93 Honda Civic VX horrible fuel economy

[imzjustplayin]

Originally Posted by add|ct

Okay, as an experiment I've gone back to the PCV valve that was on the car when I purchased it last December.

I reviewed my records and on the 2nd emisions test attempt, this AFTER the Autozone PCV valve was installed, the HC emisions were worse. Still the reason for the failure, but worse.

Also, when I pulled the PCV valve just now there was oil on the underside where the metal cylinder was supposed to slide. My theory is, if its a low pressure PCV system it may be causing a problem with the replacement part I had previously installed. I test drove it and no light, but I'll give it a week trial run.

On a specific note, the part Autozone said was 'for my car', it was a much harder fit into the slot onto the engine. The original was much more of a perfect match and it remains quite easy to pull back off of the engine block. If its a low-pressure system, this won't matter of course.

I'm confused by this post which was in another thread of yours.. What exactly were you doing with the PCV valve and why do you refer to putting the valve in a "slot" on the engine when the confusion with this PCV valve was that people were replacing an elbow and not the valve itself? Also in that thread this post was found in, you said you had an intermittent check engine light for various things.. Do you still have that? Have you checked all your grounds? Cause I bet your area has rust issues.

[add|ct]

Originally Posted by *************

Did you clean the IACV? My civic was having that issue too and the majority of the issue was caused by a sticky/stuck IACV. (Idle Air Control Valve) Clean the EGR? A lot of these suggestions were made in this very thread which you may need to read from the beginning again. I think I should create a FAQ to tuning up these cars.

IACV and EGR, and passages, were cleaned off of the vehicle last year(before this hunting RPM would happen at idle etc).

Originally Posted by benfrogg

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If you do a write up, link it here. I think it's a good idea.

Addlct-
Did you tear off the breather box and clean it? I want to know how bad that thing was crudded up. It it was bad, I'll take the time to clean mine ASAP. If not, I'll wait till the next oil change.
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I will be removing the breather box, hopefully, at my next oil change(1-2 months). +1, on the writeup idea.

[add|ct]

Originally Posted by *************

I'm confused by this post which was in another thread of yours.. What exactly were you doing with the PCV valve and why do you refer to putting the valve in a "slot" on the engine when the confusion with this PCV valve was that people were replacing an elbow and not the valve itself? Also in that thread this post was found in, you said you had an intermittent check engine light for various things.. Do you still have that? Have you checked all your grounds? Cause I bet your area has rust issues.

I have cleaned all of my engine grounds, and even added a 4 gauge ground to the valve cover. The CEL is no longer a problem, it was only related to the LAF sensor(code 48). No codes have come on since replacing the sensor months ago.

The confusion in the post above was with whether or not the car had an actual PCV valve or not, during that post, the location in question is where the elbow seats next to the runners. No one offered a straight PCV valve on my vehicle for the actual replacement until now, because I was able to find out about the real location and knew what to hunt for P/N wise finally.

[imzjustplayin]

Originally Posted by add|ct

I have cleaned all of my engine grounds, and even added a 4 gauge ground to the valve cover. The CEL is no longer a problem, it was only related to the LAF sensor(code 48). No codes have come on since replacing the sensor months ago.

The confusion in the post above was with whether or not the car had an actual PCV valve or not, during that post, the location in question is where the elbow seats next to the runners. No one offered a straight PCV valve on my vehicle for the actual replacement until now, because I was able to find out about the real location and knew what to hunt for P/N wise finally.

Well if you don't feel like fixing the rust on the manifold in select areas, I suggest running the o2 sensor on the manifold through an eye loop copper wire and ground that to somewhere on the chassis. I'm thinking of doing this myself so I can show an A-B-A comparison of how a rusted manifold can affect how the engine runs.

