VX getting lousy FE lately, what are the causes?

[add|ct]

I just can't seem to get good mileage lately with my VX. I'm ranging from 37-40(at best).

Admittedly, I haven't been able to drive more conservatively with a hospital run and higher than typical interstate speeds(65-75 instead of 60-65).

I have cruddy lower PSI in all 4 tires currently(having to run them lower)...36 max PSI(rear tires low on tread and starting to dry rot, I don't want to run them higher, and the current fronts s. u. c. k. ! )

Stop and go related, the clutch symptoms force me to use more gas; as the pressure plate/disc seem to be slipping(not sure if thats what to call it, output shaft bearing is hopefully still catching ), either way it forces me to "stay on it" more than I'd like during acceleration from a stop, especially in 1st/2nd gear obviously.

To top it off, the battery is showing signs of beginning to become flaky and perhaps the alternator is running at max output.

Aside from extreme hyper-miling techniques(EOC, even P&G), lately I've still driven in mostly 50/50 highway vs city-like driving, but a lot of my trips are of a short variety(10 miles or less), so it's been more of a go-kart mode of late. V-TEC is engaged once every trip lately, drivers are insane around here, more than usual and I'm having to aggressively merge with traffic for my area(or I'd be dead already).

Not sure what else could effect the mileage?

Fuel economy seemed to dip as soon as the hottest weather this summer kicked in. The engine, from time to time, will get a 'buckling' feel during engine braking(at the initial point that happens, especially in the lower gears), almost as if the engine 'rocking' (excessively idk?) or something? I thought of that perhaps being the motor mounts?

Now, I'm just digging, see I need some help!

I do notice improvement while using MMO, for what ever reason. FWIW. I've seen spikes from 37-38 without MMO, to subsequent tanks yielding 41-42 MPG. Could be coincidence. Just finished getting 38 MPG on my last tank(fail), and will be using MMO this time.

Before, when running 40 front/36 rear, and on a long interstate drive I could achieve about 50 MPG calculated(no MPGUINO etc to use), that was prior to replacing the 02 ( LAF) sensor. I had averaged lower 40s with a CEL for the 02 sensor, and then got mid-40s after installing the LAF, Standard Motor Products SG335, IIRC. I estimate initially the gains were 3-5 MPG once the sensor was replaced.

Perhaps I'm just not using lean-burn much? It just seems mileage TANKED this summer, no pun intended.

[benfrogg]

In my opinion, all of the things you described are attributing to your low numbers. Those things seem like they'd be more than enough to cause the drop. Do you have AC? Can I assume you are using it if you do?
My mileage/ Cd goes down a sizeable percentage when I have the window down. Especially if both windows are down. A hill that I normally see 65mph during EOC will only net 58 mph with just the drivers window fully down.
For that reason, I almost never have the window all the way down. Usually I leave it 2" from closed when it's hot. Otherwise, I bought a cheapo (>$10) clip on dc fan and keep the window closed. The extra alternator load is worth less than the increase in drag.

What about weight? Carrying any extra cinderblocks? Really though, my vx is super sensitive to weight. I'd be seeing 75-80mpg during summer if I didn't have to haul #300 of drums on 90% of my drives! I always keep the "stuff" light if I can.

I will say that if the motor isn't in perfect running condition, it is harder to maintain lean burn. And, as you know, without lean burn the VX uses more fuel than other civics that don't have it. (IIRC)
What about maintenance? How do you stand on that? What's the rpm at idle/how smooth is it?
B

[add|ct]

The assumption was correct. AC use has been a must during the day and even sometimes on the humid nights, I'm in Georgia. It's been brutal this summer...

Anyhow, I did change the spark plugs recently, around the time when the mileage started dropping. I wonder if it's worth a pull to inspect them? Maybe I damaged the plug wires somehow and didn't realize it(doubt that). They were really hard to come off the plugs, though!

I notice the VX will get the occasional 'hiccup' *not a cough or backfire etc*, during full temp idle.

I used anti-seize for the first time during the plug replacement back around the 1st of June. Perhaps I used too much and it's affecting lean-burn/combustion chamber in general??? My cylinder #4 felt 'notchy' when inserting the new spark plug into the threads(I did not cross-thread it) and it felt different from the others, in that it took more to torque it down by feel(no torque wrench). Perhaps a couple revolutions more, it sorta scared me and made me wonder if I should plan on re-threading/tapping #4 by the next plug replacement?

