gas mileage drop???

[Fake Thug]

maybe I should just write it all here, this is everything that has been done

cap(oem)
rotor(Oem)
plugs(oem)
all plug wires(Oem)
brake calipers(Oem)
brake rotors
brake pads(Oem)
pcv valve(Oem)
fuel filter
new battery(oem)
new thermostat(oem) <--car almost overheated Yesterday
new tires balanced and alignment in oct kept at 33psi
exaust is 3 years old but cat is original
unkown when o2 sensor changed tested at 16 ohms(withing spec)
no Cels engine runs great
200-205psi on compression
10-12% on leakdown
Aem shortram intake is only mod(no difference from stock in fuel consumption)
no smoke
no smells


Figure it out

replace your fuel pressure regulator,o2sensor , and check your injectors for leaks

[Stealthman80]

I'd change the O2 sensor.
16 ohms just checks the heater circuit, not the sensor itself.

Woah...a 13 year old cat? I'll have a year old one for you next week if you want it.

is it a direct fit aftermarekt replacement or a universal? how much?

[Otto]

Hows does the engine run when at WOT? Such a huge drop in MPG and everything else is done, so maybe the cat is indeed clogged for one reason or another. Although my last car was 17 with the original cat and passed emission easily. Like you said, emissions test could point you in the right direction.

As far as I understand fuel injection, it is impossible for a bad O2 to cause this problem by itself (it doesn't have that much control over the mixture), especially without any CELs. I think the OP checked for CELs, right?

Other thoughs, assuming its a combo of issues:
Try a run of Redline SI-1 fuel injector cleaner.
Check ignition timing.
What are you running for tranny and engine oil/fluid?
And as for the fuel pressure regulator, you could check if its leaking into the intake by removing the line that goes to the IM and turn the key to cycle the fuel pump. But I'd think you'd notice engine running problems if it was leaking.
Is your speedometer reading low?

[oranger]

Yea, drop in winter is normal. The gas is a different formula than summer gas, and it doesn't burn as well. Here's something to try, I just put premium Chevron in my car, and have gotten significantly better mileage so far. Premium burns more effeciently and gives better mileage. My cousins swears by using full synthetic oil, I haven't tried that yet, but it could help. Also check the 02 but you would normally get running problems (rough idle, misfire, etc) not just bad mileage. Same with cat. I dunno good ideas though, check everything again!

[starchland]

Yea, drop in winter is normal. The gas is a different formula than summer gas, and it doesn't burn as well. Here's something to try, I just put premium Chevron in my car, and have gotten significantly better mileage so far. Premium burns more effeciently and gives better mileage. My cousins swears by using full synthetic oil, I haven't tried that yet, but it could help. Also check the 02 but you would normally get running problems (rough idle, misfire, etc) not just bad mileage. Same with cat. I dunno good ideas though, check everything again!

actually your wrong. gas mileage drops because of the colder temperature affecting the lubricity of engine liquids, hence more energy needs to be transferred into keeping this at operating temperature. And premium is not reccommended for our engines; premium is harder to burn.

[Stealthman80]

The engine pulls hard all the way through the rpms and I have all genuine honda fluids. Yes id did drop when winter started but it hasnt went back up. ok I just went and bought a new o2 sensor, im gonna see if I can get that installed

[jova1993cb]

you guys are prolly not gonna believe this, but when was the last time you changed your coolant temp sensor? it can cause this as well. i am not talking about the sensor for the gauge, there is one for the ecm too. it senses the temp and then sends the info to the ecm to adjust the mixture and i think it also has something to do with the timing. mine was doing the same thing. i changed the exhaust, header all the way back and replaced the 02 sensor. it was still doing the same thing. i have a friend who is a tech at the honda dealer and he told me to try changing the cts. it solved the problem my milage befor dropped to like 340mi to a tank! now with a full tank in town i can see up to 400mi and hwy driving at around 425-440mi. try it and see. let us know.

[Stealthman80]

yeah ok, so I went and got an emission test done and it passed no problem. I took the o2 sensor back because obviosly its fine as well as the cat and egr system. So I guess what im getting now is what its gonna be, I guess its because its an a6, automantic the cars heavy and I drive around with my stereo cranked all the time

[SteveB]

is it a direct fit aftermarekt replacement or a universal? how much?

Direct fit. Make me an offer. I'm probably be going to do the big parts yank this weekend.

[Otto]

Winter gas and O2 won't cause that much decline in MPG. I've been averaging 26.XX MPG per tank this winter, and only ethanol blend gas is available to me.

Your cat seems to be fine, since it passes emissions tests and pulls hard to redline.

I agree on checking the coolant temp sensor, but I would think that would fail emissions if it were bad. How were the numbers? Did it just barely pass?

Was binding breaks mentioned or checked for? Although that would be very noticeable.

Have you ever considered that maybe you just suck at math? Kinda joking, but why not tell us how you're calculating the MPG.
And yes, a heavy foot, auto tranny, and big audio will bring things down, but still. 14mpg? O_o

What RPM is the engine at while cruising?

I'm stumped. I'm no expert or anything. I was thinking it could be a lot of little things, but you've eliminated a lot. Good luck.

[starchland]

yeah wouldnt that be embarrassing!

[Stealthman80]

oI just refigured it out and I got 11.5 litres per 100k on the last tank, which is 20US mpg highway and city. Sounds about right, the cars rated between 8 and 10.5 litres. Looks like its as good as its gonna get wihtout spending a shitload of money that probably wont even make a difference

[SteveB]

Your hydrocarbons are over THREE times mine @ cruise, dude, and nearly FIVE times mine at idle.

Clearly, something is amiss.

Over 328,000 kms, engine never opened.

[Stealthman80]

uhh aparently your car has almost no emissions?

[Otto]

I'm with SteveB, the emissions could be a lot tighter. I'm used to being on the low end, even with my old carb'd prelude.

Its not a problem per se. Just that it could be tied in with you lowish MPG. Although 20 doesn't seem terrible for your particular situation.