Engine runs rough when oil cap removed

Or maybe you hear a skipping sound when the engine is running.

engine runs rough when oil cap removed

All these are symptoms of a rough idle. Incidentally, the mechanics at JL Motorworks are experts at quickly diagnosing the root cause of your rough idle. Call to schedule an appointment today! As with many car issues, the root cause of a rough idle can either be a quick, easy, inexpensive fix, or it can be something more serious and costly.

The idle speed of an engine is the rotational speed of the engine when it is not connected with the drivetrain and the throttle gas pedal is not being depressed. According to Mister Transmission :. The drivetrain includes the transmission, the driveshaft, the axles, and the wheels. Simply put, it works in conjunction with the engine to move the wheels.

The drivetrain system is an essential component of a vehicle and the transmission is an integral part of the drivetrain. When an engine is running at idle speed, it generates enough power to operate systems such as the water pump, alternator, and power steering — but not enough power to move the vehicle itself. A passenger car will usually idle between RPMs. A properly functioning idle should feel smooth — no bumps or skips.

Express Auto Inspections says:. While modern vehicles use a fuel injector system to burn gas, many older cars use a carburetor to process fuel. As your car rolls along, the engine takes in a mix of air and fuel that allows it to keep moving.

This intake relies on a vacuum that is created between the carburetor and the piston tops… If there is a leak in this vacuum, the ability for your car to gain energy from the burning fuel is compromised, causing rough idling. Fuel filters screen contaminants out of the fuel before it goes into the engine. No need! Fuel injectors inject fuel into the cylinders to create a mix of air and fuel to burn. They need periodic TLC to keep gunk from building up. A rough idle could simply be the result of an incorrect idle speed setting.

A trained mechanic can reset your idle speed setting easily. Spark plugs create the spark that is needed for your car to burn fuel. Damage to spark plugs or spark plug wires can cause a rough idle, as your engine is struggling to process the fuel it needs to run smoothly.

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This can cause the car to have higher revolutions per minute, shake while idling, produce a high-pitched squealing noise and even begin to stall or backfire.I purchased a car a month or two ago and was recently told that if there is air coming out of the oil fill cap it was a sure fire way to tell if your car was about to die.

So out of curiosity I checked my car and discovered a light flow of air coming from the oil fill cap. My friends car does it much worse and he is also concerned about it. So my question is, do I need to be making plans to buy a new car or is the current motor fine?

Positive meaning positive pressure. Its is OK along as that postive pressure that is created in the combustion chamber and blows by the rings hence its name "blowby is not excessive. The PCV valve uses engine vacuum to scavange the cranckcase. Engines that do not use a PCV use a fixed orfice system which is really a calibrated vacuum leak. The only remedy for it is a rebuild with new piston rings, etc.

It went for another 60KM without much trouble and then I sold it mostly because of Carburetor issues rather than oil consumption. Trust us, there is no problem here. You and your friend are seeing the very normal by-product of combustion in a gasoline engine.

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Every time a cylinder fires, a lot of cylinder pressure is created, and some slips past the sealing rings of the piston, and gets into the crankcase.

It naturally increases with age as the cylinder rings wear. You and your friends cars have a lot of life left in them, most likely. If your really concerned, you can have a competent mechanic run a compression test. This is a much better indicator of cylinder condition that trying to read the blow-by gasses. A leak-down test is even better. Tester July 5,pm 2.

engine runs rough when oil cap removed

Caddyman July 5,pm 4. BustedKnuckles July 5,pm This is the case of a little bit of knowledge is a dangerous thing.Remember me. Hello and welcome to the Audizine Forums! As a guest, you are welcome to poke around and view the majority of the content that we have to offer, but in order to post, search, contact members, and get full use out of the website you will need to Register for an Account.

It's free and it's easy, so don't hesitate to join the Audizine Family today! If you're new to forums in general, be sure to check out the Forum FAQ. To start viewing posts, select the forum section that you want to visit from the selection below. PCV Valve bad? Results 1 to 9 of 9. Thread: Engine runs really rough when oil cap is removed.

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My Classifieds: 0. Engine runs really rough when oil cap is removed. Guest-only advertisement. Register or Log In now! I was told to possibly the PCV valve which I replaced 2 years agoand to check it by opening the oil cap on a running engine: 'If you can't remove the cap then the PCV is not working. Does this still indicate PCV Valve?

Engine will run bad once removing the cap regardless of the PCV being bad. You are creating a major leak. The PCV is bad if the cap is hard to remove due to suction.

If you need to use more force than usual then the PCV is bad. Sounds like its not that if it's not difficult to remove.

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Sent from my iPhone using Audizine. If you are using that amount of oil and it has been a drastic change from what you normally see I would check to see if you have separation or a crack in the valve cover.

Last edited by Theiceman; at AM. The cap should be difficult to remove with the engine idleing. What that means is that the PCV valve is working properly at idle. But as Theiceman said above, that doesn't necessarily mean that the PCV valve system is working correctly, specifically under boost conditions.

When the manifold pressure goes from vacuum conditions at and slightly above idle RPMs to positive pressure boost conditions the PCV valve closes to the IM but opens to the pre-turbo port right side front of the VC to continue to keep the crankcase under vacuum to remove blow-by pressure from the crankcase.

This part of the crankcase system should be assessed also to see if the PCV valve is functioning correctly at all RPMs. Wow such a great description brillo. Originally Posted by brillo. What that means is that the pcv valve is working properly at idle. But as theiceman said above, that doesn't necessarily mean that the pcv valve system is working correctly, specifically under boost conditions.

