Engine Vibration - Causes?

[Dangermouse]

Some of the time, my engine is pretty smooth, vibration wise.

However, sometimes, usually in the afternoon when the weather is warm, it will develop a shudder at idle in traffic, enough to make the whole car shudder.

(I like to think that other drivers see it and are amazed that I am taming a huge HP engine under the hood. :) )

If it is relevant, my idle always runs slightly high at 1100, but the vibration comes and goes.

I'm guessing fuel?

Any suggestions on where to start?

[Farrar]

Silly question: is this your DeLorean you're talking about? Because my PT Cruiser Turbo does the same thing, and it's worse when the a/c is running.

[Dangermouse]

Yes, it's my D.

This is a DeLorean forum and I can't stand it when people post irrelevant stuff on here, like movie reviews etc.

:p

It's definitely not AC related.

[Ozzie]

OK, this is probably about the DeLorean but Farrar's comment reminded me that I had the same issue on the Mazda 3. At a stop light with the AC on, the engine would shake the car a bit. Poking around the engine bay, I found that the engine mount --right by the AC--- was bad (Ford oil filled ones - which commonly leak after a few 10K miles), so when the AC compressor engaged, it shook things up a bit because the mount was not dampening.

So with relevance back to the D, if this happens always at the same idle, then you should check out your engine mounts, look for any tears in the rubber. If this is happening at different conditions on the same idle, then something may be affecting the normal idle, like leaky CSV or maybe bad spray/leaky injectors, or ...etc.

[Jonathan]

Not sure it's the same shuddering, but any time my car has done this, it was related to getting the engine wet washing the car.

A few seasons back, I must have got a bit too liberal with the hose and when I sprayed things down, and likely got a plug wire cap or two wet. It wasn't immediately, but as I went to a car show that night about 10 miles from my home, I think it did it when I pulled into the lot. I think it did it again when I left, but by the next day or so, it had dried itself up and was good to go. No more spraying wash water on the engine cover from that point forward...

[Dangermouse]

I have experienced the "wet" shuddering and this is similar but not as extreme. No rain or washing here recently.

20 minute drive in the morning, ambient of 65, engine smooth even after it gets up to temperature. No shuddering.

20 minute drive in the evening, ambient 80, the engine immediately displays a whistle (indicating a vacuum leak somewhere) and after 5 minutes, say, it will sometimes develop the shudder. But not always, so I am not sure that the vacuum leak is related. I am fairly sure that it has shuddered without the audible whistle, but I am not positive

I have to assume that engine temp is similar morning and afternoon, despite the 20 ambient differential.

Next day, same pattern.

[Jonathan]

So if the engine temp stays the same, yet the ambient air temp outside appears to have an effect... what systems could/would be affected?

(...more flow diagram type troubleshooting rather than knowing anything DeLorean specific in advance...)

If a higher ambient air temp was causing it, you could look at where that air goes. Some air comes in to the car but not all gets into the engine. If the hotter ambient air hitting the radiator was the issue, your cooling system would have to work harder to compensate. This could be one thing to look into like your fans or if they are stressing out the electrical system with their load. Any idea if your voltage gauge reads differently when the shuddering happens?

Air comes into the cabin under the windshield. Hotter air coming in doesn't really mean much for the engine to shudder unless the warmer cabin meant you were using the A/C more and that was again causing the shuddering from the compressor vibrating near a mount (like mentioned above), or the compressor cycling on was doing something with the electrical system.

Warmer air entering the engine could have an impact on cylinder firing performance... not necessarily directly, but could if it was a function of something else happening. Is your air filter in pretty good shape? I don't see anything special about the standard DMC filter which would let more or less air through dependent on the temperature of that air, but I guess if there were some foreign filter in there it could be a restriction.

Do you have the three-way valve on the air inlet over by the coolant tank? What that thing is supposed to do is keep the pathway open to outside once it gets up to a certain temperature, but if it is cold, like starting your car in the winter, it flaps over to the air pathway coming from inside the engine bay (and specifically from the exhaust manifold stove connection on the passenger side). If somethign screwy was going on with when and how that valve is moving, it could be pinching off air flow which could cause some poor cylinder firing performance among other things.

