Man, I have horrible gas mileage. It's a d15b1 dpfi it use to get like 40mpg street. Like 45 highway when I first got it. Now I'm gettin 27highway and 20 around town. Anyone have any suggestions. Only mods is a not so cold air intake. Just replaced the plugs and wires with ngk.

 

Any codes by chance? How long has it been since you changed out the o2 or fuel filter?

 

No codes changed my fuel filter almost a year ago havnt changed the 02 tho. I thought it would thow a code if it were bad

 

Any fuel leaks that you notice? or anything of that nature? Does it smell like it's running rich coming out of the exhaust?

 

Yea espically if I really step on it, it smells really rich

 

I thought it was from me not having a muffler tho

 

Are your plugs soaked with gas or anything? Have you checked the ECU to make sure there are no stored codes in the ECU?

 

How do u check for stored codes? And spark plugs are good

 

Just look on the ECU and see if there are any flashes when you turn the key onto accessory.

When you turn your key on does your CEL come on and then go off with the fuel pump priming? Just making sure the bulb isn't burnt out thats all.

 

do a compression test. clear codes.

 

sounds like you need a complete tune up...!!!

 

The O2 sensor can degrade in performance and not throw a code. Get a Denso (which is the OEM maker) O2 sensor for you car from Amazon for around $30 or less. Use densoproducts.com to find the right part number.

When was the last time the PCV valve was replaced?

See other tips specific to c. 1990 Civics at http://honda.lioness.googlepages.com/gasmileagetips

 

No stored codes and I recently did a full tuneup when I changed my head gasket. Do u check the pcv by suckin on it right?

 

check the injector

 

I throw a O2 sensor in, they're cheap and most often the culprit.

 

Here is a test you can do of the PCV valve: http://media.honda.co.uk/car/owner/m...k301/6-173.pdf

However, I do not think this test is conclusive. If the valve is non-OEM or more than five years old, replace it. Should run you $20 or so or less.

 

So pcv is good and I took the o2 out and it's blacker than night lol. So I'm goin to chang it and see what happens

 

how about your cap an rotor?

 

How about, you check the mechanical functions first, compression, valve lash, cam timing, then throw money at random electrical parts.

 

When I changed my headgasket I did a compression test.the head was worked on did a valve job and I just checked valve lash. It wasn't completely cold but it was still within spec. Cap was recently replaced and the rotor had some kind of dust on it. So I cleaned that too. Just finished my tank off and it's gettin 25.4 mpg? Wtf and I have no turbo. Lol I'm goin to get a o2 today

 

try the
injectors

 

The injectors aren't leaking..I tried octane booster injector cleaner and got a new o2. Let's see how it works out

 

Changed the o2 sensor and gapped the sparkplugs. Still getting bad mileage. It went up from 25mpg-30mpg. Could anything else cause it to run rich? It's still runnin rich but not as much as before

 

You could try and borrow a different DPFI ECU to make sure that's not the culprit. Since you have changed everything out that really deals with fuel.

 

When's the last time you cleaned/replaced the air filter?