By on May 12, 2010

TTAC Commentator Daanii2 writes:

Hello, I enjoy your Piston Slap column. My question is this: my 1994 Honda Accord gets less than 10 miles per gallon. In fact, in mixed city and highway driving it gets about 7 miles per gallon. The figures are supposed to be 20 in city, 27 on highway, and 23 combined.

Is the car just drinking gas because it’s old? It has less than 100,000 miles on it. It has been maintained fairly well (although the paint has peeled and looks like crap). The idle is a bit rough, and seems to be getting rougher.

If something can be done to get better gas mileage, I’d like to do it. If it’s time to put the car out to pasture, though, I’ll do that too.

Sajeev answers:

Unless a train hits a Honda of this vintage, it can (and rightfully should) last forever. Don’t sweat the paint, many USA-made cars from the early 1990s have clear coat issues. I heard (but cannot verify) that a change in EPA paint booth regulations at this time caught all auto manufacturers with their pants down. No matter what, a quality aftermarket re-spray (scuff and shoot, as they say) shall get the cosmetics up to snuff.

Now to your somewhat loaded question about fuel economy. But first, a slap on the wrist: telling me that the car is “maintained fairly well” is quite meaningless. I can’t narrow down the list of things needed to keep an old car running at peak efficiency with that! So dig through your records and see what parts were replaced at what date.

Got your records handy? Good, here’s the kitchen sink of replacement items that you must account for: inspect and replace any gooey/cracked/stiff vacuum lines, normal tune up items (spark plugs, wires, PCV valve, fuel filter), oxygen sensor(s), and any associated engine adjustments that may come whilst changing a timing belt. If the basics don’t cure the problem, addressing a blocked catalytic converter or performing a compression test might be in your future.

So yes, something can be done. All of which is child’s play to any competent wrench running an honest shop. So tackle the list and the Honda should be a much, much happier machine. And you’ll have a reliable and enjoyable machine for a fraction of the price of any replacement vehicle, new or used. Good luck.

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44 Comments on “Piston Slap: Making a Maintenance Accord...”

  • avatar

    Catalytic converter? Dead cylinder? Cheap fix? I don’t think so. Sounds like potentially you have a 16 year old car nearing 100k with bad paint facing major repair. Wholesale value of your sled around $1,000 with no major problems. I would take time to assess before leaping into a paint job or costly repair. If it is only plugs or an oxygen sensor, makes sense to repair.

    • 0 avatar

      On the other hand, if $1,000 into this car will give him another solid year of driving it could be worth it. I’m assuming that this car is paid for… if he goes out and buys a new Civic or Accord, he’ll lose much more than $1,000 in depreciation, not to mention the sales tax alone to buy another car.

    • 0 avatar

      When it comes to this vintage Honda, I’d have no qualms getting a replacement engine from the junkyard. $800 plus maybe another $600 for the install.

      Tell me where you can find a car this fun to drive, this practical, etc for the cost of insurance and a $1500 motor swap.

  • avatar

    Great deity of your choice. 10mpg in an Accord doesn’t just happen and you “think” something’s wrong. It either happens suddenly and the car’s driveability goes to crap or it’s the result of a lengthy pattern of neglect. No car of any age should have such a disparity between its actual and expected fuel economy. A reasonably well maintained vehicle that’s 20 years old and 150k+ miles should still get more than half (probably more than 3/4) its original fuel mileage.

    Are you sure you don’t have a leaking fuel tank or line?

    • 0 avatar

      Neighbor kid siphoning gas for his Mustang?

    • 0 avatar

      That or a hole in the tank. Notice a pool of liquid that smells like gasoline wherever you park?

      Seriously though, there is no way that an Accord gets 10 mpg without running in the 11’s

    • 0 avatar

      <10mpg? Holy Cow!

      Why do people always wait so long to call their doctor?

      It would take a hell fo a leak to cause <10mpg.

    • 0 avatar

      “Seriously though, there is no way that an Accord gets 10 mpg without running in the 11’s”

      I laughed hard at this. Thanks Detroit-Iron.

