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) |
| 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.
Finding TDC
The ECU has been used in a "fueling only" setup for the initial period. This means I could get away with only an estimate of the TDC position from counting teeth. (Injector phasing isn't yet important to me) Now I'm doing the ignition phase of the project I need accurate TDC so that the ignition tables are in real degrees.
To find "exact" TDC you need a few tools and some basic knowledge. I found some help on the Internet somewhere:
The fastest way is to use a piston stop and the degree wheel you use to degree in your camshaft. Here's how:
Mount the degree wheel on the balancer with the correct turning tool to be able turn the engine by hand. Mount a pointer on the block that will identify the numbers on the degree wheel.
With the cylinder heads on the engine you will need to use a piston stop that screws in the spark plug hole. It does not matter exactly how far in the cylinder you go just so long as the stop is secure and will contact a flat spot on the piston, try to stay away from any machining edges. In most cases you should not have a problem. If the heads are off you can use a
plate-style stop or a dial indicator. [My piston stop was made from an old spark plug and length of threaded bar. With a vent hole so the cylinder couldn't compress]
Spin the engine slowly "by hand" clockwise until you contact the
piston against the stop. Write down the number you see the pointer aimed at on the degree wheel.
Spin the engine counter-clockwise until you hit the stop again. Again, write down the number the pointer is aimed at.
Find the center of these two marks. (it is usually pretty easy to just split the difference on the wheel). Remove the stop and spin the engine to the correct TDC point on the degree wheel.
Mark your balancer as "0" on your balancer at the zero mark on your timing tab. (This would also be the place to set zero on your timing tape if you decide to use it.)
Secondary (cam) trigger discussion
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. So I need a cam trigger to provide engine phase information.
If I understand things correctly, I have all the piston 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. I understand the cam pulse can't overlap with any activities...
Building the "cam" trigger
Since the cam is difficult to get at, I thought I'd use the (now redundant) distributor body and a hall sensor instead of the camshaft wheel. They both turn at the same speed (more or less) so I see no problems.
I can bodge the dizzy to lock up the mechanical and vac advance, then simply connect the hall sensor to VEMS. There is a toothed wheel in the dizzy already. I could easily convert it to have the right number of teeth...
- MembersPage/PhatBob my Mr Cheap argument would be in favor of this in the first instance, once its working you could try for a neater installation. [edited slightly - dnb]
- Good choice "Mr Cheap". Some spare dizzy parts have generously been donated to the cause now, so I can see them being useful...
Q: Can the trigger wheel simply be one single (quick) pulse every cam rotation
- yes, normally only one edge is selected (with HALL, falling edge has slight advantages). A 180 camdegree "tooth" is not essential.
Q: Does the above affect syncronisation during starting?
- with camsync, 2 engine rotations might be needed to get sync.
Configuration
Not sure what I need to put in the configuration yet...
Let's assume for the moment that I can have a single quick sync pulse on the cam:
Q: What do I need to do to the config (in Megatune - it's easier to work with) I presume the config is similar to Auditrigger. (except without the second crank home trigger pulse to complicate matters)
Primary trigger
- 36-1 , settings above
- is this still correct ? (if so, I have to check if some changes are needed, camsync was only used with coil-type primary trigger, and 60-2 multitooth, not with 36-1 multitooth).
- Yes - still using the 36-1 with no plans to change it if at all possible.
- is this still correct ? (if so, I have to check if some changes are needed, camsync was only used with coil-type primary trigger, and 60-2 multitooth, not with 36-1 multitooth).
Secondary Trigger Settings:
Please help me fill in the blanks...
Active: I presume "Enabled" would be a good thing. ;)
Edge: I'll go with "Rising"
Edge while cranking: Not sure!
Filtering: Not sure!
Type: coil type (not "multitooth" !)
Use: Camsync
Cam sync, engine phase at next primary trigger
Position of secondary pulse edges; range 0..215 (with 216 funny degrees)
Rising Edge (cam_sync_r_edge_phase) : Not sure what either of these should be.
Falling Edge (cam_sync_f_edge_phase):
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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