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Cam Sensor Timing PDF Print E-mail
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Written by Richard McCuistian   
Saturday, 22 December 2007

What we need to know about injector timing.

 Some cam sensors are adjustable. Some aren’t  A maladjusted cam sensor can produce some weird problems. If the injector delivers its fuel too early or too late, all sorts of surges, stumbles, and starting problems can result.  So how does the average mechanic set the cam sensor without special tools? Remember, on late model Fords, the signal is supposed to be delivered exactly 24 degrees AFTER TDC, and so you should adjust the sensor accordingly. 

Why 24 degrees after TDC?  Well, that's the point at which all the fire should have gone out in the cylinder and it's save to spray the next fuel charge.  The PCM uses the CMP (Cam Position) signal to time injector firing on engines with Sequential Fuel Injection.

P0340.JPGHere's the P0340 as it shows up on the WDS screen if you're checking a Ford.  This same code is output on all cars, what with the standardization of Generic OBDII DTC's and terminology. If the cam sensor signal is lost, you'll see this code.  A 7.3L Power Stroke Diesel doesn't have a Crankshaft sensor, and it depends heavily on its Cam Sensor signal, thus it won't start if the cam sensor fails.  For these gas burners, the engine will run without a cam signal on most vehicles, albeit with reduced fuel ecomomy.  So what does a failed Cam Sensor look like?


3.0L good & bad.JPGFord 3.0L Good and bad: Watch for the magnet to fall out of the sensor on 96-99 3.0L Tauruses. If you get a P0340 code on one of these, this is the first place to look.

The rotten truth is that about six times out of seven, the synchronizer is destroyed by the loose magnet and has to be replaced.

And if you know how to adjust the synchronizer after you've replaced it, you're home free. If the synch is okay, just bolt the sensor on and let it go.  Now, how do I adjust the synchronizer?  More about that in a minute.

 3.0L Magnet.JPG

When the magnet falls out of the synchronizer the way this one did and lands right in the middle (see photo; the small cube lying in the center of the synchronizer vane cup that spins around when the engine is running) it doesn't do any damage.

If, however, it lands in such a way that it fouls the vane cup while the engine is spinning that little rascal, the resulting disaster will necessitate the replacement of the whole synchronizer, which looks like a distributor but with no bowl, cap, or wires.  It's retained by the bolt at the base of the unit, the one you can see here with the large flat washer.  It takes a 10mm socket to remove the bolt and washer assembly, then the synchronizer slides out, but you need special instructions on putting it back.  That's what this article is about. 

The cam synchronizer tool you see here is for a late '90's 4.2L engine (F-150 engine but very similar to the 3.8L) - notice how the vane and its opposing boss fit together.  You're supposed to bring the crankshaft to 0 degrees TDC on cylinder number one (using the marks on the balancer and the timing cover pointer), then adjust the synchronizer so that the connector on the sensor will be pointed in the right direction with the tool in place.

Tool and Synchronizer.JPG











(see below) Here's how I set the cam timing on a Mustang:

Cam timing 1.jpgCam timing 1: Don't have the special tool? First you have to know where 24 degrees AFTER Top Dead Center is, and I'll show you in a minute how to find that. Once you have it marked (I marked this one with whiteout), you can attach a logic probe (see photo - a logic probe looks like a test light but a wire for each side of the battery and it has an LED in it instead of a bulb) or a volt meter to the signal wire (the wire in the center on the connector), mark 24 degrees after TDC and turn the engine slowly to your mark.  Stop there. Now loosen the cam sensor synchronizer (the part that looks like the bottom of a distributor) and turn it the way you would a distributor until you find the place where the signal switches.  The LED in the probe will go off and on as you rock the engine back and forth past this point.  (photo with the LED out below and note the balancer is in a different place.

 Cam timing 2.jpg

3.8L Timing Mark. (see photo below) Here's a balancer with the tape in place, providing the 24 ATDC mark. Note the presence of the deep notch on the balancer - interesting, huh?  On the 4.2L balancer, a piece of tape 32 mm long puts you at 24 ATC. For 3.0L engines, the tape should be 31 mm, and on most 3.8L engines, 25 mm does the job (this spec could be different for Mustang and Windstar, so be careful!.  It’s best to measure for yourself, but these are a few measurements I came up with in our shop.  A math whiz can figure it out on a calculator using the diameter of the pulley.  What I did was apply the tape to the BEFORE Top Dead Center side of the zero (which is, by the way, Top Dead Center), and then cut the tape at the 24 degree mark on that side of the zero. When I got the tape the right length, I applied it to the AFTER Top Dead Center side of the zero, thus the left end of the tape you see here becomes my 24 degrees AFTER Top Dead Center mark, which is where the Cam Sensor makes its signal switch.

3.8L Timing mark.JPG

Note: Some Fords have Cam Sensors that can't be replaced separately - on those, the synchronizer has a little window in the top of it so you can see the vane and determine very nearly where it should be with the engine at zero degrees TDC on cylinder number 1. 

3.8L Cam vane 2 (Windstar):  (see photo below) Here's the Windstar synchronizer with the the engine at #1 TDC. Notice that the vane is always to the left of the connector when the synchronizer is in the proper position.  The next photo shows the plastic tool Ford released for this engine, but the same method described earlier will work on the Windstar.

3.8L Cam vane (Windstar).JPG

3.8L Cam vane 2 (Windstar).JPG











Jeep Cam sensor: (see photo below) On this 99 model 4.0L Grand Cherokee, the Mopar men set things up so that you could set the synchronizer with a toothpick! The hole in the housing lines up with the hole in the vane. Lock 'er down and you're set. As with Ford's procedure using their confusing array of tools, #1 TDC compression is your reference point on the Jeep.

Jeep cam sensor 2.JPG



Last Updated ( Saturday, 22 December 2007 )
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