By on March 18, 2012

I’ve had more Honda Civics than any other type of car (at least one example of each of the first five Civic generations), at one point owning two ’85 hatches and a CRX at the same time. The mid-80s CVCC cars were great to drive and very reliable (provided you didn’t overheat the engine— ever), but when California tightened up smog-check requirements in the early 2000s it became impossible to keep one registered. Why? This.
If I ever decide to get a huge tattoo across my back, it will probably be this Vacuum Hose Routing Diagram for carbureted 1984-86 Civics. It’s as elegant as Harry Beck’s map of the London Tube system, yet terrifyingly complex to the backyard Civic mechanic who just wants to pass California’s dyno-based emissions test. Every time I spot one in the junkyard, I stop to check it out… and remind myself how happy I am with the bone-simple EFI plumbing under the hood of my ’92 Civic DX.
Why so ludicrously complicated? The CVCC stratified-charge system started out as a fairly simple setup: you had a big combustion chamber that got a lean air-fuel mix, a little combustion chamber that got a rich mix and the spark, and a two-in-one carburetor that supplied both chambers as needed. This worked great through the 1970s and into the 1980s, but as American— and Californian— emissions requirements got stricter, Honda had to add a bunch of auxiliary systems to ensure that the car wouldn’t spew out too much HC, CO, and/or NOx out the tailpipe, no matter what the driving conditions.
So, let’s say it’s 42 degrees out and your CRX has just hit the downhill grade on I-80 at Donner Pass. There’s a sensor to tell the car’s primitive ECU that external air temperature is below 60 degrees, another one that can tell you’re at high altitude, and yet another to detect that you’ve just backed off on the throttle. This information gets turned into vacuum signals, via a bunch of vacuum solenoids and valves, and then more vacuum signals are sent to various vacuum- or electro-vacuum-actuated devices, which adjust the fuel-delivery system accordingly. If any one of the hoses or devices in this system stops working, the car will probably run just fine… but it will almost certainly fail the tailpipe emissions test.
So (after hundreds of hours of testing and parts replacement— per car— in order to get my cars through the smog check), that’s why I got rid of my CVCC-ized third-gen Civics and swore to drive only fuel-injected versions from that point on.

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50 Comments on “Quick, Why Won’t This Car Pass the Smog Check?...”

  • avatar


    Luckily we don’t have smog checks were I live. Our SI consist of checking all of the emissions equipment, but in reality, most of your mechanics have little idea of what’s actually suppose to be under the hood of a pre-EFI engine the the inspection mainly just sticks to the safety related aspects of the vehicle.

    I have a 83 CJ7 with a AMC 258 that had a wonderful “computer-controlled” carburetor on it. It was a nightmare of vacuum lines, solenoids, wires, etc. Put in a simple manaul choke 2300 Holley (350cfm 2bbl) and converted it over to a simple-as-shit GM HEI Ignition. Runs great and I can get mileage in the low 20’s.

    The nice thing about vehicles of the era; they’re pretty simple to de-smog and make great if you know what you’re doing (and don’t live in a nazi-state).

  • avatar
    MRF 95 T-Bird

    My sister owned a 80 Civic 2dr hatch 5 speed a/c 1500cc CVCC and got over 160k out of it which for the time late 80’s mid 90’s was a high mileage car. It was great and fun to drive. What made it end it’s life and end up in the boneyard was the balky carb, apparently a common high mileage Honda issue. It would shut down after running a minute, some sort of problem with the built in electronic solenoid. You have to rebuild the entire carb to replace this part. At the time a dealer replacement was quite expensive, more than the book value of the car. I looked into a Weber, another performance carb or an after market FI unit but the installation would have been a nightmare due to the maze of vacuum hoses. The diagram looked like the map of the Paris Metro. Even if you could plug some of them off operation of the accessories and overall drivability would have been impacted.

  • avatar

    Wow. I knew exactly what that diagram was before I panned down to read. Helped a friend work on one of these in high school (head gasket, IIRC) and I recall disconnecting and folding all of this aside as we raised our eyebrows and stared at this sticker. Amazing that this was able to be engineered and implemented as reliably as it was.

    It’s so incredible, it should be on a T-shirt.

  • avatar

    There is a video that Honda produced in the early 80’s to instruct dealer technicians on the proper way to deal with customers. It was mainly just about a tech handling an irate customer because his car was taking so long to diagnose and repair.

    The main thing I remember about the film was this very image of the CVCC vacuum circuit, with the narrator saying “Modern cars can be quite tricky to figure out in some cases…”.

