Honda D Series Forum banner

1 - 20 of 80 Posts

·
Registered
Joined
·
422 Posts
Discussion Starter #1 (Edited)
Hi guys,

After reading the sticky on gas mileage, I've started to replace a few things that could be the culprit to my terrible gas mileage.

Let me start with the specs of my car.

Its a d15b block, d15b7 head, si headgasket (8.55:1 compression)
Automatic transmission
Oem everything.
Tires @ 40psi
No tuning modifications at all.
New NGK Spark Plugs and Wires

Before I was getting an average of 22mpg. I just changed the fuel filter with an autozone replacement and now only got 190 miles out of the next tank of gas!! I verified there's no leaks after the replacement.

I pulled the o2 bung in the cat (obd2 cat on obd1 car, so bung closing the second O2 sensor hole) and it was BLACK as was the exhaust tip.

This leads me to a bad O2 sensor which I am going to change tonight.
I honestly have no clue how to check timing at the distributor, or valve lash so I'll be looking those up shortly after I finish this post. I highly believe it could be the distributor as I noticed recently it was only being held in with 1 bolt. I've since fixed that, so no more oil leaks at least.

From there if anyone has some ideas as to what could be causing such a major drop in economy I'll appreciate the support. I'll also be checking compression and would love to do a leak down test, but I say that term to all the tool rental places around here and they look at me as if I have 3 heads.

Thanks again in advance.

James

P.S. I have an intermitent sputter while the car is warming up, I would go as far as to say it sound like a misfire. NO cel lights

P.P.S I definitely think I have at least a distributor timing issue after reading a thread on how to set it.
 

·
CR-Vtakin
your mom
Joined
·
11,459 Posts
here are some things that have helped me increase gas mileage.

new plugs, cap, rotor, spark plug wires, fuel filter.
change o2 sensor
change coolant temp sensor
valve adjustment
double check your timing

maybe run some injector cleaner or fuel system cleaner through the car

also is the car aligned correctly? improper alignment can lead to poor gas mileage.
 

·
Registered
Joined
·
422 Posts
Discussion Starter #5
here are some things that have helped me increase gas mileage.

new plugs (check), cap, rotor, spark plug wires(check), fuel filter(check),
change o2 sensor doing tonight
change coolant temp sensor
valve adjustment
double check your timing doing tonight
maybe run some injector cleaner or fuel system cleaner through the car doing tonight

also is the car aligned correctly? improper alignment can lead to poor gas mileage.
Thanks for the advice
 

·
I no longer haz teh pink eye! Iz got STINK EYE
Joined
·
3,332 Posts
Excuse my ignorance, but how would an exhaust leak be responsible for a 10mpg+ drop in economy? Unless it was an exhaust valve leaking?

James
exhaust leak infront of the o2 sensor causing a lean reading maybe.
 

·
I survived code 9
1998 Honda Civic DX
Joined
·
1,662 Posts
Oooh otay... the o2 sensor is in the header though so that would have to be a leak between the block and the header.
I'd check the studs around the block. Just make sure they're tight. Sometimes the noise will vib. them off.

Most likely as far as leaks go, I would check by where the header meets the piping. Sometimes air will make it back up in there causing the O2 to think the car is running lean and it'll dump more fuel in there.

That reminds me, I need to pick up some spring bolts for my car tomorrow. I can hear air sifting out the collector. I just used some random bolts and I know they've come loose cause it didn't do it at first. :yes: It'll increase my gas mileage a bit.

If your distributor is held on by ONE bolt, you definitely need to bust out a timing gun and check your timing... and definitely get the other 2 bolts....
 

·
Registered
'90 CRX HF/'96 Stang
Joined
·
88 Posts
How do you drive or what is your driving style like?

Are you constantly trying to go around people, do you drive with the flow of traffic, or are people constantly trying to go around you??

Have you tried connecting up a vacuum gauge, driving around with the gauge in the car to see if you are getting normal readings? Or just hook the gauge up, start the car and pay attention as to how much vacuum you are pulling at idle, at 2k rpms... Best way is for the engine to be under load when trying to diagnose with a vacuum gauge.

BTW, driving with a vacuum gauge can very much benefit you in trying to get good mpg. I just connected one in my car about 2 weeks ago, and so far on this tank I have 177miles and I'm only at 3/4 tank to go... Driving style will affect gas mileage probably more than anything will.
 

·
Registered
Joined
·
422 Posts
Discussion Starter #10
I'd check the studs around the block. Just make sure they're tight. Sometimes the noise will vib. them off.

