• The great fuel filter myth.

    The great fuel filter myth.
    Written by Jim Hopkins, Toyota Tech Adviser
    Feb 08, 2004 at 04:00 AM

    When Toyota Engineers first developed their electronic fuel injection (EFI), they were searching for a maintenance free, self regulating fuel system that would continually maintain itself in optimum working condition, with NO maintenance. A fuel system customers would just love for it's low, low maintenance.

    They knew that the fuel must be kept clean enough to pass freely through the fuel injectors, etc. without any clogging at all. For this dedicated filtering purpose "Nippondenso" developed a very special fuel filter with over ten times the filtering surface of any previous automotive fuel filter. It is inside a very strong, rust proof metal container with high quality threaded fittings, to withstand the high fuel pressures of EFI. The filter medium is carefully pleated, so a huge filter area can be installed inside a compact metal container. It is a truly fantastic fuel filter! "State of the art"!!!

    The Engineers explained it this way. Their studies had shown that in some areas the current (small) fuel filters showed anywhere between about 60% to 15% clogging after 50K km. Therefore they had previously recommended their replacement at the 50K km service, because they felt that in some parts of the world the fuel filters may not make it to the next service at 100K km with much reserve to spare. They had found however that, overall, North American fuel was relatively clean.

    There would be even less contamination entering EFI cars fuel filters, because of the new, large filter sock over the fuel pump pickup tube, inside the fuel tank that was made quite fine to protect the high speed electric fuel pump required on EFI cars. This pick up filter sock was somewhat "self cleaning" due to the sloshing action of the fuel in the tank bottom, and most dirt would just slosh off and be captured in the bottom of the fuel tank where it could do little harm.

    Unless, of course, someone dumped a full bucket of mud into the fuel tank. They reassured us that with the smaller fuel tank filler neck it was very doubtful that this would ever happen. In any case no
    filter could ever hope to cope with a humongous, catastrophic amount of dirt entering the fuel tank, and that it would require removal and cleaning of the fuel tank anyway.

    Now! Compare fuel filters! If the older style smaller) fuel filter had a filtering capacity of 100 then this new EFI fuel filter with ten times the filtering capacity would be rated at 1000. In an "imaginary"
    comparison test we could assume that since the old fuel filters may show 50% clogging at 50K km, those fuel filters were possibly replaced when 50 of their 100 filtration units were clogged at the time of the
    specified 50K km service interval.

    At 50K km the older fuel filter car would have It's smaller fuel filter replaced with a brand new factory replacement fuel filter, according to the factory recommended maintenance schedule, so it's reserve filtering capacity would be restored from 50 to 100. Since the EFI car neither required nor received any fuel filter maintenance it's larger 1000 unit filtration area would now have only a reserve of 950
    units.

    At 100K km inspection, the same recommended services would be performed, leaving the older fuel filter car with a fresh new fuel filter, with it's filtering capacity fully restored to 100. However, the EFI car would now have it's reserve lowered to 900.

    After the 150K km service the older fuel filter car would be again restored to 100 units, while the EFI car would still have 850 units reserve.

    At 200K km the older style would be restored to 100 units, and the EFI car would be left with 800 units.

    At 250K km it would be 100 to 750reserve filtering units. At 300K km, 100 to 700. At 350 K km100to 650. At 400Kkm 100 to 600. At 450 K km 100 to 600.

    And on and on………….Till finally at "one million" kilometres the older model would have it's EIGHTEENTH new fuel filter installed, restoring it's reserve filtration capacity once again to 100 units and
    the EFI car still having it's original fuel filter would also have a 100 unit reserve filtration capacity.

    Therefore it may, just may, be necessary to recommend that the EFI car should also have it's fuel filter replaced at one million and 50k km. We should live so long!

    However, if the rate of accumulation of dirt was much lower than the predicted 50 filtration units per 50K km, during this one million km. test, then the EFI car may still have a very much larger reserve filtration capacity than we calculated. The lower dirt content would not have benefited the older, small fuel filter car at all. As well, the older style fuel filter would have contributed eighteen discarded fuel filters into a land fill, and at even five bucks a filter, cost
    the customer "ninety" dollars in maintenance. Eureka! No more fuel filter replacements! Fuel filter replacement is finally just a relic of the past! WOW!

