Civic VX 26 MPG!!!
 

Hey all! I'd like to start by saying I've been reading many posts on this forum for the past couple weeks and have been really impressed by the knowledge and determination to follow a problem to the end that I've seen by a huge number of members on here.

On to my problem, I purchased my 92 federal VX a couple of weeks ago and got a great deal(or so I thought) on it because the previous owner said the car had a horrible stumble/hesitation and that it wasn't "burning all of the gas" aka it was running rich. I test drove the car and sure enough it bucked horribly but the check engine light was on and I knew that would most likely hold the answer to my problem. I the car home and checked the code, it was for engine coolant temp. I initially thought it was the t stat as the lower radiator hose never got hot but after replacing it I found that the lower hose still wasn't getting hot. I then proceeded to look online and found that vx's run cool enough that the heater core provides sufficient cooling and that the radiator is rarely used for cooling. I then went back to the basics, what measures the coolant temp? turns out the connector for the coolant temp sensor had come de-pinned, most likely from someone trying to disconnect it improperly. so I repined it and the light went away and it's been driving great ever since.

however, I went to have an emissions test performed and the VX failed due to high HC at idle, cruise, and slightly elevated CO at cruise. the HC measured somewhere around 700ppm at idle with an allowable 400ppm. I went home and replaced the improper champion plugs with the proper NGK zrf4f-11's, and reset ignition timing, it was slightly advanced. I have yet to return for my retest as I've already burned through 1 tank of gas in 252 miles.

I'm getting 26mpg and it smells like I'm running rich but the old plugs looked ok and the new plugs still look good after 75 miles. I just put a new oem distributor cap on tonight, I'm considering buying an oem o2 sensor as I'm not 100% sure the one in there now is stock and I have yet to check it with a dvm. any thoughts? thanks

It should run about 1000 Rpm at 30 MPH in 5th gear (correct transmission).

It should have fuel pressure regulated at around 40 PSI.

A bad diaphragm in the fuel pressure regulator could dump excess fuel into the manifold.

A bad 02 sensor could be the problem.

Is the upshift light working?

The top (exit) hose should be almost too hot to hold your hand on. If not then the thermostat is not getting it hot enough.

Cam timing should be checked.

EGR passageways need to be clean enough for proper flow.

26 MPG is terrible for a VX, is your driving all short distance stop and go? You should get heat within about 2 miles if the thermostat is working to factory specs.

The VX is very sensitive to even minor changes, mine lost 7 MPG when I changed the original 15 year old Bridgestoine tires to Michelin Xs.

Brakes dragging?

Alignment?

You should be able to push the car easily, I could push mine on concrete with one thumb.

regards
Mech

Does your temp gauge go up to the middle after about 3 miles?

Check your cam shaft timing, there is a 2nd set of timing marks on the head that the upper pulley needs to line up with instead of lining up with the top of the head.

You might also make sure someone didn't put gear oil in the transmission, it's supposed to have 10WW30 motor oil, very thin compared to gear oil.

Are you confident the car is what the seller said it was? If not check things like the ECU. Does it have the right ECU for a federal lean burning VX? Because lots of guys have modded these OBD1 cars with different ECUs to try and generate more horsepower.

Have you located a factory shop manual for the VX? They're often available for free online... the full 1500 pages. Lots of details in those that can be helpful.

james

I'm 100% positive its a factory vx with all the appropriate hardware, the ecu is a p07-a00 and have p07-1 cast in the head with d15z1 on the block. I feel lean burn engaging, or at least what I believe it to feel like, feels like a small "boost" when exiting lean burn but it crosses over smooth and drives great. the alignment might be off a small amount but it coasts absolutely great. also, the engine temp rises quickly as it should to just below the middle portion of the temp gauge and stays there. the shift light is not functioning right now and idk if that's because something is wrong with it or because the bulb is out. about half of the back lighting bulbs in the cluster and hvac unit are out I just haven't had the motivation to replace them yet. also, my cluster doesn't have a tach and I thought all vx's had a tach? it does have the shift light but like I said its not functioning.