  • avatar

    This “vacuum logic” for fuel control is as byzantine as the “hydraulic logic” for gear selection in old automatic transmissions. The conditions became so numerous and complex that “computer logic” replaced it all.

  • avatar

    i guess every 5 degrees of warming the system change the modus operandi 3 times.

  • avatar
    Felis Concolor

    I must remember to use this diagram when someone says they don’t understand why I enjoy working on something as “complex” as a Quadrajet carburetor.

    Gauging complexity on a size chart, you’ve got your various Holleys as shovels, Qjets as D9s and Honda’s CVCC system as the dragline.

    With apologies to Sanrio: “Small engine, big headache.”

  • avatar

    Mother of God…

  • avatar

    We had an ’87 Mercury Tracer (=Mazda 323). The vacuum systems on the carburetor were not as bad as that Honda setup, but it still gave trouble after about 13 years. The rubber diaphragms in all those little vacuum servos all failed. Tried to replace them. Found out about “on back-order to Japan”. That and the horrid rear brake calipers sent this one to the crusher in ‘2002. Oh yeah, also rusted rear suspension point mountings. Don’t get me going on the whole rear suspension.

    That car also taught me that the heavy dollars you are charged for by the dealer for delivery prep are supposed to include an emissions check and a road test. That was spelled out in the FSM I purchased for it. I had to set up the “idle-up” system to make it run right when new. The dealer thinks all they need to do is remove the plastic from the seats, wash it, and install the wipers.

  • avatar

    And I thought the drunken octopi orgy attached to my Toyota’s R20 was bad.

  • avatar

    Excuse my ignorance, but I am curious…
    Does California require smog checks on 15+ year old cars ? Can you even find parts to get repairs done ? How often do you have to get this checked ? Or is it a random stop ?
    Where I’m from we don’t do smog checks so I am curious as to how the process works.

    • 0 avatar

      Can’t say definitively, and MM and others who lived in or still live in California can confirm, but I think California still smogs ALL smoo cars back to at least 1975 but could be wrong there.

      It may be a yearly thing when you get your tabs renewed or like Washington St, every other year when the tabs get renewed. The only other difference is once a car hits 20 YO up here in Washington, it is exempt from emissions checks as by then, it’s not worth it as most are scrapped due to wear and tear and reaching natural end of life cycle if they aren’t totaled out first.

    • 0 avatar

      California Air Resources Board (CARB) was once so eager to remove oil fume belching steel from CA roads they would even pay you for your old sled. I had found a 50000 mile 78 Dodge Aspen with a slant-6 about 5 years ago. I was thinking $400 – $500 tops would be nice for a second vehicle. “Air Resources sent me a letter that if I junk the car, they will pay me $600. I think I am going to simply junk it.” Destined instead of my second driver, to be in one of the China Bound scrapyards MM so kindly posts photos from. Today, instead of payoffs, they now administer the EV payoff program in CA.

    • 0 avatar

      Biennial checks are in “non-attainment” areas, pretty much any county with significant population. It is done at licensed private shops. Finding parts? You and your mechanic are on your own. There is no law requiring manufacturer support after the emissions warranty expires. If it fails, and not under warranty, the State will kick in a few hundred dollars toward repairs. More than half the cost of new aftermarket cat converters for a BMW we had was covered.

    • 0 avatar

      Well, I’ve got a ’95 Altima and I have a smog check every other year – from a “testing only” station. Older and high mileage cars get sent there, whether they ever had a previous smog problem or not.

      BTW, the “non-attainment” areas now are the entire state of California. That loophole for rural counties was part of the sale of smog measures. Now that CARB is firmly in charge, it has closed the loophole to put the entire state under its jurisdiction. Whoever said CARBs are bad for you had it exactly right.

      • 0 avatar

        Not true. Rural areas of the state only require a smog check when ownership is changed.

    • 0 avatar

      California requires emissions testing for all gasoline powered vehicles produced since the 1975 model year, 1998 model year and newer deisel vehicles. The testing is required for cars registered in most but not all counties. There was a push by Schwarzenegger and his environmental cronies to do away with the 1975 and older exemption, effectively outlawing classic car ownership in California. There was a push back by classic car clubs that was succesfull in stopping this ridiculous regulatory change.

  • avatar

    Didn’t Waldo get lost in that diagram somewhere?

    Murilee, if you ever do decide to get a tattoo of that absolutely incredible diagram, there’s a guy in Jamaica Plain, next to Boston, who could probably do the job, based on a tattoo from him that one of the barristas at my coffee jernt has.