I may also get the engine compression tested eventually, but we'll see. A mechanic did that back at the beginning of 2010 when the car was first purchased, and it passed compression test for a blown head-gasket, but they mentioned it was done while the engine was "only warm" and not at full temp, so 'it might make a diff' according to them if it were tested again at full temp instead. Their choice to run the test warm and not after being street driven, so I never got it done, in hindsight I probably would have asked them too. Oh well?

I "do" occasionally notice the engine, upon restart after a drive that brought vehicle to operating temp(car perhaps sits 1-2 hours?), will feel like it can't decide whether or not to sit at operating temp idle or should it run up to high-idle. Perhaps the 'in-between' idle? It tries to idle near or slightly above 1,000 RPMs, but just doesn't seem 'right', so I blip the throttle a couple of times until it settles ever so slightly and doesn't concern me. It doesn't feel like IACV issues, that was cleaned well and this symptom is different from the hunting idle problems, all together. It only has happened twice, but obviously something is affecting matters. EGR valve and ports were cleaned. My thoughts regarding this were: MAP sensor(doubt it) or Ambient Air Temp Sensor?

Then again, could that all be related to the clutch somehow(?)...

I don't carry much weight, though I do have the spare tire in the hatch area and some jumper cables.

I don't think I have the underbody panel that is supposed to reduce wind drag, the one located under the back seat/fuel tank area. It's about $40-$50 to get one, worth it eventually?

PS: Maintenance...

What I thought was affecting MPG recently were 're'-worn re-man CV joints. Replaced with new ones, MPG small blip but not like I was expecting(the reman CVs went out in 12-13 months...in that symptoms appeared anyway).

Outer/inner tie rods and boots were replaced. The shop that replaced old/installed new, used the boots for the Civics that came equipped with power steering though so they couldn't 'clamp' the end of that boot over the inner(manual steering w/o PS needs a slightly longer boot), so the grease was already leaking. Its under warranty until the end of the month, worth hassling them to make it 'right'?

Timing belt/water pump/engine and WP seals replacement(@240k, currently 254k). As well as, drive belts. Alternator was checked by mechanic and was within spec, hands on. Paid the man time so...

Replaced 02 sensor, as covered. Maybe it's flaking out on me without throwing a code, the infamous grounding issue with rusting around the exhaust manifold pre-cat?

Brakes(shoes/pads) and drums/rotors serviced. MTF replaced with Amsoil MTF 5w-30 Synchromesh, this after an 18k mile run on Honda Genuine MTF.

Using Amsoil 0w-30 with half a can of Lubro Moly MoS2. Eventually plan to do extended oil changes, but working my way up there slowly. Recent UOA showed insoluble(insols) percentage was high, perhaps crud cleaning out(Ive taken such measures to 'cleanse' engine, modest ones so not surprised, I am monitoring for trending data there).

Of course, wires(Sumitomo), distributor cap/rotor, TB cleaning has been done(I used Amsoil's Power Foam twice and sprayed at the IACV while running. Currently, I have a K&N air filter, but monitoring Silicon in my UOA to see if I want to go with OEM paper filtration instead.

Valve-adjustment done, valve cover gasket replaced, leaking seals at VTEC(housing and solenoid) both replaced.

1,800 RPMs at 55* MPH(*according to the gauge anyway with 175 tires). Bled the brake fluid and clutch fluid, though didn't completely drain and replace(nervous about that). Cleaned existing engine grounds and added another for the engine. Was concerned about motor mounts but no idea of how to inspect them with the limited tools I have? Vehicle doesn't seem to run hot(nothing above norms anyway), but when I first got the car I noticed the temp gauge climbed between the mid-high mark once. This was just before the car got it's first thorough once over, tech said coolant level was down 1/2 a gallon I believe. I haven't noticed nor had confirmed coolant entry into the oil, though, so I believe it was just left too long, IMO(that is, someone didn't actually refill correctly). After the timing belt job, the replacement coolant has stayed nice and green(not perfect but good IMO) 1 1/2 years since now.

Any other questions or thoughts?

EDIT: Oh, idle RPM full temp is around 400-550. Varies, sometimes higher of course with AC or any headlights. Of course when the cooling fan kicks on as well...RPMs adjust 200-300 then idle back down.

[theholycow]

Anyhow, I did change the spark plugs recently, around the time when the mileage started dropping. I wonder if it's worth a pull to inspect them? Maybe I damaged the plug wires somehow and didn't realize it(doubt that). They were really hard to come off the plugs, though!

