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Concorde started shuddering badly over 45 mph

755 Views 23 Replies 7 Participants Last post by  yevrah
I made a couple trips this morning and the car was fine. I was driving at around 45 when all the sudden, the car started shuddering significantly. If I stay at a little over 40 and below, the car was drivable and I made it home. It also ran a bit rough when I waited at traffic lights.

I thought it might be the transmission. In the past, it would clunk every once in a while when I coasted and then accelerated. I put the transmission in neutral, stopped at a light, and it still ran a bit rough. When I accelerated from a stop, the transmission shifted gears normally. Car just ran a bit rough, not bad. Get up in the 40's and it starts shuddering. Start coasting and it's just a little rough.

I don't think this has anything to do with the suspension or tires. They are in good shape. Check engine light is not on. I used my Scan Gauge to check for codes and there weren't any. Checked the transmission fluid and it's at the right level.

Any suggestions would be appreciated.
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Spark plugs may be going bad or something is fouling them up.
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I wouldn't lean on transmission bring the issue...yet anyway.

What motor you have there? If year 96 and up (obd2), you might have a pending code of a misfire. Ok if you have the 3.5, you might have oil fouled plugs or oil fouled plug boots from leaky tubes.

Could also be corroded coil pack towers, could be dirty injector from like water in fuel. Could be a few other things...

Forgive me for not knowing - are for someone who wants to do some diagnostic work? There are some things you can do to help narrow down where the issue is, etc.

I would at this point think it is a single cylinder miss fire based on what you describe and my own experience. Sudden onset means it isn't low compression due to age, etc. It is fuel or spark.

Any difference if engine warm or cold?

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I am having a shop check out the car. They said the compression on one of the cylinders is 15. They are removing the valve cover to investigate. Doesn't sound good to me.
That sucks. Seems the remaining 1st gens all want to retire and rejoin with their long forgotten brethren in car heaven.
Compression doesn't generally go from ok to bad overnight...

Maybe you slipped a timing belt???

I gotta look at what motor you've got.

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I don't see it. If you have the 3.5 and the belt hasn't been changed in 120 thousand miles, it might have slipped. The 3.5 is NOT an interference engine. Put a new belt on if the belt slipped a tooth.

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It's a 3.5. The timing belt was changed about 25,000 miles ago. I don't know if time matters, but that was in 2007. They did say that the compression in the two adjacent cylinders was good.

I thought engines just wear out slowly over time. It seems strange to me that a piston or valve would just suddenly fail. I've taken good care of the engine, while I've owned the car.

I haven't received any updates from the shop yet.
If it was timing, I would not think just one cylinder would be grossly affected.
Could it be the head gasket? The car has about 165,000 miles on it.
GENERALLY speaking, head gasket would take out two cylinders.

Age of belt can affect things, but like PEVA said, it would be in more than one cylinder. You'd get a wide range of differing pressures all over the place.

A ring can break, a piston can get a hole, a valve can burn... All those things are possible.

But in general, not in these engines at only 165k. The first gen 3.5 in my experience and observation, is bulletproof to 250k if mildly taken care of, and it's the crank bearings that go.

I'm really curious to know what's going on with it.

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Have you checked your oil level? If it’s above the fill mark, coolant might be seeping into the cylinders and fouling up the plugs, causing the misfire/shuddering/low compression.

I had this problem when water pump #1 showed signs of failure. My 3.5 started shaking after restarting it from a long drive. The impeller cracked in two not long afterwards.
I checked the oil about a month ago and it was the right amount. I don't usually have to add any in between oil changes. I've always used synthetic since I got it in 2007. I don't drive it that much. Maybe 1 or 2 times a week.

I think they removed the spark plug to do the compression test.

The water pump was replaced with the timing belt about 25,000 miles ago.
I would pull the covers and check the cam shafts. Severely worn lobe could be the cause of low compression in 1 hole.
If the pump has a plastic impeller they tend to wear out prematurely (that's not to say the pumps with the metal impeller are any better - the LH cooling system sucks in general).

I've gone through two water pumps and two rads in the last 10 years. Most I've ever got out of a water pump before the impeller died was about 49,000 kilometers (roughly 30,000 miles). I wouldn't be surprised if there is coolant floating around in one of the cylinders.
Couldn't they use an endoscope that they could insert into the spark plug opening and check the rings and piston? I would think they would have one.

Is there a non-invasive way that they could check the valves, besides taking the car apart?

Last I heard from them is that they were taking the valve cover off, about 1:00 PM, yesterday.
Any updates?

Removing the valve covers isn't such a big deal. To check compression you have to remove the spark plug.

No amount of water pump issues will cause low compression.

Worn cam lobes can do it, yes... But overnight? And with that low a miles?

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Finally got an update this morning.

He said after taking the valve cover off, he tighten everything down and now the compression is 140. Now they are replacing the coil pack and sparks plugs to see if that fixes the problem.

I'll post updates when I get them.
Finally got an update this morning.

He said after taking the valve cover off, he tighten everything down and now the compression is 140. Now they are replacing the coil pack and sparks plugs to see if that fixes the problem.

I'll post updates when I get them.
That's weird. 🤷‍♂️
Wow! Ok, I really don't want to see another 1st gen go down. This is exciting.

Odd, but exciting!

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