Most likely as far as leaks go, I would check by where the header meets the piping. Sometimes air will make it back up in there causing the O2 to think the car is running lean and it'll dump more fuel in there.

That reminds me, I need to pick up some spring bolts for my car tomorrow. I can hear air sifting out the collector. I just used some random bolts and I know they've come loose cause it didn't do it at first. :yes: It'll increase my gas mileage a bit.

If your distributor is held on by ONE bolt, you definitely need to bust out a timing gun and check your timing... and definitely get the other 2 bolts....
Thanks for the advice. I've already put the other two bolts in but no guarantee that timing is right.

All my gaskets in the exhaust system are new and have the oem style spring bolts.

I dont drive like a loonatic but even if i did, 19mpg from a stock d-series? :dots:
 

·
Registered
Joined
·
422 Posts
Discussion Starter #11
How do you drive or what is your driving style like?

Are you constantly trying to go around people, do you drive with the flow of traffic, or are people constantly trying to go around you??

Have you tried connecting up a vacuum gauge, driving around with the gauge in the car to see if you are getting normal readings? Or just hook the gauge up, start the car and pay attention as to how much vacuum you are pulling at idle, at 2k rpms... Best way is for the engine to be under load when trying to diagnose with a vacuum gauge.

BTW, driving with a vacuum gauge can very much benefit you in trying to get good mpg. I just connected one in my car about 2 weeks ago, and so far on this tank I have 177miles and I'm only at 3/4 tank to go... Driving style will affect gas mileage probably more than anything will.
I'll have to do some more searching as I wouldn't even know what numbers I should be looking for.

Thanks

J
 

·
Registered
'90 CRX HF/'96 Stang
Joined
·
88 Posts
Allright, didn't figure you drive crazy... How about your MAP sensor? If it's out or going out, your ECU will not know how to adjust A/F and timing and could be running some sort of standard baseline as if the car is in open loop. Are the fumes from the exhaust very gasoline smelling? Or does the exhaust smell normal?
 

·
Registered
'90 CRX HF/'96 Stang
Joined
·
88 Posts

·
Registered
Joined
·
422 Posts
Discussion Starter #14
I'll help you find a link... the vacuum gauge is really only going to tell you how healthy the engine is....

Here's the one for MAP sensors: Manifold Absolute Pressure MAP Sensors

Vacuum gauge for engine diagnostics: Browser Warning
Thanks for all the suggestions everyone.

I'm going to start with checking the timing once I can get my hands on a timing light, then go from there.

Thanks again

I'll be sure to report back

James
 

·
Registered
1988 Honda CRX
Joined
·
6,676 Posts
A quick and dirty way to check for exhaust leaks is for someone to block the tail pipe with the engine running while another person listens for leaks.
 

·
Registered
Joined
·
1,789 Posts
A quick and dirty way to check for exhaust leaks is for someone to block the tail pipe with the engine running while another person listens for leaks.
This is a great way to check for an exhaust leak. Easy too. I mentioned this because it's something a lot of people don't think about before they start throwing parts at a car. The exhaust manifold or header could be cracked. Yes, it fools the computer into thinking it is running lean.
 

·
my dd has 1800 ftlbs of torque
peterbilt
Joined
·
3,890 Posts
needs more manual trans
 

·
I also have a cool title
Joined
·
3,124 Posts
here are some things that have helped me increase gas mileage.

new plugs, cap, rotor, spark plug wires, fuel filter.
change o2 sensor
change coolant temp sensor
valve adjustment
double check your timing

maybe run some injector cleaner or fuel system cleaner through the car

also is the car aligned correctly? improper alignment can lead to poor gas mileage.
Good advice im in the process of doing the same, atleast you dont have code 45 coming off and on like a phantom.
 

·
Registered
Honda Civic
Joined
·
2,944 Posts
I know I'm late but........I had the same problem after replacing my filter with an autozone replacement. Mine went from about 30mpg to roughly 23-25. I would only get 240 to a tank.

BTW I was wanting to do a z6 or a6 block with me B7 head like you. I like the cr. I'll ask you at a later date how it was.


Back on track. Maybe a year after I changed my filter my dizzy took a crap. My back bumper has black soot right where the N1 exits. I figured bad valve seals. I'll be pulling the head soon to find out.

Pretty much all the advice given were things I've been meaning to look into on mine all year. I hope you get your situation figured out.
 

·
Registered
civic
Joined
·
62 Posts
i just had this prob in my 99 civic dx d16y7. i had two cracks in my exuahst mainifold comin from the o2 sensor hole. so def check there cuz every onne on here told me to check all the hard stuff first. i got the same gas mileage as u
 
1 - 20 of 80 Posts
Top