93 'Burb with high hydrocarbons. Any suggestions?

Discussion in 'Chevy Suburban Forum (GMC Yukon XL)' started by therealtonyg3, Sep 27, 2012.

  1. therealtonyg3

    therealtonyg3 New Member

    I took my '93 Burb to the inspection lanes in Delaware to get her registered. They performed a low idle test to check HC readings, CO2 readings, Cat functions, gas cap seal, yada, yada, yada. I bought her used and (from the dead mouse carcass by the distributor), I was pretty sure that she has been sitting for a while.

    The lane inspector (who was actually nice) allowed me to run the test three times. I wasn't sure if he was really trying to get me to pass, or if he was wasting time until 4:30, when they close. Anywho, She failed on the HC. The readings were off by 100 pts. I needed to be under 220, I was around 330.

    He stated that I should do a tune up (which I was in the process of doing), replacing the air filer (done), and replacing the air pump.

    At idle she seems to stumble intermittently. Could that be ignition (poor tune-up) related? Also the guy who I bought the truck from said that he replaced the distributor. I'm thinking...not (cause it doesn't even look brand used, let alone new), but if he had, could the distributor timing affect that? Have already replaced the EGR Valve. he said also to replace the PVC Valve, but I don't see one on my valve cover. Did the 93 Burbs come with one?

    Thanks in advance...


    1993 Chevy Suburban 5.7L 350

    "If you're not chasing your dreams, you're just running in place..." Me
  2. moogvo

    moogvo Epic Member 5+ Years 1000 Posts

    Hi Tony!

    When a vehicle sits up for a long time, fuel turns into varnish and makes a mess of everything! The best place to start is to do a good tune up, plugs, wires, cap and button, PCV valve, check your filter paper and see if it looks good. [preaching] Use AC Delco plugs and wires! Avoid Bosch, E3, or any brand that doesn't come in the truck from the factory. Motorcraft is for Ford, Champion is for Dodge and Delco is for GM. Bosch is for European cars and E3 is for tractors and lawn equipment. Use the right parts, Tony... [/preaching]

    Set your base timing for sure. When I replaced my distributor last month, I was very careful to mark the intake and distributor shaft so i could get it back exactly the way it came out. It was about 10* off. Remember to unplug the spout connector before turning the distributor, otherwise, you won't be able to time it correctly. Correct base timing is 0*

    Get a throttle body gasket and take the unit off. Clean out the throttle plates and throat really good with some cleaner and a rag. Flip it over and make sure all of the veins and passages are also clean. No need to disassemble the TBI unit at this point, just make sure it is cleaned really good, then re-install it.

    Your idle issue is likely a sticking or non-working IAC (Idle Air Control) valve. This is on the rear passenger's side of the throttle body with a square connector. I believe it is 4 wires and the connector is grey. When at idle, the throttle plates are completely closed. The IAC valve has a pintle (plunger) that moves back and forth at the command of the computer to allow air to pass through into the intake with the throttle plates closed. The valve may be full of crud and/or may have a stuck pintle. You can clean it, but be very careful as these are extremely fragile. I personally just replace them since they don't seem to last long after they are cleaned.

    Those are the starting places. Also, run a can of seafoam through your vacuum system to clean it out. Start by running the engine with the brake booster line disconnected. Slowly dump the contents of the bottle of seafoam into the brake booster while working the throttle to keep the engine running. Once the can has been dumped in, shut the engine off and let it sit for about 20-25 minutes. then fire it up and let it run until the smoke clears (and there will be a LOT of smoke when you do this!)

    I wouldn't replace the air pump until you have taken care of all of this other stuff and you can see where you are.
  3. therealtonyg3

    therealtonyg3 New Member

    Thanks for all of the helpful information. I will keep you posted on how it all turns out. I only have until the end of October before my temporary registration expires. No pressure...
  4. therealtonyg3

    therealtonyg3 New Member

    So here's the lowdown: I performed a tune up and replaced the IAC valve and took her back to the inspection lane for a recheck. I wanted to say that I had no doubt that it would pass, but a small amount of doubt found a hole in my armor of faith. Anyway the mininum allowed HC on a two speed idle test for my truck was 22o..we were under by 100! I snatched the approval papers and left a trail of rubber just in case the test was a fluke!

    All kidding aside, I had an idea the tune up was going to correct the concern, seeing that the guy who I bought the truck from said that he had fixed all of these things, but he didn't. I almost went to his place of business with all of the old parts just to show him that if not he, then his techs suck.

    I look at my truck like I do my pit bull. I rescued them both from owners who were not responsible enough to have them.

    Thanks to moogvo for the help!
    Last edited: Oct 26, 2012

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