Testing Cam Phasing, Vw Audi 2.0t Engines
Most, if not all scan tools do not allow for live cam phasing testing on Vw Audi vehicles. You may have output tests, but this only shows that the computer is able to control the solenoid. How do you know if the solenoid is actually working? how do we know oil is being delivered? How much is the cam phasing? Is your only option to take stuff apart and/or replace parts?
If you have a lab scope and power probe, you can do mighty things!!
Consult a diagram and look for your cam sensor wiring and number one ignition control.
Disconnect the plug for your cam phaser solenoid. This way you will not cause any issues with your ecm. Hook up some front probing wires to the solenoid. connect the negative lead of the power probe first. Hook the tip side of the probe up next. Polarity should not matter, it is just a solenoid. Power, ground, and it works. If you are unsure, just consult the diagram. You will see the led light turn green indicating a complete circuit. process.filestackapi.com/resize=h:1000…
Next, hook up your scope leads to number one coil, the signal return of the cam sensor, and clamp onto the power probe (to monitor activation events) process.filestackapi.com/resize=h:1000…
start the vehicle and set your scope to record. depending on your ignition coil type, you may have to adjust your voltage to get the entire trace on the screen. Now activate your power probe in short bursts. Make sure not to activate the probe for more than a second to avoid damaging the solenoid. process.filestackapi.com/resize=h:1000…
Let's look at a complete adjustment event. process.filestackapi.com/resize=h:1000…
The red trace is ignition control, the blue trace is cam sensor signal, and the green trace is the activation of the power probe. You can see when the power probe is activated, the cam signal moves in relation to the ignition control. You can also see the cam starts to phase back after the activation event. You can also see that there are 4 ignition events that happen between our cursors for a total of 2880 degrees (720 degrees X 4)
How can we measure this?
Lets look at an event before the phaser is activated process.filestackapi.com/resize=h:1000…
You can see here that the ignition control happens 122.7 degrees after the first small cam pulse
Now, lets look at the furthest adjustment process.filestackapi.com/resize=h:1000…
You can see that the ignition control happens 189.9 degrees after the first small cam pulse.
…=67.2 degrees of crankshaft adjustment.
Service information specifies 60 degrees of adjustment. This is a good phaser.
If you do not have a lab scope with rotational rulers, you can preform this same measurement with your cursors. Just take your total time and divide by the total degrees in rotation (in this case 2880). This will give you how many milliseconds per degree. Do the rest of the measurements using the time measurements and when you're done, divide your time by the milliseconds per degree.
This process should take a couple minutes to preform and will let you know if your phaser is working as intended. This process will work on any VVT engine. Just consult a diagram and service information.
I hope you enjoyed this
Great write up and if you happen to have a Transducer you can also go in cylinder to verify that it is being phased as your valve timing changes. Sometimes just gotta think outside the box and come up with testing methods that give you a solid answer as you did here.
Yep mike. This is what I had on me, and I wrote it this way intentionally to be inclusive. most people have a power probe. Coupled with a lab scope, you will be unstoppable!!
Agree with that and your approach I just figured to mention it is all as sometimes plugs can be more difficult to access so should always have a backup test that can get you the same results
Nice post Chris. I've never considered checking the phasing by monitoring the cam movement in relation to the ignition event. I've always compared the cam to the crank due to the crank position not advancing or retarding like an ignition event could. Regardless, this looks like another option that might yield faster results in some cases. Thanks for the idea.
I'd like to see how others might feel about this scenario. Let's say that you're diagnosing a camshaft to crankshaft correlation fault and you're trying to determine if the fault is a base timing issue or a variable cam timing issue. One obvious way to determine is to phase the cams as you monitor the variable cam system scan data or a scope the cam and the crank or the cam and an ignition event like you did here. Do you think that phasing a cam on an engine that you suspect might have a base timing fault could be dangerous?
for this test, we are testing the ability of the cam to phase. I tried accessing the crank sensor, and after not being on a lift, I gave up after 20 minutes of trying to access the ecm with the security bolt. I was skeptical of this method until I tried it and found it matched the factory spec for phasing. I found it to be quicker than trying to find the crank sensor under the car. testing the crank would yield the same results though.
But yes, what does everyone else think?
Yes, If you phase the cam as you monitor like you have here and you see that the cam does phase the full amount per service information, you can now suspect that your correlation is a base timing concern and not a phase concern. I like to use this test for this reason but I have been a little trigger shy performing this test. My concern has been that I might cause an interference issue if I phase a cam on an engine that actually has a correlation issue that's due to a base timing fault.
I'm sorry if my post seems redundant. I'm trying to make sure that my concern is clear. I am truly curious what others think about this.
Oh, I see what you're saying. No, if I was suspecting a base timing issue, this wouldn't be my first test. I would use this if I suspected a stuck phaser or lazy actuator.
It's a good test method as a check just to see if the cam is phasing, but not a good test if you are trying to check if the cam is off by one tooth. It's still a good test method to use in specific situations. As Brin Kline pointed out, a person would want to use the CKP signal if they wanted to be accurate down to the degree of rotation.
Another point to bring up is that the ECM will adjust ignition timing more so at idle. If you used this same technique with the rpms raised up slightly and held constant (which is tricky sometimes), then the ignition timing would be more stable. Either way, it looks like a good quick test.
Yes, as I stated before, I did it this way and saw that it adjusted to service info. I would've went for the crank first, but that wasn't quick enough for me on this particular engine.
Hi Chris, that's a nice quick test of the cam actuator however, I would be careful with the solenoid actuation. If it has a diode in it, reverse polarity will smoke the diode.
I agree, that's why I said to consult the diagram. some of these to have a diode in them. Thank you.