93 Honda Civic VX horrible fuel economy

[benfrogg]

I would agree with the transmission business. Please get back to us on RPMS at those speeds. I'm trying to determine the same thing in my VX.

I do have an update, for all.
Latest average in town 25%, 75% highway was 43mpg. Not great, but better. That's with winter fuel, about 100#'s in the back (I'm a drummer and travel a lot to make a living), driven almost exclusively in the rain (since it rained all week!), etc. Travel speed on highway is always between 63 and 70. There is a reason I keep it this fast- Here in Maine, the only way I can keep it in lean burn going up and down these hills on the interstate is to keep it above 63. Anything lower and I have to shift into 4th to overcome some hills. That's not helping me. If I let it roll up to 70 down hills, and keep it at 65ish most of the time, I can avoid leaving lean burn. At the same time, at this speed/rpm, I can get up the hills when I have to let it out of lean burn.
BTW, RPMS at 65 are somewhere near 2300 if memory serves. This car is LOW geared from a takeoff. It needs as much clutching as my 98' tacoma with oversized tires. Also, as previously mentioned, the tires are 175/70/r13's, and i factored this into my mpg. (add 1mile per 100 miles on the odo, says my GPS)

One thing I've noticed seems to make a big difference is headlights on or off and wipers. I say this because a 150 mile round trip highway daytime no rain with drums in the back gave me 52mpg; the best it's done. That same trip exactly at night with heat and headlights on was more like 43. I suppose it could be related to the new aftermarket altenator the previous owner just put on, but I can't be sure. Any thoughts on this one, everyone?

I'm going to pick up a parts car on friday for it. Found me a running 92' with 188k, rusted out. $200 complete! Including those sought after good condition alloys.

So, with those alloys, a swapped IAC, (mine rpms surge about 250 + or - when coasting in neutral) maybe some other goodies like swapping back to a stock altenator?, we'll see where that leaves me. I'm gonna save the motor and tranny if I can, but storage is becoming an issue. I might turn the rear half of it into a trailer, depending on the rust. And of course tow it behind my truck (89' Volvo 740 turbo wagon)!

Thanks for the replies! Let's keep this one moving and get a solution for both of us.

[benfrogg]

Oh, almost forgot two things:
I used aluminum sheet metal and rivets to make panels to block off the fog light openings and I blocked the grill about 75%. It looks way cooler and seemed to have upped the MPG's on it's own.

I replaced the rear drum shoes yesterday and hardware. I decided to do the drums because I could hear the drivers brake drag ever so slightly at one point during the full rotation. I figured it was warped, and why not for $20 each.

[PDXChrisVX]

okay, here's what I got with the newer vx...it's definitely not what it ought to be:

gear @1500rpm @2000rpm
2nd 18 mph 23 mph
3rd 28 38
4th 35 47
5th 42 58

seems to imply the tranny's not a vx.

Could there be any other explanation for this though? No one gave any thoughts on my question about low compression--say I had really low compression in one cylinder, or one wasn't firing at all...(not saying I think this the case, just theorizing)...Would this require higher engine speeds for a given speed on the road, or just use more gas and lug the other cylinders?...Put another way, is there always a direct, given correlation between engine speed and wheel speed in a given gear, or can that vary?

Lucky for me I've got an old vx motor w/ (assumed vx) tranny and axles in the garage. Recovered it from some kid that was tuning a lost vx. Paid $250 for it all. Not as good a deal as the $200 parts car with wheels, but it takes up a lot less room...

[imzjustplayin]

Originally Posted by PDXChrisVX

okay, here's what I got with the newer vx...it's definitely not what it ought to be:

gear @1500rpm @2000rpm
2nd 18 mph 23 mph
3rd 28 38
4th 35 47
5th 42 58

seems to imply the tranny's not a vx.

Could there be any other explanation for this though? No one gave any thoughts on my question about low compression--say I had really low compression in one cylinder, or one wasn't firing at all...(not saying I think this the case, just theorizing)...Would this require higher engine speeds for a given speed on the road, or just use more gas and lug the other cylinders?...Put another way, is there always a direct, given correlation between engine speed and wheel speed in a given gear, or can that vary?

Lucky for me I've got an old vx motor w/ (assumed vx) tranny and axles in the garage. Recovered it from some kid that was tuning a lost vx. Paid $250 for it all. Not as good a deal as the $200 parts car with wheels, but it takes up a lot less room...

Actually, assuming you have 175/70-13 tires, then those numbers for RPM to MPH are spot on.. Compression or anything that would affect engine performance aren't going to have an affect on RPM to MPH ratio unless you're driving an automatic that is incapable of torque converter lockup or just can't lockup. Once you release the clutch or the torque converter is locked up, there is a FIXED correlation between gear and engine speed. The only way to change this is to either remove the lockup by pushing in the clutch a bit, undoing the torque converter lockup or physically changing the gear ratios in the transmission itself.