    • 0 avatar

      I’ve got a 58 Chevy that gets better gas mileage than that (12 mixed, 16 highway). I would have started worrying as soon as the mpg dropped below 18. How long has this been going on? A locking gas cap might fix it. Knew a farmer that was having gas stolen from the tank he kept out in the fields. He changed the tank over to deisel and had the culprits, or at least their car, within the week. Maybe somebody is siphoning gas from your car on a weekly basis. Also could be a fuel leak, though that would be rather aromatic and hard to miss. There are so many things that could be wrong that the next step would be a mechanic.

    • 0 avatar

      Yeah, that’s what I was thinking; that or Edutorian’s neighborhood kid theory.

      My Accord, while 2 years younger, has more than 2x the mileage than this poor dude’s.

      Paint looks like absolute crap, but it’s paid for, and gets between 27-33 mpg in mixed (mostly idling on the freeway) traffic.

      This thing is a beast. I started reading TTAC several years ago when I thought the machine was going to give up the ghost. It is becoming steadily apparent that ‘giving up the ghost’ will require a cliff, a tractor-trailor, and-or a bazooka. It’s amazing how much abuse this car can take (and I can give it, knowing that it owes me nothing.)

      Mid nineties Hondas: the worlds perfect $hitbox.

    • 0 avatar

      My ’95 G20 was getting about 12 mpg in mixed (though, to be fair, mostly heavy stop-and-go city driving in a very hilly area). Tough environment, but the gas mileage was very bad, nonetheless. New oxygen sensor later, and it’s back to the low-20s in the same driving environment. It has 206,000 miles on it. I say, even though the Accord isn’t worth much, unless you can swing an imediate car payment/cash transaction (i.e. you’re driving the Accord because you don’t want to spend the money you have, not because you don’t have the money to spend), dip into the repairs. My car needs nothing else right now, I’m gunning for 300,000 miles (as I see it, the only thing that could stand in my way would be an auto trans failure, although it’s in great shape right now), and the double gas mileage should pay for the $145 oxygen sensor within a couple of months.

  • avatar

    Are you sure you’re not driving an RV? An Accord should *not* be getting 10 MPG. My parents actually had a 94 Accord and it never got horrible mileage like that. Take it to a mechanic with a clue for an assessment and go from there. I’m thinking plugs and wires, air filter, fuel filter and maybe an oxygen sensor are the minimum items you should be replacing. But a good mechanic will be able to tell you for sure. Good luck.

  • avatar

    I don’t mean to offend, but how are you calculating that? 7-10 mpg in an Accord is beyond belief, barring a fuel leak or siphoning losses. Aside from the rough idle, how is the driveability?

  • avatar

    Something is dreadfully wrong with this car. I once had a car that was not running quite right and got 7-10 mpg – it was a 5000 lb 63 Cadillac Fleetwood.
    First, I hate to sound condescending, but how are you checking your mileage. I presume that you are filling it, driving it, then doing actual math (with a calculator) of miles/gallons used. US gallons. And don’t rely on the trip odo – maybe it is not working right.
    Second, assuming this is ok, my first thought is a fuel leak. A car this old could have a small tank or line leak. Do you park in the same place every time? Look for evidence of a leak either where you park or under the car.
    If no luck, have a friend drive the car while you follow in another. If this thing is really using that much gas, the exhaust ought to be black. Or, if the cat is working overtime, you ought to be able to smell the exhaust, which should stink like crazy. And the car ought to run like absolute crap.
    Another possiblity, are the brakes hanging up? The car ought to coast well. If it does not, maybe you have a sticking brake caliper.
    Otherwise, I do not deviate from most of the above suggestions.

  • avatar

    Based on a problem I experienced with a Nova/Corolla model of only slightly older vintage during my HS days, I’d posit that there might be a breach somewhere in either the filler neck or upper portion of the fuel tank if you’re not seeing spots after departing a parking spot. And you don’t always smell gas that’s evaporating because of climactic variability.

