popping sound when 4.9 is being raced....
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HT4100 4.1, 4.5, 4.9 Discussion, popping sound when 4.9 is being raced.... in Cadillac Engine Technical Discussion; My engine also did this last season, but today i was running the car for awhile, and this was bugging ...
  1. #1
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    popping sound when 4.9 is being raced....

    My engine also did this last season, but today i was running the car for awhile, and this was bugging me....

    if I hold the gas don't so the enigne stays reved at, say, anything about 3,000rpms, the engine keeps "bucking" almost as if there is a bad misfire (but that isn't the case) I know my fathers '99 GTP, if you keep the idle high like that, the computer will try to figure out why it is idleing high and cut the enigne back a little, but then it comes back, so the revs kinda go back and fourth.... my car is doing that, but on a bigger scale....

    ...then, say if the car is parked, I race the engine to 4,000RPM's then take my foot off the gas completly, as the engine nears idle, it make s aloud poping sound, and actually "shakes" the whole car.... don't really shake... I think "jolt" is more of the word... since the engine is in there sidways, it is a forward-back kind of jolt (direction of engine tourqe) and it may do it a few times also....

    ... It isn't pining or anything, I always run premium gas in it, all the fluids are good.... I havn't done a full tune up with plugs/wires yet (will be soon) but she only has 87k miles on her... nothing of that sort should be casue this....

    When the car is being dirven (I am remembering this from last season, since the car isn't on the road right now) and I drive it, it DOSN'T make any of those noises... only when parked and raced.....

    ....the idle bounces back and fourth from 580rpm-630rpm (sometimes a little higher) but it has always done that... the infamous 4.9 rough idle.....

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    Re: popping sound when 4.9 is being raced....

    Sounds like it's running a little lean for some reason.....

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    Re: popping sound when 4.9 is being raced....

    I sometimes get a mild "pop" when I accelerate hard, but I think it's just the air suspension compensating for the rear-end "dip."

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    Re: popping sound when 4.9 is being raced....

    Funny you mention the lean..... when I was messing aorund with the OBD and checking out differnt values, the fuel/air mixture is supposed to be 128counts (14.7 A/F IIRC?) and it said a range from like 118-138 was considered normal operating range..... IIRC less then that means that the computer is not making the injecotrs open as much, thus leaning the mixture, and anything above that means it is keeping the injecotrs open longer, which would enrich the mixture.....

    .... my values were around 106... even when I raced it.... at higher RPM's it went up to 109 or so, but that is still kinda far from the "acceptable normal range" and pretty far from the optimum count.....

    ....what could cause this? I have a new fuel filter, just havn't put it in yet.... what other things may cause the engine to run lean?

    This has nothing to do with the suspension, tranny, chassis or anything, it is definitly with the engine.... and I worry that it may be damaging the engine.....

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    Re: popping sound when 4.9 is being raced....

    Fuel pump, computer, and maybe even debris in your lines could cause that. Could be something else, I dunno. Just suggestions.

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    Re: popping sound when 4.9 is being raced....

    KW... can you hook me up with a link that tell what all that stuff is in the OBD? I've found a oil pressure gauge and other stuff... but I don't really know what most of the stuff is!

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    Re: popping sound when 4.9 is being raced....

    Just wanted to say I have a 92 Eldo Touring Coupe. It has 139,000 miles on it. I bought it with about 54k on it 3 years ago. Not sure exactly when, I noticed it, but my car does EXACTLY the same thing. I'd say it had somewhere around 75k-100k on it when I noticed. I'm sure it still does it today (I don't rev up my engine that far a lot when it's parked). And you're right, it's definately the engine and the whole car jumps when it pops when you bring it up to 4000kRPM and let go. I've never thought anything of it, I assumed it was the computer trying to govern the RPMs.

