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FCV repair
http://www.lostjeeps.com/forum/phpBB3/viewtopic.php?f=5&t=60870		 Page 1 of 2
Author:  dirtmover [ Tue May 24, 2011 9:42 pm ]
Post subject:  FCV repair
My FCV just failed. Anyone opened one of these up? What goes wrong with them? Are they repairable?

I don't really feel like spending the $600 they want for the part up here but don't want to loose the safety feature it provides either. For this sort of money I'd rather purchase the GDE tune to turn off the CEL, allow me to reconnect the MAF, and benefit from the other features it provides.

Has anyone looked into pulling the actuator out of the valve and replacing it with a manual lever or servo to control the butterfly which at least provides an emergency shutdown mechanism.
Author:  onthehunt [ Tue May 24, 2011 11:23 pm ]
Post subject:  Re: FCV repair
I think the chances of you needing the safety feature are less than being struck by lightning(unless you drive on oil fields). They really needed it for the smooth shut down. I'm sure you could rig a cable to it if that's what you want. I think you would be the first to do it...
Author:  Drewd [ Wed May 25, 2011 12:20 am ]
Post subject:  Re: FCV repair
From what I read, the early versions had a plastic drive gear that failed over time and newer ones have a metal one. i like the idea of using a cable to close the valve in case of a runaway engine.
Author:  geordi [ Wed May 25, 2011 4:32 am ]
Post subject:  Re: FCV repair
You would be the first to have a cable to control it, but this isn't really a huge problem that these things have with either shutting down "smoothly" or running away with themselves. The FCV cannot assist if your engine WAS to start running away anyway, how would the computer know that there was a problem, or how would you command the thing to close and stay fully closed? You can't, the computer can't, so the FCV cannot have that function. There are legions of members on the VW TDI club that thought the same thing about their "soft shut down" flap which was vacuum controlled... But it is the same as our FCV - It is there for the EGR function, nothing more. Kill it and be happy.

Personally, I haven't been running with my FCV either active OR functional for over 75k miles now, and nary a problem has it caused. The ACTUAL function of the FCV is part of the EGR system, the reason it "seems" to be in operation when you are shutting the engine off, is that the engine is idling just before you do shut it down. Whenever the engine is idling, the EGR is potentially also being utilized. (as determined by the nanny-systems and the EPA wanting it to choke our engines to death on abrasive soot, but that is another problem)

When the EGR is activated and commanded to open, the engine MUST be at zero boost or the exhaust would not be sucked into the intake. Idle is one of the few times this is possible. Even so, the nanny systems will look for a corresponding drop in the airflow across the MAF sensor by the airbox. That is the SOLE function of that MAF sensor, along with the SECOND MAP sensor in the side of the airbox (commonly referred to as the Mercedes Logo Sensor) which measures the actual air pressure (NOT temperature). If the computer is not satisfied with the drop in airflow across the MAF from simply opening the EGR (or the dang thing is plugged with soot from being a poor design) then the computer will command the FCV TO CLOSE partway while the engine continues to run (poorly) as a means of forcing EVEN MORE suction to pull more exhaust into the intake.

You don't want this. Period. There is NO NEED to have the FCV do anything when you shut the engine down, what you are hearing is the motor releasing, and the spring tension returning the flap to a fully-open configuration. Its a strong spring. On my engine, I fixed this in three ways, any of which are completely successful by themselves at killing the FCV without harming the function of the engine.

The fastest way (but you will probably have a CEL from the failed electric motor if you don't already) is to simply remove the FCV from the engine, and UNSCREW the blocking disc from the center shaft. Put the unit back, and know that it can never hurt your engine again.

The second way is with a GDE tune. They do not completely disable the EGR from functioning, but get rid of *most* of the function and the problems the EGR causes. The FCV is included with that list of fixes. I know and understand why they cannot completely remove the EGR from the programming... Which is why I use their AWESOME tune in concert with method number 3:

The SEGR device. This is the ONLY PROVEN way to completely neuter both the FCV and the EGR from functioning AT ALL, EVER, and at the same time... No CEL. Ever. The EGR is electrically unplugged, so it cannot open. Your CRD will remain *looking* completely stock... But will be a LOT happier and cooler running.
Author:  dirtmover [ Wed May 25, 2011 6:27 am ]
Post subject:  Re: FCV repair
geordi wrote:
The FCV cannot assist if your engine WAS to start running away anyway, how would the computer know that there was a problem, or how would you command the thing to close and stay fully closed? You can't, the computer can't, so the FCV cannot have that function.


This is an interesting comment. I was under the assumption, along with most of the community, that the FCV would be used to shut down a runaway.

geordi wrote:
The fastest way (but you will probably have a CEL from the failed electric motor if you don't already) is to simply remove the FCV from the engine, and UNSCREW the blocking disc from the center shaft. Put the unit back, and know that it can never hurt your engine again.


