Fitting the Crank Trigger
There is no appropriate trigger setup on a TVR Griffith. As standard, it uses a 4 tooth wheel and hall sensor in the distributor.
I chose a 36-1 trigger wheel with a standard Ford VR sensor. A kit of parts specifically for my engine was available at a reasonable price. Since I don't have time to fabricate such things and can't take the car off the road for that long (it's a daily driver), this was the best option.
Note that this is the problematic type of wheel (for VR sensor) that has much bigger signal amplitude at the missing tooth. Adaptive hysteresis threshold (adjusted with R181) must be lower (=>worse noise immunity) than with a normal wheel, and not be close to the limits. Schedule a test to check that even +5% amplitude variation (than the actual wheel has) is handled right. See ElectronicDesign/TriggerSignalGenerator
Fitting the trigger wheel took a whole day, as the crank pulley was held together with Imperial bolts in very awkward positions! (They were supposed to be M8 according to the literature) A tool to remove them was fabricated and they were replaced with M8 cap screws.
Apart from this, the physical installation was straight forward. I set the VR sensor to be 1.5mm from the toothed wheel using a feeler gauge. No science here - just an educated guess. Now on to setting the ECU up and testing.
Setting Trigger parameters
Here's the parameters I used in the ECU:
| Edge: | Rising |
| Type: | Multitooth |
| Filtering: | Disabled |
| TDC after trigger (deg): | 58 (estimated from TDC and degree wheel) |
| No teeth on wheel: | 35 |
| Trigger tooth: | 0 |
| Next trigger tooth: | 9 |
| Crank min. period: | 1875 |
| Angular width of tooth: | 3 |
| Angular width of missing tooth: | 6 |
Parameters to calculate above:
| Rev limit: | 7000 |
| Imaginary teeth: | 36 |
| Missing teeth: | 1 |
| Cylinders: | 8 |
| dec: | 3 |
| Engine Phase in "funny" degrees: | 216 |
Testing the Crank Trigger
Bench testing has already been done, so it's time to put the ECU in the car, but only so it can monitor what's going on.
The first time things were connected, the ECU picked up crank rotation and gave a stable speed. The problem is that it is only half the real engine speed. Still, not bad for a first attempt.
Trigger works properly now the config is actually set in the ECU and not just on the PC. Doh!
- Just need to test the polarity on the VR sensor - it doesn't seem to make much difference to how it runs now.
- it's possible that it runs quite well with reverse polarity, or only counts wheel-err sometimes or above certain RPM. Actually, it is possible to configure multitooth "advanced filter" to work properly with reverse polarity VR for all RPM. But avoid it, and go with the right polarity. Publish InputTrigger/TriggerLog if uncertain.
I managed to get a clean "mde40" log file after a lot of bother with the old ECU and doing some maths. The idle was never very good as the old ECU is very crude. Polarity has been established now. As you say, it didn't make much difference - the change in missing tooth length was not much bigger than the RPM change in the engine.
Now it's all installed properly. I have a lot of extra noise now, I think it's due to the wires being closer to the old loom. Must check the shielding connection is OK tomorrow and put the sensor ground in properly.
Shielding problem has been fixed. I replaced the trigger wire with a better quality wire, and now I get 0 wheel errors. At least it was simple.
Secondary (cam) trigger discussion
This fits better on this page - the whole story can be seen now. I know I could get away with wasted spark & paired injectors... I just don't want to for various reasons.
I will be keeping the crank trigger (as discussed above) as this has worked perfectly from day 1 and I'm happy with it. I just need to provide VEMS with phase information.
Since the cam is difficult to get at, I thought I'd use the (now redundant) distributor body and hall sensor instead of the camshaft wheel. They both turn at the same speed (more or less) so I see no problems.
If I understand things correctly, I have all the crank position information I need from the crank trigger, but I need to create a "reset" pulse at approximately 70 crankdegrees BTDC for cyl 1 (or 20 crankdegrees ATDC for cylinder 2) so the engine phase can be established. This seems to be the time with the least things happening, and involves the least messing with the config.
Q Can this simply be one single (quick) pulse every cam rotation, or does it have to last 180 camdegrees so that the phase is always known?
Q Does this affect syncronisation during starting? Will this cause VEMS to sulk if the camtrigger isn't found immediately?
I have 2 choices on building a cam trigger -
I can bodge the dizzy to lock up the mechanical and vac advance, then simply connect the hall sensor to VEMS. There is a 4 tooth wheel in the dizzy already. I could easily convert it to a 1 tooth wheel...
The other choice is to get a dizzy drive shaft (about £40) and make a custom hall sensor and some kind of toothed wheel to fit on it. Or actually put a sensor on the camshaft wheel itself. (Given the amount of metalwork around this area, this is not likely to work effectively!)
Either way, I'm not sure on the requirements for cam sync triggers and could do with a little advice.
- Can I use a multi tooth (ie the 4 tooth original item) wheel as-is (purely to measure phase)?
- I think so (but requires cam-sync or distributor: not possible to fallback to wasted spark and go to work if you can't make camsync work in a day). Get the pulse 55 .. 70 crankdeg BTDC
- Not sure I explained things properly in the intro... The crank trigger is staying on the engine, so I should be ableto put the config back to "disable secondary trigger". (Thinking about it some more, this is a silly scheme that won't work robustly)
- apart from a few InputTrigger/AudiTrigger setups (135 for audi / 144 for volvo / etc ...) that need precisely timed "crank-timed but cam-masked" secondary trigger signal)
- I think I need to read up on Auditriggers then - what I need to do sounds similar.
- I think so (but requires cam-sync or distributor: not possible to fallback to wasted spark and go to work if you can't make camsync work in a day). Get the pulse 55 .. 70 crankdeg BTDC
How to know cam-pulse angle ?
- speculation
- from mechanical measurements and voltage levels
- scope
- soundcard
- beware of the polarity !
- we were thinking to "cheat-configure" as auditrigger and take mdd0c log (this won't start the car, you can even leave the fuelpump off) but rethinking it, this is unlikely to help even if the primary was a 60-2 or 36-1 multitooth
- maybe mixing the primary and secondary signal (not easy with VR and HALL) and InputTrigger/TriggerLog would help, but than the scope/soundcard seems more appealing
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