: Help with two noises from '97 Northstar

07-23-07, 01:08 AM
1997 Northstar.

Looking for help understanding and perhaps fixing two noises.

The first noise is an electrical vibration-like noise. It seems to come from one of two places: either
what I believe is the coil -- a black plastic-looking housing at the top, rear passenger side of the engine, or
the black iron-looking thing where the PCV valve inserts, with the piston firing order written in the metal.

Could the electrical-buzz sound be the coil? It sounds somewhat like an electrical transformer buzz. I think an ACDelco coil can be had for <$40.00 online. If it's the source of the noise could I swap it out for new myself?

The second noise is a clicking-like noise that follows RPM. It seems to be coming from the piston 1 area (rear, far passenger side). Based on what I've read, I suspect it's either carbon slap -- which seems unlikely since I run WOT multiple time per week -- or maybe a lifter/cam issue. If it's a lifter, are there any conservative (i.e. non-surgical) approaches that might relieve the noise? At this point it's intermittent, but it's present more than it isn't. Also, what could cause lifter problems? About a year ago the car was run for a couple days on very uncomfortably low oil (~2.5 under full @7.5 :alchi:), could that have led to the present problem?

07-23-07, 02:25 AM
It sounds like it could be the PCV making this noise, from the location and type of noise. Under certain conditions, the PCV element will rapidly vibrate, producing a clicking or buzzing (depending on the rate of vibration and on your ears) sound.

Your second sound... That one is likely not a "lifter" because this car uses a hydraulic lash adjuster of a type that does not readily collapse or get stuck closed. Also, if you've ever removed the cam cover on one of these engines, you'll see that it's really very clean even after 100000+ miles, and there is very little likeyhood of debris getting into it. Now, if it's really quiet, and relative to not only RPM, but to throttle position as well (powerbrake lightly to see), it could be a noisy fuel injector I suppose.

Start the car in the dark with the headlights off and look for arcing at the coils. If it has arcing, it may be a conductive contaminate under the spark wire, conducting the spark away from the wire contact. It could also be a cracked spark wire end boot.

Just to make sure I am understanding you right, I think it sounds like you are describing the same location for both sounds.

Also what is 2.5 @ 7.5? I am assuming you mean 2.5 quarts low. Does 7.5 refer to 7500 miles or to 2.5 out of 7.5 missing or what? It doesn't matter what the mileage is from your last oil change as far as the car being low. If you're 2.5 quarts low at 500 miles you're still 2.5 quarts low. How long did you drive it with the low oil notification anyway? My warning message appears with less than two quarts missing.

07-23-07, 03:28 AM

With the oil I never had a low oil indication. (I didn't know there was one). Shortly after I bought the vehicle I didn't know about all the oil issues with the car, and one time I checked the oil and it was low on the dip-stick, and I few days later I filled -- but to my dismay it took a little over two quarts to get back up to full. (2.5 quarts below a full 7.5 quarts).

The buzz noise really seems to come from what I'm assuming is the coil (it is black with numbers on it, sits on top of the engine, and it looks like the plugs come out from it).

The ticking/knocking seems to come from either the place where the PCV value inserts, or more likely the piston 1 area (from under the passenger rear side of plastic engine cover). Or maybe both areas. The tick/knock sound morfs to a rough idle-like sound when heard from underneath the car. A mechanic ran the car with the PCV valve removed, but the noises persisted.

Confounding all this is the grind from the power stearing pump which adds a ticking sound that bounces off the motor in that area (I purged the power stearing fluid and replaced the pump with a remanufactured one, but still the grind).

Is it possible that everything stems from an electrical issue beginning with the coil? It seems like the tick/knock noise ebs and flows with the buzzing noise. The tick/knock is intermittent but is present most of the time.

I will try to look at things more carefully tomorrow and post back.

07-23-07, 01:46 PM
Get yourself a stethoscope and listen to each coil. If one is arcing internally, you'll heard it very clearly. Sounds to me like that may be what you are hearing from your description.

2 qts low is not a problem and won't cause one. The CHECK OIL LEVEL message doesn't even come on till the level is just off the dip stick. That is 2 or 2.5 qts low (I forget exactly).

Use the stethoscope to listen to the alternator & P/S pump pulleys, idler and tensioner pulleys. One may have a bad bearing.

07-25-07, 03:23 PM
OK I'm still working on this one. (Many other things done in the meantime).

New Update:
The sound of electrical buzzing persists and continues to seem to come from one of two places:
The plastic housing on top of the rear passenger side of the engine, from which the spark plug originate (presumably the coils)
The metal housing into which the PCV valve inserts (near to coils but below and further along passenger side). The PCV valve seems not to be the source of the noise.

The clicking-like noise I described above has evolved into a knock-like sound, and may also be causing a bit of a rough idle. It seems to come from the piston 1 area (rear, passenger side of engine). The knock-sound manifests as a rough idle-like sound when listening to the exhaust. Perhaps importantly, I also have a new code, which wasn't present a few days prior to my initial post: PCM P0325 (Knock Sensor Circuit). Gasoline is 92 octane; original Northstar in '97 Seville STS.

I'm still waiting on the stethescope, and I haven't yet been able to observe plugs in the dark. (It's hard to find dark at night in the city).


The main question is this: does the knock sensor code shed more light on whether the electrical-buzz is indicative of a malfunction that causes the knock?
Any other, new ideas in light of the PCM P0325 knock sensor circuit code?
Are lifter/cam issues still low on the list as Zorb750 suggested?

In the meantime I intend to follow through with the suggestions of Zorb750 and Ranger. (Thanks fellas).