sstupid

Hi, guys. I have a 1991 Honda Civic Hatchback Base with 183K. It's just a beater, but I love her for her gas mileage..............or I did anyway. My gas mileage has gone from 30MPG to 20MPG in the last 3 months, slowly. It crept to 28, then 24, then 21, and now 20.


1) New air filter.
2) New spark plugs, gapped correctly.
3) New spark plug wires.
4) New O2 sensor.
5) Tire pressures are all at 35 PSI.
6) Junkyard MAP sensor. When it didn't work, I put my original back on. Of course, I don't know if they are both bad. I don't know how to check them for correct operation.
7) New oil change with 5W-30.
8) New fuel filter

Any ideas, anyone? Is there any way I can check that my O2 sensor is working correctly? Is there a way to check that the MAP is working correctly? I definitely have a strong gas odor when I drive with just my driver's window down. When I use my A/C in the summer, I'm used to seeing 22MPG, but this has been during the winter and I'm not using the A/C.

Riceburner247

iTrader: (1)

Just a random thought, do a compression test.

radex7

Do not forget the timing, and valve adjustment.

https://honda-tech.com/forums/honda-civic-del-sol-1992-2000-1/valve-adjustment-affect-gas-mileage-2569172/

sstupid

I ordered some of the cam-follower O-rings. When I replace those, I'll do the valve adj. Timing must be good because it runs beautifully, especially after the fuel filter replacement.

instrument

does your check engine light work? obviously running rich..have you checked your spark? still bright? and do you burn any oil?

crazyhouse2011

What kind of gas smell are we talking about? Like raw, gas station smell? Or running rich, unburnt fuel smell?

sstupid

Unburnt fuel smell, like it's running rich. I unplugged my MAP and my check engine light definitely works. I don't see any burnt oil on the back bumper. I'll check the plugs later today, after work, and take a pic for you guys. I don't know how to tell if my spark is bright.

sstupid

Well, ****. It's not running rich. I guess I'm leaking it out somewhere, then.



Don't pay attention to the oil on the threads. That's from failed cam holder O-rings. Still gotta get that done.

video_voide

Jeeze dude. Check around the fuel filter area. Maybe you didn't tighten it up. Dont be blowen yourself up, unless your into that

sstupid

The poor mileage has been going on for a while. I just put the fuel filter in last week. I checked all around the car for leaks and couldn't find anything. It doesn't smell when it's sitting and it doesn't smell like raw fuel. I think I might have found my issue when I was crawling around under the car last night, though. When I start my car, I get kind of a metal tinkling sounds until it warms up. I hit my catalytic converter with my hand last night and got that tinkling sounds re-created so I think my catalyst is broken. Probably did it on a speed bump, since my car is so low. I'm thinking a new exhaust system might solve my problem.

DWP_Racing

Where do you live? Is it cold outside? You should realize the colder it is outside the density of the air increases which leans out your cylinders SO your ecu adjusts for the Increased capacity and puts more fuel in cylinders. Thus using fuel more. Will happen every time its cold. Nothing to worry about if you are in a 30 degree or below environment. NOW if you live somewhere warm there is another problem but my guess is the cold front!

DWP_Racing

Also a clogged cat or partially clogged cat will do it. Just read your last post something about your cat.

eestoog

I get really bad gas mileage as well. Time for a valve adjustment!

Mass13

This ^

Creator

iTrader: (1)

More gas + more air = more power. With the average drive that means less throttle input, leaving you back where you started in the summer time. Sure I suspect there is a little loss in milage, but not 10 mpg.

Definately time for a valve adjustment, not sure how long you've had it, but hopefully this is not the first one for this car. Aka might already be too late.

This seems obvious but I'll ask anyways. Have you changed where you drive the vehicle. IE: I used to do all highway driving to and fro my job in the middle of nowhere, but now I work on the other side of a congested city.

DWP_Racing

Even at cruising conditions more air means more fuel compensated by the ecu. Doesn't matter how you drive it you can't change the air temps outside. So you'll see a LOSS in mpg. Ask me how I know??? Its my JOB to know! It could be another reason yes but when people ask why they get less in winter its because of the DENSE air with the easily evap fuels (winter grade)... My RSX type s does it. I average 375-425 miles per tank in summer and 300-350 in winter depending on how I drive. Average shifting at 3k rpm.

CHECK OUT THIS LINK AND DO MORE RESEARCH IF YOU WANT BUT THIS COULD BE YOUR MAIN ISSUE!!!!!!!!!!!!
http://www.metrompg.com/posts/winter-mpg.htm

sstupid

Thanks, guys. I live in Austin, Texas. It has been a little cooler than normal, here. It's definitely rarely below freezing, though.

