still manage to get the 10L/100km however…i can’t.

[EricTheCarGuy]

If that’s the case I would then check the auto trans to see if the TCC is working properly. If it’s not going into lock up then your mileage will suffer.

[Levin]

[quote=”EricTheCarGuy” post=40413]If that’s the case I would then check the auto trans to see if the TCC is working properly. If it’s not going into lock up then your mileage will suffer.[/quote]

From my limited knowledge I have done the following checks…
-Tranny shift gears (1-4) if easy on the throttle at about 2-2.2k rpm
-Once in 4th(final gear) when pressing on the gas pedal the RPMs do not jump up non relative to the speed of the car which i believe hence means the TC is locked up.
I’ve only had the TC not lock up once when under WOT after reaching 80km/h in a snow/icy condition in which casing i believe tire slip and non traction was the cause of the issue

A part of me feels as if its a sensor issue…if only i just knew/could figure out which sensor. Reason for such is as i’ve noticed that when the car sits at idle 700rpm…o2 graph doesn’t show constant oscillation and it’ll at times hang on rich or lean. However if i press on the gas pedal lightly and bring up the rpms to even 720 or 750 the o2 starts moving up down perfectly.

PS> My apologies on the late reply Eric. Due to personal family reasons just been unable to jump on here.

[The Leprechaun]

Hi there.
I’ve found with oversized exhaust you tend to burn fuel a lot faster.
Is your ac stuck on?
Do your engine timing marks line up?
Just a few shots in the dark.

Also id physically check the front brakes for dragging,if they were both dragging they’d have the samectemperature

[EricTheCarGuy]

The TCC would not be active at WOT. It’s normally active at cruising speeds after 4th, it’s almost like an extra shift. There could be a lot of reasons for it not switching until it’s off idle. Try not to read too much into things and pay attention to the facts. If you have any CEL codes that would be great. If not then keep an eye out for abnormalities and look at the fuel trim numbers. They should be as close to 0 as possible. Positive numbers mean it’s adding fuel, negative numbers mean it’s taking fuel away.

[Author]

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