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 Post subject: Flow Control Valve part #5142799AA
PostPosted: Mon May 02, 2011 11:54 am 
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Just got back from the dealer. I thought I was having turbo problems but that is not the case, luckily. The dealer did say however that I need a new flow control valve. From what I have researched on this site is that this part has something to do with the EGR. I have disconnected my MAF so does the flow control valve play an integral role in everyday driving with the EGR inactive? The dealer wanted $610 for the part plus $200 in labor to fix. The jeep is an '05 CRD with 125,000 on it. Thanks in advance for any help.


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 Post subject: Re: Flow Control Valve part #5142799AA
PostPosted: Mon May 02, 2011 12:43 pm 
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I think that one way the ECM determines a faulty AFC is from the MAF signal. Which you have disabled.

The other way could be from a detected open circuit to the AFC. The factory service manual schematics say that it is fused so I would look there first. Maybe someone here has some real world experience with that fuse (if it is replaceable).


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 Post subject: Re: Flow Control Valve part #5142799AA
PostPosted: Mon May 02, 2011 12:54 pm 
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Just disconnect the FCV. Then it stays open. You have a cel anyway from the maf disconnect so... :wink:

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 Post subject: Re: Flow Control Valve part #5142799AA
PostPosted: Mon May 02, 2011 1:02 pm 
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tonycrd wrote:
Just disconnect the FCV. Then it stays open. You have a cel anyway from the maf disconnect so... :wink:


They said it was "stuck". If I disconnect it will there be any negative side effects?


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 Post subject: Re: Flow Control Valve part #5142799AA
PostPosted: Mon May 02, 2011 1:10 pm 
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Well if it's stuck and you have no power then it's stuck in the closed position. (sounds strange to me).

Take of the intake hose, then you can look inside the FVC. You should be able to mannualy pull it open. If not you can remove the valve, it's held to the axle with two little screws.

No you will not notice anything other then a bit rougher engine shutdown.

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 Post subject: Re: Flow Control Valve part #5142799AA
PostPosted: Mon May 02, 2011 1:15 pm 
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This part has two additional functions besides EGR flow. The first is to shut off air flow to the intake manifold when the engine is shut down. This function is sometimes referred to as anti-shudder.
The second function is to stop air flow when the engine overspeeds, which might occur if the turbo seals leak oil. Without this function the engine can go into runaway mode, burning crankcase oil instead of diesel. Severe engine damage is likely. Having experienced a runaway BMW diesel, it's something which I don't want to repeat.


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 Post subject: Re: Flow Control Valve part #5142799AA
PostPosted: Mon May 02, 2011 1:22 pm 
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tonycrd wrote:
You should be able to mannualy pull it open.


Cheapest way to go until you want to pay for replacement. Know that these normally sit open and are energized closed, so pull open and disconnect electrically.


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 Post subject: Re: Flow Control Valve part #5142799AA
PostPosted: Mon May 02, 2011 1:24 pm 
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My FCV has been dead since 40k miles or so(at 111,000 now). I run with it unplugged all the time to prevent the buzzing noise it makes when it fails. There is a slightly rougher shutdown without it, but nothing you notice unless you compare the vehicle side by side with another that is working.

I would also like to note that the 2002-2004 diesels do not have a FCV.

IMO, just unplug it and move on, no need to waste $$$ on it when you already have your MAF unplugged. If you ever need to pass a emissions/inspection and need the CEL off you can just plug it back in at that time.

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 Post subject: Re: Flow Control Valve part #5142799AA
PostPosted: Tue Mar 13, 2012 5:29 pm 
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I'm wondering if in my case the FCV is bad and not the EGR cooler as suspected by the mechanic. It makes the buzzing noise as everyone states but I have no indicator lights.


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 Post subject: Re: Flow Control Valve part #5142799AA
PostPosted: Tue Mar 13, 2012 6:15 pm 
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Babydiesel, that would be correct for a failed FCV - As far as I know, there isn't any way for a non-moving-part EGR Cooler to fail, your mechanic is smoking something. The buzzing is from the broken plastic gears.

It does not make the shutdown any worse than it is normally, and I have asked repeatedly for someone to disprove my logic on the FCV being INCAPABLE of doing anything about a runaway engine (B/c the engine computer has no way of knowing about it) so doing like a lot of us have and just unplug the thing and remove the flapper will NOT hurt anything.

Wobbly - Sorry you experienced a runaway. Please explain how the CRD will be able to detect and stop a runaway engine condition, when in normal operation, the FCV re-opens less than one second after shutdown. I have detailed my thought process about this device in many threads, asking anyone to disprove me or at least cite their sources about a "softer shutdown" or runaway preventer. Nobody has yet. Please be the first, I honestly do desire to learn SOMETHING that tells me this isn't just another component whose sole reason for existing is to ruin our engine with more EGR soot.

PS: Marketing data or the image caption / part names from the Chrysler book don't count, but nobody has ever even presented those.

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 Post subject: Re: Flow Control Valve part #5142799AA
PostPosted: Thu Mar 15, 2012 12:20 am 
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The purpose of the throttle valve is to increase the deltaP between the intake manifold and the exhaust manifold in some engine points, so that the system is capable to flow a higher EGR rate with a more closed EGR valve (this allows you to have more boost for a given EGR rate).

It's also used to shut-off the air flow at shutdown in order to improve the smoothness.

