Vacuum leak?

Discussion in 'Trucks and Trailers' started by KOK, Oct 26, 2005.

  1. KOK

    KOK LawnSite Member
    Posts: 4

    I have a 350 fuel inj engine in an '88 truck that started using oil really bad (quart every 100mi). Only smokes a little upon startup, but it always did that. It has 123Kmiles and didn't consume oil hardly at all until recently. I notice the idle is also very high, around 1200rpm. And the oil gets dark very quick after it was changed. PCV valve is clear. I'm wondering if possibly the intake manifold gasket could have ruptured internally causing crankcase oil to be sucked into the intake manifold and burned?? The engine runs fine and has plenty of power, just uses oil.
     
  2. sheshovel

    sheshovel LawnSite Fanatic
    Posts: 5,112

    I'd say your ready for rings.If it was an intake leak you would get a rough idle.
     
  3. KOK

    KOK LawnSite Member
    Posts: 4

    If it were rings, wouldn't there be smoke out the exhaust?
     
  4. ASEGuy

    ASEGuy LawnSite Member
    Posts: 6

    The Dodges do sometimes suck in a chunk of intake gasket and leak internally as you mention, but I have never seen it in a Chevy.

    To test for the problem, remove and plug off the pcv hose and then plug the hole in the rocker cover. On the other rocker cover, remove the breather hose and rig a fitting in the hole which will allow you to hook a vaccuum gauge to it. When the engine is running, there should be no vaccuum. A lb or so of pressure is normal. If the intake is leaking, you will have vaccuum. If it is really bad, you will be able to feel/hear the vaccuum through the dipstick tube also. (with the pcv disconnected.)

    If the cat is working good, you can blow a quite a bit of oil by the rings without seeing any smoke as the cat will burn it off. This eventually ruins the cat too.
     
  5. Potomac Lawns Inc.

    Potomac Lawns Inc. LawnSite Senior Member
    Posts: 409

    sounds like a throttle position sensor it is throttle body injected correct? I had an 88 chevy that did that forgot how much the part was under $150.00 i think.
     
  6. Jpocket

    Jpocket LawnSite Silver Member
    Posts: 2,278

    if it were rings it wouldn't have plenty of power. the motor would have less power and less compression if it were rings.
     
  7. Jpocket

    Jpocket LawnSite Silver Member
    Posts: 2,278

    if it were rings it wouldn't have plenty of power. the motor would have less power and less compression if it were rings.
     
  8. Jpocket

    Jpocket LawnSite Silver Member
    Posts: 2,278

    if it were rings it wouldn't have plenty of power. the motor would have less power and less compression if it were rings.
     
  9. xcopterdoc

    xcopterdoc LawnSite Senior Member
    Posts: 752

    The number one thing to do is pull all the sparkplugs and have a look see. Usually a high idle on these engines is caused by a clogged idle control valve and in some cases a clogged intake or incorrect timing. A vacume check and compression check would also be in order. Do the comp check while you have the plugs out. 17 to 21 in of hg vac at ilde... steady no needle bounce. At WOT(Wide Open Throttle) increase to 0. Around 110 to 120 psi on the comp check, might be a lil lower, thats ok as long as you dont have more than a 10% split between cylinders. The smoke upon start up is caused by valve guide seals. After shutdown, oil is pooled in the top of the head and seeps by the valve onto the top of the piston. Do the basic checks... these are good engines and they dont get any easier to fix or troubleshoot. Shoot me a PM if ya get stuck.
     
  10. northwest lawn

    northwest lawn LawnSite Member
    Posts: 196

    i had a vacum leak and it runned really rough and stalled that was in my 97 f250 costed me around $80.00
     

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