Electronic engine management for the Slant 4

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Re: Electronic engine management for the Slant 4

Postby 1972nail » Mon Apr 09, 2018 10:26 pm

I found this picture of a fuel injected Firenza 2000 engine from back in 1971.



I have one of those manifolds, with the cast in bumps, that i had bought many years ago with the intention of fitting injectors.

It's interesting that the modern 'Jenvey' type throttle bodies don't look much different, the only real difference is that they will have a solid fuel rail and wiring connected to the injectors rather than individual pipes.

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"When you have a Firenza like mine, who needs any Minis?" copyright David Maxwell 1979.
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Re: Electronic engine management for the Slant 4

Postby 1972nail » Sat Apr 28, 2018 9:20 pm

Today saw the start of fabrication for this project. The first thing to do is modify the distributor to act as a low resolution trigger and still operate as basic distributor to fire the correct plugs. Here's how.....

First of all mark where No 1 plug lead on the cap is in relation to the distributor body.


This is important as both advance mechanisms have been removed and locked down and advance will be handled by the ECU. This means that when running at maximum or minimum advance the rotor must still be close enough to the plug connection to transfer a spark.

To cut a long story short, a few calculations show that my average advance will be about 25 deg BTDC and the idea is to accurately align the rotor with the plug lead at 25 deg BTDC so that when advance is at minimum or maximum the tip of the rotor will still be close enough to the lead to fire reliably and not fire on to the next lead instead.

Next thing to do is fit the Accuspark module which I'll use as the trigger for the ECU. The distributor has to be completely dismantled to do this.

As the distributor runs at half crank speed this trigger will only provide 2 signals per revolution just like points. When cranking the engine to start, the ECU cannot calculate an accurate figure for revs using only 2 signals because the revolution speed changes considerably as the pistons come up to and go off compression. This means the ECU cannot calculate an accurate sparking point. The trick is to tell the ECU to fire immediately it sees a trigger signal at cranking speed, i.e. below about 500 to 600 RPM.

This leads on to the next task, aligning the Accuspark to trigger at the correct time in relation to the rotor at a static ignition timing of 10 deg TBDC. To help with this I made a simple timing disc from a clear plastic CD disk using a protractor.


To use the disk TDC on No1 cylinder has to be set correctly on the engine. This can be determined with various mechanical methods but on the Slant 4 Vauxhall very kindly machined a TDC timing mark onto the block so that when the centre of the crank pulley keyway is aligned with the mark and the camshaft alignment marks are correct then you've found No1 TDC. I've highlighted and extended the mark with paint on the old engine I'm using to experiment on so that it can be seen easily,

I marked TDC, 10 and 25 Deg BTDC on the disk, enlarged the hole in the centre and fitted it close to the block behind the lower crank timing belt pulley.

Next up rotate the crank clock wise almost 2 full rotations to the 25 deg mark BTDC on No1 cylinder and install the distributor so that the rotor aligns roughly with the No1 plug lead mark on the body, then swing the distributor to accurately align. Bolt the distributor down tight.


You'll notice that it will be at one extreme end of adjustment or the other depending on which gear tooth you engage on the aux drive shaft. I suggest that you engage the gear wheels so that it at this extreme end of adjustment to avoid later problems such as the distributor cap clip being under the thermostat housing and not being able to get it on or off! It also aligns the base plate better for the locking procedure described later.

Next up align the 10 degree mark, this is where we align in the Accuspark.

Attach the block or distributor to the negative side of a 12v battery to provide a ground/earth and the RED wire on the Accuspark to the positive side. Then connect up a voltmeter as shown, red lead to Accuspark red (12v+) and the black lead to Accuspark black.

You should see a very small residual leakage voltage if all is OK.

The black wire is the wire which sends the trigger signal to the ECU and we must align that trigger to 10 deg BTDC to get a fixed cranking advance of 10 deg. To do this I gently and slowly swung the base plate with the Accuspark in place CLOCKWISE until I saw a large momentary voltage spike up to 12v. The meter may not be fast enough to read the full 12v so you could see anything from 6 to 11v register. This is the leading edge trigger point. If you swing anti clockwise you will see the trailing edge trigger which is about 15 deg out. You may need to practice this to get it accurate. Once found I marked the base plate and distributor body and took the distributor out.

I then drilled a hole through one of the redundant holes on the base plate and the bottom of the distributor body and locked the base plate in place with a self tapper.

Job done!
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"When you have a Firenza like mine, who needs any Minis?" copyright David Maxwell 1979.
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Re: Electronic engine management for the Slant 4

Postby Colin » Wed Jul 18, 2018 2:22 pm

A very interesting article, David.