    At this time (twenty years ago) fuel filters were completely deleted from all Toyota service maintenance schedules for all EFI vehicles. The oil change, air filter change, etc., remained, and were covered in
    great detail in all factory service manuals, etc. But, all references to "fuel filter replacement" were deleted for all time from all factory service manuals. A whole half page of the factory service manual is devoted just to inspecting fuel pipes for any kinks or
    deformation (including illustrations of a leaking fuel line). Text and illustrations of the precise, recommended placement of the rubber fuel line's spring hose clamp is fully covered, but absolutely NO mention
    whatever of "fuel filter replacement". There is absolutely NO mention of any fuel filter replacement in any owner's manual (does anyone ever read them?) Do you think that the factory repair and owner's manuals
    were trying to tell people something??? Did you get the hidden message??

    The fuel filter was considered to have a service life far exceeding the projected life of the majority of most of the vehicle's other components, and was fully expected to outlast the cars. Replacement of the fuel filter made much less sense than the replacement of the fuel tank or the replacement of the ignition key, or the trunk lid emblem.

    Great! Parts people were instructed to anticipate virtually zero fuel filter sales. One less maintenance service problem??? Great! Wow! Customers would love this!!!

    But, much to the dismay of many Engineers, fuel filter replacement sales for EFI equipped cars remained telatively high. Why? Discarded fuel filters were reclaimed, opened up and found to contain almost no
    dirt at all. Why were people replacing them??? The best laid plans of mice and men often go astray! Who knew why???

    There was great concern that there was a high risk involved because some dirt could accidentally enter the fuel system, downstream of the fuel filter during the fuel filters replacement, and damage the downstream fuel injectors etc. There was also concern that all fuel line fitting gaskets, etc. would not be properly replaced with new ones, and that the fittings torque might not be correctly reset to factory specifications, as this was a very high pressure EFI fuel line.

    This part of the EFI system was intended to be serviced "only" by trained mechanics, yet it was apparent that it was being serviced by people who, clearly did not know what they were doing. There were many complaints that replacement fuel filters were much too expensive, and much too difficult to replace. Why were people still replacing them??

    Nobody seemed to know.

    Believing that the fuel filters were too highly visible they were painted black, and the Engineers tucked them up under the intake chamber where they were very difficult to see or service, on the 7M-
    GE models, to discourage needless replacement, but people kept on replacing fuel filter, despite the difficulties. Why???

    It was suggested that a sticker be applied to warn people not to replace the fuel filter. This had been done previously to discourage needless spark plug replacement. The warning sticker helped, but many
    people simply ignored the warning sticker and replaced the spark plugs anyway. Another very hard to break habit, that still continues today. Nobody wanted to commit to stating "NEVER" replace fuel filters, as
    that's a very, very strong statement. Should the sticker read:

    WARNING! Replace fuel filter every one million kilometres, or 25 years, whichever comes first!

    I think a sticker on the fuel filter stating: Warning! "This is not a fuel filter", may prove to be more effective.

    Do you think that fuel filter replacement is genetic?? My father always replaced his spark plugs and fuel filter, and I am fully committed to continue replacing mine too, and to the preservation of this fine family tradition. I don't know???? I just can't explain why
    people insist on performing these seasonal, cultural, fuel filter rituals. It must be passed down from father to son as it's been going on for over 20 years! No warning sticker can ever overcome that kind
    of dogged determination.

    Why were people in North America still replacing these costly and difficult, and risky to replace fuel filters with NO instructions or any valid technical reasons for doing so??? It soon became apparent
    to the Engineers that fuel filter replacement was so deeply ingrained into the North American culture that people just could not break their highly addictive fuel filter habits.

