[CometCyclone]

One of my clients calls me today to ask me what could be wrong with his car. I am not a mechanic by trade, but this time of year I do some minor auto work if thats whats asked of me. A few weeks ago, I did a complete maintenance job to his son-in-law's truck, and bled all 4 brakes.

So, his car is either a 1999 or 2000 Buick Park ave Ultra. It has the great supercharged 3.8L V-6. He has taken relatively good care of it and had the maintenance done about on time throughout it's life. It now has 198,000+ miles on it.

As of the last time I drove the car to put air in the tires(it had a slow leak), it was running fantastic. That was about 1 month ago. He hardly ever drives it anymore, as he is now retired. But he lets his daughter and son in law drive it, even though they have their own cars.

So, he calls me today and has his son in law explain the trouble. The son in law said he drove to the local grocery store, about 2.5 miles away, and it ran just fine getting there(according to the son in law(?). But when he came out of the store to leave, the car started running really badly, totally out of nowhere..

He said it started up, but was idling badly, and their was a a noticeable shaking that he could feel through the steering wheel and his feet. When he revved it up, it acted as if it wasnt getting enough gas or maybe air, and didnt rev up smoothly or properly. But he said he drove it back home, and once it got up in speed and revs(I suppose), the shaking seemed to lessen, but once he hit a red light, the shaking got worse again.

I asked if there were any odd or strange noises when it was running, but he said no. No knocking, etc. I asked if the transmission seemed to shift alright, and work right, and he said that there wasnt any noticeable transmission problems. He just said that it shook and didnt want to idle and had problems revving up. I was unable to get over there today, and they have a day trip to go on tomorrow, so I wont be able to look at it tomorrow either, but maybe later in the week.

I recommended that he drive it 1/2 mile, or have it towed 1/2 mile to the nearby Goodyear fix it shop, but he said he didnt want to(?) He wants me to look at it first. He doesnt trust many businesses.

So anyway, it shakes badly, doesnt idle right, doesnt rev right, the shaking gets a little better at speed, but worse at low rpms at red lights. Supposedly no bad noises or knocking, no trans issues, etc.

I thought maybe an engine mount broke, but that wouldnt explain the idling problems or revving problems. If it was a major internal engine problem, there should be some nasty noises going on, but he said no...... I cannot imagine that just not getting enough fuel or air would cause bad engine shaking, at least not in my experience. It started completely out of the blue, according to the son in law.......

Note: I dont necessarily trust the son in law 100% when it comes to a potential problem that he couldve caused. He is VERY lazy, and doesnt do almost anything that he is asked to do, even though he is 48. It's possible that the problem started some time before, and he finally decided to tell my customer about it today, because he knows they were supposed to drive the car on a day trip tomorrow, so maybe he waited til the last minute to mention this problem(But I could be wrong, and I hope I am)

What could it be?

[starnest]

Sounds like a vacuum leak, but could easily be a bad plug, wire, or distributor cap/rotor. Less likely, but possible is a clogged fuel filter.

Do the easy stuff first.

Visual inspection:Check for vacuum leaks, particularly a cracked, loose, or broken hose.

Check plug wires for cracks, abrasions, or burn marks.

If these visual checks don't find a problem, then you have to check for fuel and spark to all 6 cylinders.

Check for spark:
I'd check spark first, you know how to pull a wire and let it arc to ground?
You might have to check all six to eliminate spark as a problem.

Check for fuel:
No (or low) fuel - check fuel filter (caution - release pressure in the fuel line at the schrader valve before disconnecting lines to filter). Note that pressure at the valve doesn't guarantee fuel flow. Also listen for fuel pump motor (turn key on - don't start, it should hum nicely for several seconds before shutting off). It's not likely that the pump isn't working at all or the car wouldn't run.

If you haven't stumbled across the problem yet consider/check:

Vacuum leaks on intake (spray wd40 along intake gasket(s) with engine running, listen for idle to smooth out (temporarily).

Clogged catalytic converter.

Bad O2 sensor, TPS sensor.

