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 Post subject: Testing the flow control valve (FCV) out of the car
PostPosted: Sat Aug 01, 2020 9:00 pm 
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Joined: Mon Jan 28, 2019 3:54 pm
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2006 2.8 CRD Liberty/Cherokee European version...

Is there any way to properly test the flow control valve detached from the vehicle? Service manual seems to advice to test it indirectly from the car side interface in a strange way - if everything OK, then FCV must be faulty (as I read it). I can of course check from the FCV's connector that there are no shorts, but that doesn't tell much. Does anyone know the specs for the PWM control signal (voltage, pulse ratios vs. flap movement)?

Reason I'm asking is due to:
- FCV is already off the car
- I can't get the DTC codes read (by 3 times key off-on), and at least my ELM327 OBD reader does not show any related fault codes
- Throttle control light was regularly blinking for about 15 min after every start before the ongoing repair (by shutting down and re-starting with warm engine it did not start blinking at all)
- Authorized service is quite far away
- Just spent several hours to get the darn thing out
...and I must be stingy by nature as I just don't want to spend 300 on a new FCV without a clue whether it's OK or not

Mechanically it looks OK, flap moves with reasonable force and is not sticking, and I can feel/hear the servo gears running all the way when I move the flap so they should be OK.

What I did find when pulling out the FCV and EGR was a leak in the gasket between FCV and intake + a failed EGR valve - I suppose either of those could already lit up the ETC light?

(For some reason my car has pneumatic EGR valve valve in opposite to what the service manual says. Never mind, easier to check. They must have made an update to electronically controlled somewhere in the middle of 2006 as the installation in my car surely looks like a factory one).

Side path to code reading trick - is the hand brake engaged really needed during key cycling as some references claim?

Thanks in advance for any proposals - this forum is really an invaluable source of Jeep knowledge!


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 Post subject: Re: Testing the flow control valve (FCV) out of the car
PostPosted: Sat Aug 01, 2020 9:03 pm 
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Oh, and before somebody proposes to remove the EGR, please don't cause I can't. Emissions are tested in local MoT, and the limits are quite strict.


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 Post subject: Re: Testing the flow control valve (FCV) out of the car
PostPosted: Mon Aug 03, 2020 4:21 pm 
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Joined: Mon Jan 28, 2019 3:54 pm
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OK, I found a way by playing with it.

I first measured the interface on car side by a multimeter as proposed by the service manual - It's a four pin connector with +12V, GND, and a CTL signal lines connected.

The connector in Liberty/Cherokee is keyed or asymmetric with pin #1 on the straight edged side of it.
Image

With ignition in ON position and FCV disconnected you can first check the car side interface rather easy by measuring +12V on pin #4, and some small voltage (by heart around 1 V) on pin #2 (CTL signal). Multimeter set in DC voltage range. The CTL signal is a PWM signal, hence the arbitrary output. Check also that pin #1 has good connection to ground.

If you can't find the battery voltage on pin #4, you have an issue with the voltage feed and there is a relay and fuse involved, but that's another story.

Power on test method, option 1:
I noticed that if you then cut the power, connect the FCV, and switch power back on (key in ON position), the ECU activates it (flap might move a bit, and you may hear some buzzing from it as a result of PWM control and mechanical slacks - this might also indicate a future failure if loud enough or flap really visibly vibrating). If you now try to move the flap (still power on, engine off), you can feel the resistance of the servo, and it will also return to it's desired position after you let go. Do this at your own risk, as moving the flap by force might damage the servo gears. The best part is that when you switch the ignition OFF, the flap moves briefly to a nearly closed position, and then returns to wide open, so you can really see that it's properly controlled and moving.

Power on test method, option 2:
I also noticed that if you connect the FCV while power on (key in ON position, engine off), the ECU detects it, and does some sort of self test by moving the flap nearly closed, then back open (as in powering off). Then you can also try to move the flap as in option 1. Note, that in addition to servo mechanics, the ECU might also suffer from connecting such components on the fly. However, I didn't seem to damage anything by doing it either way.

Voilà, seems to work. Should be an easy way to test the FCV also in place without removing anything but the charge air hose from FCV side.

Tested on Cherokee/Liberty CRD 2.8 2006, and hope this helps somebody else in any case.

Here's also a link (as long as it's available) to relevant service manual pages as long as they are available...


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