The proposed EFI engine management system appears quite advanced.. (sorry, another unintended pun)

If I correctly understand your installation sequence for your modified electronic ignition system it's similar to static timing of a standard points system? (As an aside, we sometimes used to use a transistor radio to static time points ignition. The radio signal would crackle when the points were just beginning to open. It used to work though! :) )

I'm now looking at installing electronic ignition to replace standard points on my standard 1975cc Viva GT. With this in mind, just a couple of quick questions -

1) Would the below used Lumination system on ebay be worth bidding on? Does it appear to you to be complete?

https://www.ebay.co.uk/itm/VAUXHALL-VIC ... 1438.l2649

2) I think the standard Delco distributor for slant four OHC is the D200. How would you rate the Accuspark system for this application? I think Accuspark kit 32 is correct for slant 4 OHC?

https://www.ebay.co.uk/itm/Vauxhall-Vic ... 0290.m3507

3) I have a new unused 1599cc OHC narrow slot distributor. I'm wondering whether it might be possible to press out the narrow slot drive gear retaining spring pin and press the drive gear from the shaft, replacing it with a wide slot drive gear. Is this possible?

If I understand correctly this will just leave the question of mechanical advance curve governed by bob weights and springs. I will look at replacing those fitted to the 1600 distributor with those from the 2000 distributor. Does that sound feasible?
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Re: Electronic engine management for the Slant 4

Postby 1972nail » Wed Jul 18, 2018 3:50 pm

Yes, it is like static timing but you have to time two items independently, the rotor arm and the pick up sensor. The rotor arm needs to be fixed at roughly the middle of your proposed advance and the pick up at the start of your proposed advance.

The original mechanical advance system kept the rotor tip roughly aligned with the plug lead contact when the spark arrived at all engine loads and RPM's, however this is all now done away with and dictated by the ECU. The spark will now arrive at the rotor before the plug lead contact or after the plug lead contact depending on the advance programmed in the ECU for that RPM, engine load etc. The rotor has to be aligned so that the leading tip meets the plug lead at minimum advance and the trailing tip is just leaving the plug lead at maximum advance.

The sensor on the other hand has to send the signal at the minimum timing advance and the ECU can work out the rest from the programmed map. It is not strictly essential to time the sensor in this way, but advisable, in case the ECU looses the map and then the sensor takes over. This lets the engine run on one advance 'limp mode' dictated by the position of the sensor, ie, minimum advance. Or if the whole ignition side of ECU fails, it's a simple matter of using the Accuspark as an electronic ignition in it's own right, running on minimum advance, just by swapping a few wires.

I've no experience of running a car on the Accuspark as an ignition system so can't comment on it's performance. Many who have say it's a good modification and have no complaints. By the way, it's a D300 distributor and if you can't find a suitable Accuspark on eBay then search for Vauxhall Victor, Bedford CF, or as a last resort, Triumph TR7, it's the same.

The Luminition kit does look complete, however, many Luminition kits are 30 + years old and things like capacitors etc can be past their best. Many who have old Luminition units are now finding them unreliable.

As far as swapping over the drive gear, it is possible, but be aware that the pin hole was manually drilled during original assembly and may not be at the same angle, height or whatever to the one you're replacing so the pin may not slip straight in. You may have to drill a new hole in a different place to get it re-assembled. My drive had 2 holes and the shaft one.....

P.S. The Victor Accuspark in the eBay link is the correct one. Also swap over your vacuum capsule just in case it has a different advance, some are 3 1/2 deg others 6 and 9 degrees.
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"When you have a Firenza like mine, who needs any Minis?" copyright David Maxwell 1979.
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Re: Electronic engine management for the Slant 4

Postby Colin » Wed Jul 18, 2018 9:59 pm

Many thanks, David. All good useful advice.

I'm embarking on a bit of a quest to find the most accurate and reliable electronic ignition system for my car. The engine was fully rebuilt a few years and about 2000 miles ago but I think the old standard distributor still fitted is worn and inaccurate. So unless I can find something better I think I will be going with the Accuspark system on the modified NOS distributor described above.

Have you begun to fit your ECU managed modified electronic ignition and EFI yet? It will be very interesting to see how well it all works. I imagine it should result in a considerable increase in power and tractability. Good luck with it and keep us all informed of progress. :goodluck:
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Re: Electronic engine management for the Slant 4

Postby 1972nail » Wed Jul 18, 2018 10:56 pm

Life has stopped progress on it at the minute so no, I haven't fitted it yet.
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"When you have a Firenza like mine, who needs any Minis?" copyright David Maxwell 1979.
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