94 4.9 Weird Rattle Question...
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HT4100 4.1, 4.5, 4.9 Discussion, 94 4.9 Weird Rattle Question... in Cadillac Engine Technical Discussion; I've already searched around and found other people describeing similer problems but haven't found any answers. Here's my problem. Last ...
  1. #1
    coldnsnowy is offline Cadillac Owners Member
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    94 4.9 Weird Rattle Question...

    I've already searched around and found other people describeing similer problems but haven't found any answers. Here's my problem. Last night for the first time I heard a rattle that sounded something like a lifter rattle coming from under the hood. And it went away. Checked the oil, full. Tranny, full. Reved it up, nothing, running great. Put it in gear and slowly take off and there it is again! So I figured out it only happens in gear and I have to be moving at slow speeds (either forward or backwards). Also, it doesn't do it when its cold, as I figured out today, I live in ND and the windchill was like -25 this morning. It only did it when it warmed up. I can't get it to do it unless the car is literally moving, if I hold it in gear (forward or reverse) and give it throttle, nothing. Like I say it sounds like lifter rattle but it's only brief when it does happen, it comes then quickly fades away. No codes. It seems to be running perfect. About 170k on it. I do have a broken front motor mount but I don't believe that has anything to do with it. Any suggestions anybody? Any help or direction would be greatly appreciated.

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    Dave S Texas's Avatar
    Dave S Texas is offline Cadillac Owners Enthusiast
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    Re: 94 4.9 Weird Rattle Question...

    Noise when moving only means power-train problem. I'd be check the CV joints. Cold weather exacerbates problems in moving parts...suspension/driven-wheels.

  4. #3
    coldnsnowy is offline Cadillac Owners Member
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    Re: 94 4.9 Weird Rattle Question...

    It's definatly not in the suspension. I'd like it if that was the case, really I would. But like I say it's definatly a rattle/clatter that sounds just like a car thats out of/low on oil. It's just weird how it only happens barely moving with minimal throttle, and if I hold the throttle at the same spot the rattle starts the same but goes away right away. It only happens for like 5 seconds at a time. Also I forgot to mention the car doesn't have any type of ride control anymore (regular struts with overloads on the rear). It's been that way since I got it.

  5. #4
    Dave S Texas's Avatar
    Dave S Texas is offline Cadillac Owners Enthusiast
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    Re: 94 4.9 Weird Rattle Question...

    it only happens in gear and I have to be moving at slow speeds (either forward or backwards).

    CV joints and suspension are different systems. The CV(constant velocity) joint is what drives the wheels...the power/drive train. It wouldn't hurt to check them.....

  6. #5
    coldnsnowy is offline Cadillac Owners Member
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    Re: 94 4.9 Weird Rattle Question...

    already have checked them, again it's not c/v joints or suspension. It's mechanical and only at slow acceleration take off. Lifters sound nothing like c/v joints.

  7. #6
    Dave S Texas's Avatar
    Dave S Texas is offline Cadillac Owners Enthusiast
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    Re: 94 4.9 Weird Rattle Question...

    well I tried to help. good luck to you.

  8. #7
    coldnsnowy is offline Cadillac Owners Member
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    Re: 94 4.9 Weird Rattle Question...

    Thanks alot anyway. Appreciate your time. Anyone else have any ideas?

  9. #8
    Edahall's Avatar
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    Re: 94 4.9 Weird Rattle Question...

    You might try bumping the catalytic converter with a rubber mallet or something that is equivalent and see if the CAT rattles.

  10. #9
    Submariner409's Avatar
    Submariner409 is offline If it won't run, stick on fender vents
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    Re: 94 4.9 Weird Rattle Question...

    EGR valve pintle and passage might need cleaning - a sticky or slow EGR will cause a slight ignition rattle at part throttle, low speed. The characteristic of the rattle will change or disappear as the engine warms and the fuel trim changes to open loop.

  11. #10
    coldnsnowy is offline Cadillac Owners Member
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    Re: 94 4.9 Weird Rattle Question...

    That sounds like it might be something. How do I clean it? And what is the pintle??? I did clean out the tubes under the throttle body this summer, how ofter do they/can they plug up? It does as you say, change with the engine tempature. When it's cold it does nothing, it's just when it warms up that it does it. Edahall, I'll try knocking on the cat but I'm pretty sure thats not it. Would the EGR being sticky or slow cause a fault code? It's really giving me nothing.

  12. #11
    Submariner409's Avatar
    Submariner409 is offline If it won't run, stick on fender vents
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    Re: 94 4.9 Weird Rattle Question...

    The EGR has a solenoid and/or vacuum actuator which lifts a tapered poppet valve (pintle - think heavy-duty needle valve) by some amount determined by gas, air, and power demands. The system returns a measured portion of the engine exhaust gas to the intake tract in order to cool (slow down) the combustion process. If the exhaust gas tube(s) or pintle are clogged or "sticky" then the car acts as if the ignition timing was a tad over-advanced for the throttle opening.

    The EGR usually (but not always) sets some P code(s).

    EGR is but one of several things that can cause "rattles", but it's one more diagnostic tool to check it..............

  13. #12
    coldnsnowy is offline Cadillac Owners Member
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    Re: 94 4.9 Weird Rattle Question...

    Well I checked the EGR just by pressing up on the diapraham by hand. It seems to move alright but is really squeaky. To best discribe it, sounds dry. I have a parts car as well and when I press on the egr on it, it's nice and tight and not 'squeeky'. Also, with my car running I pressed on it and the idle dropped pretty dramatically, so it seems to be working but maybe it is sticking? I also forgot to mention that my gas mileage (for lack of a better way to put it) sucks. Right now my gauge tells me 12.9. The car seemes to be running fine and has lots of power but this will drive me crazy so I got to figure it out. It's such a mechanical sound. Not like a 'ping' of timing being off, but like I said a rattle. I'm really hopeing it's the egr valve. Would the valve itself rattle??? Also if anyone else has any idea's I'd love to hear them. I'm going to be going over to my dad's today so I can have someone else help me listen to it. I'm not illiterate on cars I just don't know alot about these newer one's. I'm more into the 60's and 70'2 cars when all you needed was gas and spark and everything was simple. Thank you again for all they help you guys give me. This forum has been more valueable to me them then I can even describe.

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