What are the symptoms of failed FCV

bugnout · **Posted:** Tue Mar 06, 2012 12:26 pm

Lately, after starting, the engine stalls or almost stalls a couple of seconds after a cold start. always occurs about 3 seconds after it starts. Occurs even on restart. Haven't noticed this when the engine is at operating temps.

Also at high torque 16-1800 rmp, every once in a while I feel what sounds like a backfire under my feet on the drivers side of the engine. Only occures before I get the engine to full operating temp.

I'm thinking this is a stuck or failing FCV. What do you think?

papaindigo · **Posted:** Tue Mar 06, 2012 4:00 pm

Cannot comment on the FCV but have you checked for a clogged fuel filter or air in the fuel filter head?

bugnout · **Posted:** Tue Mar 06, 2012 4:44 pm

Yes, not a fuel issue, not a performance issue, no codes, everything runs great. Just the two symptoms.

My theory is the FCV is a bit gummed up and is slow to open/close. I think the FCV is being activated on engine crank and isn't opening or closing fast enough.

Don't understand the thump I hear everyonce in a while at low rpm/ High torque. The sound/thump is coming from the area of the FCV/EGR, so I think they are related

papaindigo · **Posted:** Tue Mar 06, 2012 5:16 pm

Ok then another thought. The flow control valve, notwithstanding a lot of chat about shutdown, is not system critical. The valve itself is a simple butterfly valve, like in a carberator throat, that's activated by an electronic signal that drives a plastic gear. I suppose it's possible that crud thru the intercooler has gummed up the butterfly pivot point or the plastic gear is stripping. Easy check; pull the driver side intercooler hose; look inside the FCV and IIRC you will see a couple of really small screws holding the butterfly to the pivot shaft; remove those screws (BE CAREFUL NOT TO DROP THEM - I imagine they are steel and if so use a magnetic screwdriver); then remove the butterfly. Drive and if the problem goes away it's solved just leave the butterfly out.

maxwellp · **Posted:** Tue Mar 06, 2012 5:30 pm

If your problem goes away good. But I would not leave the flow control valve butterfly out for good. The FCV closes on shut down for a smooth shut down. This will also and more importantly help stop a runaway engine by choking off the air and shutting it down. With out it in the event of a runaway the engine will only stop if the air or fuel source is removed. By the time you do the that the engine already ate itself. I have seen it and the aftermath.

ACRucrazy · **Joined:** Wed Feb 15, 2012 8:10 pm **Posts:** 32

maxwellp wrote:

If your problem goes away good. But I would not leave the flow control valve butterfly out for good. The FCV closes on shut down for a smooth shut down. This will also and more importantly help stop a runaway engine by choking off the air and shutting it down. With out it in the event of a runaway the engine will only stop if the air or fuel source is removed. By the time you do the that the engine already ate itself. I have seen it and the aftermath.

Does shutting the key off stop fuel flow? If not, what is the other way this is done if a FCV fails to close in a situation as mentioned above?

CATCRD · **Posted:** Tue Mar 06, 2012 9:12 pm

ACRucrazy wrote:

maxwellp wrote:

If your problem goes away good. But I would not leave the flow control valve butterfly out for good. The FCV closes on shut down for a smooth shut down. This will also and more importantly help stop a runaway engine by choking off the air and shutting it down. With out it in the event of a runaway the engine will only stop if the air or fuel source is removed. By the time you do the that the engine already ate itself. I have seen it and the aftermath.

Does shutting the key off stop fuel flow? If not, what is the other way this is done if a FCV fails to close in a situation as mentioned above?

The fuel is shut off when you turn the key off. The valve also closes at that point just to reduce engine shake from the compression bounce of the pistons.

GreenDieselEngineering · **Joined:** Sun Jun 07, 2009 5:10 pm **Posts:** 1111

Can you unplugged the FCV wiring connector (black connector 1"x1/2") on throttle valve assembly? This will rule out any electonic issue. Hopefully the noise disappears.

bugnout · **Posted:** Wed Mar 07, 2012 12:05 am

I'll give that a try and let you know.

geordi · **Posted:** Wed Mar 07, 2012 12:10 am

maxwellp wrote:

If your problem goes away good. But I would not leave the flow control valve butterfly out for good. The FCV closes on shut down for a smooth shut down. This will also and more importantly help stop a runaway engine by choking off the air and shutting it down. With out it in the event of a runaway the engine will only stop if the air or fuel source is removed. By the time you do the that the engine already ate itself. I have seen it and the aftermath.