    I had many phone calls: "Where the hell is the dam fuel filter any way?? What lame brained idiot put the fuel filter up there where I can't even get at it? He sure didn't know a dam thing about what he was doing! I could sure teach him a thing or two about engineering
    cars." All I could say was " Why are you replacing the fuel filter?? Why?? The answer was usually " I always replace fuel filters. I won't ever risk having a fuel filter plugging up. So I asked, "Have you ever had one plug up???" Of course not stupid! Because I always
    replace them. That's why" How can you ever argue with such success???

    I suppose that if people derive some deep inner spiritual satisfaction by performing their traditional "fuel filter replacement" ritual, they
    are free to continue to do so! it's a free Country!! But I really wonder why they insist on doing it??

    Instead of applause, the poor Engineer receives insults!

    I see from reviewing many of the posts on this site that the grand tradition of fuel filter replacement continues on unabated. It continues to be, by choice, the first recommended line of attack, to resolve almost any performance problem. I see posts from owners whose crankcase breather pipes must be so badly clogged with hardened crud that a "Roto Rooter" couldn't clear them (engine oil forced out
    through the distributor??), I'll bet those same vehicles have probably had their fuel filters replaced. WHY? I have never, ever seen the replacement of a fuel filter successfully resolve any problem. Why do people always recommend first replacing the fuel filter??? Any suggestions????

    I suspect that with tens of thousands of Toyota fuel filter sales, that a great many people are accumulating a nice nest egg to finance their early retirement. Americans spend many millions of dollars a
    year on fuel filters. Would this money not be better spent elsewhere?

    Perhaps a: "I gave up replacing my fuel filter so that a starving child could eat! , type of charity. Are fuel filters car owner's pacifiers, or security blankets??

    I have cut discarded fuel filters apart , but I have never found anything inside that would ever restrict fuel flow. They appeared almost as clean as new inside?? If anyone has ever found one of these
    "Denso" fuel filters that was ever actually clogged with dirt?? I would sure like to hear from you. They may exist?? But, I have not found any in twenty years. Please post if you have ever replaced a fuel filter because there was real evidence that the fuel filter was actually restricting fuel flow, and a replacement filter actually solved the problem by restoring the fuel flow. Please post if one of these fuel filters has ever passed a particle of dirt that damaged a
    fuel injector.

    I believe that the fuel filters very, very clean passing through these fuel filters as I have not yet seen a dirt clogged fuel injector.

    I have found fuel pump residual check valves leaking from what I assumed was a spec of dirt (too small to see) as discussed in my previous post on fuel pumps, but I have always believed that this was because the fuel pump check valve was only protected only by the fuel pump intake filter sock, and not by the actual in line fuel filter.

    The fuel pressure regulator never seems to leak residual fuel line pressure. I think it's because it's fuel is all completely filtered??? Anyone ever found a leak fuel pressure regulator???

    I have only experienced one incident of fuel supply clogging, and that was because someone had attempted to repair a fuel tank by pouring an epoxy treatment inside to seal a damaged fuel tank The epoxy coating
    peeled off and completely clogged the fuel pump filter sock, inside the fuel tank, but the fuel filter was still OK. I recommended replacement of the fuel tank and the fuel pump, as it had become overheated while sucking away on it's plugged inlet filter sock. Never
    had a restricted fuel filter though.

    Please post if you have ever found a restricted fuel filter????

    Anyone???