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    Re: popping sound when 4.9 is being raced....

    all this info is in my factory service manual (well worth it)

    Now that I think about it.... when I would do WOT runs, as the engine got near 4,000RPM and until shift, it would make a strange noise.... kinda like a pining sound, but the engine is NOT pinging.... I can't explain it, and after seeing the low fuel/air ratio... I am thinking if it is running a little lean.....

    ...what other things can I do to try to find out the problem, or maybe fix it?

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    Re: popping sound when 4.9 is being raced....

    I know what you mean about the popping, and as far as I can tell all the 4.9's do it. When I dropped one into my 87 it did it, my 92 does it too. Someone posted some audio files of his caddy on here a couple weeks ago, and you can kinda hear it there too. I wouldn't be too worried as long as it's just when ya rev it out of gear.

    D.

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    Re: popping sound when 4.9 is being raced....

    I think what you are describing is perfectly normal....the PCM intervenes in an neutral/park idle overspeed to keep the engine speed down...sort of a rev limiter..


    Drunks have a habit of coming home from the bar at 2:00 AM and putting the car into park and then passing out...with their foot on the gas. If no intervention is taken the engine will rev wide open and overheat and possibly induce an unwanted thermal event under the hood....with possible distress resulting to the occupant who is passed out....so....there is a "drunk mode" intervention in the PCM software to prevent high revving in park/neutral....blame the trial lawyers.

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    Re: popping sound when 4.9 is being raced....

    BTW....it is hard to tell from your description exactly what is going on there...but...there is another situation with the F7 trans or the 4T60E that you could be encountering. If the intermediate sprag clutch is getting worn it can sometimes engage on a neutral rev. You 'll feel this as a sudden lurch when the engine is revved as the overrunning style clutch grags (when it shouldn't...) suddenly and momentarily causing the trans internals to suddenly rotate. Usually it will happen with a "clunk" that sounds pretty grueome. If this is what you are experiencing it is NOT a good thing. In my crystal ball I see trans problems in your future. To keep them at bay as long as possible DON'T rev the engine up in park/neutral to keep experiencing this phenomenon....it will just shatter the sprag clutch one day and then the trans will have to come out.

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    Re: popping sound when 4.9 is being raced....

    Quote Originally Posted by HippieD9
    I know what you mean about the popping, and as far as I can tell all the 4.9's do it. When I dropped one into my 87 it did it, my 92 does it too. Someone posted some audio files of his caddy on here a couple weeks ago, and you can kinda hear it there too. I wouldn't be too worried as long as it's just when ya rev it out of gear.

    D.
    that was me with the audio files, my car has that popping noise because of the exhaust that i have on it. i think the popping sound you are refering to is more of a raspy sound produced by the muffler and the backpressure, correct me if i'm wrong.

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    Re: popping sound when 4.9 is being raced....

    Quote Originally Posted by bbob
    BTW....it is hard to tell from your description exactly what is going on there...but...there is another situation with the F7 trans or the 4T60E that you could be encountering. If the intermediate sprag clutch is getting worn it can sometimes engage on a neutral rev. You 'll feel this as a sudden lurch when the engine is revved as the overrunning style clutch grags (when it shouldn't...) suddenly and momentarily causing the trans internals to suddenly rotate. Usually it will happen with a "clunk" that sounds pretty grueome. If this is what you are experiencing it is NOT a good thing. In my crystal ball I see trans problems in your future. To keep them at bay as long as possible DON'T rev the engine up in park/neutral to keep experiencing this phenomenon....it will just shatter the sprag clutch one day and then the trans will have to come out.
    Could it be a stuck throttle valve? According to ConsumerGuide "trouble spots" there were problems with the earlier 1990-92 transmissions that would shift late, or not at all because of this.

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    Re: popping sound when 4.9 is being raced....

    Quote Originally Posted by Ralph
    Could it be a stuck throttle valve? According to ConsumerGuide "trouble spots" there were problems with the earlier 1990-92 transmissions that would shift late, or not at all because of this.

    The complaint was noise....not shifting late.....

    No relationship between the intermediate sprag being worn and a stuck throttle valve.....

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