Sorry, I don't think so. The FCV is commanded to close based on the direction by the computer. How exactly would the computer know that the engine is in runaway, which by definition means that the engine is operating on another fuel source, such as its own oil? It cannot. I do not believe that it does anything to "soften" the shutdown because my CRD shuts off exactly the same now as it did before. Where I think everyone's belief that the FCV does something at shutdown (because of the noise of the motor after the engine stops) is because you wouldn't normally be shutting the engine off while at high load. At lesser load, the EGR system is liable to be employed, which also can engage the FCV. If you have a GDE tune, this is not the case, but in all situations, the following is true:

How can the ECU know when you are about to shut the engine off and activate that FCV before the fuel itself is cut off? Stopping the fuel flow is an elec`tronic signal, it happens instantly, and the compression pressure will stop the pistons within 1 revolution. I would contend even faster - Whichever piston is entering the compression stroke is the "brake" that stops the motor. In all cases, the engine stops rotation EXTREMELY quickly. Like within that one compression stroke, because you don't hear the engine releasing pressure. Can the electric motor of the FCV, fighting against that strong spring, move 90 degrees to fully closed in 1/4 second? I seriously doubt it!

At the same time, what purpose would this serve to "soften" anything about the shutdown? The cylinders will be doing their thing, one will be in compression, valves closed. The air in that cylinder cannot be affected by the FCV. The ONLY cylinder that MIGHT be affected is the one on the intake stroke... And what difference will creating a sudden vacuum in the intake make to stopping the engine? The volumetric size of the entire intake is much larger than just the volume of one cylinder... So it won't be a true vacuum, it will be more like a low-pressure-but-still-has-air situation. I don't see that changing anything.

Can someone please examine this and try to explain how it does work, if you believe that I am wrong on this? I seriously do not see how it can do anything with regard to the shutdown. I heard the same kind of suggestions on the TDI forums about the "EGR flapper" on those engines.... And the shutdown there was EXACTLY the same both with and without it on my Jetta. (FYI: That "FCV" device was vacuum controlled, not electric)

dirtmover · **Posted:** Wed Mar 07, 2012 9:53 am

Geordi, if you're hypotheses are correct then what exactly is the purpose of the FCV? With a failed FCV I experience no difference in the shutdown behaviour so would tend to agree that it plays no part.

bugnout · **Posted:** Wed Mar 07, 2012 2:20 pm

geordi wrote:

maxwellp wrote:

If your problem goes away good. But I would not leave the flow control valve butterfly out for good. The FCV closes on shut down for a smooth shut down. This will also and more importantly help stop a runaway engine by choking off the air and shutting it down. With out it in the event of a runaway the engine will only stop if the air or fuel source is removed. By the time you do the that the engine already ate itself. I have seen it and the aftermath.

How can the ECU know when you are about to shut the engine off and activate that FCV before the fuel itself is cut off?

ECU can't know that your about to shut it off, but certainly will know the state of the ignition key. I think the point is that by cutting off intake air, its preventing a runaway condition. Makes sense to me. Are you just questioning the smooth shut down claim?

geordi · **Posted:** Wed Mar 07, 2012 5:09 pm

I'm reasonably certain that the true purpose of the FCV is to ensure the diesel engine has a proper collection of useless parts.

The computer commands it to close to varying degrees when the EGR is supposed to be in operation, if the computer doesn't like the drop in flow across the MAF sensor.
The program runs something like this:
EGR open, start stuffing crap and filth into the engine.
Monitor reduction of clean life-giving air across MAF sensor.
Is flow across MAF reduced to CARB-approved levels (so no life-giving air left)? No? Hmm...
Begin closing FCV valve, thus increasing suction on the sewage-inlet that is the EGR.
Has MAF flow decreased, indicating increased EGR? Yes? Good... Continue starving the engine of air and reducing its service life with abrasive soot.
No? The EGR flow hasn't increased / MAF decreased? CHECK ENGINE LIGHT - Insufficient EGR Flow code, take vehicle to dealer and have entire financial system drained.