    If you have ever replaced your Supra's fuel filter, did it improve your car's performance?? Did it bring you security, peace of mind?? This question has haunted me for a long, long time(20 years).
    Comments 19 Comments
    1. tekdeus's Avatar
      tekdeus -
      So true, I remember back when I was a teenager with my first Mk2 Supra, and figured fuel filter replacement was part of a regular "tune-up". It was incredibly hard to reach and replace, and cost way too much. I wish I had known to just leave it!
    1. toyotanos's Avatar
      toyotanos -
      Not that it's Toyota, but I pulled the fuel filter apart from my 1990 RX7 and it was full if crap! I can tell a (long) tale, but it was plugged and the whole fuel system was in trouble. New tank, pump, sock, flushed lines, filter and cleaned injectors fixed it, though!
    1. kwayne's Avatar
      kwayne -
      Yes, I replaced the one on my 87 7mgte. After 22 years it was full of crude. However, it's geat to know the new one can go another 20 years.
    1. Pyrite's Avatar
      Pyrite -
      This is really good to know. I had been looking at my fuel filter with the intention of replacingit because when i bought the car it came with an extra I see now that I will be storing that filter for a few more years.
      Thank you.
    1. bigaaron's Avatar
      bigaaron -
      We have had more then a few cars that had the fuel system rusted so bad that we felt compelled to change the filter. I guess in recent years the ethanol content in our gasoline has gone up, which seems to cause the fuel system to rust and gum up in the lines and filters on vehicles that sit for long periods of time. We have had several cars that had the rubber fuel lines turn to goo, with fuel that turned to something like varnish. A lot of people decide it couldn't hurt to change the filter when installing a new fuel pump, since most MK3 Supras are now 20 years old, or older.
    1. apexi287's Avatar
      apexi287 -
      I had one issue with a fuel filter but it would only effect me once i was at a 1/4 of a tank and lower, and it was WOT under boost I would just experience fuel cut towards the higher rpms. The rest of the time everything was fine and fuel pressure was normal, I replaced the filter though and it fixed the problem.
    1. Ash's Avatar
      Ash -
      Quote Originally Posted by bigaaron View Post
      A lot of people decide it couldn't hurt to change the filter...since most MK3 Supras are now 20 years old, or older.
      Bigaaron makes a good point here. Sure, the filter is designed to go for 20-25 years, but our Supras ARE getting to be that old! As has been previously said though, it's nice to know that the next filter will last far longer than we will.
    1. AcIdBuRn02ZTS's Avatar
      AcIdBuRn02ZTS -
      The fuel filter on my supra was almost plugged completely and when I replaced it (it was the oem piece) the car ran considerably stronger....

      However... the reason for it being plugged is the car had been sitting for nearly 10 years without running... and when I bought it... we tried to get it running... found that the fuel pump was fried... drained and flushed the 2" of sediment and rust out of the tank and replaced the fuel pump... got it running and put 3k miles on it... decided i should replace the fuel filter at that point...

      Went to change it and it pppooouuurrreed liquied rust and solid contaminents out of it... cut it open and it was CAKED full of rust and dirt... replaced with a new filter and the car had noticeably more power....

      Then again... considering how old our cars are getting... and with moisture/cheap fuel... I would say that they should be replaced atleast once...
    1. 4U2QUIK's Avatar
      4U2QUIK -
      lol this article rings true to me. Just in general, I've owned a lot of different vehicles in my lifetime, and I have only had one clogged fuel filter in my entire life!!!! and to be perfectly honest, it's usually the verly last thing I consider when having fuel issues just because of that reason.
    1. ae86ma70's Avatar
      ae86ma70 -
      I replaced mine once, took a gawd awful long time due to the location above the third member. You see, ever since i bought the car, it would run great for a few minutes and then run like a turd. I hypothesized everything. Bad FPR. Clogged injectors. Checked for kinks in the lines. Replaced the fuel filter (despite years ago having already read the aforementioned tale). I even had the previous owner replace the fuel pump. I replaced everything I could think of, upgrading each component in the process. Turns out that the fuel tank was full of rust. Pulled the (new) pump, and the sock was completely caked brown. Now I have the best fuel system possible, short of having dual pumps, or a $500 Aeromotive. So... if you've done everything else you can think of, drop the tank (or the drain plug). It's much faster than half of the things I did to troubleshoot along the way.

      And yes, I suppose that it does offer me some peace of mind to know that the fuel filter has been changed at least once in my car's 23 years on the road.
    1. mkiii222's Avatar
      mkiii222 -
      My 95 Celica had a plugged filter at around 180k. It had developed a miss that would occur at idle only.

