yoeddynz

DIY Fuel injection thread.

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 1 tooth per combustion event is all you need for dizzy.   ecu sees trigger pulse and fires coil.  dizzy sorts the rest.   will need to setup the teeth so you have one of them pointing at sensor when engine is at tdc

do you have any external vr conditioners.  or vr straight into ms?

 

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46 minutes ago, kpr said:

 1 tooth per combustion event is all you need for dizzy.   ecu sees trigger pulse and fires coil.  dizzy sorts the rest.   will need to setup the teeth so you have one of them pointing at sensor when engine is at tdc

do you have any external vr conditioners.  or vr straight into ms?

 

VR conditioner is built in to ecu.

 

Also the tooth needs to point at sensor quite an angle before from TDC (like 60 deg or so) with megasquirt, that point gives a hard limit on the maximum timing advance possible.

 

The problem with only one tooth is that the engine speed can change significantly over the space of 180 degrees of crank rotation, so it can really end up being a guessing game for correct timing. The original 7K-E distributor was just 4 teeth and timing controlled by the ecu, but Toyota seems to use a better vr conditioning system than MS, giving cleaner signals during cranking.

 

If 4 teeth was fine for giving accurate timing then why does Toyota use 24 teeth + a single tooth wheel in shitty old 4A-FE engines?

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Because they can. 

Just put a tone wheel on your crankshaft already. The freeplay in the drive between crank and dizzy is going to be greater than any inaccuracy caused by low tooth count anyway.

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can you snap off the opposite tooth to the missing tooth and tell the ecu the sensor is as crank speed with a 15-1 trigger. 

thats what ive done with my dizzy mounted sensor (12 tooth hall effect wheel with two oposing missing teeth). unsure if 15 teeth is any better for the maths though. 

 

HOWEVER. 

i also have a 36-1 crank mounted trigger wheel waiting to go on when i also change the superchrager pulley for more boost (is doest fit with the current pully) because im 99% most of my shitty idle and roughish cruise is down to all the backlash in the dizzy setup and all the tricks made to get it to run thinking its got a crank trigger. 

 

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45 minutes ago, BlownCorona said:

can you snap off the opposite tooth to the missing tooth and tell the ecu the sensor is as crank speed with a 15-1 trigger. 

thats what ive done with my dizzy mounted sensor (12 tooth hall effect wheel with two oposing missing teeth). unsure if 15 teeth is any better for the maths though. 

 

HOWEVER. 

i also have a 36-1 crank mounted trigger wheel waiting to go on when i also change the superchrager pulley for more boost (is doest fit with the current pully) because im 99% most of my shitty idle and roughish cruise is down to all the backlash in the dizzy setup and all the tricks made to get it to run thinking its got a crank trigger. 

 

Tooth (prior to removal of one) count needs to be a multiple of the number of cylinders, as with a megasquirt the ECU links a physical tooth with a "tach" signal (one tach tooth per cylinder) and then counts a set time after that to send the ignition pulse. This lets it resynchronise timing every 720/#cyl, rather than once per 720 degrees, supposedly improving accuracy.

Since 30 doesn't divide by 4, the system can't accept it. And removing any other teeth to try and make it work won't work either because then the tooth spacing won't be correct.

It's a bit of a shit limitation but that's just how they made it.

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1 hour ago, Yowzer said:

Because they can. 

Just put a tone wheel on your crankshaft already. The freeplay in the drive between crank and dizzy is going to be greater than any inaccuracy caused by low tooth count anyway.

I do get what you're saying, but I'm stupid so won't take the easy route.

 

The freeplay isn't really that much of an issue.

 

The timing chain is short, so there is minimal stretch there and there won't be much vibration going on causing changes in effective length between pulleys.

The distributor is always under load from the oil pump, so the backlash isn't an issue (ignition timing on deceleration isn't even important anyway).

The main source of inaccuracy would be if any of the gears in the system had teeth that weren't perfectly spaced, but that would also be pretty minimal.

The 7K-E distributor is also better built than a 4K distributor as it has a big sealed bearing on the shaft instead of just a bushing.

 

 

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1 hour ago, ajg193 said:

VR conditioner is built in to ecu.

 

Also the tooth needs to point at sensor quite an angle before from TDC (like 60 deg or so) with megasquirt, that point gives a hard limit on the maximum timing advance possible.

 

The problem with only one tooth is that the engine speed can change significantly over the space of 180 degrees of crank rotation, so it can really end up being a guessing game for correct timing. The original 7K-E distributor was just 4 teeth and timing controlled by the ecu, but Toyota seems to use a better vr conditioning system than MS, giving cleaner signals during cranking.

 

If 4 teeth was fine for giving accurate timing then why does Toyota use 24 teeth + a single tooth wheel in shitty old 4A-FE engines?

I was more saying it works, rather than use 4 tooth.

I'm still going with the  vr sensor itself (or megasquirt depending how you want to look at it)  is the issue.      If they are still like they used to be,  the ms has issues with at least the toyota / denso vr sensors.    All the ones that worked properly had a daughter board, or some kind of add on vr conditioner.   even ms3 didn't work properly with the onboard setup.

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Tooth count mostly affects transients rather than steady state.
IF your engine speed was exactly steady then you'd not need triggers at all once its going.

