Ok 2 weeks ago i swapped in a minime (b7 block z6 head) into my 93 DX hatch.
At first the ecu i had was fryed so i got another P28 and cleared the codes. when i bought the motor it was a tooth out of time and i didnt catch it till i drove it. (done many swaps and also know what a tooth off feels like) So i fixed this thinking it was my problem with the gas milage but afterwards it is the same. I dont know what else it could be? Seems to be running ok, there are no fuel leaks anywhere. Any guesses guys? i mean 200 miles a tank? cmon... Let me add it was getting over 30 mpg with the old dx motor so im thinking the longblock somewhere contains the problem

 

sounds like its runing rich

 

whats the voltage on the o2 look like? is it getting lazy?

 

It may be rich, my eyes are watering and the exhaust is stinky when i drive it, i havent pulled a plug yet, also i replaced my O2 sensor... Can it run that rich to lose 10mpg?

 

Possibly a bad map sensor?

 

I removed the one off the firewall on the civics, and have been running the one on the intake manifold. I had 2 when i did the swap.

 

change the fuel filter and spark plugs also check the air filter and change the oil if its dirty.

 

Air filter new, fuel filter replaced, changing spark plugs i dont think would make it run rich, or dirty oil. but hey i could be wrong, i dont know everything...

 

yeah if you stand behind your car and your eyes water then its deff running rich...i know this because i have a 94 rx7 and i get 9 miles to a gallon and i idle at 11.2:1 but this is normal for my car because its a rotary engine...

what size injectors do you have and whats the fuel pressure?

 

How do i lean it out a little?

 

Anyone else have any guesses? I suck at trouble shooting.

 

So tonight i replaced my spark plugs and my old ones were black. Obviously i am running rich, what could be causing this? I am on a stock p28 and oem fuel system.
Just want it to lean out without having to tune it. obviously something is causing it to run this way, i also replaced my o2 and it wasnt the problem...

 

What is the map from that you are using now? I would guess and say you are running the wrong map or the map is not getting proper vacumm

 

Its kind of a longshot, but take a peek at the inside of the cat. If they get too hot, they will melt, and cause major blockage.

Otherwise I would guess its an O2 issue more than anything. If it went bad (or the signal wire was touching another) and reported a voltage for richer conditions, the ecu will run it rich thinking its stoimetric.

 

I am using the map on the intake manifold from the z6 head. I swapped map sensors to see if that was the problem and it wasn't, again i have no cells and car seems to be running decent except for the 20mpg. What else can i check that could be causing this? Could an injector be stuck open? and if so how do i check with a meter? Im so stumped on this 20 mmpg thing, i mean it shouldnt be hard to find its losing 15mpg!

 

You could try using a fuel pressure gauge to see where your fuel pressure is at.

 

Someone told me to check the coolant sensor even though im getting a temp reading on the cluster the ecu could still think the motor is cold and dump extra fuel while im driving. Anyone heard of this?

 

possible intake leak, bad rubber around injector, vacuum leak somewhere I would guess. But hey I am learning these hondas as well.

 

Anyone else have any sugestions? 20 mpg sucks...

 

Ya there is also a temperature sensor on the back of the intake I believe, I assume thats ok too?

 

i got a friend that can chip you ecu to make it run better =] not sure about gas mileage though

 

I dont want my ecu chipped, i want my car to run correctly, i have done many ecu's myself.
Anyone else had any fixes that solved bad gas milage?

 

well, if your old map sensor was on your firewall and now your running the one on the throttle body then maybe you connected the wrong connector. which one did you use the connector on the dx/si harness or firewall mounted connecter?

 

Its the same connector for both map sensors, i have a dx harness with vtec wired in