If it is a vacuum leak, of course sealing the leak up is ideal. But why you would only hear the vacuum leak above a certain ambient temperature would seem like it was some vacuum pathway that only opens at certain temperatures. I don't know too much about what all those pathways are, but in terms of ones that come on and off at any time regardless of temperature, you might look at the connections on your vacuum solenoid valve. Make sure the electrical connection is good and the hoses are on the right ports. This thing opens and closes when your idle microswitch is engaged and if you're saying you see the shuddering at idle when stopped at a light, it could be something screwy with it.

Vacuum routing picture attached.19355

[Ron]

However, sometimes, usually in the afternoon when the weather is warm, it will develop a shudder at idle in traffic, enough to make the whole car shudder. Try pulling the plug wires one at a time while it is acting up. If you get to one that don't change the engine (you should since it is "extreme") check out that plug (shut it off immediately and let it cool first to protect the threads in the head). Which plug (or none) can give you good clues.... check out vacuum lines ports, runners, wires, etc. for that cylinder. Maybe swap lines/injector...anything to narrow it down systematically.

[dmc6960]

An audible whistle is often a dislodged fuel injector. Check all your injectors and retention clips to make sure they are fully seated. A dislodged injector could also easily cause a shudder.

[WelmoedJ]

Do you have the three-way valve on the air inlet over by the coolant tank? What that thing is supposed to do is keep the pathway open to outside once it gets up to a certain temperature, but if it is cold, like starting your car in the winter, it flaps over to the air pathway coming from inside the engine bay (and specifically from the exhaust manifold stove connection on the passenger side). If something screwy was going on with when and how that valve is moving, it could be pinching off air flow which could cause some poor cylinder firing performance among other things.

The so-called three-way valve (actually called air inlet valve, part to the cold start air system) uses a temperature controlled valve with wax to open or close the valve.
This system doesn't always function properly.
Sometimes the valve doesn't open fully when the (ambient) temperature should make it stay open fully.

A lot of car owners have removed the valve and use a cold air intake, avoiding the possible problems of the air inlet valve.

If your car still has the original air intake system, check that valve or remove it.

[Ron]

Unless you are going concours, the best thing to do is remove it, in our area. They do little more than cause problems, on all cars, in similar areas.

Consider:
"The flap is fully open to exhaust manifold heated air at temperatures below 15°C (59°F). As ambient temperature increases, the flap allows a mixture of hot and cold air to enter the engine until 25°C (77°F) is reached."
And, how long it takes to get the exhaust manifold up to 77°F in the ATL area...

[Dangermouse]

An audible whistle is often a dislodged fuel injector. Check all your injectors and retention clips to make sure they are fully seated. A dislodged injector could also easily cause a shudder.

Funny you should say this. I have been wondering if they are too loose/weak, so I just ordered a single boot and clip (as a test) to exchange and see how tight a new one is. If there is a noticeable change, then I'll order the other 5.


Unless you are going concours, the best thing to do is remove it, in our area. They do little more than cause problems, on all cars, in similar areas.

Consider:
"The flap is fully open to exhaust manifold heated air at temperatures below 15°C (59°F). As ambient temperature increases, the flap allows a mixture of hot and cold air to enter the engine until 25°C (77°F) is reached."
And, how long it takes to get the exhaust manifold up to 77°F in the ATL area...

Nope, removed this a couple of years ago. My first HP upgrade :thumbup:

[Ron]

Funny you should say this. I have been wondering if they are too loose/weak, so I just ordered a single boot and clip (as a test) to exchange and see how tight a new one is. If there is a noticeable change, then I'll order the other 5.Unless I am missing something, I wouldn't think it would come and go the way it sounds...

[Dangermouse]

Well, I think in the end this vibration may have been cause by our old friend - bad grounding.

I noticed that the vibration was worse on damp or rainy days, with the voltmeter reading low. A first I thought it was a result of having lights and wipers on, but that may just have been part of it but another thread on here about impulse coil voltage and erratic running made me look again at it.

So I cleaned the connections on the alternator (4 brown wires) and the main frame ground on the RR engine mount. Cleaned the (what I presume is) oil pressure switch connection while I was there.

Voltmeter is reading a bit higher now and the engine has smoothed out with no bad vibration. Litmus test will be the next time it is damp or the humidity is high.

Interested to note that my engine temp gauge jumped up a segment too, presumably as a result of the cleaner Engine ground. Used to sit at the first mark and now is at the center one.

Bad part is that my oil lamp flickers sometimes at idle. Self inflicted or a real issue - more investigation is needed.