      After taking it to the dealer to get the timing done, replacing the plugs, replacing the wires/rotor button, and still having a miss I decided to try the fuel filter. Sure enough it had some black/brown crud floating around. After it was replaced with a new Toyota filter the car ran like it just left the showroom up until it's unfortunate demise at 215k.
    1. 87nasupra's Avatar
      87nasupra -
      I had a weird miss after WOT and sometimes it would stall.....I finally decided to do a fuel system cleaning and pressure test after about a week because I had done tune-up, plugs, wires, etc. about a month before. It showed for, some reason, 20psi after WOT...then would gradually build pressure back up and miss fire was gone. I had already replaced my fuel pump with a walbro when I baught it. I pulled the filter and replaced it since it was good practice to do so when you buy a car that sits for long periods of time. Mine sat 6 months, but was cranked every couple of weeks though.....the filter was almost completely clogged. Could barely blow air through, it either way. Car ran better then before with the new one installed from Toyota
    1. BOOSTEDSUPRA's Avatar
      BOOSTEDSUPRA -
      my 87 mkiii turbo sat for aprox 5 years. in a field b4 i got it. motor blown up with rod out the side, turbo waaaaay wasted.

      when i got it running, i just changed it for piece of mind, i knew the quality of the ff and just wanted a new one since i drive this pig all over the country.

      after i replaced it a buddy of mine and myself pressure checked it, against the new one. it indeed was a little restrictive, but in no way plugged.

      in short, i replace EVERYTHING i can get my hands on when fixing up a car im gonna rely on to get me home.
    1. geartech's Avatar
      geartech -
      Very informative post. Porsche went one better. They eliminated the external filter all together and made it part of the fuel tank sending unit. Some don't even have that just the pick up sock in the tank.
      But seeing as my 87 mkIII is reaching the replacement age I might just do it if it hasn't been done already.
    1. 346fc3s's Avatar
      346fc3s -
      Both Mercedes and Mazda now run fuel filters that are part of the fuel pump assembly and can not be replaced separately. I've replaced a few fuel filters due to clogging, one was from a bad batch of bio diesel that gelled up in the filter and locked it solid. The others have both been similar to the previous stories where cars sat for loooong periods of time and the tanks were rusty. I still replace all the filters when I buy a older used car though, it's just peace of mind and a distrust of the average auto owner.
    1. gersain's Avatar
      gersain -
      i have a 1990 7mgte with 213,000 miles and i get fuel cut at 2500 when i bought the car it already had the problem and the owner gave me the fuel filter with the car
      could a bad fuel filter lead to such a bad fuel cut? i cant give past a inch of throttle or else car sputters like its choking
    1. xXSupramanXx's Avatar
      xXSupramanXx -
      Quote Originally Posted by gersain View Post
      i have a 1990 7mgte with 213,000 miles and i get fuel cut at 2500 when i bought the car it already had the problem and the owner gave me the fuel filter with the car
      could a bad fuel filter lead to such a bad fuel cut? i cant give past a inch of throttle or else car sputters like its choking
      car doesnt "sputter" when fuel cut hits
    1. Suprafiend's Avatar
      Suprafiend -
      On the old Toys I've had (about 20, all gens of Supras, many parts cars though), very few if any had any issues resolved from changing the fuel filter. However I've changed many that were restricting flow which would no doubt put extra strain on the fuel pump (and I've had many fuel pumps wear out). Whenever I change one I always blow on the intake side to see how clogged it was. A good one will give you almost no resistance as you try and blow through it. I've had many that I could barely blow any air through at all, yet the car ran fine.

      The big however though (besides dealing with old\dirty gas from sitting as many have run into), is altitude. I spent a summer working at a mechanic shop in Lake Louise, Alberta, which is somewhere north of 3000 feet above sea level, and some of the mountain passes up there are much higher. That was pretty much all we did up there, replace fuel filters all day. Any car that came in running rough, down on power, hard to start, or mysterioulsy stopped running, the first thing we would ever do is change the fuel filter and usually that was all it was. Your 1000 unit math does not take into account altitude. I don't know if the filters that were acting up were half used up or more, exposed to alot of lousy gas, or were just poor quality aftermarket ones, but we sure had to change alot of them up there.
    1. tiger956's Avatar
      tiger956 -
      Good info! when my 7M-GTE came off the transport truck in FEB of this year, i changed the oil and fuel filter. Now i'm not going to worry about it for quite a while again, though.
    Links monetized by VigLink