Air intake opening too far too fast

Can't go anywhere without a working drivetrain
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Jonny
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Air intake opening too far too fast

Post by Jonny »

My lack of terminology is making it hard to search for the right info on this one.

When you push the gas down far, you hear a hiss of much more air being brought into the motor. The sound of secondaries opening on a 4 barrel carb kind of thing. I know the motor is EFI, but the sound is much the same.

A few days ago as I pulled out of the driveway, barely touching the gas going about 20, the motor changed from the mmmmmm sound to the zzzzzzz sound exactly like it would if I'd have floored it. No change in acceleration just that hissing sound. Not a noise like it, it was the air intake gulping air.

Now does it constantly. Barely on the gas from about 20mph on, it sounds like its on the floor. Let off the gas it stops and sounds normal for a sec then like a light switch right back to the massive air intake.

Any ideas on what term i would search for this issue? Not sure what sensor or item controls the air intake. Again, no change in acceleration motor is smooth and fine just that super loud air hiss every time I touch the gas.
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skater
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Re: Air intake opening too far too fast

Post by skater »

If it were the intake opening, the engine would run badly because it'd be getting too much air, I think. (Even if the computer were compensating with fuel, it'd still not run correctly.) I suspect you either have a vacuum leak (which would usually make it run badly) or the intake plenum itself is leaking and that's what you're hearing.

You didn't say what year or engine you have, but my '91 460 had a connection in the top of the air intake that would sometimes drop down in, leading to a massive air leak. I wouldn't be surprised if that would cause the noise you are hearing.
1991 Airstream B190 - bought, 2005; sold, 2011; bought 2017
1995 Airstream Excella 30' trailer

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Jonny
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Re: Air intake opening too far too fast

Post by Jonny »

Finally took it in to a garage, as the problem was getting worse, more frequent, and it was losing power when it would make the insane hissing noise.

Turns out the converter is plugged. Too much gas equals too much back pressure and the extra comes back through some egr something or other tubes. They wanted $900 to fix it, with about $600 just for the converter.

Then the mechanic said he had one of these awhile back and just punched out the converter with no issues. Although technically illegal I'm told, he said it doesn't increase noise or anything, you just can't pass an emissions test.

Thoughts?
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skater
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Re: Air intake opening too far too fast

Post by skater »

Jonny wrote:Turns out the converter is plugged. Too much gas equals too much back pressure and the extra comes back through some egr something or other tubes. They wanted $900 to fix it, with about $600 just for the converter.

Then the mechanic said he had one of these awhile back and just punched out the converter with no issues. Although technically illegal I'm told, he said it doesn't increase noise or anything, you just can't pass an emissions test.
You already know the pros and cons - you can't pass an emissions test. Maybe not a problem for you, but potentially a problem for a buyer.

I'd look for another estimate though. I just did a quick search for catalytic converters for a '91 460 at jegs.com, and they came up in price from $75-$425, so $600 seems a bit much.
1991 Airstream B190 - bought, 2005; sold, 2011; bought 2017
1995 Airstream Excella 30' trailer

WBCCI #13270, Washington, DC Unit
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Planck
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Re: Air intake opening too far too fast

Post by Planck »

I thought I had read somewhere that you can get a converter replacement tube to eliminate the converter. I think they may be called temporary, or test as obviously they can't be marketed as and eliminator. I would check with some muffler shops and maybe try google. The state I live in has no emission tests so could get by without a converter here.
EricZ
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Re: Air intake opening too far too fast

Post by EricZ »

In some catalytic converters there are multiple distinct blocks of the honeycomb material that performs the converter's function.

It can happen that one of the blocks comes loose or becomes damaged while leaving the rest in place. It's sometimes possible to break up the damaged block from the outside (with a stick or other long implement) and shake out the fragments (being careful not to breath the dust). If you are very lucky, the remaining honeycomb material will be undamaged, and very well might still perform sufficiently well to pass a smog inspection.

If you do need to replace it, you might find one for less than $600, as Skater says. In addition, installation should be VERY fast. I think I could remove and replace the cat in my 1993 Airstream 190 in 10-15 minutes. If the clamps are badly rusted, perhaps 30 minutes. Thus I'm a bit concerned about the additional $300 it seems they want for installation.
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craigmar
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Re: Air intake opening too far too fast

Post by craigmar »

In an earlier post under "drivetrain" 94-460 fuel pump problem by keystone Aug 17 there are a few posts about the problem and the catalytic's. In my post's about the problem I replaced both cats for about $200 each including the labor. Problem solved with no further problems and even though we inherited a class "C" we are still using the B-van as well.
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