joelmatt89

So i had a post maybe a week back explaining my situation, 93 ex coupe w/ b16a2 swap i/h/e, gsr cams etc., the ecu is a p28 chipped by phearable.net, this last tank was after i had fixed my vacuum leak and cleaned the o2 sensor i got 120 miles from ten gallons. That is alot worse than what i was getting but i think it is because i spent alot of time with it idling while i was working on stuff. Regardless it wasn't enough time idling to give me that kind of mileage. I know that getting it tuned on a dyno will help, but i talked to john at phearable and he said there is something else causing this so don't tell me to get it dyno'd. Here are some things i have noticed; when i sit at a light I smell gas, to the point of discomfort, i am assuming this is from my exhaust fumes. Also i have been working on trying to get my idle steady but nothing I I have tried will completely fix it. I would think it is quite possible the two problems are related so I will explain my symptoms. It idles fine when it is cold or right after i start it up, but when i have been driving for a little bit and i come to a light when i let off the gas it will drop to 2-300, then sometimes it will go to 750 and stay there but most the time it jumps around from 200-1k. It seems to be intermittent it doesn't really do it all the time. Right now I have no vaccum leaks, the ignition timing is perfect, somehow the spark plugs look perfect don't ask me to explain how that is possible. I think the o2 sensor is a bosch and i also think it might not be the the right one for the engine. I know i should get a new one but in the mean time I would like to rule out as many things as possible. If I had a leaking gas line or something along those lines i would think i would either see gas on the ground when it sits idling or it would smell very bad in the engine compartment is this correct?

So if you guys can give me other things to check i would appreciate it basically anything that could cause bad gas mileage throw it at me and i will check it. Does anyone know how to check if the iat is working properlly?

EDIT: So I got a new oem o2 sensor and my gas mileage may have improved the slightest bit, like 1-2 mpg, but the o2 sensor is still getting covered in carbon in very little time, which makes me think there still something else causing poor mpg. PLEASE HELP ME OUT I HAVE TESTED EVERY SENSOR AND JUST ABOUT ANYTHING I CAN THINK OF... I AM DESPERATE.

Former User

I assume that no CEL codes are being thrown?

I was struck by the fact that you believe that the O2 sensor is a mismatch for your engine. Given the critical importance of this sensor in selection of an appropriate air/fuel ratio, I think this potential mismatch issue should be resolved first.

Also, have you measured the fuel pressure and checked whether the fuel pressure regulator is working properly? In addition, look for a possible exhaust leak near the primary O2 sensor and check whether one or more of the fuel injectors be leaking.

Leak in the EVAP system, especially the purge solenoid valve?

joelmatt89

yeah i know i really should get a new o2 sensor but i just have a bad feeling it won't fix it and just want to rule everything else out first. Your correct there are no cels, i haven't measured fuel pressure yet i would like to do that soon i just need a gauge, there aren't any exhaust leaks i checked that with the car on jacks. I don't think any injectors are leaking, i will take a really good look at those in a little bit, but it seems like something along those lines would make sense since my plugs look so good. The purge system was taken off by the previous owner and the line coming from the gas tank has been capped.

ahhwhat?

you may have some sort of vac leak....or it could be the injectors...im not too sure.

joelmatt89

i doubt it has a vacuum leak cause it dies right away when i cover the tb, are you saying like the injectors may be bad i ran cleaner through them but it didn't do a thing is there any way to remove them and manually inspect them

honda.lioness

Be aware that the ECU does not use the oxygen sensor voltage signal to adjust the air-fuel ratio until after warmup. Thus your symptoms above do IMO tend to point to a malfunctioning oxygen sensor.

How does the car run before and after warmup when you are cruising steadily at say 30-45 mph?

AFAIC for now, your suspicion of this jumping around of the idle speed being Thee Cause of the low MPG is dead-on justified.

I would bet the engine is running extremely rich, meaning a heckuva lot of fuel is going unburned due to the air-fuel ratio being all messed up. Yes, this can be smelled.

There are tests one can do of the oxygen sensor, as long as you are willing to rig up a test harness that allows the sensor to still send a signal to the ECU while you measure the O2 sensor's output with a multimeter. Many sites on the net discuss these basic tests of the O2 sensor's signal voltage; they're all about the same, regardless of the make or model of car.

