Discussion and questions related to the course EFI Tuning Fundamentals
Hi. What other inputs synchronize the crank position? I have a vw16v. I know there isn't a camshaft sensor. Is it synchronized when I set the timing?
Perhaps there is a sync sensor in your distributor.
Some motorcycle engines will use the MAP sensor to provide a sync signal -- this works for single cylinder engines, or V-twins with individual map sensors.
You don't need a cam (sync) signal if you are not running sequential injection. You only need a missing or additional tooth on the crank trigger to be able to identify the Top Dead Center cylinder 1.
Non-sequential means you are either running a distributor for ignition, wasted spark coil packs, or coil-on-plug wired for wasted spark.
Another term for non-sequential is "Batch fired", with many engines when one cylinder is at the point where the ignition is triggered, another will be on the exhaust stroke in the same relative position - ie, for your engine it may have the timing cause ignition on #1 at 25 degrees BTDC, on #4 the piston is also at 25 degree BTDC on it's exhaust stroke. This means the ignition can be triggered at that point for both and while one ignites the mixture, the other is 'wasted' - which is another term for this ignition arrangement - "wasted spark".
With fuel injection, most of us are familiar with the sequential system, when the ECU takes the camshaft, or distributor, position sensor to tell if it is approaching #1 TDC on the compression or exhaust stroke, and applying one continuous injection of fuel as required. Again, injectors can be batch fired, with half the fuel supplied on the induction stroke, and half on the firing stroke - there is some controversy on whether there are some benefits to doing it this way, such as cooling of the charge and better vapourisation leading to a small power gain, but I don't know the truth of that.
As David said, you may not have a camshaft sensor and have batch firing from the factory - exactly what year and model is your car/engine?
Oh, bit of a wild guess, but you aren't getting a little confused with the camshaft position sensor as used by vehicles with variable camshaft timing?
As the guys mentioned without a cam reference it will be running batch fire injection and wasted spark unless the 720 sync signal is derived from the distributor.
Some OEM's around the mid to late 90's ditched the distributor and used wasted spark ignition with a compression sensing logic circuit to calculate a theoretical sync signal allowing for sequential injection - google GM Ecotec CSI for some decent technical documents.
David is quite correct and some motorcycle engines used an additional map signal for sync reference. The Aprilia RSV4 is a good example, having struggled together with Cosworth engineers to get an reliable sync when using an MQ12 on an RSV4 engine I can say its much easier to weld a boss on the cam cover and use a cam lobe for reference - it only needs to see a signal when cranking so the rounded edge of a cam lobe and HE sensor worked ok.