I bought this car with 158k on it, for 800 bones. 2 years later, it has 187k or so. I tried to do a valve adjustment on it when I bought it, but I think the rockers are pitted, so I still get clacking when it's cold. I'll try another valve adjustment when I get my cam holder orings. I really think my cat is screwed, though. I guess I'll buy a new exhaust this summer. I want something as quiet as possible, though. I'm old and don't like that raspy crap. It's a 50hp killer, I know. Thanks for all the help! I'll keep you guys posted.

Viwil89

for me i had something similar it was bad timing and a stressed rocker arm. on my CRX

avrfan

I wonder, did the OP ever fix his problem and what was the cause?

Cannot wait to solve this issue of poor fuel economy and incredible rich fuel mixture. (tail pipe sooted black inside the tip)

----- here's my story ----
I have had a similar problem with my 88 CRX HF pgm-fi mpfi D15B6 engine. Pretty much did a full tune up, new plugs, cap, rotor, wires, spark plugs, oil and filters, ignition timing, valve lash adjusted. I noticed the mpg went really low like 33mpg in the winter driving through idaho, montana and north dakota in the fall. Then in the sub freezing winter in North Dakota, the fuel economy hit an all time low of 20pmg. I did spend a bit of time running the car in the morning to defrost the windows and heat up the interior so I am sure that was part of the reason but it was really bad I mean 20mpg?

After the winter, I head back to california weather. The fuel economy improved when passing through Arizona. But after I was back in Cali, the mpg would be good one tank and bad the next. The worst I would see is 32.5mpg. The best as good as 53mpg in Arizona dry heat and 49mpg in California.

Things have gotten much worse Lately. The engine is developing a misfire. The exhaust smells funky, and spark plugs are fouled up. The only engine code I get is when driving at night with my lights on, I get a code 20 for ELD. I noticed also that my exhaust was kinda smokey and it seemed like a greyish white colored smoke. I noticed my coolant is low but the oil is clean. I don't know where the coolant is going. I also noticed that my PCV valve hose collapses on itself when idling from the vacuum. I think maybe my PCV valve or the oil trap box on the back of the engine is plugged. Would this cause really bad fuel economy and smoke or oil burning?

Out of curiosity, I checked my fuel pressure. I noticed it wasn't holding pressure it would go up to like 30psi and when the pump turned off it would drop to 20psi. I repeatedly primed the fuel pump by turning the key on and off, eventually it got up to 35psi but it would just fall back down to 20psi. I started engine and pressure hovers around 28psi during idle. If I pull the vacuum hose from the pressure regulator, it shoots up to like 38psi. If I pinch the return hose, the pressure goes up to 50psi during idle.
After this I turned off the engine, and fuel pressure would prime to 36psi and hold around 34psi. I think it was suspect because earlier it would not hold pressure after priming, but after messing with the vacuum hose and return line, the regulator started holding pressure. I could not reason as to how this might affect fuel economy

but I went ahead and got a good looking used FPR from the a junkyard. The car ran noticeably smoother and had more power. Misfiring seems reduced. I have yet to pull the plugs to see if they are burning cleaner.

Oddly I cannot be sure this fixed my fuel economy until I check at my next fill up and / or pull my plugs. Some reason it was running incredibly rich. I think the PCV blockage caused pressure in the crank case which forces oil and engine blowby gases into the combustion chamber through the rings and the valve guides and seals. I think it also contributes oil fouling of my plugs and increased oil loss . All of this caused engine misfiring and thus lost power and economy as much fuel was going out of the tailpipe unburned.

I think also the regulator not maintaining proper pressure, for example if it was too low, it would cause likely a lean fuel condition. This could lead to more misfiring, but also ECU compensation (via O2 sensor feedback) by running the fuel injectors at a higher duty cycle and longer pulse width. This is purely speculation as I am not very skilled in fuel injected engine diagnostics. Suppose the FPR is sticking low, then goes high pressure or sticks at high pressure and goes low at random, this would cause poor efficiency with the engine and its ability to run optimal A/F mixtures.

I have not checked the MAP sensor yet and its been a few thousand miles since I changed the fuel filter.

I have yet to check the distributor but I was beginning to speculate that maybe the distributor (containing 3 different signals to the ECU which it uses for Fuel and Ignition timing) would be having problems. I don't know how to test it though. I figure an oscilloscope would be a good way to check its waveforms form the 3 sensors to see if there is anything unusual. I am not sure how this would make it burn excess fuel however. I think it would just cause the car to not run or go into some kind of Limp mode or Safe mode with reduced power.

I began to think maybe its just a bad ECU but don't know yet.
-----

I wonder, did the OP ever fix his problem and what was the cause?

Cannot wait to solve this issue of poor fuel economy and incredible rich fuel mixture. (tail pipe sooted black inside the tip)
Thanks

kp

Man, you bumped an old thread with a ridiculously formatted novel describing 10 different problems with your theories on each of them.

Start a new thread. Ask a few questions based on what you know.

Former User

Make your own thread.