: 1994 Eldorado 4.6L Tapping Noise



akrull
07-17-04, 04:45 PM
In January, 2004, I purchased a 1994 Eldorado (4.6L 275 HP Northstar) with 33,000 miles for $9000. The previous owner had passed away and used the car only occasionally (I later found out the car was not used at all in the last 18 months of his life). His two sons are friends of mine, and the car was mechanically excellent and cosmetically perfect (no paintwork).
I replaced several components to cure some minor problems: A factory remanufactured engine computer module (new not available) fixed a shift-point problem, and a new ignition module, wires and plugs addressed other minor driveability issues.
I drive this car VERY gently (shift points at 12, 20 and 40 mph) and use only Amoco premium fuel. I attempted to use Mobil 1 synthetic, but the engine started to make noise so I drove maybe 300 yards, turned around drained the synthetic and replaced the conventional oil. I change the oil every 2800-3000 miles as did the previous owner; my friend who owns a large shop serviced the car for us both. He feels some Northstar engines are sensitive to synthetic oil.
After about three months of frequent (but not daily) use, the engine developed a tapping noise. The noise occurs ONLY at idle (in park/neutral) and ONLY at normal operating temperature (200+ degrees F.) (in other words, after the car has idled for 5-10 minutes in the driveway or has been driven). This noise was minor at first, but has worsened and can now be heard at something like 100 feet away without ambient noise.
My shop-owner friend listened with a stethoscope, but was still unsure, so he sent me to a contact at a local Cadillac dealer who suggested using Marvel Mystery Oil. After several weeks, no change. I suggested to my shop-owner/friend that the problem was not that something was sticking, but that a component was loose and that the Marvel was doing nothing. He then said that if could be a number of things, including a loose wrist pin, but that the only way to tell for sure was to open up the engine.
This friend concluded that I should leave the problem alone and "live with it" since I could probably drive the car for ten years without any difficulty. When I insisted that the noise was worsening, my friend advised me that if I really wanted to eliminate all the noise, I would have to replace the engine with a new one (approximate cost with labor about $10,000). He said that he has attempted to fix this type of problem before by repairing the engine, but that it may not completely disappear. He also stated that in his experience, a short block has not always cured the problem. Since I have invested some $10,000 customizing the car, I will not sell it; nor can I live with the noise -- the car is beginning to sound like a truck. Therefore, I am about to place the order for a new engine. Therefore:

1. Any last-minute suggestions for a total fix shy of a new engine?

2. Did synthetic oil cause or contribute to the problem in the present engine?

3. Can I use synthetic in a new engine after the first 4000-5000 miles?

4. In addition to a new engine, I have asked my friend to replace any components that would prolong engine life, including the oil pump, water pump and belts. He said most of this (if not all) comes with the engine. Any other components which should also be replaced?

5. I wanted to use a 300HP Northstar instead of my present 275HP. My friend said he would not undertake that change because too many components (including the harness) must be changed. How feasible is this change?

6. I would like to use a 1996 or later engine because it accepts organic-based coolant. How feasible is this?

elwesso
07-17-04, 08:50 PM
1. Just for kicks, look inside the oil filler cap and tlel me what it looks like... you should see clean metal... If its black with caked on stuff, its possible he didnt change the oil much if at all (33k on an oil change).....

2. Doubt it, what weight oil were you using.....

3. Yes, Id start using it right after the inital break in

4. The new engine youll be getting will probably be a short block and they will transfer all of your components (water pumps, accessories, etc)... The more you replace while the enigne is out the less you will have to do later and ultimately the less you will have to replace later.......

5. No, the 275 model has a different tranny and final drive (almost said rearend. LOL) optimized for htat power curve...

6. Next to impossible... Complete redesign incuding OBDII... The basic engine didnt change so I would assume you could use this organic coolant (your talking dex-cool right)..... I would be leary of using anything but the ethelyne-glycol coolant, which is even what dexcool is based from......

Another note: It could be there is just some gunk built up..... I would try driving the car more aggressively and see if that does anything..... get that oil pressure up and the stuff moving......

Welcome to the forums, thanks for signing up :wave: Bummer on finding a ultra low mileage with bad condition......

