I believe my trigger wheel and mag sensor setup might be giving me problems which are preventing my engine from starting. I'm using a custom machined trigger wheel and a BMW mag sensor from an E36. (I actually snatched this from my brother's BMW parts pile so I don't really know what car it's from.)

I first noticed the issue while sitting in the car entering the parameters into WinTEC to start the engine. When I accidentally hit the shifter to the side and jarred the engine slightly, I heard the fuel pump switch on and the Engine Monitor showed the RPM jump to about 25-50 RPM. Upon further investigation, I found that by lightly tapping the mag sensor or even the wiring from the sensor to the plug, it produced this same fuel pump on/RPM increase. Even the slightest vibration produced this problem - the vibration from softly turning the crank bolt with a ratchet even caused it. It seems as vibration at the sensor produces a signal output which the TEC interprets as trigger wheel movement (thus turning the fuel pump on, etc). I think this is messing with the TDC signal thus causing the no-start.

Am I using an appropriate sensor? I was told that these BMW sensors are usable with the TEC.

Here is a picture of the set-up.



Thanks for the help!

The BMW sensors are generally usable. However there are two kinds of sensors. I don't remember how to tell them apart. Hall sensors generally have three wires (power, signal, ground) and mag sensors generally have two (signal and ground). Though BMW sometimes adds the sheild into the connector as a third pin in the connector on their Mag sensors. I'll see if can get Uwe to chime in on how to tell one from the other for sure.

That said, you may actually have a bad sensor. If you can snag a different one to try, that will likely tell you a lot.

These are three wire sensors, which I believe pick up the cam position on an M20 (318is). I looked into the BMW factory service manual for wiring instruction and found that there is a +ve, -ve, and shield, and wired to the TEC appropriately. I have another similar sensor which I tested and produced the same results. I used these because I thought they were mag sensors... maybe they are hall sensors?

I have the other sensor which came from the crank position (which has the same 60-2 tooth wheel as OEM) that uses a different style tip (flat as opposed to having a raised tip on the cam sensors). I'll try swapping that in and see if it works. Hopefully my sensor mount will work.

+ve, -ve and shield strongly suggests to me that it is a mag sensor. I'm not really sure what would cause that over sensitivity. The next thing to check would be for lose grounds and/or power wires. Finally, going over where your power and grounds go and making sure that it all makes sense. Do a little looking in the TEC3r and TECgt sections, I'm sure that power wiring has been discussed.

A friend and I were testing different things out today and have come to the conclusion that these BMW mag sensors don't work with my 4.5" OD trigger wheel.

The BMW trigger wheel that matches the mag sensor I'm using looks like its 8" OD, and has unequal tooth and gap widths. I don't know how exactly these sensors work and what factors determine compatibility with the trigger wheel, but I have a strong feeling that this sensor is the culprit just based off the differences in sizes between the two wheels and the strength of the magnet in the BMW sensor.

I tried increasing the air gap from 0.025" (0.005" per 1" of dia") to 0.060" and the TEC started throwing two different mag sensor codes. I'm going to go to Ford tomorrow and buy one of the suggested wheels on the electromotive alternative sensor listing (http://www.electromotive-inc.com/pdf_fi ... ensors.pdf).

The list states that the Ford sensors require at least a 5" dia trigger wheel, will my 4.5" wheel work? Close enough?

It's probably close enough. The thing that makes a sensor work or not with a particular wheel is the size of the teeth vs the size of the pole in the sensor. If the pole is larger than a tooth or the gaps between, the senor will have trouble.

Is there a reason you won't use one of ours? They work perfectly on the 4.5" wheels and are probably cheaper than that sensors at the Ford dealer would be. Should also be available from any dealer. Where are you? I could point you to one.

The pole on this particular sensor was large enough to cover a tooth and a gap... which means it can cover half a tooth, a full gap, and half a tooth. I had assumed the sensor was good because the TEC showed RPM under cranking and the coils and injectors fired. I guess they weren't firing at the right time though. That, and even the slightest vibration such as putting the transmission in gear caused the sensor to send a signal. While moving the shifter around and watching the TEC, I was able to get the engine monitor to show to 25-70 RPM

I've got an Electromotive type sensor on the way and it should be here tomorrow. I sourced one with a threaded body to make adjusting air gap more precise. I'm hoping the engine will fire right up with this new sensor. Keep your fingers crossed for me.

OK it didn't fire right up, but its definitely trying to start. Only when cranking, and for a split second after, its sputtering. It sounds like the timing is WAY off, so I checked the sensor alignment and its bang on the trailing tip of the 11th tooth at TDC. I've played around with different UAP, POT and timing setting and nothing seems to change how it runs. UAP was set at 18ms, POT 5ms, Timing advance set to zero and advance goes to about 2deg during cranking. I'm running individual coils and 2x 440cc primary injectors and 2x 440cc secondary injectors. Engine is a street ported 13B rotary.

I know there are a million different possibilities, but if anyone could point me in the right direction, I'd appreciate it. I'll mail you a box of cookies if you have a similar set-up and send me your base map

Thanks!

Looks like you have WAY too much fuel going in. Create a new file and use the UAP the wizard gives you and a POT of 0. See where that gets you.

A 440cc injector is about 42lb/hr by the way.

I tried that and it doesn't help. The engine doesn't even fire.

I'm using a 3 bar MAP sensor on an NA engine (going turbo soon) and I believe the UAP is so high because it is scaled for the 3 bar map sensor.

I closed the sensor gap down to 0.010" and was playing around with the UAP and POT.

I entered 30ms UAP and it fired right up. I had to shut it down so I didn't gas out the neighbourhood children playing on the street. I'm just playing with UAP and POT, and ignition advance to get it to idle properly.

There's nothing like hearing an engine fire up for the first time

Glad you got it running.

I know what the issue is but I'm embarrassed to say...

The Denso MAP sensor I'm using, although showing the proper MAP reading with the engine off, is scaled in the opposite to the GM MAP sensor the TEC is compatible with. MAP increase translates to a decrease in voltage from the sensor, rather than an increase in voltage. Need I say more?

Off to the auto wreckers tomorrow to get a GM MAP sensor!