When the manifold pressure goes from vacuum conditions at and slightly above idle rpms to positive pressure boost conditions the pcv valve closes to the im but opens to the pre-turbo port right side front of the vc to continue to keep the crankcase under vacuum to remove blow-by pressure from the crankcase. This part of the crankcase system should be assessed also to see if the pcv valve is functioning correctly at all rpms.

When your PCV valve goes bad, it will be damn near impossible to remove it at all. Another sign of it starting to fail is oil getting pushed through your valve cover bolt seals or having oil on your oil cap. The excess pressure pushes on the cap making it almost impossible to open and the excess pressure will try to push oil out anywhere it can, like the cap or bolt seals.

Originally Posted by EvolutionArmory.I'm trying to sell my car.

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Twice this week people came and while the engine was running they removed the oil cap which caused a change in the sound of the engine. Now my 'check engine' light comes on. Is it because of what they did?

Top 10 Causes of a Rough Idle

Why were they doing that? Should I stop people from doing that? Is this likely to need an expensive fix? They are checking for blow by, when the rings go bad, it will cause pressure to build up in the crank case and you can tell by removing the oil cap. If I were looking at a used car, and the owner told not to take off the oil cap, I would walk away, so if you want to sell the car, your going to have to let them check it over.

Yes it might be related to that. Go to autozone and have the code scanned and reset. Hopefully it won't come back. People should NOT check for oil or open the oil filler cap when the engine is running. Just explain to the people that is a dumb thing to do and turn off the engine first.

If nothing else, it will splatter the oil all over your engine valve cover. As with most all 4 stroke cycle engines. They use a vent whether PCV positive crankcase ventilation or small engines use similar vent.

This is designed for a negative atmospheric pressure. A vacuum. Why anyone would take oil fill cap off is beyond me. This will clear any codes that came up.

I think that your vacuum was lowered due to removal of oil fill cap.Our Address. Kings Mills, OH Hello Eric. I have a Nissan N17 car. Since some days, my car is not running smoothly.

Sometimes it gets back to normal, then again I get the same problem. At first, I thought that there might be problems with the spark plugs. So I changed all of them and inserted new NGK spark plugs. But the problem persisted. I then thought that it might be due to leakage in the exhaust pipes. I brought the car to a specialist in repairing exhaust system. There was no serious leakage but still he changed the old pipes with new ones as a precaution. The car came back to normal as I was driving back home.

engine runs rough when oil cap removed

Then, I took it to a garage. The mechanic tested the spark plugs, their cables. He then started the engine and removed the oil cap. However, as soon as he opens the oil cap, the engine shuts down. All the mechanics at the garage have seen such a situation like this for the first time :ohmy: They say perhaps there are some problems related to the cylinder head. Is it normal that the engine shuts off after the oil cap is removed? Is it related to the rough idling and not running smoothly?

The mechanic inserted synthetic oil, also changed the oil filter. Well that is a weird and unusual problem. About all it does is let air into the valve cover area. Which suggests that there is something wrong with the 1 or 2 hoses that go from the valve cover to the PCV valve and to the air intake. If someone accidentally swaps those two hoses, then the PCV valve is not in the right hose and taking off the oil cap will send lots of air into the intake manifold, basically a large air leak after the throttle plate and mass airflow sensor.

The engine is sealed to give a negative air pressure condition when running. The injector pulse width gets very small and the engine roughens or dies.

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So, no worries that is normal and demonstrates the importance of gaskets sealing in negative pressure systems. I have seen bad valve covers cause running issues. Thanks bro! I actually discovered that when I had a Nissan Z when I was in high school. Took it to a friend that worked at the Nissan dealer and he explained how it worked to me. Mine does the same exact thing. Mine a Buick 3. I just never noticed it before. Mine will run very badly and shut off!

Finally the problem has been solved. The mechanic has actually discovered a defective ignition coil that was causing this problem. He said this is a common problem with Nissan Cars.We use cookies to make the site easier to use. Read our cookies policy.

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Hi there, Have a vw polo for sale. Had a buyer come round to see it, and with the engine running, he removed the oil cap on the engine. As soon as he did this the engine started whirring and wheezing. He did this a couple of times and pointed out that something might be wrong with the engine? Could he have caused any damage to the engine? And was he right? LandyAndy Forumite Strider Forumite Gloomendoom Forumite Forums New posts Search forums.

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Runs rough with oil cap removed

Log in Register. Search titles only. Word Count:. New posts. Search forums. Log in. JavaScript is disabled. For a better experience, please enable JavaScript in your browser before proceeding. Engine idle drops when oil cap is removed.

Guessing this isn't normal? Thread starter dcx13 Start date Mar 29, Tags cap engine idle oil. Put the cap back on The only other oddity, with similar effect on rpm, is when the brake pedal is depressed, there's an increase of roughly rpm. Because both are changing rpm characteristics, it leads me to believe there's some sort of a vacuum issue.

But the oil cap off weirdness has me really scratching my head on this. Any thoughts? That is normal. Don't take the cap off while the engine is running! I was under the impression that this is normal. Basically the PCV system is able to suck in a lot more air through the hole for the oil cap which messes with stuff. When you press the brakes, the RPM increase is potentially an issue with the brake booster. If it stops fine I would just drive it.

The booster may have a leak in it I'm not an expert at these things but I wouldn't be concerned. Someone else who knows better may chime in. Joined Oct 15, Messages 3, Location sacramento, ca. Oil cap removed is letting in unmetered air. This is normal. The grime around the oil cap is probably because some people take off the cap, invert it, and lay it on the table or on the radiator support. Then when you put it back on, it will make an oily mess around the cap.

I noticed this when I was changing my oil one time. Now I just leave the cap with the oily side down and place it on a dog food sack or something disposable. Valve cover stays much cleaner now. Totally normal, you're introducing unmetered air into the intake via the PCV. Tools R Us.


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