    I want one of these diagrams. Then I can give everyone a civics lesson!

    Shoot, just seeing the photo of your old civics is making me nostalgic.

  • avatar

    That is, in essence, a circuit diagram of a vacuum based computer. Look at the circuit diagram of an integrated circuit, and the CVCC computer doesn’t look so bad.

  • avatar

    It would’ve been a lot simpler to R&R if the hoses and fittings were color-coded. It also might’ve been an unintended work of art.

  • avatar

    I know about the old CVCC as I had an ’83 Civic 1500 DX hatchback, with AC and 5spd manual. A truly great car that one was.

    I bought it used in 1992 and it had just under 113K miles on it and ran like a top, save for the clutch and the clutch cable, while they did the job, the clutch slipped and the cable was stiff. I also had the timing belt and water pump done at the same time and it was good to go.

    The only thing the car ever did from the get go was upon a cold start in the mornings or after several days of not being driven, it would briefly belch a cloud of blackish smoke for a second or two upon startup and it’d run clear after that. yeah, by 1997, the car was getting a tad cantankerous, especially in the cold mornings as it would stall, start it back up and it’d run fine after that though but by that point, I think I had around 170K+ on it.

    Always passed smog, though after 2 tries, I finally got it to pass smog in Medford Or when down there after getting a job at a podunk TV station.

    I don’t recall ever having to deal with the system ever again, just make sure it was fully warmed up before I took it in to have the smog test done and it’d pass with no problem.

    Drove that thing to just shy of 183K miles on it, though the last year I had it, it leaked water, the AC quit but it continued to run fine, even after it got rear ended. Nothing damaged but the rear frame rail and perhaps a side rail (or both) but all doors closed more or less fine, including the liftgate. The car leaked water inside and when I sold it, the rear seat was getting a bit moldy as a result.

    The 83 Civic’s diagram was pretty complex, but I’m sure it was nothing compared to the 3rd and 4th gen models while still carbed though.

    I can see the diagram as a poster and perhaps as a t-shirt.

  • avatar

    I must say, as complex as this system was, Honda did a good job of A) using quality vacuum hoses that (usually) didn’t crack or split even after 15 years (in stark contrast to the hoses Detroit used) and B) printing the line number on each vacuum line, corresponding to the diagram.

    • 0 avatar
      Athos Nobile

      Regarding B), they are needed to help the poor souls that had to put that madness together. In a cycle time no longer than 60 secs, possibly in 3-4 stations.

      Although I haven’t seen a CVCC engine, I think the spark plug wires must be also numbered. I remember that from my Isuzu Impulse and the Saipa 141.

      TPS (in this case error-proofing) in action.

  • avatar

    Forgot to mention: when you do a head gasket on one of these cars (which you’ll need to do if you ever overheat the engine), there are so many vacuum hoses going to the intake manifold that it just hangs there with the head removed. In fact, it’s held so firmly by the dozens of vacuum lines that it can only be moved a couple of inches.

  • avatar

    Back in the day GM engines were all painted different colors. Orange for Chev,blue for Pontiac,gold for Olds.

    I worked in final assembly, “B” car. Emission hose routing was a nightmare. It made it slightly easier when the assembler could indentify the engine by color.

    Oh yeah then some bean counter decided “lets paint them all flat black”

    They told us it made the engine compartment look less complex?

  • avatar

    I’m dying at the concept of getting this tattooed. “CVCC 4 Life”

  • avatar

    This proves how well-estabilished the Honda cult was by the mid-80s. I’m sure many of these cars were traded/junked when the vacuum lines cracked.

    For a refreshing contrast, here’s the vacuum routing diagram for my 85 Chrysler LeBaron GTS (non-turbo), which had less than a dozen hoses:

    • 0 avatar

      I think Mopar went to EFI before Honda. Makes a big difference!

      • 0 avatar

        We have a 1986 Dodge Ram Van with the 5.2 (CA emissions) It has the simple 2bbl carb that our ’66 had, but with a solenoid-operated idle jet. Yes, there are vacuum lines and sensors, but nothing like that Honda. For smog checks, we just retard the timing such that it will barely idle and it passes.

  • avatar

    I had a NZ new 85 Civic great little bomb and fortunately without the plumbers nightmare o vacuum hoses the US variety got

  • avatar
    Athos Nobile

    @ Mikey

    I actually was thinking about that when I saw the diagram. How did they assembled THAT without mistakes?

    Did you put them in layers? did they come pre-assembled?

