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Discussion Starter #1
Morning all -

I purchased a 1989 Deville Sedan. A little over 100k on it.
On idle she purrs like a kitten, timing seems perfect smooth as silk. It does tend to take a while before idle speed comes down to normal. What is the proper RPM for a 4.5 L V8 for this model? When I drive the car, the engine seems to make a knock/rattle type sound. It only does it when it's being driven.. You don't hear it at all on startup/idle. Any ideas? It doesn't have any heisitation at all, in fact, I accidently pushed a little too hard on the accelerator and it planted me back in the seat! LOL - it's the front wheel drive model. I am a first timw Caddy owner. Thanks for your help!

WebMan
 

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webman_1_2000 said:
Morning all -

I purchased a 1989 Deville Sedan. A little over 100k on it.
On idle she purrs like a kitten, timing seems perfect smooth as silk. It does tend to take a while before idle speed comes down to normal. What is the proper RPM for a 4.5 L V8 for this model? When I drive the car, the engine seems to make a knock/rattle type sound. It only does it when it's being driven.. You don't hear it at all on startup/idle. Any ideas? It doesn't have any heisitation at all, in fact, I accidently pushed a little too hard on the accelerator and it planted me back in the seat! LOL - it's the front wheel drive model. I am a first timw Caddy owner. Thanks for your help!

WebMan
You have to be using 91 oct fuel (if your not already). If you are currently using 87, then this should help.
 

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miishmiish said:
You have to be using 91 oct fuel (if your not already). If you are currently using 87, then this should help.

Thanks for the note. Really? This will help, it's an 1989 so I figured it took 87 octane with the non MB additive (which is in all gas today). I will run this tank through and switch to a better gas. I hope it helps. A friend of mine even thought it was the main bearing, which I don't want to even think about..
 

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mine too

95 Sedan DeVille, 4.9 liter.

Mine knocks, too. When cold, she runs fine, but as she gets warmer, she starts to knock a bit when accelerates. I don't have a timing light thing to c'k the timing. I may just have to turn the distributor a bit until it goes away... (gas is > 91 octane)
 

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Discussion Starter #5
Re: mine too

100 said:
95 Sedan DeVille, 4.9 liter.

Mine knocks, too. When cold, she runs fine, but as she gets warmer, she starts to knock a bit when accelerates. I don't have a timing light thing to c'k the timing. I may just have to turn the distributor a bit until it goes away... (gas is > 91 octane)

Cool. Maybe it will last a long time this way! LOL
I am running through the tank gas it had when I bought it, I put a bottle of gum out cleaner in it. I am going to try 89, then up again. It has gotten any worse or louder, just the knock when accelerating. It doesn't even knock on idle after it has been warmed up.

Have a nice weekend!
 

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Re: mine too

If the fuel doesn't clear it up, you should get it to a mechanic ASAP. There are MANY things that can cause a noise like you describe. Some are little more than nuisances and some are VERY damaging to the engine. Unfortunately it's virtually impossible to diagnose it over the internet.
 

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Re: mine too

!! I didn't know that. Thank you for your advice.

I will take it to the mechanic. Do you suggest me to go to the dealer?
Or someone who has experience with 4.9 liter engine would be
assumed knowledgeble enough??

Katshot said:
If the fuel doesn't clear it up, you should get it to a mechanic ASAP. There are MANY things that can cause a noise like you describe. Some are little more than nuisances and some are VERY damaging to the engine. Unfortunately it's virtually impossible to diagnose it over the internet.
 

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Re: mine too

I think if you took it to any ASE certified place, youll be fine...... This engine is pretty oldschool, so they shouldnt have a problem handling it.....

It sounds like a timing issue to me, or at least thats my gut feeling....... Unlike the northstar, the 4.5L and 4.9 (which BOTH require premium) dont use knock sensors to determine if the engine is knocking..... So, if somehow your timing got advanced, the engine has no way of correcting itself..... That being said, this is why it is ESSENTIAL, CRITICAL, NECCESSARY to run PREMIUM ALL THE TIME..... NO EXCUSES!!!!!

And only when its cold does make SOME sense, although I kinda doubt it....... As the engine gets warmer, the metal expands...... Meaning that the piston is expanding JUST enough to make it detonate...... My guess is that when its cold its a minor enough knock that you cant hear it (noticeably)....

Whatever the case is, spark knock is VERY dangerous to the health of the engine and should be addressed IMMEDIATELY........
 

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Re: mine too

Thanks bud I appreciate it. I am going to fill it with 90+ Octane today and a buddy is going to help me replace the spark plugs with Bosch Platnum models. I will also check on the timing.

Thanks for your help! I will keep you posted.
 

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Re: mine too

If your gonna replace the plugs, use OEM AC/Delco.... I havent heard anything terrible about Bosch, but the OEMs seem to have a better reputation..... personally I would ONLY recommend OEM sparkplugs.... That particular sparkplug was DESIGNED for the engine and the combustion chamber.....