Then definitely run through the lists suggested above by Old Mech and Ryland. They know their stuff when it comes to these cars about as well or better than anyone on this site. Both have tutored me through mechanical troubles. Also, there are a couple other threads where guys have recently dealt with both the shift light problem and low MPG in a VX. Maybe you have seen them, but if not, search and study. Your answers might be there too.

I can hit 26 MPG, in my Fiesta, within a mile of a dead cold start and then a climb up a 10 foot rise from my garage to the street. I could probably beat 26 in a VX with a 2 mile, each way commute.

Smells rich=too much fuel. focus on the pressure regulator and the 02 sensor, see if you can get rid of the smell. Clamp off the fuel supply hose with needle nose pliers to make it go lean and see what that does. Pull a vac on the fuel pressure regulator and see if it is leaking gas into your vacuum souce (bad regulator diaphragm, leaking fuel into the manifold through the vac hose).

Check compression and cam timing.

regards
Mech

Alright so I'm a lube tech at a gmc dealer and I had out shop foreman look at it. Fpr isn't leaking, and Now that I think about it the distributor is almost all the way retarded to set it at the 16 degree mark so my cam timing might be off being that the distributor shouldn't have to be maxed out to achieve a factory timing. I will check the cam timing when I get home along with the o2 sensor

Check the Timing belt for proper D15z1 settings. http://img163.imageshack.us/img163/8660/timing.jpg
After that, leak down test (or compression as a poor second choice)

Cam timing could be a lot of your issue. I would not replace the sensor until I had driven it a while with the cam timing right, also reset your timing after the cam timing is right.
If you get it aligned set the toe to the minimum spec.

regards
Mech

update: so I went to set the timing and ran into a stupid issue, like a ton of other d series, a valve cover bolt sheared off so I had to take the number 1 and 5 cam caps out and drill and tap them for a helicoil in each...that was stupid, at the same time I checked the valve lash and found that 2 exhaust valves were slightly tighter than the .25mm allowable tolerance so I set them to .25mm. I also did an oil change, reset ignition timing, checked for vacuum leaks using smoke and I failed emissions again.

This time was slightly worse for HC yielding 794 ppm with an allowable limit of 400 at idle. HC was also high at 2500rpm but not as drastically high as it was at idle. CO% at idle was also slightly elevated at 3.5% with an allowable limit of 3.0% so that improved slightly but not much.

so to recap, I've replaced plugs, cap, set cam timing, set ignition timing, checked valve lash, changed the oil, checked for vacuum leaks and I'm still failing emissions.

Man, that suck a lot. Just spitballing: the catalytic converter?

forgot a couple things,

would the o2 sensor test bad if its not throwing a code? I've read that they don't always throw a code when they go bad but I'm experiencing such horrible fuel mileage one would think that its running so rich that the o2 sensor would fowl and throw a code.

also, I did a quick cleaning of my egr valve and ports using carb cleaner and when I took the valve off the exhaust side, or the round hole, was dry black carbon as one would expect to see, however the intake side, or the rectangular hole, appeared to be wet, almost black oily looking. The "oil" substance had no smell too it and it was pitch black. Is this normal?

and finally, I was told by a master mech. at my work that the cat should be colder on the inlet side than the exhaust side. I find this to be true due to continued combustion in the cat however, this wouldn't solve my issue. theoretically a fuel injected engine shouldn't need a cat to completely burn all fuel.

ive seen bad o2s cause driveablility issues on these engines without an engine light but it only knocked mileage down 3-5 mpg. even if you unplug the sensor and run in limp mode they still get high 30s low 40s.

what about fuel injector spray pattern or leak down after sitting?could someone have replaced the injectors with larger ones? the cx and vx came with 190cc injectors i believe. dx,ex,lx,si came with 220cc. maybe a previous owner had them replaced and didnt know they were different?

