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Old 04-15-2013, 01:13 PM   #1
SD_Rider
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Signal to VCT solenoid?

I have a cam timing advanced code.

My mechanic's troubleshooting found that the square wave signal to the VCT solenoid dies after (what seems like) the car warms up. It then goes to a constant 12V state.

If you shut the car off and restart, the signal returns but quickly goes away. He showed me and I verified what he was seeing.

The mechanic thinks that the computer is bad....any thing else to check???

For troubleshooting purposes...If I go to the local auto yard, can I just pull the computer from an SVT and will it be plug & play?


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Old 04-15-2013, 01:49 PM   #2
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Was the t-belt changed and then the code appeared?
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Old 04-15-2013, 02:05 PM   #3
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Quote:
Originally Posted by Insaniac View Post
Was the t-belt changed and then the code appeared?
It had a timing retarded code, then the t-belt was changed, and now has a timing advanced code.

I also have installed a new VCT solenoid.

The mechanic says he has tested everything. I visually watched as the car warmed up and the square wave dropped out.

He said the signal is from the computer and is not affected by anything else. I am thinking of having the dealer verify as well, but have never had good luck at dealers....always feel like I'm getting ripped off. :/
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Old 04-15-2013, 06:40 PM   #4
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Quote:
Originally Posted by SD_Rider View Post
It had a timing retarded code, then the t-belt was changed, and now has a timing advanced code.

I also have installed a new VCT solenoid.

The mechanic says he has tested everything. I visually watched as the car warmed up and the square wave dropped out.

He said the signal is from the computer and is not affected by anything else. I am thinking of having the dealer verify as well, but have never had good luck at dealers....always feel like I'm getting ripped off. :/
Do you have any means to verify the timing alignment? My guess would be that the timing is off and not a bad sensor. Its very common when the new belt is installed and the tension is set for the VCT gear to get pulled slightly off full positive dead stop and get the advanced code.

If possible, pull everything back apart enough that you can install the crank timing pin and then check if the timing bar will fit in the ends of both cams. I'm willing to bet the cam bar will only fit into one of the cams.

To get the timing set correctly, you have to hold the VCT gear against full positive dead stop with a strap wrench via the VCT housing to keep it from rotating *AT ALL* when the tensioner is set and the inner bolt in the VCT housing is torqued down. Where this gets messed up and you get a CEL is when the tension is set, you can watch the belt pull the VCT gear off of full positive dead stop. >>This<< thread is a gold mine of useful information regarding properly timing an SVT zetec engine. Its what I referenced when doing my t-belt and Ive never gotten a CEL.

Admittedly, I can't readily verify what the signal wave should look like on a good car with no CEL but if the timing belt has been messed with at all I would put my money on the timing being incorrect. What was he using to watch the signal wave? If I can locate a similar device I might be able to verify what the wave looks like on my car that doesn't have the CEL.
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Old 04-15-2013, 10:45 PM   #5
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The signal from the ECU is an output. There has to be an input controlling it, namely the Cam Position Sensor.
Log the Cam and make sure it's still reading when the VCT drops out. If it's not the car will go into a failure mode and run on known good values. Which means the VCT is good.
That may point to the cam timing not being done correctly.
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Old 04-15-2013, 11:23 PM   #6
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Please be specific.
The VCT actuator is at the front of the engine, the timing and accessory belt side of the engine.
The VCT sensor is at the rear of the engine on the transmission side.
The actuator should not have a signal unless the VCT is actually commanded. At idle, the VCT is NOT commanded, so there should be no or a small signal.
The VCT sensor is a hall efect sensor that produces voltage every time the position sensor wheel passes. There are 3 tabs (I believe) that pass the sensor every rotation.
If the engine speed is low the change in signal can be seen easily, but at higher engine speeds, like a quick rev in neutral, unless you have some pretty high accuracy reader (a volt meter will NOT likely ready the voltage changes, an o-scope would work) the meter will miss the voltage changes. Doing the math, at 2000 rpm /2 for half speed of the cams, and 3 tabs on the encoder you have 50Hz, which is pretty fast...

Just want to be sure you are getting the correct measurements...
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Old 04-15-2013, 11:43 PM   #7
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There are 5 tabs; ~83Hz @ 2,000rpm.
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Old 04-16-2013, 12:04 PM   #8
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Quote:
Originally Posted by Insaniac View Post
Do you have any means to verify the timing alignment?
My mechanic swears up and down that he checked and double-checked per the TSB for the timing.

Someone (you?) referred me to the thread on FJ. I showed it to him and he says that it is set correctly.

Quote:
What was he using to watch the signal wave? If I can locate a similar device I might be able to verify what the wave looks like on my car that doesn't have the CEL.
An automotive oscilloscope.

Quote:
Originally Posted by paulg127
please be specific
Connected to the VCT solenoid that is in the valve cover.

He also showed me that he checked the wire to make sure it wasn't shorting, back to the ECM.
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Last edited by SD_Rider; 04-16-2013 at 12:09 PM. Reason: additional info
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Old 04-16-2013, 12:06 PM   #9
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Quote:
Originally Posted by iminhell View Post
The signal from the ECU is an output. There has to be an input controlling it, namely the Cam Position Sensor.
Log the Cam and make sure it's still reading when the VCT drops out. If it's not the car will go into a failure mode and run on known good values. Which means the VCT is good.
That may point to the cam timing not being done correctly.
Thank you! And that's what I was curious about...what signal, if any, it was dependent upon.

How do I log the cam?
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Old 04-16-2013, 10:35 PM   #10
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There are several parameters that you can look at to determine what the VCT is doing and the adaptive values for the cam timing. If you log the commanded and actual VCT angle you can see if it is moving. There is an adaptive term that corrects the encoder wheel on the cam (the strategy assumes perfect cam timing) and the difference is accounted for in the strategy. The adapted value must be within +- 3 degrees of correction before you will set a code.
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