Ranger
07-18-04, 12:23 AM
Did anyone check to verify that there is infact oil pressure? If there is none, you may have a check valve stuck on the oil pump. If that is the case, overfill the crankcase by 8 qts and rev the engine to about 3000 RPM. That will submerge the pump, mounted on the crankshaft snout and force it to prime and flush out any debrie in the check valve.

wake
07-18-04, 12:53 AM
The 94 I previously owned developed a slight tapping also, but it seems you already tried what cured my problem (Marvel Mystery Oil)... Synthetic shouldn't have caused you any problems... I've been using synthetic oil for almost 15 years now in various cars without any problems...

I'm wondering if maybe there is a reason the car only had 33K miles on it???

akrull
07-18-04, 10:34 AM
Did anyone check to verify that there is infact oil pressure? If there is none, you may have a check valve stuck on the oil pump. If that is the case, overfill the crankcase by 8 qts and rev the engine to about 3000 RPM. That will submerge the pump, mounted on the crankshaft snout and force it to prime and flush out any debrie in the check valve.
Thanks very much for the info. I will have my shop perform the test with me on Monday.

Gratefully, Alan

akrull
07-18-04, 10:41 AM
The 94 I previously owned developed a slight tapping also, but it seems you already tried what cured my problem (Marvel Mystery Oil)... Synthetic shouldn't have caused you any problems... I've been using synthetic oil for almost 15 years now in various cars without any problems...

I'm wondering if maybe there is a reason the car only had 33K miles on it???
Good. I will use synthetic after the break-in period. Since the two brothers who sold me the car know they would never hear the end of it if I suspected any questionable history on the car and have been friends of mine for years, I would think they would not attempt to sell me other than a "straight piece".

Grateful for your reply.

Alan

Spyder
07-18-04, 01:18 PM
Just a shot in the dark, but check the belt tensioner and pulleys to make sure they're tight enough...Scared the hell out of me one day after getting on it hard and heard a tick tick tick that was loud enough to hear over the radio with the windows closed...turned out I had a loose motor mount which caused the tensioner and pulley to both be loose...probably nothing to do with your problem, but its worth a free check, eh?

akrull
07-18-04, 01:27 PM
Just a shot in the dark, but check the belt tensioner and pulleys to make sure they're tight enough...Scared the hell out of me one day after getting on it hard and heard a tick tick tick that was loud enough to hear over the radio with the windows closed...turned out I had a loose motor mount which caused the tensioner and pulley to both be loose...probably nothing to do with your problem, but its worth a free check, eh?

Thanks for the input. I'll pass it on to my shop on Monday.

Raze
07-19-04, 11:23 AM
Hey if you can't diagnose the problem and you end up just swapping out the engine take a look at www.jasperengines.com, they 'beef up' the standard parts and fix known issues, for instance they timsert every N* use better pistons and heads and some other parts. A new engine (provided you send them your used one) will run you about 5k. Add installation, and it still has to be cheaper than the 10k you're willing to drop on a Caddy dealer install. Oh btw, did I mention the engine comes with a 3 year/75,000 mile warranty, you really can't beat that for that price on a new N*.

just my .02

KingCaddy
07-19-04, 04:30 PM
Akrull,

I agree with elwesso: " It could be there is just some gunk built up..... I would try driving the car more aggressively and see if that does anything..... get that oil pressure up and the stuff moving......"

You may have carbon rap from not getting on it..These are high performance motors, not grocery getters..
Get out and floor it...watch to see what blows out the tailpipes...you won't hurt anything...get it good and hot and run it up to 80mph in second gear , then let it coast down to 40 mph..do that 5 or 6 times and tell me that it doesn't run and sound better... :bouncy:
just my .02

jim

97cherry
07-19-04, 05:54 PM
Sorry to "dip" boys, but could "not getting on it" be the reason my 97ETC, while at idle, sort of sounds like a desiel? Sort of ?...I'm affraid to "get on it" as I'm recovering from an Inner oil pan leak (fixed, under warr)..
Thanks.....I love this site...I'm getting all my queries answered..YA'LL ROCK.