Some folks run down to the junkyard and get an OEM 4-wire sensor (hopefully matched up to your engine) on a younger engine, plunk it in, and see if it makes a difference.

joelmatt89

it seems to run fine at anything other than idle regardless of whether or not the engine is warmed up. It feels like it is running really strong and doesn't bog down at all or anything, but i have never driven this car before the problem. For some reason i cannot find any good junk yards in my area for honda parts I was told that most b series engines you can interchange the o2 sensor with, but I can't find any with a b series engine. I did find a denso oem replacement one for it online for $60 a little bit ago so if i can narrow it down to that being my only problem i will get that. I am gonna try looking up how to do that test for the o2 sensor with it hooked up. Also i forgot to mention it does seem like the carbon builds up quickly in my exhaust although just looking at the exhaust coming out it seems pretty clean.

toolbox01

have u tried doing a tune up or adjusting ur timing

joelmatt89

yeah i checked the timing is good, the engine has a new fuel filter, air filter and plugs.

joelmatt89

so i just tested the voltage coming off the o2 sensor i read somewhere that it should be rapidly fluctuating between less than .2v and more than .7v for most o2 sensors. So i warmed up the car and i was reading a steady .75v not fluctuating at all is there any way i could be screwing up this test, if not it seems like i have a bad sensor on my hands. But the thing is i read that if it is reading above .45 that means that the mixture is too rich so does this necessarily mean my sensor is bad or is it working properly and just telling me what i already know, that i am running too rich. So on the website i read they said if it is running rich like that to try making a vacuum leak and you should notice the reading go down, i went back out there and know the readings are all in the upper 30s to low 50's but still i tried making a vacuum leak and it didn't change the readings when i did which i guess would indicate it is not reading correctly.

honda.lioness

1.
Was the sensor still hooked up so it was sending a signal to the ECU during this test? If it is not hooked up, then the computer sees no exhaust feedback and so will be in what is called "open loop," so how the O2 sensor responds is pretty meaningless for purposes of this thread here.

2.
Was the car fully warmed up such that the rad fan came on twice? If not, go drive at 40 mph or more for 15 minutes, then park in garage and let the engine idle until the fan comes on twice. Repeat the test of the sensor.


Keep in mind that if for some reason the engine was running rich for a period, then the richness can cause an oxygen sensor to degrade. Thus the underlying cause of the richness has to be corrected. With all the other maintenance and repairs you have done recently, it might be a good assumption for now that you fixed the underlying cause but now have a bad O2 sensor from when the engine was not running at the correct a/f ratio.

If the O2 sensor you plan on purchasing is #234-4099, then Amazon now has these for $56.

joelmatt89

i did leave it plugged in to the ecu when i tested it, but i think i will try it again and make sure the fan turns on twice. The one i was looking at is 234-4011 which is the one for the engine, i posted a thread on here a few weeks ago and the unanimous answer was get it for the engine.

White civic

just change the 02 sensor first

honda.lioness

? I think the one direct answer was to get the O2 sensor that would work with both ECU and engine. Specifically it seems like the poster was saying that ECUs which in stock configuration use 4-wire O2 sensors must still have 4-wire oxygen sensors, but any 4-wire would work. The guidance seems to have been: Find the O2 sensor that the sensor maker says goes with the engine, then make sure it has the same number of wires as the ECU being used.

I suppose the advice on matching the sensor to the engine is mostly about getting the electrical connectors (sensor's and engine harness's) to be plug-and-play.

At any rate sounds like you have ordered a Denso O2 sensor that will work correctly, according to reports here.

joelmatt89

bump for update on the first post

kenny707

maybe you need a new rotor/cap? my del sol was doing the same thing til i changed them

joelmatt89

i mean i guess that couldn't hurt, but the engine only has 43k and i have inspected the rotor and cap and they both look mint.

V8 Eater

The first thing I would do is go out hunting for a friend or a friends friend that has a b16a2, or a person who is trying to sell a b16a2 swap,offer them some cash then swith parts.once your sure his car is running pretty ok than switch parts that may lead to this type of failure such as tps,map,o2 sensors, dizzy,wires,plugs,pcv,iavc,fast idle valve, t-stat,cat and finally and most importantly the ecu. I would start off by seeing if the stock virign b16a2 ecu helps? then replace the parts above with the healthy b16a2 to see if they make a difference? my bet is that the ecu is running extremely rich though!

joelmatt89

thanks thats a good idea i think maybe i'll try posting a thread on my local forum looking for someone. I appreciate the list i was hoping someone would give me a list like that of every possible cause. If anyone else reading this can add to what v8diet just mentioned please do