If it is fuel injected you should be able to hear the injectors clicking with the engine idling. Problem could be a clogged injector, identify by inspecting spark plugs, the bad injector should cause a lean condition and it should show on the spark plug.

BTW: Ignore the SIL description, first thing is start the car and hear it/drive it yourself - no sense in working on it to discover the shaking was his cell phone on vibrate.

Good luck and let us know what you find.

[LATECH]

The plastic intake was known for cracking on those, right next to th EGR standpipe in the inside of the intake. This allows coolant to get into the intake, and makes it run like poo.
It may not be this at all, but look at the coolant level and see if it is low.
After driving and shutting it off, the heat soak may have flooded the intake with coolant, after it cracked.
I have seen this hydrolock an engine, one shop told a guy he needed a new engine, I pulled a few plugs and dried them, cranked the motor over blew out the coolant and started it up, and it ran great. I only ran it for a minute to be sure the engine was OK. then we put a new intake on it.

[T-bucket23]

Sound like a classic bad coil pack. With it at idle using a well insulated pair of pliers pull the wires off the coil packs one at a time and see which ones dont make a noticeable difference. Most likely you will find 2 on the same pack that dont make any difference. Could also be the module but the coil packs are the most common failure item. once you fine the bad one you can swap it with one of the others temporarily to see if the problem moves with the coil pack or stays with the cylinder. You can then determine if the coil pack is bad. They are held down with 2 small metric screws, 5MM i think.

[sbchevfreak]

I would do the coil pack test, as well as pressure test the cooling system. The intake leak or the coil pack will both make it run horribly. Also, the coil pack will kill 2 cylinders, so it will really run like an old John Deere.

[delawarebill]

u didn't say if u got a ck engine lite ???? mileage too... if your over 100k then i'd start looking at the coil pack too... plugs if not changed since new...

[Rhansen]

X2 on a vacuum leak. Be sure to check the T underneath the supercharger snout (not easy to see) as they are prone to cracking. Also spray around the injectors while running, might need some new o-rings.

The plastic intake was known for cracking on those

The L67 didn't get the plastic intake (eaton M90) but still had the crummy intake gaskets from GM.

good luck

[rsfyj]

ill bet he got on that ole Buick and it couldn"t take it cause it has been babied most of its life... hmmm been there

[LATECH]

Originally Posted by Rhansen

The L67 didn't get the plastic intake (eaton M90) but still had the crummy intake gaskets from GM.

good luck

10-4 Rhansen, i wasnt certain if it did.It was one of those things that came to mind. I know there was an upgrade to the replacement for the previous ones that failed.
Good lookin out

[Rhansen]

aye, you can get aluminum intake gaskets for around $70 (at least they were the last time I replaced a set...)

[1966 f100 rod]

I Bet It It Is A Chicken Staring At The Shrub Beetles As The Glance Back Twice Brother
Yours Truly The Wisperer

[Glenny Good Guy]

Have you pulled the codes? Might tell you which cylinder is missing. Then you would know which plug, coil, wire or injector to look at.

[CometCyclone]

Originally Posted by T-bucket23

Sound like a classic bad coil pack. With it at idle using a well insulated pair of pliers pull the wires off the coil packs one at a time and see which ones dont make a noticeable difference. Most likely you will find 2 on the same pack that dont make any difference. Could also be the module but the coil packs are the most common failure item. once you fine the bad one you can swap it with one of the others temporarily to see if the problem moves with the coil pack or stays with the cylinder. You can then determine if the coil pack is bad. They are held down with 2 small metric screws, 5MM i think.

UPDATE:

There are 2 mistakes in the OP that need to be cleared up: The first one is that the car is not a 2000, it is a 2002 Buick Park Ave Ultra. Also, after going over to look at the car today, it was obvious that the "bad shaking" was over stated. He had also said that the check engine light was flashing on and off and sometimes staying on. So, that combined with his claim about the terrible shaking led me to believe that something was broken, out of balance, etc. Like a motor mount or something. But other people here seemed to see through the overstated shaking claim.

