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  1. #1

    Default 1994 suburban smog

    getting 350 ppm HC reading at idle and 46 at 2500rpm everything else passes, what would cause this? low compression?

  2. #2


    Worn out cam, or low compression. I've seen readings like that with as few as 100,000 on the 5.7. Unless you have to pass emissions or worried about power, I wouldn't worry about it.

  3. #3


    ya it needs to pass smog, think this might be the last year for the suburban haha almost 300,000 miles on original engine, no work ever needed

  4. #4


    so i did a compression test and i was getting about 115 psi on all cylinders that seems pretty low is that low for these?

  5. #5


    Make sure the truck is nice and warmed up before you bring it in for a smog test. That is the biggest problem usually.

    Take it out for a nice long highway drive and blow the gunk out before the smog check.

    That compression does sound low but then with that man miles that is to be expected. The truck doesn’t have to pass new truck standards, just for the year it was made.

    If you know the guy doing the test he just might let you rev the engine up to where it will pass. Just a thought.

    Technology is great, when it Works,
    And one Big Pain in the Ass When it Doesn’t.
    Detroit Iron Rules, All the Rest are Just Toys.
    94 GMC Burban, 5.7L (350), 4X4, Auto
    86 GMC Burban, 350, 2 WD, Auto
    79 GMC pickup plow truck, 400, Full time 4X4, Auto
    86 Pontiac Fiero SE, 2.8L, Auto, only mid engine American car
    See a Pattern yet?

    15 year GM assembly line worker.

  6. #6


    might run a can of seaFoam in the vaccc side and in the fuel tank and a can of engine restore in a fresh oil change and run for 2 tanks worth of gas and drive untill good and warm and retest....i bet all pickup and passes. i got 321,000 miles and original cats and O2s and she passes just fine and gives me 18MPG out of the 35 still.....mike
    Michael Collins
    1993 4X4 Suburban
    many other toys as well

  7. #7
    Legend unplugged's Avatar
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    Sep 2006
    High Deserts of SoCal


    Has the cat been replaced yet? Mine gave out at 240k or so. New cat and a 3" catback system only set me back $240.
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    High Desert SoCal
    93 K1500 burb (personal) 350 AT 3" Lift 250K+
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