It's not used for runaway.


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 Post subject: Re: Flow Control Valve part #5142799AA
PostPosted: Thu Mar 15, 2012 12:41 am 
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MrMopar,
So are you saying that if you blew a turbo causing lubricating oil to be sucked into the intake, that a functioning airflow control valve would not kill the engine if you turned the ignition key to the off position?
Thanks,
D


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 Post subject: Re: Flow Control Valve part #5142799AA
PostPosted: Thu Mar 15, 2012 3:46 am 
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Source for this "shutdown smoothing" logic please?

Everyone keeps repeating the same thing, without ANY explanation about how it is supposed to work.

Think about it logically. The air volume in the intake is constant, because at idle you aren't making any boost. So this is a naturally-aspirated engine at that time. The valve opens for the intake stroke, and just as it closes and starts the compression stroke, the next cylinder enters its own intake stroke. You shut the key off, instantly cutting the fuel flow on the compression stroke cylinder. Now you have 500 lbs of pressure STOPPING your engine from rotating, because it is already sealed in that cylinder. The next cylinder might get to the compression stroke, further adding an additional 500 psi of sealed-in pressure to stop the engine.

Since only ONE cylinder at a time is on the intake stroke, and the power to STOP your engine is actually coming from the sealed-off compression stroke cylinder... How can closing a flap on the intake many inches away from these cylinders do ANYTHING AT ALL?

This lack of ability has been borne out by two of my own personal vehicles (Jetta TDI and Jeep CRD) and other members here that have chimed in and stated that without the flap in the intake, the engine shutdown is EXACTLY THE SAME AS BEFORE.

Please, cite some source or explain the logic process to continue stating that it is a shutdown softener. This is simply not logical.

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 Post subject: Re: Flow Control Valve part #5142799AA
PostPosted: Fri Mar 16, 2012 12:03 am 
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Based on real experiences with this...

If you leave the throttle open and shut off the engine, the engine decelerates very quickly to the zero speed point and then rolls backwards some amount and forward again which is giving you the severe shaking feeling.

If you close the throttle at the shut down, you basically create an infinitely large pumping loss for the entire engine. Given that at 760rpm you have 12 rev/sec, you have multiple intake valves opening every second. This huge pumping loss against the engine creates a massive vacuum in the intake manifold and helps to decelerate in an almost controlled fashion the rate at which the engine approaches zero speed and help to prevent the engine rotating back and forth once it 'stops.'

EVERY diesel on the market that I have benchmarked is doing this: Audi, VW, BMW, Jeeps, 'HD' trucks (3500 series, etc).
It's good for the engine and also the mounting systems.

plenty of data exists showing the benefits of it working, just have to be a calibrator to see it :)


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 Post subject: Re: Flow Control Valve part #5142799AA
PostPosted: Fri Mar 16, 2012 1:08 am 
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I do not discount what you are saying, but at the same time, color me skeptical about the engine rotating backwards.

So I will do what I usually do when logic fails - experiment. I have friends with high-speed video camera systems. I will paint lines on the back of my serpentine belt at some interval (probably every 2-3 inches) and then film the engine running and stopping. My FCV does not exist, so the first test will be as it is currently. Then I will do it again, and at the instant that I shut the key off, I will have a friend push a baseball against the FCV inlet.

This will be an interesting test, but it will take me some time to get this set up for everyone to see.

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 Post subject: Re: Flow Control Valve part #5142799AA
PostPosted: Fri Mar 16, 2012 11:08 am 
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 Post subject: Re: Flow Control Valve part #5142799AA
PostPosted: Sat Mar 17, 2012 5:00 pm 
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Geordi, ever hear someone turn off a Cummins engine and hear the accessory belt screech when the crank reverses direction? It happens.

As a thought exercise, picture an engine spinning in a total vacuum - no atmosphere at all. There would be no compression in the cylinders, and no piston would be forced back down by it. That's what the FCV basically creates in the cylinders at shutdown - a near total lack of air. No compression = no bounce.

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 Post subject: Re: Flow Control Valve part #5142799AA
PostPosted: Sun Mar 18, 2012 1:21 am 
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MrMopar64 wrote:
The purpose of the throttle valve is to increase the deltaP between the intake manifold and the exhaust manifold in some engine points, so that the system is capable to flow a higher EGR rate with a more closed EGR valve (this allows you to have more boost for a given EGR rate).


How does it do this?

MrMopar64 wrote:
Based on real experiences with this...

It's good for the engine and also the mounting systems.

plenty of data exists showing the benefits of it working, just have to be a calibrator to see it :)


I can understand the mounting systems benefit, but besides a functioning EGR, how is it good for the engine?

I am just trying to understand. Thanks.

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 Post subject: Re: Flow Control Valve part #5142799AA
PostPosted: Sun Mar 18, 2012 2:52 pm 
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http://www.myturbodiesel.com/1000q/stop ... how-to.htm
Above link is about a runaway and what the FCV function is. I found the information interesting. Granted they are talking about Audi and VW but interesting. IMHO

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 Post subject: Re: Flow Control Valve part #5142799AA
PostPosted: Sat Mar 24, 2012 10:14 pm 
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I can't wait for your video results but I do believe you will see a reversed rotation due to residual compression. I have been attempting to find the reason for the harsh shutdown of our CRD since we bought it a year ago. I am willing to spend the $$ to smooth it out.

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