vems pnp with 5 window dist

[carl]

So, i'm having problems with my vems pnp, i've done quite a few things but i can't get a good signal when cold starting < 5C or when the battery is low (for example hot day, afterrun fan hitting the battery in a parking lot, coming back to car and wont start/no
crank signal. ). After the car starts i have no problems, no trigger errors, or anything, trigger signal is perfect up to redline. I've tried running a 0 gauge wire to starter from battery +, then tried battery - to engine ground, no change. Moved ecu ground around, no change. Moved ecu power directly to battery same deal. Also changed starter to see if i could get more cranking speed/less voltage fluctuation, same deal. The ecu just quickly pulses the pump relay(s) "click " without the pump even having time to run.

Anyways i'm wondering, is it possible to run the vems pnp ecu with cop/sequential inj on a 5 window distributor ( maybe need to bridge the crank home vr signal momentarily so ecu grabs the hall signal?) so i can start it up, then using table switching switch to the usual 3 trigger setup?

[Marc]

So, i'm having problems with my vems pnp, i've done quite a few things but i can't get a good signal when cold starting < 5C or when the battery is low (for example hot day, afterrun fan hitting the battery in a parking lot, coming back to car and wont start/no
crank signal. ). After the car starts i have no problems, no trigger errors, or anything, trigger signal is perfect up to redline. I've tried running a 0 gauge wire to starter from battery +, then tried battery - to engine ground, no change. Moved ecu ground around, no change. Moved ecu power directly to battery same deal. Also changed starter to see if i could get more cranking speed/less voltage fluctuation, same deal. The ecu just quickly pulses the pump relay(s) "click " without the pump even having time to run.

Anyways i'm wondering, is it possible to run the vems pnp ecu with cop/sequential inj on a 5 window distributor ( maybe need to bridge the crank home vr signal momentarily so ecu grabs the hall signal?) so i can start it up, then using table switching switch to the usual 3 trigger setup?

generate a trigger log so you can see what is or isn't signaling. My guess is that your reference pin is a bit small and giving poor signal at low rpm. What flywheel?

[carl]

Well there is nothing getting generated in the trigger log, not one vertical line. I do get a road speed sensor spike/line from the cruise control unit in there if i turn cruise off and on, to test that it's actually sending data. Other than that nothing from primary or secondary. Here is a vems log of trying to start right after playing with throttle, also had a couple of spark plugs out. I have the 7a fidanza.

[Marc]

you need about 1v peak to peak to get a signal from any of the relevant sensors (flywheel teeth and reference pin). if the car is cranking slowly, your grounds are marginal, or you have sensor or sensor gap issues then voltage from the VR sensors is going to be weak. if the car were in my shop I'd be putting an oscilloscope on the signals to see whats up. in the absence of that, try adding a small ground strap between the intake manifold grounds and the chassis.

[carl]

Well, i haven't had a chance to scope them yet. I'm wondering on the connectors coming from ecu, what should i be reading with the vems ecu turned on and having them disconnected from the vr sensors? 5v, 0v? I'm asking because i'm getting +2.8v on the rpm signal cable center wire (pin2), while on the tdc connector i read 0 across all pins.

[carl]

Well, i did some tests today on a scope and i'm getting a little less than 100mv while cranking while connector is plugged to ecu on the tdc crank sensor. Saw that the lm1815 minimum is 100mv Ordered a new crank sensor from aip, we'll see how it goes, maybe sensor magnet has lost some of it's power or something over the years. I wonder if swapping to a max992* chip would help.

[carl]

Well...., new sensor is marginally worse lol. Reflashed firmware and logged via serial using laptop vs usb adapter and tablet. Now i get some teeth signals (could be corrupted flash again, could be usb baud rate or vems software version that was making it show absolutely nothing in triggerlog and csv). I know, not very analytical way of doing it but i'm just freakin tired of this crap. Still... it wouldn't fire and no tdc signal.

For now i have unbridged sj7 on the vems unit so i can start the car and so i can move it near a welder to create a bigger pin on crank wheel or weld a tdc pin to outer damper and make an bracket.

Running on hall only seems to give me trigger errors 3/4 of the running time. Engine runs rough as hell too even if i checked timing on cyl1. Bought a 3009 relay on the way, should be able to flick it on via ground feed to vems unit to open sj7 for security when i get no start issues.

Wonder if i replaced the pulldown resistor on the tdc feed if i'd get more noise or a better signal.