    Gas evaporates quickly, and the mileage numbers you are seeing is what I saw before I realized the problem was from a hole in the filler pipe. Mileage went from about 40-45 to 15mpg without any power loss or other driving maladies, for the record, before the patch.

  • avatar

    Question: when you park the car for the evening, do you leave it running? If so, that’s probably your problem right there.

    If you’re getting 10 mpg in a car that should get 30, you’re either ejecting 2x as much gas as you’re burning, or you have 2/3 of your power being lost in friction somewhere. How is driveability and power? Does the exhaust smell very rich?

    If both those are fine, you have a leak or someone is stealing your gas. If your exhaust smells clean but you lack power, you may have a locked up brakes or something. See if your wheels are really hot after a drive. Could also be massive blow-by with a clogged PCV.

    If your exhaust smells like gas & you lack power, replace the plugs, cap, rotor, and wires first followed by sensors, starting the the O2 sensor.

  • avatar

    I would add checking the evaporative emissions system to Sajeev’s list. If the seal is bad on your gas cap, or there is a leak in the tubes and canisters that contain the gasoline vapors, then your fuel could be evaporating out because the system cannot contain the fumes.

  • avatar

    probably a weeping leak in the gas tank. I had an old mazda b2200 once that started getting crappy mileage. It turned out to be a leak right on the seam of the gas tank which was right at half full for the tank. So when i would fill it up, it would slowly leak down to half a tank if I wasn’t driving it off first. My solution as a broke college kid was so only fill it half full :) I did eventually get some time and nice weather in the summer to get under there with some putty and seal it back up, a cheap and reasonably easy fix that should get you another 10 or 20k miles out of it.

  • avatar

    If it’s not the gas leak as others have said, I just can’t imagine the car still runs right with if it is producing that kind of mileage. The car should stop running way before there is that kind of discrepancy. I assume your car has an automatic transmission, are you sure it’s shifting correctly? If your car is stuck in a low gear that will cause your fuel consumption. Besides that, it will most likely be a sensor. You need a good tech that will be able to hunt down this issues. Are you sure you don’t have a Check Engine Light? Besides that, all your usual maintenance needs to be done, to make sure it is not what’s causing your issue like Sajeev said. Plugs (NGK platinum properly gaped), Wires, new PCV valve (get this from the dealer, the correct flow rate is very important), check vacuum hoses, replace the air filter, and fuel filter, get a fuel induction service performed, and even new O2 sensors might be a good idea. I still shouldn’t think anything like these maintenance issues should cause your car to consume that much fuel and still run, but should be done anyway and could cause a different issue to have a more severe impact.

  • avatar

    Drop a hundred bucks at a decent Honda shop and let them tell you why it’s getting such poor economy. It does little or no good to just throw parts at a problem. Get a diagnosis, and either let them fix it, or do it yourself. It could save you some dough in the long run.

  • avatar

    If it is your O2 sensors, your cat is probably toast by now too.

  • avatar

    in the case, the problem is more likely completely out of left field/non-mechanical. c’mon if you’re really getting 10mpg you’d notice an obvious symptom of the problem (pools of gas, nasty exhaust, noise, etc).

    +1 for someone stealing your gas or
    double check your math or odometer, lol

  • avatar

    Is there any air in the tires?

  • avatar

    The O2 sensor will not cause 10mpg drop.

    I would go and take out 1 spark plug to see if it has a lot of black stuff on it.
    If this is the case, I would say, you get too much fuel into the cylinder at once. Look at the fuel line right before the injectors. There must be a little cylinder there, which is a fuel pressure regulator. If that part is not working you will burn a lot of fuel.

    You can measure fuel pressure on the out port. You will need a gauge and to know normal pressure (25 to 60 pounds of pressure – call dealer).
    You can try do disconnect vacuum hose. You should see increase in pressure. Check if the vacuum hose to the regulator works.

    Basically, I suggest to start with fuel pressure regulator. The numbers and “how to” stuff can be researched.
    I am surprised that people here and Sajiv himself are diving into the theories while it is rarely anything like that happens. Mostly it is simple things, like something old and rusted out.

