inferno5000

The last few weeks I have noticed really poor fuel economy. I'm getting somewhere between 19 and 23 highway/city mixed. It really doesn't matter how hard I drive it or how fast I go. I have tried staying at a steady 60 and keeping good driving habits. Racing up the mountains near my house got me 21mpg and I just got 21mpg on my tank commuting (all highway). To put this in perspective for some of you that don't calculate your mpg, I'm getting 160 miles a tank pretty constantly. A couple of months ago I got 27+mpg (250 miles per tank) mixed driving...since the mpg dropped I have changed:

Catalytic Converter
Resonator (rattled)
Cap
Rotor
Spark Plugs (BKR7E)
Switched from 92 to 89 octane
Fuel Filter

Just before the mpg dropped I also replaced:
IACV (still having idle problems)
Intake Manifold (64.5mm opening with 58mm TB)
O2 Sensor

All of that and not a bit of improvement. This weekend I will get my tire pressure checked, change my oil to 20w40, change my throttle body (65mm finally), and make sure its nothing with my suspension, which I know is starting to sag. I'll report back by tomorrow night. Any other ideas guys?

Also, big shout out to Bucky's in Bremerton. They hooked me up with the catalytic converter and resonator combo for just over $200 installed. If you're in the Seattle area, I highly recommend them.

White_EG1

Thats your problem.

inferno5000

I did that in response to the mpg dropping. I had 21 mpg before I switched from 92. I read on a few forums here that you could squeeze mpg out by reducing octane and making sure you're keeping your foot off the gas, but it hasn't made a difference. I'll probably switch back to 92.

White_EG1

Since you have a b16 head on the motor, that rose the compression, therefore you need to run 91 octane or higher. By running 87 your risking the motor.

By filling up and on a empty tank counting the miles on the trip meter is not accurate. Tell us how you are calculating this.

After installing the vtec cylinder head did you get the motor tuned?

inferno5000

I filled up the car with 92 today and topped off my oil. I got 24mpg with a semi aggressive driving style from Tacoma up to Bellingham. I usually do just use the trip meter and divide the miles I drive by the gallons of gas that I pump to full. What would be a better way?
I'm running a chipped p06 ecu that is using the tune from what the previous owner had. As far as I can tell its a decent tune for power, but from the smell of my exhaust I'm definitely running rich, even at idle. I've changed enough parts to need a new tune, but the only tuner I have found really doesn't seem reliable. I keep calling to make an appointment and he won't keep a date or return my calls. Definitely looking for a tuner in the Seattle area.

White_EG1

That is a accurate way to calculate it. Thought you were just counting the miles.

Rich tuned is in auburn, and highly recommended.

Speedfactory is in tacoma, which I would say is worth the drive. Highly reputable work.

inferno5000

Thanks. I've seen the honda-tech mythology of rich. I didn't realize he actually had a shop near me. I'll give him a call tomorrow.

kingkau

Check the tire pressure, air filter and run some fuel injector cleaner.

inferno5000

I already did the first two. I don't think I will need the fuel injector cleaner...

So after an entire day tracking down various incredibly expensive sensors and wrenching, this is what I did:
New MAP sensor
New TPS sensor
New S2 65mm TB
Added a capacitor to my HID lamps
Disconnected a nonfunctional oil catch can and re-routed some of my hoses back to "factory."

Fun fact: NAPA wanted 270 dollars for a new MAP sensor and no auto shops in a 2 city radius had the sensor I needed. I drove 40 miles to get an OBD2 sensor for a 98 civic. I will see if I can order the correct sensor and see if that deals with my new vacuum gauge issue...

And the record breaking fuel economy numbers on my way home:
*fanfare*
11.5mpg

My a-pillar gauges showed me running stupid amounts of vacuum pressure (-12 to 0) and way too much fuel (rich). I can usually lean it out by taking my foot off the throttle and the keep vacuum around -20, but even completely off the gas going downhill, I was stoichiometric at best and around -12 vacuum pressure.
I'm pretty sure my tune was kind of like "Dafuq am I supposed to do with all this air? MOAR FUEL. But wait, I'm not getting enough air, MOAR AIR."