This will probably be my chosen approach. I detected the FCV fail with my weekly code scan, the CEL is already lit from the disconnected MAF :wink:. I don't really care about the CEL and neither does the emissions guy. He simply warns me that it may fail, goes to the back of the vehicle and looks at the tailpipe, says "yeah, that looks OK", hands me the certificate and charges me 40 bucks for the privilege :roll:.
Author:  Sir Sam [ Wed May 25, 2011 11:53 am ]
Post subject:  Re: FCV repair
dirtmover wrote:
geordi wrote:
The FCV cannot assist if your engine WAS to start running away anyway, how would the computer know that there was a problem, or how would you command the thing to close and stay fully closed? You can't, the computer can't, so the FCV cannot have that function.


This is an interesting comment. I was under the assumption, along with most of the community, that the FCV would be used to shut down a runaway.


I don't know about "most of the community," this is the first I've heard of anyone talking about the FCV being used for a shutdown for runaway.

But food for thought.......the 02-04 CRDs do not have an FCV, the 05+ do, because its needed for the newer emissions.

The FCV closes down on the intake path and creates a venturi effect allowing exhaust gas to be driven into the intake path more readily. Just about every Tier III and interim Tier IV engine uses a butterfly valve to create a wicked amount of EGR flow.

Basically just unplug the FCV if the buzzing sound bothers you, every two years I plug mine back in and clear the CELs to get it emissions tested. With the MAF plugging in and EGR working I get all sorts of hesitation and wierdness that goes away with the MAF and FCV disconnected.

More proof that this engine just gets gummed up and messed with by the EGR system. I'm happy to have it disabled.
Author:  dieseldoesit [ Wed May 25, 2011 12:39 pm ]
Post subject:  Re: FCV repair
geordi wrote:
how would the computer know that there was a problem,

maybe by the difference in TPS reading vs engine rpm?
Author:  Sir Sam [ Wed May 25, 2011 1:36 pm ]
Post subject:  Re: FCV repair
dieseldoesit wrote:
geordi wrote:
how would the computer know that there was a problem,

maybe by the difference in TPS reading vs engine rpm?


There is no TPS, but there is an APPS. But we all know that APPS doesn't translate to the engine RPM directly, only desired fuel.
Author:  Wobbly [ Wed May 25, 2011 1:39 pm ]
Post subject:  Re: FCV repair
For a description of the VW anti-shudder valve which prevents engine runaway, see "Shutting off the Air" section here:

http://www.myturbodiesel.com/1000q/stop ... how-to.htm

Perhaps, GDE Keith can comment on how the ECU controls the FCV .
Author:  dieseldoesit [ Wed May 25, 2011 1:42 pm ]
Post subject:  Re: FCV repair
Sir Sam wrote:
There is no TPS, but there is an APPS. But we all know that APPS doesn't translate to the engine RPM directly, only desired fuel.

TPS, aka the pedal? Doesn't the ECU know what the pedal is doing? Looks like that is what the APPS is. Had to do a little research. You are correct that the APPS is not a linear relationship with rpm, but I assume it is pretty easy to figure out when the APPS and rpm does not correlate to a correctly functioning system.
Author:  Sir Sam [ Wed May 25, 2011 2:00 pm ]
Post subject:  Re: FCV repair
dieseldoesit wrote:
Sir Sam wrote:
There is no TPS, but there is an APPS. But we all know that APPS doesn't translate to the engine RPM directly, only desired fuel.

TPS, aka the pedal? Doesn't the ECU know what the pedal is doing? Looks like that is what the APPS is. Had to do a little research. You are correct that the APPS is not a linear relationship with rpm, but I assume it is pretty easy to figure out when the APPS and rpm does not correlate to a correctly functioning system.


All the APPS does is tell the ecu the desired fuel level.

But, you can be off the throttle and still have much higher RPMs, depending on what gear you are in. While not as prevalent in Autos(though plenty of engine braking still occurs) this is easily noticable in the manual KJs.

But this is starting to digress..........I am of the opinion that the FCV serves no purpose on our CRDs other than to create a venturi effect for higher EGR flow. The older engines with less EGR flow do now need the FCV to flow suffiecent amounts, and have no such device on the intake.

Picture is worth a thousand words:
Image
Author:  geordi [ Wed May 25, 2011 3:07 pm ]
Post subject:  Re: FCV repair
Sam, you've got a big problem with that engine... Someone stole the transmission!
Author:  Sir Sam [ Wed May 25, 2011 3:23 pm ]
Post subject:  Re: FCV repair
geordi wrote:
Sam, you've got a big problem with that engine... Someone stole the transmission!


