MPG/Fuel Consumtion Issue...brainstorming ideas..???

[001Stunna]

Allright well lately after some certain issues my fuel consumption has gone to the dogs. Before i would be able to get about 340-360km by the time the needle would be at the half point. Now im lucky if i'll even get 300km by the time the needle hits half point on the gauge.

These are the things that have happened since when fuel consumtion was good to now that its ****.

-Front o2 sensor threw a car running to lean code. Got the sensors checked and front one was lazy and rear one was not working properly so both sensors got replaced with Denso FirstTime Fit Sensors.

-After the sensors got replaced the Cat was rattling, turned out the insides were loose and rattling inside so the cat was replaced with an aftermarket.

-After the cat got replaced i got a cel stating "cat is performing under threshold". I asked back at the shop where i got the cat changed and was told its just due to the size of the cat being a tad smaller. i did the sparkplug nonfouler trick and that made the CEL go away and never came back again.

-This past week whats been happening sometimes is when starting the car the rpms will go to 700-800, then start dropping lower and lower and the car shudders. At times the car will even turn off as the rpms hit 0.

-I've had passengers at times tell me that the exhaust smells like gas, and ive noticed it myself at times too. Ive checked the front o2 sensor and it is working properly and circulates from about 0.3 to 0.8.

Now the car has had its oil changed every 3000km, tranny fluid changed once a year, plugs and wires were done 2 years ago with platnium ngks and ngk wires. Air filter is new.

Only things that havent been done is cap and rotor and havent flushed coolant, power steering or brake fluid.

I read around some TSB's and even got an account at alldatadiy.com and read about a tsb regarding the fuel pressure regulator and thought that maybe thatd have something to do with it and from talking to some people ive been suggested that it might be the

-temp sensor telling the ecu the engine isnt warmed up yet and dumping too much fuel
-egr, and itd require cleaning


Any other ideas, suggestions to try out ??????



PS. Car is a 99 Accord LX+Abs - 4 cyl - sedan.

 

[ryan s]

i had a cat below threshold (p0420) and a fuel pressure code (p17-something) along with a code for one of the O2 sensors (cant remember which).

cat replaced
fuel pressure regulator replaced
codes disappeared

i would say clean out your EGR to start. if that doesnt help, the last thing on the list really is the regulator. that's what solved my issue, at least. especially if you can smell gas...theres too much of it.

 

[CG6Lemon]

do ur distrib cap+rotor and clean ur battery terminals.

 

[finch13]

Let's see... the fuel pressure regulator could've blown it's diaphragm... there is a vacuum hose on the top. Turn the ignition to ON/II to run the fuel pump, turn the key off, unplug the vacuum hose and smell for gas. That can cause rich mixture issues, usually the car is hard to start.

If you have an AllData account, there should be diagnosis instructions for the ECT sensor. Does your OBDII reader have a live data function? You should be able to see what the ECU *thinks* the coolant temp is.

 

[001Stunna]

Well i cleaned out the TB, changed the PCV Valve, changed the plugs to iridiums(plugs that were in where only 2 year old iridiums but changed them anyways. Old plugs seemed to be in fine condition though just some wear on them).

The FPR came in the mail yesterday and will be prob put on sometime this week. Battery terminals were re-cleaned and cap+rotor arrived and will be done this week too.

Tested with the OBD reader and the ECT sensor seems to be working allright so took that off the list.

2 days ago however after sort of flooring it on the highway and reaching about 160-170km/h after about 2-3 mins i got a running to lean, and fuel trim is too lean codes. P0171 and P0170

 

[sodaks2k]

It would help if you actually figure your mpg's (kpL's) instead of just using your fuel per half-tank "measurement."

Has the temperature changed (consistently colder) since your consumption has increased? I know the colder it gets outside the worse my mpg's get.

 

[001Stunna]

It would help if you actually figure your mpg's (kpL's) instead of just using your fuel per half-tank "measurement."

Has the temperature changed (consistently colder) since your consumption has increased? I know the colder it gets outside the worse my mpg's get.

I have actually calculated it comparing the km on the odometer to how much gas i put in to bring the tank up to full again. ie. odometer shows 450km since last full fill up and to bring it back to full again i put in about 47-48L of gas...hence meaning the car is running at about 10.5L per 100km. Before id get about 8.5-9.5L/100KM. There's times when its also ran at 11L/100km.

To simplify i was getting these numbers before...
L/100 km = MPG
8.5 = 27.673
9.0 = 26.136
9.5 = 24.760

to This now...
10.0 = 23.522
10.5 = 22.402
11.0 = 21.384

and the driving is pretty much 50km highway daily(in early morning(ie no traffic) and afternoon(ie. light traffic), and some city driving as well but no major bumper bumper traffic to kill gas.

 

[sodaks2k]

I have actually calculated it comparing the km on the odometer to how much gas i put in to bring the tank up to full again.

Excellent! There are too many people that just estimate the tank useage as their "mpg's."

Looking at your numbers, that is a pretty big decrease in mpg/kpL. I doubt the temperature has had that much of an effect on it.

 

[finch13]

Put that new FPR on and clear the codes, then we'll go from there. Fixing the FPR should help out your fuel trim.

 

[FunnyVictor86]

it sounds to me like it's due to the o2 sensor ... i know the defouler trick is used to keep from throwing a cell but i assume it would cause a problem, the sensor isn't sending accurate information to the ecu ... causing the ecu to change your air/fuel ratio ... just a thought