Could be the car doesn't like the plugs you put in, or they weren't gapped right, or they're defective. Could be damaged wires too.

I have cruddy lower PSI in all 4 tires currently(having to run them lower)...36 max PSI(rear tires low on tread and starting to dry rot, I don't want to run them higher, and the current fronts s. u. c. k. ! )

Rot of visible rubber doesn't affect pressure holding ability. Increased pressure may slow the rotting process (by reducing sidewall flex) so you may want more pressure to help them last longer. I have one rotted tire that I often run 15psi over its max.

Fuel economy seemed to dip as soon as the hottest weather this summer kicked in. The engine, from time to time, will get a 'buckling' feel during engine braking(at the initial point that happens, especially in the lower gears), almost as if the engine 'rocking' (excessively idk?) or something? I thought of that perhaps being the motor mounts?

Mounts would match that description. Also, fuel supply. Failing fuel pump, clogged fuel filter.

I don't think I have the underbody panel that is supposed to reduce wind drag, the one located under the back seat/fuel tank area. It's about $40-$50 to get one, worth it eventually?

I'm not familiar with the part, but can it be made with standard DIY belly pan materials and techniques?

Outer/inner tie rods and boots were replaced. The shop that replaced old/installed new, used the boots for the Civics that came equipped with power steering though so they couldn't 'clamp' the end of that boot over the inner(manual steering w/o PS needs a slightly longer boot), so the grease was already leaking. Its under warranty until the end of the month, worth hassling them to make it 'right'?

You do want to make sure grease stays there, whether by greasing often or by using the correct boots. It would be a shame to replace your brand new tie rods prematurely. It won't affect FE though.

Brakes(shoes/pads) and drums/rotors serviced.

Check for free spinning of wheels, a bad caliper or drum cylinder/hardware could mean sticking brakes.

Bled the brake fluid and clutch fluid, though didn't completely drain and replace(nervous about that).

You don't drain those systems. You remove all fluid from the reservoir, clean the reservoir, put new fluid in the reservoir, and bleed the other end (clutch slave cylinder, brakes at each wheel) until only new fluid is coming out. The clutch may move enough fluid that you don't need to bleed it, you can just empty+fill the reservoir periodically and eventually it'll be almost all new.

[add|ct]

Thanks for the tips, HC. I believe the VX came with this belly pan, but mine doesn't seem to have it. At least, maybe I need to double-take under the vehicle, going from memory on my post last night and it sorta hit me.

I'll see about getting the boots, re-done. Lame COA as I really don't want to go back to the shop. Someone there(an "ASE" certified mechanic) was trying to take me for a ride claiming the pre-mature CVs going out was 'rod knock'(during a phone conversation after the tie rods didn't stop the noise I heard), and that my engine was just getting too many miles(worn out) and would probably need a new engine. Oh, but not to worry they can drop in a nice performance one and that they 'have other civics' lined up for a drop. Did I mention this same ASE certified mechanic did throw out 'needs a new clutch soon', while I was there in person but didn't mention my engine had rod knock? Yet, I should just throw money at this same engine?

Ugh, makes me not want to go back there. It sounded like the mechanic that worked on my car and not the owner, so you know who will be hearing what I have to say before they touch my car again.

Anywho, I'll pull a plug or two and check, they all looked identical before I installed them(NGK 4043/stock OEM), and the plugs come gapped to .043; what the VX calls for. Though, quite frankly I don't think it's an issue with them, as it 'feels' like something else, could be missing in one of the cylinders I suppose it's possible, #4 comes to mind. Ugh!

[benfrogg]

The missing underbody panel will help a little, but doesn't explain the problem you have now. That is to say, it wasn't there before FE dropped. Fixing would help a little. I wouldn't spend the bread on the real part. I'd get something like coroplast or plastic anything and fill it in with that. There's plenty of surfaces to hook to, with small panhead coarse thread screws or tie wraps, etc.

I run 5w30 engine oil (mobil 1) in the trans. Every person I talked to said engine oil is what it took. I suppose MTF wouldn't hurt though.

1+ for checking all wheels for easy movement. Jack a wheel at a time up and spin it. The fronts will spin somewhat less than the rears. Good rears should spin for a long time on their own after you put some spin into them. You could well have a sticking brake and that would hurt FE a lot.

The extra a/c usage is very likely a strong culprit. There aren't really any alternatives though, if your climate wont allow for driver comfort otherwise.