Image
Author:  dkenny [ Wed May 25, 2011 7:25 pm ]
Post subject:  Re: FCV repair
it would be possible to compare the engine RPM to the TPS/APPS..to determine a problem..
for any given fuel level request a 'normal' rpm could be determine. all it would take is to compare the APPS to the RPM and check it see if its in 'normal' parameters.

the other way..a run away run into RPM limits..say 3500 RPM..at 3600 RPM..KILL the ENGINE..think rev limiters on gas engines..
same idea but implemented differently..hey its a diesel anyway.;)

but did they do this..If I were to bet on this..NO..
they cut to many other corners..this would take time and effort.
remember they cut out a $100 lift pump..

-dkenny
Author:  Wobbly [ Wed May 25, 2011 7:57 pm ]
Post subject:  Re: FCV repair
If the FCV is not shut by the ECU on engine runaway, at least it will shut when the ignition is switched off. With a manual transmission it might be possible to kill the engine by shifting into low [EDIT: high] and popping the clutch. With an automatic the only way I can think of stopping a runaway without a FCV is by blocking the air inlet.

Here's a video of a runaway diesel engine:
http://www.youtube.com/watch?v=5zx3qKX_ ... re=related
Author:  flman [ Wed May 25, 2011 9:17 pm ]
Post subject:  Re: FCV repair
Wobbly wrote:
If the FCV is not shut by the ECU on engine runaway, at least it will shut when the ignition is switched off. With a manual transmission it might be possible to kill the engine by shifting into low and popping the clutch. With an automatic the only way I can think of stopping a runaway without a FCV is by blocking the air inlet.

Here's a video of a runaway diesel engine:
http://www.youtube.com/watch?v=5zx3qKX_ ... re=related


Well, that is the first I have ever seen or heard of a run away diesel, and I visit alot of diesel forums. I have the failed FCV on my one Jeep unplugged and I won't be having any nightmares about it. :frankie: :grim: :dead:

I also removed the EGR from my 02 Jetta TDI and my 98 TDI never even had and FCV from when it was new, along with my 7.3 Navistars, Power Strokes, Cummins ISB, old Mercedes Benz cars, etc. and so fourth.

It is just a pollution device but it can stop the one in a million run away diesel as well.
Author:  Turbo Tim [ Wed May 25, 2011 10:05 pm ]
Post subject:  Re: FCV repair
Funny my Cummins doesn’t have a Anti Runaway Valve or FCV. Probably doesn’t need one.
Anyway, the SEGR switches in the FCV valve only in Park or Neutral. The rest of the time it has a 1K Ohm resistor switched in to fake out the ECU to keep the CEL trigger circuit happy.

Again it is only switched in to aid in shutdown when you turn the key off.
You don’t have to have it switched in at all if you don’t want it. Just don’t connect pin 9 on the SEGR module if you want the FCV valve switched off (open) all the time.
Author:  Wobbly [ Wed May 25, 2011 10:10 pm ]
Post subject:  Re: FCV repair
The VM CRD FCV is not just an emissions control device. It's also an anti-shudder valve similar to those used by VW. It allows smooth engine stops and prevents a runaway engine by shutting off air flow. I've had very high mileage diesel engines without a similar device and never had a problem.
However my BMW 534TD engine lost a turbo seal at 60,000 miles and went into runaway mode. Turning the ignition off and pulling the IP pump stop lever did nothing to stop the soaring RPMs.
The probability of a runaway engine may be very low. Whether it's worth the money to repair a defective FCV is a personal decision. I wouldn't want to take the risk of this occurring to someone else driving my vehicle in heavy freeway traffic, though.


As far as runaway engines being an unheard of topic on diesel forums, a search for "runaway engine" on the TDi forum had over 1000 hits. Granted most posts are not reports of occurrences, but the topic is not unknown.
Author:  WolverineFW [ Thu May 26, 2011 12:18 am ]
Post subject:  Re: FCV repair
I would be interested in knowing if the fuel control solenoids on the injection pump cut fuel flow when the ECU is off. On the Yanmar and Kubota motors I work with, they both have fuel solenoids on the pump that cut the fuel flow when controller is switched off to prevent runaway motors. If the solenoid fails, it fails closed.
Author:  Wobbly [ Thu May 26, 2011 12:36 am ]
Post subject:  Re: FCV repair
WolverineFW wrote:
I would be interested in knowing if the fuel control solenoids on the injection pump cut fuel flow when the ECU is off. On the Yanmar and Kubota motors I work with, they both have fuel solenoids on the pump that cut the fuel flow when controller is switched off to prevent runaway motors. If the solenoid fails, it fails closed.


A runaway diesel uses crankcase oil for fuel, not diesel fuel oil. My BMW 524TD engine has a Bosch VE fuel injection pump with a fuel solenoid which fails closed. It also has a mechanical shut off lever. Neither device prevented the runaway.

EDIT: It is possible to have a runaway engine running on diesel and not crankcase oil.
The Bosch VE pump (not used on the CRD) can be misadjusted by breaking factory seals to cause this condition.
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