Scratching my head

[A_Bigfoot]

Have a 93 Tony Tbi 5-speed...Was getting around 35 MPG.....Now the last 5 gas ups. I'm barely getting over 27.....Got me scratching my head...no codes

Here's a list of all the new parts I've put on...and no i didn't do all this just to try to get that 8 MPG back..just replacing 15 year old stuff..
Preventive Measures is what i'm calling it

Mobil 1 oil 10w30
Mobil 1 long oil filter
K&n filter
Timing belt
Denso oxygen sensor
Map
TPS
AIS
Coil, plugs, wires
EGR
High-flow 195 thermosat

Timing is all good both Belt and Igintion

cap, rotor, fuel filter, and fuel pump was done back in Feb...Maybe these have something to do with it??

Cut the Cat out...much better flow

It runs great..idles perfect...I'm just confused at where that 8 MPG went

and no there's not a lose nut behind the wheel....Top speed I drive is 60...I have a 40 mile round trip for work everyday


What you guys think???

cap, rotor, fuel filter???

maybe:
Temp sensor?? appears to be working correctly
Injector?? doesn't seem clogged or lazy...no leaks
FPR?? nice strong spray pattern...no leaks

Idk....any help would be awesome

[NAJ]

First question would be are you using the same gasoline from the same station and if so has the fuel blend changed? In N.J. they use oxygenated fuel in the colder months, do not remember if it starts in Oct. or Nov. and runs thru March but my mileage drops 3-4 mpg when they do.
If you want to verify a problem exists use a voltmeter and tap into the O2 signal wire and watch the voltage while cruising and at idle. The voltage should be crossing above and below .450 ideally not going below .250 and above .750 but depends on throttle position, temp, etc.
If you want other ideas see my post in the thread, "spark plugs looking black, burnt" in the engine general section.

[pobort]

Quote:

Originally Posted by A_Bigfoot Have a 93 Tony Tbi 5-speed...Was getting around 35 MPG.....Now the last 5 gas ups. I'm barely getting over 27.....Got me scratching my head...no codes Here's a list of all the new parts I've put on...and no i didn't do all this just to try to get that 8 MPG back..just replacing 15 year old stuff.. Preventive Measures is what i'm calling it Mobil 1 oil 10w30 Mobil 1 long oil filter K&n filter Timing belt Denso oxygen sensor Map TPS AIS Coil, plugs, wires EGR High-flow 195 thermosat Timing is all good both Belt and Igintion cap, rotor, fuel filter, and fuel pump was done back in Feb...Maybe these have something to do with it?? Cut the Cat out...much better flow It runs great..idles perfect...I'm just confused at where that 8 MPG went and no there's not a lose nut behind the wheel....Top speed I drive is 60...I have a 40 mile round trip for work everyday What you guys think??? cap, rotor, fuel filter??? maybe: Temp sensor?? appears to be working correctly Injector?? doesn't seem clogged or lazy...no leaks FPR?? nice strong spray pattern...no leaks Idk....any help would be awesome

i dont believe for a second you could even get close to 35 mpg with a 2.5 stick daytona, unless you are counting miles on the wrecker
i owned a 2.2 stick tbi omni since new and the best mileage i ever got was 36 and i drive a grandma in a car thats 700# lighter than a daytona.

[A_Bigfoot]

Didn't think about the gas...I get it from the same station everytime...I always run 87 in it..I changed to 89 is see if there was a difference...Haven't noticed anything yet. Changing of the blends makes sense....now on to the non-believer...I backup my proof. With over 50 gasups all ranging from 29 to 35...mosty all of them in the 32's. that I have on record in my log book. "Mileage divided by gallons used" When I fill up


Anywho..I believe i have 225 65 15 tires on it..bigger than stock
and I've done alot of work in getting all of the air restrictions out of my car except tinkering with the heads or exhaust manifold. Lot of work in the air cleaner assembly plus I fab'd up a custom Cold-air/Ram-air system. Works very well...doesn't suck up water even in extreme rain. You can feel the sucking power. Plus i have the whole air cleaner assembly covered in heat reflective material to keep the heat away from the cool charge of air coming in.

Thanks NAJ for the advice and knowledge..

[IROCNOROLL]

Couple or three things come to mind. Fuel formulation changes this time of year are a reality. More light ends are included in the fuel formulation to aid in cold start performance. They add to the formulation of deposits as well as burning off too quickly, often in the intake tract valve area and the back of the valve itself, to contribute to making power.

Carbon deposits in the intake tract are a reality. They interfere with the low lift airflow as well as the fuel delivery, and can cause many irritating drivability symptoms, and mileage drops. The fuel companies are finally acknowledging this condition and are adding a small amount of cleaning agents into their products. They help, but not to the extent of cleaning all of the pre-existing contamination. Off the shelf tank additives might sometimes help, but rarely work as well as claimed, while a professional fuel system cleaning like the Sun carbon-clean or the Motorvac systems roll out very positive results. We watch the engine vacuum at idle, engine hot, fan cycling. A gain back of 1 - 2" hg initially and a little more after a day or two of light throttle driving is very usual, with the related drivability and mileage gains. Not an advertisement, just personal experience.

A mechanical issue, such as normal wear with the resulting reduction in compression, cam timing changes, valve-train wear, valve / seat wear, and so on will also reduce the efficiency. Even though the engine seems to run very well, the slow degradation of the engine as an air-pump due to normal wear is often overlooked as it happens over such a long period of time. Just food for thought.