There you have it, straight from the original programming notes. :SOMBRERO:

msilbernagel · **Posted:** Wed Mar 07, 2012 5:37 pm

Truth

METCRD · **Posted:** Thu Mar 08, 2012 2:18 pm

When my FCV failed it gave similar symptoms of going into limp mode. Moderate throttle response at initial pressing on the go pedal but would not allow the engine to rev properly. Pedal pushed to the floor would only bring the rpm's up to 2800 (the point was not to redline, but to determine if the throttle was responding properly). I could drive the city more or less "safely" but highway speeds were difficult to attain and took a great deal of time getting close to them. When this occurred I had someone sit in the jeep and rev the engine while I observed under the hood. My crude trouble shooting method brought me down the path that the turbo sounded like it was spooling just fine, but I was not getting the boost to the engine. While the engine was being revved I could actually see the hose from the turbo to intercooler expand and contract with the pressure.

A quick check similar to what papaindigo said would be to remove the CAC hose next to the FCV to examine the butterfly valve. You wouldn't need to remove the disc but could just stick your fingers inside and try to move the valve. It should move easily fully open and fully close, mine was jammed at approximately 10% open so nearly shut.

I have had my FCV disc removed for approximately 9,000 miles with no ill effects as of yet. My gears were broken so I plan on removing them and casting polyeurethane replacements when I have time this summer. Long winded but I hope it helps.

geordi · **Posted:** Thu Mar 08, 2012 6:25 pm

Don't waste your time trying to rebuild the FCV - you can buy mine, it has been disconnected since I bought the new engine. All you would need is the disc from yours.

The FCV is part of the EGR system. Its SOLE PURPOSE IN LIFE is the closing off of the intake to enforce even more EGR flow. EVERY TIME you are at part throttle or idle, (such as when you are about to shut the engine off) the EGR is trying to work, which is why you hear the FCV relaxing against the spring (driving the motor backwards) after the engine does stop.

The engine computer cannot know when the engine is operating in a runaway condition, because that would be detecting something it isn't programmed for. Operating on another fuel source. Closing the FCV completely might stop the engine, but I do not believe it would take place within 1 revolution like a normal shutdown procedure does. As such, the FCV releasing control to the spring immediately after power-off is also not an indication of anything more than "power was just cut to this motor while it was engaged for EGR flow at idle" not that it magically knew exactly when you turned the key off and somehow slammed shut at exactly the same instant to stop the engine within one revolution.

Think about it logically, and you would be hard pressed to disprove this theory of operation. I'm not claiming any of this as fact, but it fits all the available evidence I have ever seen about the diesels I have seen / played with.

maxwellp · **Posted:** Thu Mar 08, 2012 11:37 pm

The FCV will help shut down in a runaway if you shut the key off. Yes the ECM will not know what is happening but with the key turned off the FCV will close. As far as it used for a smooth shut down, this is what I have read it was also for. I have never unplugged it to see how it shuts down with out it. I agree that it's primary purpose in life is to control EGR flow.

geordi · **Posted:** Thu Mar 08, 2012 11:49 pm

Read about it where? Please provide a link to your source that says that it actually is designed to stop a runaway.

I'm not being argumentative about this, but I have heard the EXACT SAME THING from the TDI crowd about the flapper in their intake systems. Why is it, if this is such a great thing that it somehow "softens" the shutdown, and it has the ability to stop a runaway engine... That the diesels from the mid 80s that ACTUALLY DID experience runaway engines on their own oil leaks.... NEVER HAD ONE???? It isn't like it was a computer commanded thing, the VW design is vacuum powered, and could be connected to the shutdown relay with a vacuum switch. Is this needed? No, because anyone that installs the DieselGeek Racepipe removes this useless flapper and returns their TDI to the way they were before EGR was inflicted on them.

Please cite your source. Nobody on the TDI side ever could show where this idea of a runaway-stopper or "soft shutdown" actually originated or was anything more than marketing hype. If it actually does something, there should be documentation SOMEWHERE of a mechanical description of the function and how it affects operation.

What are the symptoms of failed FCV

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