Why do OEM have lots of teeth on triggers?
Probably because transient conditions are by far by far the least controllable part of engine operation when it comes to emissions and economy.
Also some ECUs do fancy stuff like look for minor accel/decel through the crank angle to spot misfire issues or as part of a knock detection strategy.

Also I guess having fewer teeth makes it more of a problem at lower rpm than high, as you've got a much longer time period between engine speed "updates" 
Just doing some low effort maths, if you have a 4 tooth trigger on cam only, then at 1000rpm you're getting engine speed updates at 33hz. 
That seems less awful than I would have thought, unless my half arsed maths is wrong.
 

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7 hours ago, Roman said:

Tooth count mostly affects transients rather than steady state.

Also I guess having fewer teeth makes it more of a problem at lower rpm than high, as you've got a much longer time period between engine speed "updates" 
Just doing some low effort maths, if you have a 4 tooth trigger on cam only, then at 1000rpm you're getting engine speed updates at 33hz. 
That seems less awful than I would have thought, unless my half arsed maths is wrong.
 

4 teeth at 1000 rpm -> 500 signals per minute -> 500/60= 8.33 per second

 

These are the exact situations where fuel only is crap, it's much harder to get rid of the stumble when jumping on the throttle at low rpm because the ecu is always 180 degrees behind the engine. With the 20-1 setup all hesitations were completely gone. And during cranking you need the most resolution, as the engine speed is the most variable throughout the cycle. 4 teeth during cranking just results in a shit timing signal.

 

The way Toyota dealt with this issue (with 4 tooth distributor VAST ignition) was with a go between module between the distributor and the ecu. If the module didn't receive a signal from the ecu it would just fire whenever it got a pulse from the distributor (the teeth were set at base timing) - but obviously one pulse later.

 

 

 

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13 minutes ago, yoeddynz said:

In the amount of time you've spent fucking about talking about trigger wheels you'd have cut and filed one out by now. Honestly--it's not a rocket science job. Tools you'll need. 

Vice, 

Hacksaw, 

File. 

I'm just going to throw a piece of steel at the mill some time this week and let it do all the work. No hassle, no stress.

I am in no rush to get back to doing it right now and I have other stuff to do.

+ The two tools I don't have at home are a vice and hacksaw.

+ I don't really want a crank trigger. I want to hide it in the distributor.

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Crank trigger setup and then use dizzy as secondary input for cam position. Easy and less fucking around than this whole discussion has been. Crank triggers still look OEM unless you use flashy billet parts or some shit. 

You seem to be making it harder for yourself, for the sake of making it harder?

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22 minutes ago, kws said:

 

You seem to be making it harder for yourself, for the sake of making it harder?

Precisely. Just want to see what I can actually get to work. If I wanted to do it the easy way I would have either used a crank trigger or just put a 4A-GE in.

But also, crank triggers are absolutely disgusting on this type of engine.

 

 

Doing this sort of stuff is a good way for me to learn as much about machining as I can. There's not really much point in me doing it if I'm not really learning much.

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Fair enough, can't blame you for trying different things and going against the grain. 

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4 hours ago, ajg193 said:

 

+ The two tools I don't have at home are a vice 

 

 

I'm sure you'll get advice from someone on here.....  :-)

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8 hours ago, ajg193 said:

4 teeth at 1000 rpm -> 500 signals per minute -> 500/60= 8.33 per second


Thats 500 cam rotations, not 500 times that a tooth swipes past the VR. You get 4x as many signals as that? 
 

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18 minutes ago, Roman said:


Thats 500 cam rotations, not 500 times that a tooth swipes past the VR. You get 4x as many signals as that? 
 

Probably. Was too early in the morning to do math.

 

4 cyl, 4 stroke gives 2 combustions per revolution -> 2000 combustions per minute -> 33 Hz

 

Yep. You are correct. I still believe my argument of engine speed fluctuating significantly at low rpm/cranking is valid though.

 

 

This is a 60-2 crank wheel during cranking:

Sample+tooth+log+60-2+wheel+while+cranki

You can see pretty clearly that if you only have 4 teeth on a camshaft, you will have no idea what the real position of the engine is for the vast majority of the cycle during cranking.

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Yeah agree, especially if you're fighting VR voltages too. 

More the merrier! 

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I've found a 70 mm diameter bar of cast iron, internet seems to reckon that has a low magnetic coercivity so should be good as a VR trigger.

 

I have no idea what sort of steel the last wheel was made from, for all I know it would have turned into a permanent magnet within a week and stopped working.

 

I'll make up some G code and throw it through the mill tomorrow evening and see how it goes. Should end up being fairly minimal work if I get the code right,

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On 24/03/2019 at 19:21, ajg193 said:

Tooth (prior to removal of one) count needs to be a multiple of the number of cylinders, as with a megasquirt the ECU links a physical tooth with a "tach" signal (one tach tooth per cylinder) and then counts a set time after that to send the ignition pulse. This lets it resynchronise timing every 720/#cyl, rather than once per 720 degrees, supposedly improving accuracy.

Since 30 doesn't divide by 4, the system can't accept it. And removing any other teeth to try and make it work won't work either because then the tooth spacing won't be correct.

It's a bit of a shit limitation but that's just how they made it.

Right, understand now. So just put PLL code in another arduino and rescale the output frequency. Isn't that what software is for? Fixing hardware screw-ups (caused by other software requirements).

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