    • 0 avatar

      Fuel pressure regulator was my thought too, although when mine went out (in a Jaguar) it only took a hundred miles to go from running fine to running rough to barely running. But it’s very easy for any shop to check, worth looking at. Bad news is running rich may have killed your catalytic converter. Good news is replacing yours will probably be a lot cheaper than mine was.

      I’m not sure how Accords are set up, but on the Jag the pressure regulator is actually at the end of the fuel rail past the injectors, as it relieves pressure at the injectors by feeding fuel back to the tank.

      As far as the paint, I had a 93 Escort that had paint problems, so my limited experience supports Sajeev’s theory.

    • 0 avatar

      Skavuta, I must disagree.

      My Odyssey’s mileage abruptly dropped by 50% (to 9 mpg) last winter. No idiot lights, and it ran just fine…the root cause was the Denso O2 sensor(s), a nice easy fix. Wound up having to replace both because fixing the one that really matters (pre-cat) fools the computer into thinking the cat is no longer doing its job, thus lighting up the idiot bulb. Warning: this phenomenon has been exploited by many Honda dealerships to sell unneeded converters.

      Step 1: computer check, preferably a freebie at an AutoZone or the like.
      Step 2: some of the other readers’ obvious suggestions, like odometer accuracy, locking gas cap and so on.
      Step 3: pull those 16yo sensors yourself, use Bosch, drive on.

    • 0 avatar


      I gave practical suggestion. I will say, unless it is really a leak (which I don’t believe without gas smell) the fuel pressure regulator will be 99%. This is why you look at the spark plug. With bad O2 sensor you may use more fuel in the regular sort of way (as designed. as computer tells). But with high fuel pressure the engine gets flooded and spark plugs have black buildup on them. On the way, the injectors might not operate properly because of pressure.
      To have same drop in fuel economy from O2 it has to be exceptional case. Mostly O2 sensors will cause 3-5mpg drop.


      Positioning of FPR as its design could be important. Just as thermostats, it can get stuck open or closed. Also, FPR can be OK. It could be bad vacuum hose. Honestly, never saw a bad hose but plenty of bad regulators on older cars.


      No need to scare a guy with big $$$ for repair. This could be a $20 junk yard part that he needs. If the mileage is low on the car and suspension is in good shape then it make sense to invest even $300-400 for repairs. This car will have a few more years.

  • avatar

    My Explorer went from getting 16mpg in town down to about 3mpg in a tank, I had noticed it was tapering off slightly but chalked it up to a change in jobs and driving at different times. but its refill schedule was still normal, about once a week.

    Right before I went on a trip with it, I filled it up and reset the trip odometer to record mileage like I always do. Went to my buddys house to pick him up, and looked at the odometer, it said 25 miles had passed when in reality it should have been 45. We go on to Colorado in it, and in that 800 mile drive, it gained 200 miles on odometer.

    Turns out the rubber odometer drive gear had disintegrated causing the odometer to quit working well. New gear in the odometer and it goes right back to it’s normal 16mpg in town mileage.

    Just recently it nailed 25mpg on a road trip to E. Texas, and it’s got 265,000 miles on it. Not too shabby for a vehicle rated for 14 and 19,

  • avatar

    Actually, to get to <10MPG in an old Accord, everything must be broken.


  • avatar

    I keep thinking about “It has been maintained fairly well” and wondering how brightly (and for how long) the check engine light must have been on, yet no mention of it.

    Assuming the CEL is working, the gas is being lost or stolen or there is one heck of a drag on that car.