[imzjustplayin]

I was reading about your car listed in your "garage" and I noticed you say you deleted your exhaust heat shield. You should put the heat shield back on because the heat shield helps the manifold retain heat and slows down the cooling off which helps reduce the likelihood of cracking your manifold. Have you checked to make sure your manifold doesn't have any leaks? I noticed in your gas log that you're noticing a discrepancy in the mpguino and your actual fuel usage.. Perhaps you have a vacuum leak? You may be able to rent for free a vacuum gauge at an automotive parts store to see if you have a vacuum leak.

[benfrogg]

The heat shield was "deleted" because it was rotten. It was hanging on by a very small piece of metal and was vibrating noisily. I assume it would help retain some heat, but I was pretty much out of options. Scrap yard shields are in the same shape in my region.
No cracks in the manifold. I've scowered it a few times.
Vacuum leaks are still possible, but that still wouldn't account for a changing discrepancy between the MPGUINO and actual; if there were vacuum leaks causing leaner a/f ratios, the MPGUINO would pick that up. I'd have to use more throttle opening to achieve the same speed. Thus, the injectors would fire for longer duration.
Good ideas though.
I'm on my first tank from a new gas station. Things are already looking promising. More on that after the middle of the week when I fuel up again.
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[imzjustplayin]

I noticed you're still getting a discrepancy in your fuel economy numbers from the tank to the MPGUINO.. Can you try for a tank or two not doing ANY EOCing? It'd be also helpful to know what kind of fuel economy you can get without going to extreme measures? I mean if you can actually get 70mpg while cruising at 55mph on the freeway and show that in your fuel log, I think we would all be able to agree that your car is running exactly how it should. I mean highway fuel economy is only one factor but it's the easiest one to control variables for which is why I suggest it. For those who aren't aware, the CAFE fuel economy numbers (1975 opposed to 1985-2007 or 2008+) on the Civic VX are around 70-72mpg and I've found that driving a steady 55mph with highly inflated tires is usually what's needed to achieve those numbers.

[benfrogg]

I can't get 70 mpg cruising at 55mph on the highway without extreme measures. No EOC and driving the car like normal person puts the trip FE to 50mpg or so. I know this because I've had others drive the car without knowing that I'm testing what a normal person's driving does at 55mph. Not to mention the fact that I've got a full underbelly, fender skirts, kammback, grill block, high pressure tires, etc. Unless the early FE numbers are just not realistic, I still say there may be some unresolved issues. It's probably just time for a rebuild.
The discrepancy in the fuel log is still there, but its smaller than before (average the numbers not individual tanks) and it doesn't vary as much. The latest fillup was an over-fill for sure. The needle didn't leave the top of the "full" mark until I was over 200 miles on the tank. In about a week I'll let you know what the new numbers are.
My girlfriend's civic is getting better FE by a similar percentage as a result of going to the new gas station. There's got to be some weight to it.
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[imzjustplayin]

Hey benfrogg, when you do your fillups, can you please note the time of day you're doing the fillup, on a warm or cold engine, ambient air temperature, topping off or not, angle the car is parked at, etc? Because when you're dealing with such high fuel economy numbers such as yours, I see small variables showing up quite obviously. One thing I noticed is that on a cold engine in cold weather, I can stuff more fuel into the tank than on a hot engine in hot weather.

[benfrogg]

*************-
Yes. I have noticed the same thing you have. I notice it more during the winter, however. After a long drive on low fuel, I can get less gas in the tank than if I'd just driven from my house to the station.
I've also noticed that if the front end of the car is lower than normal (because the concrete pad drops off and the front axle is lower than the rear) I can put nearly a gallon more fuel in than the 10.5 gallons I normally don't exceed.

All of my fillups in the log are at the same station, same pump, same orientation of the vehicle. (noted that I switched stations recently) The only variable is the relative temp/ temp of the fuel.

I'll note my ambient temp and whether I've just driven a long trip or not in the log from now on.


In other news, since using the new station exclusively, it's become clear that the former gas station was inaccurate. I've been within 2-3mpg's of the gauge since switching. That's what it was before. I won't be going back to that gas station again!
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