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1991 seville
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Discussion Starter #1
Just bought an old man 89 deville, 111000 on it. Under load, mostly accelerating from a stop with a bit of throttle, I can hear what appears to be slight lower end knock. I think I am correct in saying that it is common for these cars to do this. Am I correct in saying so? Thanks for the comments in advance.
 

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Master of the Dark Art of Diagnostics
2003 DHS - two-2002 DHS, 2003 SLS, 1995 Sedan DeVille, 1989 Coupe DeVille
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Just bought an old man 89 deville, 111000 on it. Under load, mostly accelerating from a stop with a bit of throttle, I can hear what appears to be slight lower end knock. I think I am correct in saying that it is common for these cars to do this. Am I correct in saying so? Thanks for the comments in advance.
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are you running premium gas?

be sure the EGR tubes in the TB are clean and open -
 

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1992 DeVille
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seville1991 said:
Just bought an old man 89 deville, 111000 on it. Under load, mostly accelerating from a stop with a bit of throttle, I can hear what appears to be slight lower end knock. I think I am correct in saying that it is common for these cars to do this. Am I correct in saying so? Thanks for the comments in advance.
Yeah man, inspect the vac lines for the egr system. Make sure no hoses are disconnected cracked or broken. If they are replace.

Also with the engine running press up on the underside of the egr valve and the idle should stumble like the car is gonna stall.

Are you getting any codes (like an e48 egr system fault)?
 

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White Diamond '03 DHS (with DTS floor shift)
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Sounds like you might be talking about the "Main Bearing Thump", but I've only heard of that in the 4.9.
 

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1991 seville
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Discussion Starter #5
I'm using 89 octane, 87 is regular. It doesn't say anything about needing premium, but been using it. No codes. Maybe I am just being sensitive, it's like I am looking for a flaw in the engine. You don't hear it at idle.
 

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1991 seville
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Discussion Starter #7
I'll try the 91 octane, it was my understanding that premium was required for the port injection, but not the throttle body. The manual and gas door say unleaded. That's a cheap enough fix. It does have a low end knock. Not when its idling, but there seems to be a spot under acceleration from a stop. Egr valve will make the car sputter if it is pushed up.
 

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1992 DeVille
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seville1991 said:
I'll try the 91 octane, it was my understanding that premium was required for the port injection, but not the throttle body. The manual and gas door say unleaded. That's a cheap enough fix. It does have a low end knock. Not when its idling, but there seems to be a spot under acceleration from a stop. Egr valve will make the car sputter if it is pushed up.
Good to know. If the higher octane gas doesn't fix it part of the egr system is probably at fault.

Are you getting any codes?

(Also all gas these days is unleaded.)

The detonation/knock you're hearing, if egr related, should happen under light acceleration in low rpm range.

(I know my 92 says use premium on the dash and also I think on the fuel door)

Did you check the hoses and egr tubes inside the throttle body?
 

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1991 seville
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Discussion Starter #9
I'm so frustrated that I bought this car and didn't hear this knock till it was mine. Suggestions now, knowing that it was an old man car probably driven at low speeds and small trips for 21 years? Could it be carbon on the end of the Pistons? Engine cleaner? Suggestions??
 

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1991 seville
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Discussion Starter #10
Dchavezo- you may be onto something, but I'm not sure exactly what I'm checking. The knocking is definately lower engine, not pinging like you would get with low octane gas. My owners manual says 87 octane. It is under load when accelerating that it happens. At idle you do not hear it, revving the engine in the driveway you do not hear it, nor cruising. Thanks for following and helping
 

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1992 DeVille
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seville1991 said:
Dchavezo- you may be onto something, but I'm not sure exactly what I'm checking. The knocking is definately lower engine, not pinging like you would get with low octane gas. My owners manual says 87 octane. It is under load when accelerating that it happens. At idle you do not hear it, revving the engine in the driveway you do not hear it, nor cruising. Thanks for following and helping
Only during light acceleration?

If you hear it and push the pedal to 50 percent throttle in order to down shift, do you hear the noise at that point? Try it and let us know. If so, my money is on egr issue.



Ranger said it before. It very well could be the main bearing thump. I wouldn't know without hearing it

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Detonation/ping related to egr system or preignition usually has a metallic clatter to it. The bearing thump doesn't have the metallic sound as much at all
 

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White Diamond '03 DHS (with DTS floor shift)
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Main bearing thump is usually at idle if I remember correctly.
Detonation is a totally different thing (and sound).
Can you get it to knock in neutral when you have your head under the hood? Keep an eye (and ear) on the belt tensioners.
 