Also, replace the wires....... By now, their probably gone..... Costs about $50

Along with that, get a can of GM TOP ENGINE CLEANER (get the liquid, not the aerosol)..... You may have excessive carbon deposits causing detonation also.......
 

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Re: mine too

Found out that the timing was a little bit too advanced. It has been
corrected. It is better now, well, still she knocks slightly when she
gets warmed up.

The mechanic told me also that he noticed that the water temperature
was somewhat high. It went up to 215F at idle when the fan kicked in.
He suggested to consider changing the thermostat and the coolant
temperature sensor.

Just curious, what is the normal operating coolant temperature for
4.9 liter??
 

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Discussion Starter #12
Re: mine too

100 said:
Found out that the timing was a little bit too advanced. It has been
corrected. It is better now, well, still she knocks slightly when she
gets warmed up.

The mechanic told me also that he noticed that the water temperature
was somewhat high. It went up to 215F at idle when the fan kicked in.
He suggested to consider changing the thermostat and the coolant
temperature sensor.

Just curious, what is the normal operating coolant temperature for
4.9 liter??
That's great news! :) I just did a tune up on mine. I have not had a chance to get the timing checked yet. But the spark plugs in the rear WERE ORIGINAL!?! That's right, they were so hard to get too, they never got changed, I could not believe it. All 8 plugs AC/DELCO had so must rust corrosion, we almost could not get them out of the threads - they were completely seized in the block. The car has all new plugs and a new cap and rotor now. The wires were changed, but not the plugs it seems. 107,070 miles on 14 year old plugs!! The rattle is still present but better. The rotor button was so worn, it was begining to arc through the plastic. I noticed a huge fuel mileage difference already! WOOT!
 

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Re: mine too

215 is pretty good for the 4.9..... They run hotter than normal......

Id still recommend doing a top engine cleaner decarb..... I bet it will help.....

Temp sensor may just need to be cleaned, but if he is knowledgeable then it may need replaced..... Tstat definitely......
 

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Re: mine too

Glad that webman_1_2000 was able to change the spark plugs
after so many years of service.

By the way, thanks for the interesting info, elwesso.
The previous owner replaced the engine, so the engine has
only about 20K miles on it (about 2 yrs old). Do you still
think there are some carbon deposit in the engine??

Talking about the temperature sensor and thermostat, I will
definetaly work on them.

Another question: does anybody know what the standard
design life time of the waterpump on the 4.9 liter? I am
sure it is the original parts (so about 8yrs old and 84K on it),
so I want to know when I should replace it as a preventive
maintenance...
 

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Re: mine too

I dont think there is a "design life"..... I dont think they normally fail..... Or at least at a certain time.......

Id say its possible there are carbon deposits, but at that low mileage its kinda doubtful.... Hey, the can is only $5 and it can only do good!!!!! Might as well try the easy stuff first!!!!
 

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Re: mine too

"The mechanic told me also that he noticed that the water temperature
was somewhat high. It went up to 215F at idle when the fan kicked in.
He suggested to consider changing the thermostat and the coolant
temperature sensor.

Just curious, what is the normal operating coolant temperature for
4.9 liter??"

i see temps up to 235 degrees with little or no knock or ping , took me two months to get rid of the ping , 90% of the time im running around 215 degrees (useing the the engine computer's PCM data "pm04" to get my data or was it 11 sorry its been awhile )

i persoanly see no reason to touch the distributor , only reason it may come out of adjustment is timing chain strech as he distrib is driven by the cam and even then i dont think it would be enough to screw things up

but i would get it to a mechanic to see what "knock" you have and how much $$$$ will make it go away

edit: i have 117,000 miles on the orignal water pump , keep up on basic coolant and cooling system maintenace and itll be fine
 

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You might wanna check the torque converter to flex plate bolts. I have found a few of them that had loose bolts and makes it sound like the engine is knocking! Just my 2 cents! :bouncy:
 

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The mechanic I saw couldn't tell what was causing the knock.
He only guessed...

I should take my car to someone who knows more.

elwesso, the waterpump on my previous car (83 Eldorado) faild
at 140 K. The bearing seal broke and lost all coolant while the
car was running on the highway. That's why I was wondering
the life time of the waterpump. You are right, top cleaning does
good, so why not to try.

By the way, I learned a little bit more about my OBD-1 and was
able to monitor the coolant temp. Stoneage_Caddy, you were
right, it was PD04 to get the temperature. Mine was running almost
always at less than 100 C (< 212 F), I suppose it is pretty good.
The distributor was removed, at least, twice. When it was transfered
from the old engine (the engine was replaced about 20 K ago) and
when I installed the new one. I don't want to admit, but I may not
install exactly, so unfortunately, there is a possibility...

Anyway, thanks for all help!
 
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