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air pump

Discussion in 'Trucks and Trailers' started by 84'GMC4x4, Dec 26, 2000.

  1. 84'GMC4x4

    84'GMC4x4 LawnSite Member
    from MA
    Messages: 84

    my truck recently failed the MA state inspection for emissions. the mechanic told me i need to put an air pump on it. (and of course manifolds w/the air tubes too.) my truck has a HD 350 (vin M) that came stock non-cat, but according to the mechanic it should have the air pump on it. the motor does have the bracket for the A/P but i'm not sure that it's the original motor.
    truck is 1984 GMC 3/4 4x4 w/350

    my question is, does anyone know for sure that these trucks came w/A/P?
    on a side note, how does pumping air into exhaust make it any cleaner?

    if i havent given enough info to tell if my truck should have A/P let me know.
    thanks for any help

  2. thelawnguy

    thelawnguy LawnSite Silver Member
    Messages: 2,411

    The air pump will do nothing for emissions without a cat. The airpump injectsair to "fan the fire" and make the cat run hotter.

    Post some numbers along with state threshholds and see if we can help ya get that pig thru emissions.
  3. 84'GMC4x4

    84'GMC4x4 LawnSite Member
    from MA
    Messages: 84

    Bill, that is just what i figured. air, in & of itself will do nothing to make the emisions cleaner. so the mystery remains, if the truck is non-cat from the factory, why would there be an air pump? the only thing i can think of is that the extra air might dilute the nox & co2 & whatever else is there enough to make me pass the test, which would be fine for me although i cant see the factory putting it on there just for that reason.

    i have the printout w/the limits & my test #'s somewhere, i'll post them as soon as i find them

  4. John DiMartino

    John DiMartino LawnSite Silver Member
    Messages: 2,555

    The air pump will help,even without the Cat,it keeps the exhaust very hot,especially before the muffler,as you know,more heat=cleaner exhaust.Then ther's the dilution factor-remeber they arent measuring the quantity of exhaust,just the quality,so an air pump can be used at idle only in most cases,until the engine is totally up to temp to dilute the exhaust with Oxygen.That little bit of oxygen is enough to get some trucks that are borderline to pass an emission test.If the air pump valve sticks on or rusts up and check valve leak,which is common when they get old,air will be allowed to flow ,even at high engine speeds and after warmup,I have seen the entire exhaust manifolds glowing red,the Y-pipe and front pipe totally red from the heat that adding oxygen for to long or at high speeds.You failed the visual inspection,before you even got to the sniffer right?.Do your exhaust maniflods have the bosses for AIR tubes in them,with brass plugs in them?If so thats a give away someone removing the AIR equipment-the tubes rot out or a backkyard mechanic breaks them doing valve cover gasket job,and plugs them instaed of replacing them.If i do a VC gasket job on one of them trucks-the customer drops to the ground when i give em a price-i always put new air tubes on,figure it into the price,because they always break off when you bend them down or try to remove them.As for the Air pump brackets,some engines have them even thoiugh they dont use a pump-its just cheaper to puit the same bracket on all trucks.The emissions sticker under the hood or on the radiator shroud should read like this. Non Catalyst,AIR. if you need an air pump,if it says just NonCatalyst and nothing about an AIR puimp,them you dont need it and never did-never will.Why these idiot environmentalists bother these old trucks is beyond me-there aret many on the road,and they account for hardly any of the miles run every day.I thinlk in NY if your car/truck needs more than 200 worth of work and it is more than 12 yrs old,they will give you a waiver so you can get inspected if you cant afford the fix-Im not sure if there's truth to that or not.

    [Edited by John DiMartino on 12-26-2000 at 03:48 PM]
  5. 84'GMC4x4

    84'GMC4x4 LawnSite Member
    from MA
    Messages: 84

    John, the exhaust manifolds that were on the truck when i bought it do not appear to have the holes for air tubes. (they are pretty rusty though & i havent cleaned them to get a good look)
    unfortunately the truck is very frankenstein-like, the VIN says its an 84 w/350 yet the sticker under the hood says its a 6 cylinder & the entire front end is 82 style.
    i'll have to check the A/P bracket for any signs of having been used,i assumed it had, but never checked since i didnt think it would be there otherwise. come to think of it, i think the mechanic decided that it should have AIR just because he saw the bracket there.
    perhaps the dealer can tell me what exactly it should have if i give them the VIN?

    a friend does have a set of man's w/the tubes & the air pump that i can slap on there for the test if it comes down to it. i would hate to do that though since i would need to screw around w/my exhaust pipes to make them match up.