So, I read the opinions listed here this morning before I got started, and the coils seemed to be a likely answer to the problem.........Til I started the car. I started it up, and there was absolutely no noticeable problem with the car. It was running fine! So I let it run for 3 minutes, then took it for a ride. After driving it for about 12 minutes, I pulled into the drive way. Up til then, it had been running perfectly. BUT the check engine soon light was on the whole time.

But once I got into the driveway, it showed the first sign of hesitation. So I put it in park, and it was idling just a bit rough. So I revved it up and it hesitated a bit, but got up to 2000rpms. So I decided to shut it off, and come back in 15 minutes to fire it up again.

When I came back and fired it up the 2nd time, the hesitation was definitely worse....... It was worst just off idle, and it was slow to rev up, but it did clear up a little at higher rpms. So I shut it off.

At that point, I started to think that it probably isnt the coils, because if they were going bad, it wouldnt run good for 15 minutes, then start running worse, then get even worse after being shut off for a while. Bad coils should cause it to run somewhat consistently rough(I would imagine)

So, I then agreed with what a few other people here had posted......That there might be a coolant leak somewhere that is getting into the intake. That might explain why it ran good at first, but got worse over time, which has now happened twice.

But, the engine is sideways(as usual in newer cars), and it is also covered with a large shroud over the supercharger and 80% of the engine, plus the whole front of the engine is covered by 1. the supercharger snout/pulley, 2. alternator, 3. coil bank. So it is not so easy to look down around the engine. But the bottom of the supercharger snout was soaking wet with something, but I couldnt tell what it was because when I wiped some of it off, it mixed with 198,000 miles worth of grease, which turned it black, so I couldnt tell if it was coolant, but it was thin and runny.

Also, The intake manifold seems to be aluminum, not plastic. I can only see about 10% of it, but it is right under the supercharger, and it looks aluminum. There were no pools of coolant under the car on the driveway. There appeared to be a small pool of something by a bolt around the intake, but I couldnt reach it.

I did smell coolant as soon as I opened the car door when I got back from the drive, and when I opened the hood. There does not appear to be coolant mixed with the oil that I could see when checking the dipstick, but when I opened the radiator, there was some foamy, oily tan colored foam inside the reservoir under the radiator cap. (I have that same foamy stuff inside my oil fill tube in my work truck in the winter. I was told that it gets condensation in it.) The actual overflow tank was empty.

So, could it be an intake gasket, or a head gasket, or a coolant leak from somewhere else?

[Rhansen]

I did smell coolant as soon as I opened the car door when I got back from the drive, and when I opened the hood. There does not appear to be coolant mixed with the oil that I could see when checking the dipstick, but when I opened the radiator, there was some foamy, oily tan colored foam inside the reservoir under the radiator cap. (I have that same foamy stuff inside my oil fill tube in my work truck in the winter. I was told that it gets condensation in it.) The actual overflow tank was empty.

probably the lower intake gasket.
from your description it sounds like the car isn't overly well maintained so dont be surprised if there is more than one problem with it.

If it is the gasket, here are some useful links for the repair
http://www.regalgs.org/topic/48255-d..._1#entry286911

http://www.regalgs.org/topic/46841-d..._1#entry272983

http://www.regalgs.org/topic/44983-l..._1#entry258152

[starnest]

Originally Posted by CometCyclone

UPDATE:

So, could it be an intake gasket, or a head gasket, or a coolant leak from somewhere else?

Yes. The brown foamy stuff under the radiator cap means that some oil is getting into your coolant. At the beginning these leaks are small so you only have a little bit of oil in the coolant. Eventually it will probably leak coolant into the oil. (I just drained 13 quarts of milkshake from the crankcase of my son's monte carlo - different thread).

Since you found signs of an external link on the intake, maybe you are lucky and it is an intake gasket.

You will need to remove the supercharger, then the intake. Take your time, mark (and photograph) all electrical connectors and hoses, bag and tag your bolts. Mostly look at everything as you take it apart, look for breaks in the gaskets.

I was lucky on mine, I found the broken intake gasket (two places), and was fairly confident I didn't need to remove the heads (although some suggested I should anyway). I replaced the gasket and fixed the problem, I wasn't trying to rebuild the engine.

Good luck.