Looks like I'll be commuting in my Chevy Truck until I get a tune, gents. Now the real question: Before I tune, should I port-match the 1.5mm difference or naw?

On the plus side, I completely eliminated the idle problems that I have been chasing after in the fitv and was able to reconnect my iacv without revving to 3500 rpm at idle My Honda purrs at 750rpm for the first time in almost a year...would I undo my pandora's box? In a heartbeat.

White_EG1

Can you tell us how you are diagnosing this problem? Did you test the MAP, or TPS first before just replacing? Because if you do the test properly, and the voltage is spec, you just wasted who knows how much $. Hope you got the TPS for a 99 civic SI and not just a 98 civic.


Yeah man sounds like you got a shitty tune, not saying rich isnt good, but that would be my last resort. I honestly would go to speedfactory, I know people who drove from cali just to get there motor tuned from them, they do great work. I Personally know the owner of the shop. He is my cousin's, childhood friend. Your in good hands man.

inferno5000

I came out to my truck today and saw a clean eg hatch with a huge speedfactory sticker across the entire thing parked right next to me. Out of 400 or so parking spots he was in that one on this day. Then I read this post. I can't say I'm much into superstition or anything, but that was the stars aligning, so to speak.

The TPS sensor was chump change for an obd1 del sol vtec that I wanted to throw money at anyways. The MAP sensor was from a 98 civic base model. They're apparently "universal" according to a dude who owned a Honda at O'Reilly. I needed the MAP sensor because the skunk2 throttle body was a different style than my jdm spec b16 throttle body. I'll upload a picture to illustrate what I mean.

inferno5000

Say something about this photo





Old MAP sensor was mounted on the firewall.





Top mount MAP sensor on Skunk2, while JDM B16 throttle body had a vacuum line to MAP.





Everything looking good

inferno5000

So just to give an update:
I got the map sensor changed back to the original and the problem ended up being that the new obd2 map sensor uses a different obd version than my ecu is tuned for. Looks like I will need to re-tune. At least I have been getting close to 30mpg when I'm driving to school.

hybridmiklo

that doesn't make sense. You are most likely running in open loop through ecu and its not even paying attention to the 02 sensor. When you get back to your tuner have it set up for closed loop. All map sensors are the same. They use the same 5 volt reference. Some obd1 models have a different "style" but work on the same concept. Only difference will be the plug and which pin the reference, signal, and ground goes. Nothing else.

inferno5000

It actually makes perfect sense. Unfortunately it seems like the previous owner tuned for an obd0 map sensor, not obd1. So while obd1 and 2 map sensors may be the same, obd0 seems to be slightly different. I will probably have to check the distributor and all that jazz to make sure the map sensor is the only obd0 part installed.
When I get a tuner that is reliable and doesn't cost an arm and leg, I will make sure he checks for that oxygen sensor thing you mentioned. It hasn't given me trouble before, so I'm not sure why the o2 sensor would do anything funky.

SpokaneSpeed

20w40 is pretty heavy for a daily with stock internals... guaranteed you'll gain a few mpg by just switching down to a lighter weight oil..

inferno5000

I ended up using 10w-40 instead. I have a tendency to hit vtec at least a couple times a week, so I'd rather have reliability than an extra mile per gallon.
I'm confident in being able to find miles per gallon in other ways. I know some of the guys on here report 40+. Since I'm in the low thirties, I know there are other things I can do.
I've been playing with the idea of updating to obd2 so I can run newer injectors too. There's an obd2 dizzy on CL for 70 bucks. It would probably also help to replace my sohc dizzy.
Maybe I should start a new thread on eco modding an lsv.

hybridmiklo

Now that I think about it, the obd1 map sensors also dictate density of the air when key is in the on position while the obd0 does not and uses a separate sensor located under the dash for that, either way it is the same sensor. As for the the o2 sensor, this is what dictates air/fuel ratio while driving and at idle so that the ecu can pull or give more gas to give the optimal gas mileage as well as help the catalytic convertor oxidize. And if you are running in open loop your ecu is not looking at the o2 sensor and instead relying on maps that are inserted "chipped ecus". This sensor has a dramatic effect on your gas mileage.