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1991 seville
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Discussion Starter #13
OK guys, here is todays update, and still needing help. The EGR ports in the throttle body I am assuming are the two gold colored cylinders in the middle, put a coat hanger down them, nothing in there. Took it over to a mechanic for a quick listen, and he said he thought it sounded like it was missing. I don't think so, but I changed all the plugs. No change in my condition. At idle, the car sounds as smooth as silk. Put it in gear, one foot on the brake and one on the gas and it knocks, but I can't tell where it is coming from. I know its not top end, and it is not a metallic sound, it is a deeper knock. Im lost, because if it was a rod, you would hear it all the time. When I bought the car, the oil was old and thin, and I don't remember hearing this noise. Now with the new 10 30 in it, its there. I am at a loss. Suggestions?? I tried to get the egr off with no success, will try again tomorrow. After changing all the plugs, which was horrible, I'm sure I can figure something out to get it off.
 

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Master of the Dark Art of Diagnostics
2003 DHS - two-2002 DHS, 2003 SLS, 1995 Sedan DeVille, 1989 Coupe DeVille
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OK guys, here is todays update, and still needing help. The EGR ports in the throttle body I am assuming are the two gold colored cylinders in the middle, put a coat hanger down them, nothing in there. Took it over to a mechanic for a quick listen, and he said he thought it sounded like it was missing. I don't think so, but I changed all the plugs. No change in my condition. At idle, the car sounds as smooth as silk. Put it in gear, one foot on the brake and one on the gas and it knocks, but I can't tell where it is coming from. I know its not top end, and it is not a metallic sound, it is a deeper knock. Im lost, because if it was a rod, you would hear it all the time. When I bought the car, the oil was old and thin, and I don't remember hearing this noise. Now with the new 10 30 in it, its there. I am at a loss. Suggestions?? I tried to get the egr off with no success, will try again tomorrow. After changing all the plugs, which was horrible, I'm sure I can figure something out to get it off.
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At idle, the car sounds as smooth as silk.
Put it in gear, one foot on the brake and one on the gas and it knocks,
but I can't tell where it is coming from.


OK - here is what I would do -

but you are going to need an assistant -
SOMEONE YOU CAN TRUST -

train your assistant to listen for -
and hear EXACTLY what you are hearing -

train your assistant how to feather the throttle
just enough to make the sound as obvious as possible -
while in gear - and holding the brake -
oh - reverse should work just as good as forward -
and would be much safer -

when you and your assistant are "dialed in" -
try this -

using an insulated spark-plug-wire removal tool -
or WELL insulated pliers - with a thick glove on -
remove and replace each plug wire at the cap -

ignore the "sound" of the misfire -
and pay attention to the knocking sound -

you should be able to determine which cylinder is making the noise -

I'm trying to remember the noise patterns -
between the three common causes -
rod bearing - wrist pin - and piston/skirt slap -

but I don't want to give erroneous information -
 

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1992 DeVille
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What you described sounded like that main bearing thump. I'd consider trying what bass suggested if you can find a buddy. If not, I'd say it's safe to rule out EGR.

Tps shouldn't affect it at idle. You can navigate to diagnostic mode and after the sequence ends, press low and then the display should shift to readout for various parameters. The first of which would be throttle position.

What reading do you get when you do that?

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Have you been running premium for a while? I'd run a few tanks of the highest octane and see if that stops the knocking.

I know you said you wee gonna try. Did you??
 

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1992 DeVille
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Sorry I forgot to say after you press low 9.0 displays. Then press high. Then it'll say p.0.1. My reading is .9 most of the time. Normal idle. Sometimes it's like 1.3 slightly higher but still okay
 

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1991 seville
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Discussion Starter #18
Ok, so took it to a mechanic and they test drove it. Said they do not think it is internal engine. Possibly exhaust or torque converter bolts. I'm not convinced. Anyone know what timing should be when the car is running at idle??
 

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1991 Cadillac Sedan deVille
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I have a '91 Sedan DeVille with only 63K miles and I have a knock as well. It didn't seem to start until my mechanic put on a new EGR valve and all 8 fuel injectors. I thought maybe he "tested" my car too rough, but I was told here it could be the EGR solenoid, which I plan on changing soon. It is around $40.00, but if it don't work, I am going to take it back. Mine sounds like a rod knock at low speed acceleration, especially from a stop.

Hope you get your issue figured out, mine has drove me crazy too.
 

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1991 seville
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Discussion Starter #20
Does anyone know how much it would cost or how hard it is to tighten the bolts between the torque converter and flex plate? I'm thinking that is what it is. Does it need to be done asap??
 
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