[PDXChrisVX]

okay, that makes sense...I thought maybe I was overthinking it.

I am running 175/70 13s on this car.

I thought the engine speed, especially in 5th gear, seemed a little high, but I need to do the same exercise in the red car...I've got studded tires on it right now and haven't been driving it at all, but after one more trip up the mountain later this week, I'll be putting the vx wheels back on it, with brand new sumis in the original 165/70 13 size.

If the tranny's not to blame, then what are the big spots I might address? The car seems to be running fine, with fewer stutters than the other, and flew thhrough DEQ (emissions) with flying colors. I've put new plugs and air filter in it, with no discernible change in mileage.

The guy I bought the other vx from, the original owner, told me he was a big believer in the fuel additives ("injector cleansers"), especially for this car...credence?...

I will say that the ever-revered shift arrow has been perplexing me. Sometimes it seems normal, but often (usually during warmup) I feel like it's not coming on when I'm shifting where I should be, or where it would be telling me too in the red car.

I'll post my results this weekend for the same test with the red car....

[Fuel Miser]

Originally Posted by benfrogg

At that time, the 02 sensor was in need of replacement. I replaced it with a new one (non- cali 5 wire).

I can't help but be suspicious of the O2 sensor. It's malfunction could create your situation exactly. Don't rely on a CEL to alert you to a bad or incorrect sensor. Try unplugging your sensor (be careful the wires and/or connectors don't touch the exhaust manifold shield) and see what changes are effected. You should get a CEL on and your upshift light will not operate. See if you can still "feel lean burn happening".
Spend five minutes online searching for an O2 sensor. It's like attending a monkey's wedding, a hot mess littered with misinformation and outright fraud.

[benfrogg]

As for my New 02, all seems well with the world. I'll try pulling the plug and see if it goes into lean burn, but I suspect it wont. The old bad sensor kept the car from going into lean burn. Now it does.

So a new theoretical possibility from searching the forums and someone else' experience-
I changed the timing belt but never brought the motor to TDC. I find this step generally useless if the car runs good before, you make good reference marks, and you don't let any of the pulleys move during the process. That being said, someone said they "fixed their timing belt issue," and now they get into the 50's mpg wise. I'm wondering if this is my situation. A possible piece of evidence is the severely retarded timing. Assuming the distributor is firing based on cam position only, and the timing belt was off by one tooth, the ignition timing would be instantly off (from the marks on the cover to the harmonic balancer) as well, correct? Say 5 or more degrees retarded or advanced?

If so, which way is my cam off? My timing was retarded by around 5 degrees BTDC.
I'm thinking if this is my problem, it could also be PDXchrisVX's problem too. Just speculating.
Thanks all.

[benfrogg]

So, sort of answered my own question. I checked the cam timing today. Brought the motor to TDC, pulled everything off as though I was changing the timing belt (except the timing belt). Aligned the harmonic balancer to the marks on the plastic cover first. Cam looked off at that point (to it's two marks). After pulling the harm. balancer, I noted that the mark on the gear was not perfectly in line with the mark on the block. So, I moved it so it was (maybe 3/16"). Now the cam was exactly where it wanted to be.

What'd I learn? My marks on the plastic cover are about 1/8"-3/16" off. I made a reference mark on the harm. balancer so I could retime to it. I retimed to this mark (which is now the most advanced mark stamped on the pulley, of the three), instead of the middle mark of the three which where the car says it should be.

The question now is, what's the best ignition timing (how many degrees advanced or retarded from the center mark) for maximum FE?

I can't wait until winter fuel is out of the pumps.

B

[PDXChrisVX]

Sorry I'm so slow with this process...I finally went through the gears on the red car (the one with good mileage at 266k miles), and I did NOT get the same numbers as the blue car... second gear looks more or less the same, but then they skew a bit as I go up the gears.
@1500rpm @2000rpm
2nd 18 25
3rd 31 41
4th 39 52
5th 48 64

Granted the tires are different on the two cars (different makes), but they're nominally the same size 175/70-13. I went through this exercise with the studded snow tires still on the red car, and now I've mounted the vx wheels with the new 165/70-13s The difference seems significant enough to me to reckon it's not just slight difference in tires size among brands.

Anybody out there with 175/70 13s willing to go through this for me? Speedo read at 1500 and 2000 rpm in 2nd through 5th gears. Might be helpful to know how a cx or dx or other does with the same test.

Should I be back to the swapped tranny conclusion?

thanks,
Chris

[theholycow]

That's way more difference than could be explained by different size tires, let alone nominally the same size. Transmission swap confirmed.