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Old 01-10-2004, 13:09   #1 (permalink)
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VCT gutless, please help

Well, after Heathcote I've found that my XR6 VCT is absolutely gutless in the low revs. Anything under 3500rpm and it wont pull the skin off warm milk

Now, based on my limited knowledge of the AU VCT setup, the runners/cam change at idle to one position, then to the other postition until 3700rpm, then back to the first position. Considering my car is dead all the way up to 3500rpm I have to make an assumption that my runners/cam are locked into one position and causeing this problem.

Now, can anyone tell me exactly how I can test to see if this is the problem? If it is I will know what to get sorted at Ford, otherwise I'll have to look at other possible problem.

Thanks guys.
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Old 01-10-2004, 14:03   #2 (permalink)
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Re: VCT gutless, please help

To test the BBM, simply disconnect the vacuum line which is going to the vacuum diapragm at the front of the manifold.
Do this while the engine is idleing and if it is working the butterflies should relax back to the short position. If it doesn't move, you have a problem.

Do this simple test and post back.

Rick.
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4L I6, naturally aspirated producing 173.5rwkw.
14.410 @ 96.49mph with street radials.
What's that?..... Did I hear you say TQE power?
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Old 01-10-2004, 14:09   #3 (permalink)
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Re: VCT gutless, please help

Soxx, thanks, I will do this. But I am an engine idiot (yes, I work in IT - I can make a computer dance but changing oil is my engine limits.)
Can you explain exactly where the vacuum line is and what I should be looking/listening for? Then I'll go straight out and do it.

Pics are good
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Old 01-10-2004, 14:21   #4 (permalink)
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Re: VCT gutless, please help

Just disconnect the small rubber hose in this picture.
The little actuator should move when you disconnect and replace the hose whilst idling. The idle itself will barely change however.
If it doesn't, you have a problem.

Rick.
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4L I6, naturally aspirated producing 173.5rwkw.
14.410 @ 96.49mph with street radials.
What's that?..... Did I hear you say TQE power?
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Old 01-10-2004, 14:27   #5 (permalink)
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Re: VCT gutless, please help

yep, tested and it moved. Also got wifey to rev it and it moved at the right time. So the runners are moving I assume. So why is it so gutless?

Soxx, you seem to know your stuff, can you help me?
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Old 01-10-2004, 14:41   #6 (permalink)
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Re: VCT gutless, please help

Yep, it's working.
Sounds like the VCT mechanism may not be working.
I've had bugger all experience fault finding these though, sorry.
Check to see if it's plugged in?

Rick.
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4L I6, naturally aspirated producing 173.5rwkw.
14.410 @ 96.49mph with street radials.
What's that?..... Did I hear you say TQE power?
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Old 01-10-2004, 14:45   #7 (permalink)
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Re: VCT gutless, please help

I had another thought, you can follow that little hose you disconnected back to a place behind the washer bottle and there will be the VSV solenoid.
Follow this back out and it should join a vacuum tree at the back of the manifold, try disconnecting it from the manifold and see if actuater at the front still stays where it is after 10 secs or so at idle.
This will tell you if the one way valve at the solenoid is stuffed or not.
What this does is let the vacuum actuater hold vacuum even at full throttle when vacuum is almost zero.

Rick.
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4L I6, naturally aspirated producing 173.5rwkw.
14.410 @ 96.49mph with street radials.
What's that?..... Did I hear you say TQE power?
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Old 01-10-2004, 14:49   #8 (permalink)
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Re: VCT gutless, please help

yeah, the cable that connects to the thing at the front of the head appears to all be plugged in. Looks like I have a dud. I guess my only option is to get it on a dyno and see what the numbers say.

Thanks for the help Soxx.
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Old 01-10-2004, 15:14   #9 (permalink)
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Re: VCT gutless, please help

Well, I tried to trace the cable but without pulling all sorts of things out I couldnt find the vacuum tree, I'm not 100% what I was looking for. So I resorted to the old test of revving it. Basically, the actuator appears to be moving when it should and staying open at higher revs. I can only assume that the runners "appear" to be working Seems I have a problem somewhere else.
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Old 01-10-2004, 15:33   #10 (permalink)
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Re: VCT gutless, please help

Ok, just before the vacuum tree, there is (and I'm not 100% sure, because I'm looking at my ute in hope that it's similar) a rubber block with a few vacuum hoses coming out of each side. One of these is the feed for the VSV valve. This is the one which will go behind he washer bottle and needs to be disconnected while the engine is running to see whether it is holding vacuum.

I'll explain myself a little better on what the one way valves job is.

The VSV/BBM relies on engine vacuum to do it's job. When the throttle is floored at low revs, vacuum drops to almost zero. In this instance the vacuum actuater for the BBM would not be able to keep the butterflies in the long runner mode, so what is needed is a one way valve to hold vacuum at the actuater even though the engine is not actually making any vacuum.

My XH had this same problem when I first converted to BBM and the symptoms were on initial full throttle application it would accelerate great, then after about 1 second it would die and feel flat up until about 3500-4000rpm.

I only found out the problem on the dyno because I could see the actuater move about 1 second after the throttle was floored, even though it was at only 2500rpm or so, way before the 3800rpm BBM switchover.

If you are able to disconnect the correct vacuum line, just before the one way valve, you should be able to see the actuater move a second or so after you disconnect.
If the one way valve is functioning properly, it should hold vacuum for several minutes.

BTW, you can't simulate the actual problem (without disconnecting anything) whilst the car is stationary as the engine needs to be under load to simulate a no vacuum condition, such as driving or on a dyno.

Rick.
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4L I6, naturally aspirated producing 173.5rwkw.
14.410 @ 96.49mph with street radials.
What's that?..... Did I hear you say TQE power?

Last edited by Soxx; 01-10-2004 at 15:39.
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