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'98 Dodge vacuum leak?

Discussion in 'Ram Trucks' started by cwby_ram, Dec 14, 2011.

  1. cwby_ram

    cwby_ram Senior Member
    Messages: 907

    I'm trying to get the bugs worked out of my plow truck and looking for some advice. It's the '98 in my sig. Seems to be an intermittent vacuum leak. A big one. Sometimes when I start it it'll start sucking air (it sounds like), then stall out unless I give it gas. Other times it'll run fine for awhile then suck air and stall out. We sprayed carb cleaner all around the intake as best we could and couldn't find a leak there. I was gonna rip the intake off and replace the gaskets, but before I go to all that trouble, I thought maybe someone out there has had similar issues and might be able to point me in some other direction? Thanks in advance!
     
  2. leepotter

    leepotter Senior Member
    Messages: 122

    I believe the IAC valves get dirty/worn out and can cause this. located on the back of the throttle body. Can get them for like 15 free shipping on ebay.
     
  3. cwby_ram

    cwby_ram Senior Member
    Messages: 907

    Thanks, Lee. That sounds like a good place to start. I replaced the TPS today, but the problem came back. It sure sounds like the hiss is coming from back there. I've got a whole list of possible causes piled up. I'll try the IAC tomorrow before I yank the throttle body. Do you know if the '98's still have EGR valves, I looked around for one, but I sure couldn't find it.
     
  4. DAFFMOBILEWASH

    DAFFMOBILEWASH PlowSite.com Addict
    Messages: 1,598

    If it backfires through the intake when you get off the throtle then I would suspect the intake gasket.
     
  5. USMCMP5811

    USMCMP5811 Senior Member
    Messages: 267

    Is the check engine light on? any stored codes?
     
  6. mnglocker

    mnglocker Senior Member
    Messages: 923

    98 shouldn't have an EGR IIRC. Sounds like a bad TPS sending incorrect signal to the IAC valve. Common problem on these engines.

    Check the TPS for proper voltage range and replace if needed. If needed replace the o-ring on the throttle shaft, as it has worn likely allowing dirt to enter the TPS and cause malfunction.


    If the TPS checks out ok, the magnum MPFI engines have plenum leaks often enough. You need to remove the intake manifold to fix that. If you do go that route I'd recommend replacing the original "beer keg" intake with a Mopar Performance M1 single plane air-gap manifold. It's a direct bolt in and has no plenum to leak.
     
  7. cwby_ram

    cwby_ram Senior Member
    Messages: 907

    Thanks for the tips guys. I replaced the TPC yesterday, though I never drained the battery. No backfiring. The engine light is on. Maybe I'll try to drive it in to get that read today too. If I remember right, I think something (presumably the issue I'm trying to work out) has tripped an O2 sensor code.
     
  8. mnglocker

    mnglocker Senior Member
    Messages: 923

    You don't need to drive it in to get the code.

    Dodge you can do the 3 turns of the key trick:

    Turn the key on and off several times (on, off, on, off, on), ending with the engine on. Do not crank the engine. The digital odometer will read out the P0 codes which you can look up in a shop manual or online.
     
  9. cwby_ram

    cwby_ram Senior Member
    Messages: 907

    That makes it easy. I'll do that when I head over in a few. Thanks!
     
  10. cwby_ram

    cwby_ram Senior Member
    Messages: 907

    Ok, replaced TPS yesterday, IAC today. Sounded better for while, but the hiss and stalling out came back (though maybe not as bad?). I need to pick some more starting fluid tomorrow, but I'm suspecting throttle body gasket now? My last little spurt of carb cleaner seemed to ramp the engine up, but it was a quick little spurt and couldn't been the engine catching itself. Looked into the M1 thing, I don't think I wanna put that much into it if I can avoid it. Still have ball joints and tie rod ends to address at some point. I'm kinda leaning away from the intake itself leaking, it's so intermittent. I dunno, starting to get a little frustrating...

    EDIT: I also replaced the PCV and it's hose just for good measure today.
     
  11. leepotter

    leepotter Senior Member
    Messages: 122

    There should also be a gasket where the are cleaner attaches to the throttle body.
     
  12. cwby_ram

    cwby_ram Senior Member
    Messages: 907

    I need to check that, I keep forgetting to look when I have it off. I think (crossed fingers) that I found a vacuum leak around the throttle body gasket. I sprayed it with starting fluid tonight when it started sucking air and it seemed to catch, although it wasn't as definitive as I'd have liked. Gonna replace that gasket tomorrow, and see if the one on top is there. If that doesn't work I guess I'll rip the intake off. It seems to be getting better, but it's still there.
     
  13. justme-

    justme- 2000 Club Member
    Messages: 2,138

    grab and wiggle the vacuum and emissions lines while it's running- at that age the rubber is breaking down- could be a line anywhere in the engine compartment that has a break which could vary in size due to engine vacuum, vibration, etc.
     
  14. cwby_ram

    cwby_ram Senior Member
    Messages: 907

    I'm still coming up empty, guys. Replaced the TPS, PCV, IAC, throttle body gasket, along with a good cleaning of the throttle body. was going to replace the gasket between the throttle body and the air cleaner, but CarQueset couldn't find one, and it seems that if that were it, the hissing would be more consistent. Sprayed around with carb cleaner, quick start fluid and propane and came up empty. Can't seem to reproduce the hissing, just have to wait for it to show up. Always at idle (giving it throttle makes it go away), sometimes it comes quick, other times it takes awhile. I have vacuum at the PCV at idle (is that right?) Could it be an internal vac leak? The cat has a leak where one side of the exhaust enters, could that be related? I'm at my wits end!
     
  15. DAFFMOBILEWASH

    DAFFMOBILEWASH PlowSite.com Addict
    Messages: 1,598

    Has the CEL ever illuminated?? Perhaps check for codes clear them and run it. How does it run when cold?? Better or worse??
     
  16. cwby_ram

    cwby_ram Senior Member
    Messages: 907

    CEL does light. Seems like it lights when the hissing thing happens. It's not always on. As far as idling, it doesn't seem to matter hot or cold. We took it a couple miles down the road this afternoon to pick up my father-in-law's truck, and it was a little herky-jerky before it got up to temp. But after it warmed up it drove better.
     
  17. mnglocker

    mnglocker Senior Member
    Messages: 923

    Double check and make sure it doesn't have an EGR. I may be wrong you're right at or before the change year.

    If it has an EGR the EGR tube will come off the rear of the passenger side exhaust manifold.

    Also when the truck is hissing, does it idle really low and rough?
     
  18. cwby_ram

    cwby_ram Senior Member
    Messages: 907

    I'll look again. I'm pretty sure mine is after the EGR was gone, but now I know where to look for sure.

    That's exactly right, idle's low and rough, often to the point of stalling.
     
  19. doo-man

    doo-man Senior Member
    Messages: 387

    Subscribed

    Same issue on 2000 Ram with 5.7L Mag :-(
     
  20. mnglocker

    mnglocker Senior Member
    Messages: 923

    How's the oil consumption?