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egr valve?

Discussion in 'Chevy Trucks' started by Arrow, Aug 26, 2003.

  1. Arrow

    Arrow Junior Member
    Messages: 27

    Help, Hunting is 4 days away and the truck broke. It's a 95 chevy 1/2 ton 350. It started about a week ago when my truck would have a rough idle but when you gave it gas it picked up and ran O.K. The other day I started it from work and it started fine but died a mile down the road like it was starving for fuel. Tried a new fuel filter - no luck.
    Moved the plunger in and out on the egr valve and it started, but it was rough and I had to floor it to get 2500 RPM. removed the egr and found a chunk of carbon I think on the end of the rod and removed it. Reinstalled egr and it started. Tried it again a few minites later and the symptoms re appeared. I got a new EGR valve and set it up per instuction and installed. Truck fired up right away. I would press on the gas and it would hesitate a little but ran o.k.. Started it a couple more time to verify and all was well and it ran good. A half hour later I started it to go home and the same problem came back. Any ideas?
     
  2. wyldman

    wyldman Member
    Messages: 3,265

    Maybe it's not the EGR ? It could be something else.you needed to have the truck checked out,and pull the codes,to see what's going on.

    Since you've had the EGR off already,I'd pull it back off,and clean out all the passages inside the intake with an old coat hanger,to get all the carbon out.Blow them out after you clean them and re-install the EGR valve.If the problem is still there,you could try disconnecting and plugging off the vacuum line to the EGR.If the problem now goes away,you may have a bad EGR solenoid,or a plugged vent.The vent is on the back side of the EGR solenoid,just a little platic nipple,sometimes with a piece of foam over it.

    Other possible causes could be a bad fuel pump,or a plugged catalytic convertor.If messing with the EGR doesn't fix it,then take it somewhere to have it properly diagnosed.The money spent on a proper diagnosis will be much cheaper than just throwing parts at it.

    Let us know what you find,and if you need any more help,feel free to ask.
     
  3. EZSnow

    EZSnow Senior Member
    Messages: 205

    Ive been having a similar problem on a '71 vette. I'm in the process of checking for vacuum leaks... these things use vac to run EVERYTHING! My deal is a really rough and stumbling idle unless I crank it up to about 1200rpm. As soon as it's off the idle circuit, it goes like crazy, but it won't idle smoothly below 1200. Anyway, I found a minor leak and got it improved a few hundred rpm, but there must be more.

    Anyway- I can't say this is your problem, but it might be a place to look. It was suggested to me to spray WD-40 on suspect areas, or just here and there. If the motor idles up, you got your leak!

    Good luck!
     
  4. CARDOCTOR

    CARDOCTOR PlowSite.com Addict
    Messages: 1,310

    if you still have carbon at the egr valve
    remove valve block vacuum port
    start engine rev it hopefully all the carbon will blow out



    cardoctor:salute:
     
  5. Arrow

    Arrow Junior Member
    Messages: 27

    Update: 2 days till hunting. It seems as though when I start it cold it runs fine until I get to operating temp. Then when I give it gas it wants to die out. It idles o.k. Anymore suggestions?
     
  6. wyldman

    wyldman Member
    Messages: 3,265

    Next step would be to check fuel pressure and manifold vacuum.Could be a fuel pump,or plugged cat.
     
  7. Arrow

    Arrow Junior Member
    Messages: 27

    Forgot . I changed the fuel pump yesterday. When I pull the vacuum hose from the EGR valve, after the engine warms uo it has vacuum on it. When I first start the engine it has no vacuum. Is this the correct operation.
    Thanks for your help
     
  8. Arrow

    Arrow Junior Member
    Messages: 27

    Is there a diognostic procedure for checking the cat. converter?
     
  9. wyldman

    wyldman Member
    Messages: 3,265

    The EGR should NOT have constant vacuum when it is hot,or never for that matter.Only should have vacuum off idle.Leave the EGR disconnected,and plugged,and take it for a ride.
     
  10. wyldman

    wyldman Member
    Messages: 3,265

    There are three ways to check the cat.Banging on the outside may reveal that the catalyst material inside is broken up,and it could be plugged.Using a vacuum gauge,and looking for engine vacuum dropping to almost 0 when problem occurs,or the best way is to do a backpressure test,to show how much restriction is in the convertor.
     
  11. Arrow

    Arrow Junior Member
    Messages: 27

    Well, when I disconnect the vacuum hose from the egr and give it some gas it does seem to run better. I will check the cat. for loose particles later this morning. I would take it to a shop but one I don't think I could afford it and 2) I'm a tech at work and as a technician I would really rather find out whats wrong with it myself. I don't get a service engine light but should I invest the $30.00 for the diagnostic reader?
    Thanks so much for your help.
     
  12. Arrow

    Arrow Junior Member
    Messages: 27

    Although I don't have a vacuum gage handy when I unplug the hose from the egr and give it gas there is enough vacuum on the end of the hose to start sucking my finger into the hose.
     
  13. wyldman

    wyldman Member
    Messages: 3,265

    I wouldn't bother with a code reader yet.You can actually just jumper two pins in the ALDL connector and it will flash out the codes.

    I'd disconnect the EGR,and plug the hose,and drive it for a while,to see if the problem is gone.Report back what you find.
     
  14. Arrow

    Arrow Junior Member
    Messages: 27

    pulled and plugged vacuum port for egr valve, it idles and is driveable but looses power around 2000rpm.
     
  15. CT18fireman

    CT18fireman Banned
    Messages: 2,133

    Pop of the exhaust and drive it. If there is no problem then you have a plugged cat.

    The act that you say that the egr has vacumn after the truck has warmed up and I assume is idling troubles me. During warm up at a high idle there should be vacumn. The idea of the egr is to scavenge unburned fuel from the exhaust under acceleration and resend it into the intake. When the throttle is opened you should get vacum and egr valve movement. Egr valves really only cause problems when they get stuck open. As Wyldman said disconnect it and plug the hose.
     
  16. wyldman

    wyldman Member
    Messages: 3,265

    While that is a good way to test the cat for being plugged,I wouldn't recommend it unless you have new gaskets (donuts),studs,springs,and nuts handy for the Y-pipe to manifold connections.You also may need a torch or drill to get broken studs out.

    The studs will most likely snap,or if they don't,you won't be able to get the nuts back on the studs,as the threads will be too short.Stupid design on GM's part
     
  17. Arrow

    Arrow Junior Member
    Messages: 27

    Seems to run good at idle with the egr hose plugged the rpms increase fine until I hit about 2000 rpm. then it bogs down almost acting like a vapor lock. When I let off the gas it idles fine again. I also tapped the cat. with a hammer and it doesn't't sound like anything is loose in there. During warmup I did not feel any vacuum at the port but after a few minutes of running I could give it gas and there is good vacuum on the egr line. One and a half days and counting. Appreciate the ideas keep them coming please
     
  18. Arrow

    Arrow Junior Member
    Messages: 27

    Any ideas?
     
  19. wyldman

    wyldman Member
    Messages: 3,265

    Get a vacuum gauge on it,to manifold vacuum.Run the truck,and when the problem happens,read the gauge.If the cat is plugged,the vacuum should drop to almost zero.
     
  20. Arrow

    Arrow Junior Member
    Messages: 27

    Thanks wyldman I am going to check that right now. I read in another post that you said to drill a hole in the pipe on the engine side of the cat. Should I try this to verify or not? My truck is about 15 miles from my computer so it takes awhile to check it and get back with you.
    Thanks Again!!