Injectors could be the issue, I feel like they've at least been taken out as one of them is rotated like 45 degrees so someone has messed with them, I was told to do a leak down test on them but I'm not sure how to being that there's no scherader valve on these fuel rails are there? This weekend I plan on pulling them and checking/cleaning them and if need be I'll take them to dr injector and have them flow tested and cleaned there

To do it by fuel pressure a sophisticated fuel pressure tester will have the adapters for Hondas. It attaches to the fuel filter. You could remove the fuel rail and crank the engine with the injectors squirting into little jars or bottles and watch the pattern. And turn the key on and see if any drip without cranking.


Edit: also check to see if any part numbers are on the injectors and run them

Just put a gauge on them (injectors) and see if they hold pressure.

I've seen bad 02 sensors drop mileage by 25%.

Your VX should putt along at 30 MPH in 5th at 1000 RPM smoothly.

A flow test of the injectors, comparing the volume of fuel would be a good idea. It's very possible that someone replaced one with the wrong replacement, especially if you see evidence of tampering.

regards
Mech

alright so I tested the o2 sensor today and to my disappointment it is still functioning as it should. It reads .24v at idle, when in lean burn at a steady cruise I was getting around .88v and when not in lean burn i.e. flooring it I was getting -.78 or so. other times I would get higher and lower numbers but those seemed to be pretty consistent.

We also tried to check the cat to see if it was bad or clogged using an infrared thermometer to look for higher temps on the output side of the cat however this was impossible due to the stupid heat shielding around the cat and exhaust and the few small spots in which I could read around the heat shielding I wasn't able to get a reading because the temp sensor doesn't read that high.


One thing to mention is that we checked the resistance of one of my spark plug wires and found that it only read .25k ohms and then we tested a much much newer ngk wire that I had sitting on the shelf and it measure 18.4k ohms....is this anything to be concerned about?

and I want to reiterate that it runs flawlessly. I daily this car around 16 miles each way and it doesn't even so much as hiccup. the shift light comes on as it should, I feel when I'm in leanburn and when I'm not. it just smells rich, wont pass emissions and I'm getting horrible mileage. should I suspect the ecu?

What does the temp gauge read when it is warm, possible thermostat? OEM stats fail open so the car will run too cold which could mean fuel enrichment. Should be just below halfway on the gauge when warm and should warm up within two miles. I don't see wires as the problem.

regards
Mech

I'll take a pic of where it gets too, its just below half way on the gauge and it warms up quicker than any car I've owned. and I replaced the thermostat a couple weeks ago and I've yet to have it actually open yet as the PO removed the coolant valve going into the firewall and bypassed it with a piece of pipe so I always have heat.

Alright it won't let me upload a pic from my phone but the temp gauge needle gets to just below the temp symbol and holds steady

plugged air filter? sounds silly but ive seen it throw rich codes on obd2. too much fuel not enough air.

did you reset the ecu after fixing the coolant wiring? i always pull the 7.5 amp fuse (in the underhood fuse block) for 10 seconds after making any changes or fixing somthing on my hondas. especially if the engine light was on.

I'm actually running no air filter lol, I'm fully aware that that's a bad idea but it still wouldn't make it run really rich, and yes the ecu should've reset when I pulled it out and took the cover off to inspect it for things like broken solders or water damage, neither of which are present

ok pretty sure my cat has gone bye bye. Correct me if I'm wrong but a cat has "honeycomb" shaped cells in it or a sort of lattice right? mine is completely hollow. I pulled the o2 sensor out and looked inside with a flashlight and all I see is a big empty cat, I can see the walls of the cat and the exit hole on the bottom, its not like its been hollowed out, the walls are completely smooth, it seems like its just completely depleted everything inside of it.