    • 0 avatar

      @ Athos Nobile….Some of the hoses were pre-assembled,and they had to be routed in a certain order.
      In the early eighties we ran “B” American, and Canadian Pontiac. each came with its own engine options,including the rare Buick V6.
      Every engine had different hoses,and routing.

      Mistakes! Oh yeah we also ran the “famous” Diesel, “A.K.A reworked Olds 350”. I wonder how many GM buyers were soured for life after buying that Diesel.

      Find a way to blame the UAW for that mess.

      • 0 avatar
        Athos Nobile

        Thanks. In Venezuela the Caprice and Malibu had plenty of “Made in Canada” parts sprinkled generously inside the engine compartment.

        “Find a way to blame the UAW for that mess.”


  • avatar

    I had an ’85 Prelude with dual carbs (meaning a similar but more complicated diagram). I learned really quick how to mark hoses with pieces of tape when having to disconnect them. I actually thought it was fun, and was proud for having that diagram memorized (at the time)! Yes, I am a bit crazy!

  • avatar

    At the place I worked at in the late ’70’s doing smog testing in Las Vegas, we had roll upon roll of vacuum hoses in all the normal sizes in the back room, ’cause we sold an awful lot of it, to Hondas and Toyotas included. The heat just killed those hoses back then. I never have understood the love of these cars at all, for many reasons, but the Carolla that decided to drop itself into reverse when I was doing the “high speed” (2500RPM) part of the test and nearly killed me didn’t help, I suppose.

  • avatar

    I owned four 1986-87 Civics (this same basic diagram was used up through the 1987 model year for the lower-trim Civics) and I used to have that chart about memorized. One vacuum leak somewhere and you are toast. God help you if it was buried deep inside one of the two black boxes, which each contained numerous solenoid valves and a gordian knot of vacuum lines.

    I had one of these running as late as 2007 (gave it to my MIL), when the 2007 Chehalis flood wiped it out while parked at a repair shop waiting for an ignition switch. It was a one-owner, pristine car with just over 100K miles on it. The A/C system still worked flawlessly at 20 years old with its original R12 charge in it.

    I will never own a carb’d Honda again. And even if you want to, NOBODY out there in mechanicsville knows or remembers how to work on these any longer.

  • avatar

    There’s an old trick that people use around here on pre obd2 cars to get them to pass the smog check. They put about 5 gallons of fuel in the tank and add a 16 oz. bottle of isopropyl alcohol to the tank. It even makes worn out oil burners pass.

  • avatar

    the easy answer is just to get an 86 or 87 Si model! goodness, those were fun little cars. i will own another one..

  • avatar

    It’s the gulp valve.

    Always the gulp valve.

    In the “old old days” the dern’ trouble-making younguns’ would move spark plug wires around to harass the older folks.

    When the “smog years” hit hard the cars/trucks with 5 or so mile’s worth of vacuum hoses were the targets of the varmints who would move, remove, alter the routing, etc. of some or more of the vacuum hoses making life miserable for the targets of the neer-do-wells.

  • avatar

    Yikes! That diagram needs a couple more colors to be readable.

  • avatar

    Funny to see this post. I just bought a pristine ’82 Honda Prelude and was puttering around the engine compartment over the weekend. It runs fine, as long as you pay attention to the proper starting procedures, but I took one look at the vacuum line chart (similar) to this one and was amazed. The CVCC engines were engineering marvels at the time, but, but by the 80’s, the emissions issues were getting serious. Luckily, I live in a state without emissions inspections — I plan to drive it until it says “no more”.

  • avatar

    It looks just like the Tokyo Subway map, maybe that was inspiration.

  • avatar

    I’d loved my ’83 Civic S 1500 hatch… 160k flawless miles, 30 mpg easy. By today’s standards it would be considered dog slow, but back then (and as 16 year old) it seemed very quick.

  • avatar

    If CA is so bent on reducing smog, why do they insist on building all those huge housing tracts, freeways, and strip malls? Why do drivers insist on owning SUV’s where it rarely snows? Why did they do away with the light rail in LA?

    Also, they can’t blame Detroit for smog and sprawl, when Imports dominate there!

    • 0 avatar

      1. People buy them, because people can’t afford to live near work, or don’t want to live in crappy urban areas.

      2. The SUV problem is everywhere, not just in CA. What do SUVs have to do with snow?

      3. LA does have a subway system.

    • 0 avatar

      The smog doesn’t dissipate readily because it’s trapped in valleys and basins.

      LA actually has one of the smaller carbon footprints of a major US city because of generally good weather and relatively new housing stock.

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