Civic VX 26 MPG!!!

[nwrubicon]

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

[user removed]

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

[Ryland]

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.

[California98Civic]

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

[nwrubicon]

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.

[California98Civic]

Originally Posted by nwrubicon

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.

[user removed]

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

[nwrubicon]

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

[Superfuelgero]

Check the Timing belt for proper D15z1 settings.
After that, leak down test (or compression as a poor second choice)

[user removed]

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