  6. John DiMartino

    John DiMartino LawnSite Silver Member
    Messages: 2,555

    Is there any waiver or program for older trucks that need a lot of work to bring into compliance?If you took that truck to a repair shop to have the work done,It would cost over 750 easy-figure a new air pump,all new plumbing,new manifold with air tubes,new headpipes or new headpipe for the Y-pipe,labor etc....With an estimate you might be able to just get a waiver in order to register it,since the work needed is at least 1/2 the value of the truck.Here's my estimate,all Gm parts exc AIR pump.New manifolds-57 each,AIR tubes with check valves,85,air pump 105-core charge 25,AIr lines and clamps,AIR muffler and prefilter 27,belt,bolts, studs,misc,spark plugs,gaskets,70.Y-pipe mods 50.Labor- 5.5hrs -rough estimate .You end up with 480 in parts,and it would be 302.50 labor at our shop@55 per /hr.Add tax and disposal fees,you are over 800-and it could be higher if one of the bolts in the exhaust snaps in the head.I know you will do the work yourself-but i feel this is a lot to ask you to pay to clean up your cold start emissions slightly.The price could be even higher if your existing vacuum lines need to be replaced or the thermac switchesarent there or are broken off-this job,worse case could cost 1000 at some shops.
  7. plowking35

    plowking35 LawnSite Bronze Member
    from S.E. CT
    Messages: 1,687

    I have an 84 K-20 and I dont believe it has the air pump and tubes, I will look on wed to confirm. I do have an 89 k-30 and it has no cats but has dual air pumps. I also had an 86-k-30 that was the same.

    OBRYANMAINT LawnSite Senior Member
    Messages: 555

    85 blazer,305,rebuilt top end rebuilt quadrajet, a few years later it would not pass my mechanic(and others) recommended that it its close some rubbing alcohol will do the trick i think i put like a quart in to around 8 gallons passed then no probs was told only with carb and no cats

    first choice would be to waiver out if the price is right you may find your mechanic can help you with the figure if you treat him right
  9. mike reeh

    mike reeh LawnSite Member
    Messages: 229

    I had a 77 K10 with a smog pump and no cat. Also have a 77 K20, same deal (california emissions too, they started using cats in 78 AFAIK)

    Have a friend with a 79 suburban with a cat but no smog pump. theres really no rhyme or reason to it but Ive heard and read several times from different sources that the air injected into the exhaust actually helps complete combustion with unburned fuel (HC).. I admit I dont understand it fully, but thats what they say. I seriously doubt that the original purpose was to dilute the exhaust in order to pass the sniffer.

    as for the rubbing alcohol thing, Ive never heard of that one before! but im interested in how and why it works... maybe i'll look into it.. anyone know the answer to that one??

  10. 84'GMC4x4

    84'GMC4x4 LawnSite Member
    from MA
    Messages: 84

    John, thanks for all the info. i do think there is some type of waiver you can get in MA. the only caveat is that I'm pretty sure B4 you can qualify you need to have all stock smog equip on the truck, so that brings me back to where i am already. as soon as i get the time, I'll call the dealer to see if they can tell me what should be on the truck. then, assuming it is non-cat non-air i will look into that waiver. otherwise i guess i'll need to put the air pump on.

    OBRYANMAINT, i have heard about putting rubbing alcohol in the gas & also about putting white vinegar directly in the carb right b4 the test. i've never actually heard of anyone who did it though. i dont think the vinegar will work for me because the test they run now involves running the truck on a dyno up to highway speeds, and any benefit from the vinegar (assuming any) would probably be gone by then. the alcohol sounds like a better bet (if i'm brave enough to try it) did the rubbing alcohol change how it ran at all? any idea how close to the limits you were?


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