  • avatar

    Be prepared for some huge $$$ repaires. A paint job on this car will cost more than the car is worth. Accords of this vintage also eat automatic transmissions, timing belts, fuel pressure regulators, A/C components and certain engine related sensors around this same mileage point. The fact that your only getting 10 MPG or less says that something is drastically wrong but it may just be a failed component like the above mentioned fuel pressure regulator. If your cat converter were plugged you would have no power, especially on the highway. If you had a bad oxygen sensor you would lose some mileage and notice a black sooty substance on your tail pipes. Of course it could be a combination of issues contributing to the whole. If it were my car I would get it connected to a good full function scanner which will check for codes, detect misfires, bad oxygen sensors etc and then go from there. Personally I would only put the money into getting a car from this vintage running right and not bother with thousands of dollars in new paint jobs and cosmetics. It would be like buying an older house for $60,000 putting 40 grand in repairs and then selling it for 100 grand. Doesn’t make much sense.

  • avatar

    Detroit Iron: 11s ? The gentleman who does my lawn in Tampa claims his Civic runs in the high nines. I believe him, and ignore his attempts to get me out with the AMG.

    Soap used to seal gas tanks.

  • avatar

    I remember getting 15mpg in a Corolla of that vintage. The thermostat stuck open and engine would never get to the working temperature. Car computer (calculator? hamster with arithmometer?) was making the fuel mix richer to help the engine to warm up.

    I don’t think that would explain such terrible milage in May, but it worth looking into.

    • 0 avatar

      You’re forgetting the lag time between question asked and question answered. :P But I second the “go to a good shop” suggestion.

      Oh and BTW on the “farmer switches tanks” further up the thread. In my teen years a neighbor who farmed did that to his own son who was lying about taking Daddy’s gas. Didn’t get far in his late 80s LeSabare either.

  • avatar

    A gas engine needs 3 things for combustion: air, fuel and ignition (spark.)
    80% of the time, the cause can be found in the electrical system.
    Then fuel, and last air.

    If the engine is not running rough at idle (missing ignition or air leak), then I would take a hard look at the fuel system.

    Another reader mentioned the fuel pump. That’s a good start – you can have the fuel pressure measured vs. spec.
    I would also replace the fuel filter without giving a second thought. It’s cheap and relatively easy to do.

    If you have good fuel pressure and a new fuel filter doesn’t solve your low mileage problem, then just replace all of the fuel injectors. It’s not worth trying to troubleshoot each one – there are only 4. A defective injector will cause your engine to get all of its power from the other 3 cylinders, killing your mileage.

  • avatar

    My 72 yo Dad still has his 1994 Accord – won’t sell it b/c he loves it. It has 315k miles on it and still running very strong – and he lives near Chicago (though washes it regularly to clean off the salt / cancer they coat the roads in). He has the car maintained religiously and gets ~ 33mpg combined (they live in a small town so occasional city driving).

    To get 7mpg in this car – there is something majorly wrong and you should be smelling a big gas leak. The Accords from the early/mid 90’s where some of the most well built, fuel efficient mid-size cars.

  • avatar

    I’d be checking the EGR valve for that sort of mileage. Rough idle + piss poor mileage and no codes thrown is usually EGR.

  • avatar

    If you have a rusty fuel tank, that means other components are also near failure, such as brake lines and critical unibody components.

    The 10/7 mpg Accord will likely need a lot of $$$ repairs, not to mention the paint job.

    Dump it.

  • avatar

    Sheesh. I get worried if my 99 Accord’s (stick) mileage drops by 1-2mpg. I recently got 32 on a trip.

  • avatar

    Peeling paint is very common on cars of this vintage — both domestic and foreign brands. Back in the day, the Feds forced the car makers to cut paint VOC’s. Took a while to get the new formulas just right. So if your old car looks like it has a skin disease, thank the Feds.

  • avatar

    Get that Accord to a Honda shop ASAP. End of story.

  • avatar

    You’re basically wasting half of every tankful of gas that goes into that Accord, so with a 16-gallon capacity (guessing) and a gas price of $2.75/gallon, you’re wasting $22 every time you fill up.

    Like others have said, this is a no-brainer: Once you rule out gas theft and a tank leak, take it to a good shop and at least get a diagnosis. The gas savings are likely to pay for the repair in less than 10 tanks, not to mention the peace of mind you’ll have.

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