93 Honda Civic VX horrible fuel economy

[Farlander]

@ Benfrogg,
Indeed it does appear to be a major triumph. Hard to believe you went from 30 up to 60 mpg... can you outline everything you did again? I recently acquired a '94 VX with 177k miles and almost every problem you could imagine except the body is completely rust free. The check engine light is on for code 48, Air/Fuel sensor, but it looks relatively new, so I intend to replace the ground wire first. Also, it takes about 12 cranks before it will fire up, could that be fuel filter? Unfortunately I have 14" steel wheels with brand new 175/65R14s, I hope to do an rpm to speed report here too soon. Thanks!~

[theholycow]

Originally Posted by Farlander

it takes about 12 cranks before it will fire up, could that be fuel filter?

No. A clogged fuel filter would start ok but would run badly or stall after a few seconds. You have a fuel pressure leak, either a leaking fitting/line or the check valve in your fuel pump.

[imzjustplayin]

Another idea which I think I should mention that I think absolutely noone has thought to think of...


Check out the clutch switch that is depressed when the clutch is released, NOT engaged... why? Well the ECU apparently needs this switch on the D15Z1 engine, and I'm thinking it's for the lean-burn. I have this switch on my '98 LX and found it was working intermittently which affected the cruise control. This same switch is used on the D16Y5 engine and the D15Z1 engine as specifically mentioned. I guess the only reason you'd have this switch is if your car has a Y5, Z1 engine or cruise control.

[benfrogg]

You could be right about that.
I've noted that this more power/less fuel thing happens (addressed in the repair forum, "VTEC-E question" or something like that) now after I restart the engine. If it's not doing what I want it to do, I have to use the kill switch and restart the motor. Then, most times, the power/higher mpgs are back.
During that process, I have to take the car out of gear with the clutch, and restart it with the clutch. Thus, the clutch is active the whole time.

I wonder how to test it? I can pull it and put a multi-meter on it. Maybe that'll do it.

I wonder if it would throw a code or not?
B

[imzjustplayin]

Originally Posted by benfrogg

You could be right about that.
I've noted that this more power/less fuel thing happens (addressed in the repair forum, "VTEC-E question" or something like that) now after I restart the engine. If it's not doing what I want it to do, I have to use the kill switch and restart the motor. Then, most times, the power/higher mpgs are back.
During that process, I have to take the car out of gear with the clutch, and restart it with the clutch. Thus, the clutch is active the whole time.

I wonder how to test it? I can pull it and put a multi-meter on it. Maybe that'll do it.

I wonder if it would throw a code or not?
B

It's definitely not going to throw a code and yes you test it with a multimeter. My multimeter has a continuity tester but yours may not, only thing I can suggest is doing an ohms test if you have no continuity tester and just watch the read out. Take the switch out, hook up a multimeter to the contacts and then depress the switch which should give you continuity. In my case, I found a few things with the switch. When you press the switch down, as it's being pressed, there is continuity, then pressed more it lost continuity. Clicking the switch all the way gave continuity some of the time.

So, first thing I did was "scratch" the electrical contacts in the plug where the harness goes in as I found a little corrosion on there which I think was affecting the readings I was getting from the meter. Anyway so after I noticed it was working intermittently, I just pressed the button like several hundred times, twisting the button, just doing that a bunch of times and then I tested for the continuity once again. I guess what it did was re-scratch the contacts inside which were probably slightly corroded, revealing fresh metal to make contact with. Now when I touch the switch half way-all the way, there is continuity which is how it should be. To confirm that this worked, I put the switch in the freezer for several hours and tested it again while still cold, still had continuity.

I haven't started up the car since I've fixed to confirm that I indeed fixed that switch because I'm in the middle of cleaning the interior so I can't drive the car (seats are removed).. There is nothing worse than having an intermittent switch. Anyway if I have any more issues with the cruise, I'll just replace the switch now that I know the issue is with the clutch switch.

[benfrogg]

Well, I tested it.
More correctly [I]them.[I] There are actually two of them. The top sensor that has an open circuit when the clutch is up and completes a connection when the clutch is all the way to the floor.
The lower sensor does exactly the opposite because it is engaged when the pedal is in the same position, whereas the upper switch is not engaged in the up position. This switch also functions as the bump stop/free play adjustment for the clutch.

Observations:
The upper switch functioned flawlessly. The lower switch (which is supposed to be open circuit when the clutch is up) was open, but made contact twice through the movement of the switch; it also wasn't always giving contact when the clutch was down, which would certainly confuse the ECU.
The car doesn't seem to drive any differently, but I've got some highway drives this week to see if I can recreate the lean burn condition.

Also--
Excessive wind dramatically reduces my FE. A trip that normally nets 65-67mpg will go down to 55-58mpg in a strong headwind. We've had quite a bit of wind the past few days to boot.

Thanks for the heads up, let's see what changes.
B

[imzjustplayin]

Originally Posted by benfrogg

Observations:
The upper switch functioned flawlessly. The lower switch (which is supposed to be open circuit when the clutch is up) was open, but made contact twice through the movement of the switch; it also wasn't always giving contact when the clutch was down, which would certainly confuse the ECU.
The car doesn't seem to drive any differently, but I've got some highway drives this week to see if I can recreate the lean burn condition.

Well I tested the car yesterday because I had to smog the car AGAIN despite smogging it last year and passing with flying colors. So I put a seat back into the car and drove it around before smogging it, which gave me the opportunity to test out the clutch switch that I had recently "repaired". Turns out the repair was successful because now I can use cruise control when ever I feel like it, no second guessing whether or not it'll engage despite the switch being on and being above 25mph.

As for you, assuming you think doing lean-burn is "easy" for you, I would try and disconnect that lower clutch switch and see if you can do lean-burn at all. Since a disconnected clutch switch would be the same as pushing in the clutch which might signal to the ECU, no lean-burn is allowed. In the mean time, maybe you could try what I did to "repair" my clutch switch or just replace it outright.

[benfrogg]

I did try the repair, although I forced some QD electronics cleaner into the switch while doing it. After cleaning, it tested fine. There's no extra contact point in the switch anymore. I think the upshift light might be a little more relevant now, we'll see.

I'll have to do some driving with it not so windy to determine how much effect it had.
B

[imzjustplayin]

Originally Posted by benfrogg

I did try the repair, although I forced some QD electronics cleaner into the switch while doing it. After cleaning, it tested fine. There's no extra contact point in the switch anymore. I think the upshift light might be a little more relevant now, we'll see.

I'll have to do some driving with it not so windy to determine how much effect it had.
B

So what you're saying is, the switch works properly now? If so, do some testing with the working switch and then with the switch disconnected so that I can use this thread as a reference to what happens when you have a dysfunctional clutch switch on the VX/HX.

[benfrogg]

Okay, I'll see if I can find some time tomorrow.
The plug is very difficult to get unplugged, or was the first time anyway. It's located up under the fuse box, behind the pedals, etc. I'll see what I can do.
B