92 VX only getting 33mpg

[thewizard182]

----Edited to update progress as i check things, so people don't have to read the whole thread - last edit 1/31/08---

Started with 33mpg
Best tank so far with california ECU 43mpg
Swapped in Federal ECU and got 49 mpg

Background info:
90% highway driving, 100 miles a day
Average speed is 55-65mph
I don't drive like a hypermiler, but i do get passed alot
No CEL on
It is a california car, has the l00 ecu but has a 5-wire o2 sensor. Apparently this happens sometimes on the 92 models.

So far i have changed/tested:
Switched to VX rims and 175/70r13 tires losing a total of 44lbs
Compression tested 170-180 all cylinders
Replaced zfr5f-11 spark plugs with zfr4f-11
Front calipers not dragging
One of the rear drums had a little resistance, will check further
Checked O2 sensor, readings posted below
Checked and adjusted timing
Swapped in federal ecu

So far on the list to do is:
Get alignment
Check EGR (my egr ports on manifold look to be welded/sealed up, is that normal?)
Check vacuum

What else should i check?

[brucepick]

My favorite tire size calculator:
http://www.wickedbodies.net/Tire-Size-Calculator.htm

Completely aside from rim size, if the overall tire diameter is different from that of the original spec tire then your speedometer will be off. Larger tires would mean you've actually driven further than the odometer shows. So use the calculator to check your current front tire size vs. the original spec size. It will show you the % difference.

[jadziasman]

Check your engine vacuum at idle then slowly increase it to 3000 rpm.

If you don't have at least 20 inches of steady vacuum under these two conditions, then you have a compression issue in one or more cylinders. An exhaust gas analyzer would help to confirm if your VX is running super rich.

My 92 VX holds 24 inches of vacuum at idle and at 3000 rpm. I'm getting about 42 mpg but I live in Michigan and it's been cold lately. I average 44 mpg over the entire year. You should be able to achieve this easily. I'm running the 175/70R13 size now on the OEM VX wheels and have lost 1 mpg or so from what I had with the stock 165 width. I drive 70% highway at 70 mph.

[thewizard182]

That is my tire corrected mpg.

I will try and test the vacuum later and do a compression check.

Thanks.

[thewizard182]

Haven't got a chance to check anything yet, but i did pick up some VX rims. Spent all day stripping the green paint off of them, I'll either paint them white to match the car or if I'm feeling bored try and polish them.

The car seems to run just fine, except for the low mileage. The only thing is it makes a little noise with the clutch out and the car in neutral, goes away when you press the clutch in. Not sure if that is normal or not though as this is my first honda, and first front wheel drive car.

[jadziasman]

You might have a bad bearing in the transmission. It is usually one of the two ball bearings on the mainshaft that goes bad eventually - especially when the axle seals leak. Don't let it go for too long or the bearing may fail - which will trash the tranny altogether. I was lucky to catch it before the cage broke. The ball bearings were all gouged up. The bearing issue should not affect the mpg issue though.

I replaced the bearing myself but it isn't a easy one man job. The toughest job is pulling the tranny from the engine. The dowel pins hold the tranny pretty tight to the engine. I did this with the engine/tranny still in the car. You might as well put a new clutch in while you've got it apart.

[Jonathan_ED3]

It could also be something like a caliper that is dragging.

Or a wheel bearing that is going bad and dragging.

Also check your alignment and all related suspension components.

How fast are you driving on the highway? I get the best mileage at 60mph...anything over that and the mileage drastically decreases.

jadziasman...which bearing did you replace? You make internal transmission work sound like a job for a novice, which to my understanding wasn't? lol.

Can you provide a little more info? I've got 230K+ miles on my transmission and am getting ready to do a clutch job, and if it's something a mechanically inclined guy can do, please let me know as I wouldn't mind replacing any bearings that I can access.

[StorminMatt]

Originally Posted by thewizard182

The car seems to run just fine, except for the low mileage. The only thing is it makes a little noise with the clutch out and the car in neutral, goes away when you press the clutch in. Not sure if that is normal or not though as this is my first honda, and first front wheel drive car.

It depends on how much noise the transmission is making, and what kind of noise. The fact of the matter is that ALL transmissions will make SOME noise when spinning in neutral. And this will cease when you disengag the clutch. If this noise is just a fairly subtle sound that kind of sounds like water flowing in a faraway mountain stream (for lack of any better way to describe it), then you are okay. But if it is a louder hum, howl, whine, or grindy sound that you just can't ignore, then you have problems. Of course, you have a choice here - tear down the transmission or replace it. Replacement is certainly MUCH easier,and likely cheaper, too. But you risk getting another bad one. Replacing the bearing is a much more sure fix. But if you are not familiar with tearingdown transmissions, then itis probably not the best idea. Since D-series trasmissions are cheap, you can always get one used, replace it, and pracice working on your bad one to gain more familiarity.

As for your mileage, this doesn't sound right. I get the same mileage with my CRX that is powered by a 200HP JDM ITR motor. And I drive that car 80+MPH on a daily basis.

[thewizard182]

Originally Posted by StorminMatt

It depends on how much noise the transmission is making, and what kind of noise. The fact of the matter is that ALL transmissions will make SOME noise when spinning in neutral. And this will cease when you disengag the clutch. If this noise is just a fairly subtle sound that kind of sounds like water flowing in a faraway mountain stream (for lack of any better way to describe it), then you are okay. But if it is a louder hum, howl, whine, or grindy sound that you just can't ignore, then you have problems.

Water flowing is a decent description of it. It doesn't sound like an obvious problem to me, i didn't notice it until driving the car for a few days. Most other people can't hear it. I'll have to have someone familiar with hondas sit in it and see, but i think it's probably ok.

[thewizard182]

Spark plugs were zfr5f-11, I changed them to zfr4f-11

I changed out my rims and tires and lost 11lbs per corner for a total of 44lbs. Better acceleration and much easier to turn. Previous combo was 16" tenzo dc-6 and 205/40 falken azenis tires and weighed 35lbs. Vx rims and tires weighs 24lbs.

Compression check was 170-180 on all cylinders.

Should know if any of this helped in a few days as I drive around 100 miles a day.