Replace the battery if it tests bad or failing. The alternator in the VX does turn off the field (or actually, the ECU does that...) when it reaches certain parameters. Such as: battery voltage above 12.something volts, engine above a certain rpm, below a certain mph, etc. That helps with FE a fair amount and if it's not working because the battery is tired it will hurt FE. Advance/battery places can test your battery usually for free. Worth it because you don't want to be stranded either.
Good luck!
B

[add|ct]

I had the battery tested twice, once by a counter employee at an O'Reilly Auto parts place 1-2 months ago, and about 1 month ago by an Interstate Battery location.

O'Reilly's "test unit" resulted with the employee saying: "Bad battery".

Interstate Battery's employee said the battery(after being driven 6 miles to the location), had an estimated of 13.4volts at the battery terminals. This was also with the engine off, and re-tested with the engine on(at the bat term) to see what the alternator was keeping the voltage at(all at idle off course), and it was showing 14.2v or so. Their 'print out' from the hand-held tester said the battery was 'Marginal' and to replace it before seeing temps as low as 21 degrees F or extreme heat; otherwise difficulty starting may occur. So far, so good this summer as far as starting...

I suppose the following: The shot start and subsequent cut-off could yield the battery too low(or completely drained) before the alternator can put back enough?

I haven't checked for free wheel play, will do that, though I hate to use the bottle jacks I'm resigned to using(kidding).

When you mention the alternator in the VX turns off 'the field' what are you referring to? I'm still new to understanding how a car truly operates with the battery/alternator(I guess the field means the electrical system?), so I don't necessarily understand the term 'field'. Are you saying if it's operating at full capacity, under certain parameters, the vehicle won't use lean-burn or something along those lines; due to 02 sensor not being used while alternator is doing 'extra' re-charging?

PS: The car came with MTF, Honda Genuine(HG), and it was a slightly thick multi-grade 30. The newer Type-II HG is more like a 20 spec multi-grade engine oil, though truly a MTF.

Engine oil(10w-30 or 10w-40 as per the manual; modern 5w-30 okay) can be used instead of MTF if you can't FIND any MTF, it's better long-term to use true MTF as it has Friction Modifiers(FM) to help with shifting(sychros). Protection should be adequate with the M1 engine oil, but not "ideal" for long-term use. Just from what I gather, anyway.

[GasSavers_Erik]

Most alternators have a wire that supplies 12 volts to the alternator field when the key is ON. The field is part of the alternator windings. If the field is energized with 12 volts, the alternator will charge. If the field windings do not get 12 volts, the alternator will not produce any current.

On most hondas, under certin conditions, the ECU grounds one of the terminals on the regulator and this causes the alternator field not get get current and thus load on the engine is reduced and mpg increases.

[benfrogg]

What Erik said!
Good explanation, far better than the one I would have given.

As for your battery-
Part of the test procedure is to test performance under load, IIRC. I've had a few batteries over the years that performed well in the voltmeter test but ultimately weren't up to the task of starting/running reliably anymore. I'd say use it as long as you can/feel comfortable with but plan on replacing it before cold temps arrive.
Incidentally, my Volvo wagon would barely start (and often not start at all) during this past winter. The car only sees 3k a year, so it hardly seemed worth buying a battery for. It has started flawlessly all summer long. I will be replacing it as cold temps arrive this year when jumping it wont work anymore.

EOC shortly after starting could be problematic on a tired battery. A new battery would tolerate it much better. It would still diminish the life span of the battery to some (likely) marginal degree.

I'll have to swap to MTF on the next change. I've been doing it once a year or so, which is over 20k. The honda stuff is SO pricey. I know, I know, it's best, but I'll be scowering the internet for info on reputable alternatives.

B

[add|ct]

Thanks for the reply and believe cold weather will push this battery over the edge. If I didn't have to save to buy my tires, I'd probably throw in the battery for good measure ahead of time. Oh well. '

As for the MTF, I saved a site recently that sells the original Honda Genuine, but most folks have good results(it seems) with Amsoil's MTF. 1 year intervals on motor oil should be fine, otherwise. I doubt you did any real harm, if at all. I do believe I got better shift performance right away after a swap to HG a while back, it's just once the FMs were worn out the shifting got much worse(more notchy, need to rev-match a lot). The issues are worse now with a clutch that is now having slipping during WOT. The Amsoil MTF, on the other hand, has seemed to be a little more solid overall. Not sure if the dealer has the original HG MTF, but I'd try to find it instead of the newer Type-II.