I'd love to "blow the cobwebs" outta her.
kdw :)
:) :bouncy:

STS 310
07-19-04, 08:00 PM
Make sure your oil is topped, and cooling system is ok, then womp on it!!!!! :burn:

akrull
07-19-04, 10:06 PM
Hey if you can't diagnose the problem and you end up just swapping out the engine take a look at www.jasperengines.com, they 'beef up' the standard parts and fix known issues, for instance they timsert every N* use better pistons and heads and some other parts. A new engine (provided you send them your used one) will run you about 5k. Add installation, and it still has to be cheaper than the 10k you're willing to drop on a Caddy dealer install. Oh btw, did I mention the engine comes with a 3 year/75,000 mile warranty, you really can't beat that for that price on a new N*.

just my .02
Checked out Jasper and have sent the link to my repair shop (who actually is not a dealer). Thanks very much. Things may not be as dismal as I thought.

akrull
07-19-04, 10:11 PM
Akrull,

I agree with elwesso: " It could be there is just some gunk built up..... I would try driving the car more aggressively and see if that does anything..... get that oil pressure up and the stuff moving......"

You may have carbon rap from not getting on it..These are high performance motors, not grocery getters..
Get out and floor it...watch to see what blows out the tailpipes...you won't hurt anything...get it good and hot and run it up to 80mph in second gear , then let it coast down to 40 mph..do that 5 or 6 times and tell me that it doesn't run and sound better... :bouncy:
just my .02

jim
Took that advice and drove at about 95mph for 8-10 minutes. Then about 60 in 3rd. Let the car cool down with easy driving for 10 minutes and then listened. Unfortunately, no change, but thanks, nonetheless.

Ranger
07-19-04, 10:38 PM
Sorry to "dip" boys, but could "not getting on it" be the reason my 97ETC, while at idle, sort of sounds like a desiel? Sort of ?...I'm affraid to "get on it" as I'm recovering from an Inner oil pan leak (fixed, under warr)..
Thanks.....I love this site...I'm getting all my queries answered..YA'LL ROCK.

I'd love to "blow the cobwebs" outta her.
kdw :)
:) :bouncy:
In a word, YES. Babying it can cause excessive carbon build up in the cumbustion chamber. When the piston contacts in at TDC it causes the piston to rock on the wrist pin and the piston skirt slaps the cylinder wall, hence piston slap. Cure this by planting your right foot firmly on the floor and do not remove it til it shifts aka WOT shifts. If you are carboned up you'll see clouds of carbon in the rear view mirror. Do this until you no longer see it and then once a week as preventive maintainance.

97cherry
07-20-04, 10:40 AM
Well, I don't know if I "baby" her. I drive 80 mph to work every day, that's 25 miles each way? Other than that, I am careful. Would you say that's baby-ing?
(when oil is hot, I see the "add" is covered on dipstick, but that's it, should I put in more oil?)

kdw ;)
:bouncy:

Ranger
07-20-04, 12:30 PM
Well, I don't know if I "baby" her. I drive 80 mph to work every day, that's 25 miles each way? Other than that, I am careful. Would you say that's baby-ing?
(when oil is hot, I see the "add" is covered on dipstick, but that's it, should I put in more oil?)

kdw ;)
:bouncy:
Yes, that is babying it. At 80 it's probably turning less than 2500 RPM. It needs to be wound right up to shift point (about 6000 RPM) at WOT. That will keep it cleaned out.
No, do not add oil. Run it at the "add" mark. If you top it off to the full mark you'll just suck it thru thre PCV and burn it. I only put 7 qts. at oil change and don't add till it drops off the dipstick or the "Chech Oil Level" indicator comes on. My oil consumption has been cut in half with these two proceedures.

97cherry
07-20-04, 01:40 PM
Sweet...I never knew I was such a "mother"..hahahh, OK, I'll do it....So, should I "floor it", literally?....She (cherry, my girl, my car) always shifts and runs around 2.500 rpm. you got that right mister....I really, really, really appreciate ya'll..
Oh, can you please explain what "WOT" means? (I'm a girl, but w/ a mechanics heart, and LOVE for cars)

kdw :)

elwesso
07-20-04, 06:20 PM
WOT is WIDE OPEN THROTTLE.. Pedal to the metal.....


you really gotta, for lack of a better term, beat the shit out of these cars in order for them to really stay nice... I took my Q45 (which has an engine essientially the same as the northstar) and there was a stretch of a mile or so where she didnt see anything below 40000..... The car LOVES being treated like this...

Believe me, if your fluids are good and its been maintained, you cant drive these engiens too hard..... I make it often to make sure I get the revvs up.....

Go out there and let the northstar stretch its legs out... Redline as often as you can... The thrill is unbelieveable...... :burn: <---- Except with the front wheels!