(Still an occasional whistle though. I'll post a video later as I am wondering if it is mechanical rather than air. )

[Ron]

Just a thought, maybe related...
I noticed in another thread you mentioned your oil fill cap was loose. That is a source for a vacuum leak and throwing off your CO setting...

[Dangermouse]

That's certainly one of the things I am looking at. I have tried clamping it down to see if it made a difference. It didn't seem to, but if course it may not be sealing completely.

[WelmoedJ]

Just a thought, maybe related...
I noticed in another thread you mentioned your oil fill cap was loose. That is a source for a vacuum leak and throwing off your CO setting...

The oil filler cap is a breather for the crank case (PCV).
No vacuum there.

[Ron]

The oil filler cap is a breather for the crank case (PCV).
No vacuum there.
From D:06:02

"The engine oil filter cap is also connected to the
cold start valve air tube. This allows any engine
vapours to be drawn from the crankcase through
the left valve cover to the cold start valve air tube.

...

4. The closed crankcase system does not have an
air inlet for air circulation within the crankcase.
This system applies manifold vacuum to the
crankcase which is completely sealed to
outside."

EDIT: FYI- PCV means "Positive Crankcase Ventilation" ...Positive means it is under vacuum.

[WelmoedJ]

From D:06:02

"The engine oil filter cap is also connected to the
cold start valve air tube. This allows any engine
vapours to be drawn from the crankcase through
the left valve cover to the cold start valve air tube.

...
According to information on this PCV system air is drawn from the air cleaner through the oil cap and then routed into the intake manifold (using its vacuum).



4. The closed crankcase system does not have an
air inlet for air circulation within the crankcase.
This system applies manifold vacuum to the
crankcase which is completely sealed to
outside."

EDIT: FYI- PCV means "Positive Crankcase Ventilation" ...Positive means it is under vacuum.

Although vacuum in the intake manifold is used to create a flow from the air cleaner via the oil cap to the intake manifold, it doesn't mean there's a vaucum inside the crank case.
The air flow created by the intake manifold vacuum is only used to draw (blow-by) vapours from the crank case.
If there was a vacuum inside the crank case, the vapours would stay inside the crank case.

So, there is a vacuum - I agree to your correction of my previous statement.

[David T]

According to information on this PCV system air is drawn from the air cleaner through the oil cap and then routed into the intake manifold (using its vacuum).




Although vacuum in the intake manifold is used to create a flow from the air cleaner via the oil cap to the intake manifold, it doesn't mean there's a vaucum inside the crank case.
The air flow created by the intake manifold vacuum is only used to draw (blow-by) vapours from the crank case.
If there was a vacuum inside the crank case, the vapours would stay inside the crank case.

So, there is a vacuum - I agree to your correction of my previous statement.

In the strictest sense the crankcase is not under vacuum. There is air flow, enough to keep the crankcase at atmospheric. Air is going in to replace the air being removed. Positive Crankcase ventilation means the air is being forced (directed) as opposed to the earlier type of ventilation, an air tube usually coming off of the highest point of the motor, generally a valve cover and any pressure being expelled to the atmosphere. In PCV that air is run through the motor so any hydrocarbons can be burned. Most manufacturers use a calibrated orifice AND a check valve to prevent any blow-back from a back-fire. The Delorean only has the calibrated orifice. Too much vacuum and you suck oil in from the valve stem seals.
David Teitelbaum

[Ron]

Not me Welmoed, I just cut and pasted it LOL


I was looking up something else and spotted this just one page down (D:06:03...figures ;-).
Would have been a much simpler answer:

b. An air leak in the engine crankcase will
cause a lean running condition since the
crankcase is connected to the intake
manifold. Possible air leaks could be the oil
dip stick not installed completely, oil filler
cap not sealing properly, or leaking engine
gaskets.

[Dangermouse]

Interested to note that my engine temp gauge jumped up a segment too, presumably as a result of the cleaner Engine ground. Used to sit at the first mark and now is at the center one.

Bah humbug! The DeLorean gods poke me in the eye once more.

Higher reading on the temp gauge wasn’t due to improved grounding. It was due to higher coolant temps due to non-operational cooling fans:


http://dmctalk.org/showthread.php?7467-Frickin%92-Diodes-!-%28Cooling-Fan-Circuit%29&p=109269#post109269