Also, I checked resistance on all 4 injectors and they all measure either 12.1 or 12.2 ohms. although they could potentially still be leaking

would not having any backpressure from the cat being hollow cause a false reading from the o2 sensor causing the ecu to dump more fuel?

my cat has been gutted for 30k miles on mine and its returning 50 mpg.

however if it did come apart it might have gone into the exhaust and plugged it somewhere.

since there is no air filter is there any other modifications that are done to this car that are not brought to our attention?

Ditto that. And would removing an airfilter from this car have any or all of these possible consequences? (1) increased airflow (2) colder air (3) changes in the MAP sensor readings (4) changes in AFR (5) increased pumping losses??? Couldn't this mod at least be part of the problem?

alright so just filled up again and got 35mpg that tank, does anyone know if not having the white connector(shift light connector) plugged into the back of the gauge cluster does anything? because It wasn't plugged in until about half way through this tank and suddenly I'm getting almost 10mpg more...

Did you check the MAP sensor out?

I'd put that air filter back in asap. Only takes a tiny bit of dirt to trash the valves/valve seats and accelerate wear of the rings/bore. Running without one is an astoundingly bad idea (and probably hurting your mpg).

Did you replace the rotor with the cap? They wear together and should be replaced as a set. I also always replace the plug wires at the same time with OEM honda, which seem to be the best quality available.

FWIW in 220k miles the worst mpg our VX has ever done was 37 I think. That was just all city in hot weather with the AC cranking.

OK HERE IS THE SOLUTION.!!!
My vx was getting max highway about 48, average about 43 hwy, and city was about 33mpg.

I did all the other things everyone else did and still no improvement until I did the following:

Check the fuel pressure like the honda service manual says. My testing found it to be below spec.
I replaced the fuel filter and the pressure went up a little on one test but was still low on the other test(having to do with the vacuum line on the fuel regulator).
The test said that I should test the regulator, and if that was working it was the Fuel pump that was the problem. Which was what I did.

I replaced the Fuel Pump and the two pressure tests passed!
It ran amazingly different, but still had a tiny "miss" it seemed like, which was reduce quite a bit from what it was doing.

I decided to replace the Fuel Pressure Regulator just to make sure. (ebay $15)
The MPG went up dramatically with these fixes.

But, it was still feeling like the motor was off a little. So I checked the timing and it was off quite a few degrees! Must be the new pump and stuff affected the way it was firing and timing.

After setting the timing it ran perfect! No "missing", no hesitation, lots of power, smoother, quicker, 70 and even 80MPG on the highway on certain straight stretches.

I drove from Lake Charles LA to Tallahassee Florida and with the MPGUINO calibrated I got 61 MPG going 55-63MPH. That was a tank average after about 474 miles. The fillup said I got 59.7MPG

So Recap;
New O2 Sensor(NTK), new ntk plugs or E3 plugs, new cap/rotor, distributor, wires, cat convertor never got it above the 48-52mpg average for hwy.

BUT
A new fuel pump and screen, fuel filter, and fuel regulator, then re-setting the timing to proper 16 Deg BTDC(?) fixed all the problems of:
poor fuel economy, poor acceleration, poor power, poor smooth idling when it got hot, poor morning starts requiring me to try starting the car twice before it fired.

I can not tell you how freaking awesome this car runs now! It really amazing. It runs like it was brand new.

Oh, also add MotorKote to the engine oil to reduce friction. This product is amazing. It makes the surface tension of the metal tighter thereby reducing friction. Other additives dont do this, except a product called Militec(?).

Key words: How to get better MPG from honda civic VX?
My vx MPG sucks.
My civic vx wont start the first time, but will the second time i try to start.
My civic vx is missing at highway speeds.
My civic vx is not getting good mileage mpg need to increase.
My civic vx has poor acceleration weak power poor idle wont idle good.

I hope this helps people. It took me a few years and no one on the forums had solutions for any VX owners with these problems that solved it. This one works!!

Let me know if it helps you.