Question for 2Sheds !
Discussion
Tim ,
Just had a new ECU in the SEAC , question is , were the SEAC chips "Special" or "Standard " 'cos I will have to swap them if they are .
......... and I suppose with our resident comedians , it won't be long will it before I get a fish joke ?
>>> Edited by NHyde on Saturday 29th May 21:31
Just had a new ECU in the SEAC , question is , were the SEAC chips "Special" or "Standard " 'cos I will have to swap them if they are .
......... and I suppose with our resident comedians , it won't be long will it before I get a fish joke ?
>>> Edited by NHyde on Saturday 29th May 21:31
Depends if it's flap-type or hotwire injection. Hotwire: chips away! 
Flap: new potatoes
On the flap system, the ECU uses two ICs that were made specially for Lucas by, IIRC, Ferranti. The thing is a basic analogue computer I think; it adds and subtracts values, obtained from the engine sensors, from a reference curve and uses that to modify the 'on-time' of the injectors. As the only info it gets regarding engine speed is the trigger signal from the ignition system, it has no way of knowing which cylinder is firing next (unlike modern systems which have crank position and speed sensors, so they know when no. 1 is at TDC, for example). Since it is only necessary to have the right amount of fuel hanging around in the inlet tracts, it divides the injectors into two banks of 4 and fires each bank alternately. The pressure regulator keeps a constant supply of fuel to the injectors (at, say 50 psi), so a known quantity of fuel will pass through an injector in the time it's open. If you were to switch an injector on and point it into a jar, you would get a predictable amount through in a given time, and in fact injector makers do quote the amount that the injector will flow in a given time (eg 190cc/ minute), assuming a particular delivery pressure.
Now the faster the engine spins, the faster the ECU has to switch the injectors on and off, until eventually they are as good as permanently open. At this stage, you have max. flow.
With a tuned (or increased-capacity) engine, you are trying to get more air & fuel into the cylinders. You can get more air into the Lucas system easily enough, but getting the extra fuel to keep the mixture correct is the problem. So you turn up the fuel pressure, and what happens now is that more fuel gets through during the 'on-time'.
Problem here is that you will create a rich mixture throughout the rev range, not just at max throttle. So the fuel pressure regulator includes a vacuum-operated diaphragm that senses the manifold vacuum and modifies the fuel pressure at certain areas of the rev range.
Of course the ECU doesn't know what injectors it is firing, or what the fuel pressure is. You can only increase the fuel pressure so far before you run into other problems (such as the injectors can no longer close because the fuel is keeping them open!), so you then look for some 'fatter' injectors that flow more fuel in a given time, for the same pressure.
Or you go down the hotwire route...
Ian
Flap: new potatoes
On the flap system, the ECU uses two ICs that were made specially for Lucas by, IIRC, Ferranti. The thing is a basic analogue computer I think; it adds and subtracts values, obtained from the engine sensors, from a reference curve and uses that to modify the 'on-time' of the injectors. As the only info it gets regarding engine speed is the trigger signal from the ignition system, it has no way of knowing which cylinder is firing next (unlike modern systems which have crank position and speed sensors, so they know when no. 1 is at TDC, for example). Since it is only necessary to have the right amount of fuel hanging around in the inlet tracts, it divides the injectors into two banks of 4 and fires each bank alternately. The pressure regulator keeps a constant supply of fuel to the injectors (at, say 50 psi), so a known quantity of fuel will pass through an injector in the time it's open. If you were to switch an injector on and point it into a jar, you would get a predictable amount through in a given time, and in fact injector makers do quote the amount that the injector will flow in a given time (eg 190cc/ minute), assuming a particular delivery pressure.
Now the faster the engine spins, the faster the ECU has to switch the injectors on and off, until eventually they are as good as permanently open. At this stage, you have max. flow.
With a tuned (or increased-capacity) engine, you are trying to get more air & fuel into the cylinders. You can get more air into the Lucas system easily enough, but getting the extra fuel to keep the mixture correct is the problem. So you turn up the fuel pressure, and what happens now is that more fuel gets through during the 'on-time'.
Problem here is that you will create a rich mixture throughout the rev range, not just at max throttle. So the fuel pressure regulator includes a vacuum-operated diaphragm that senses the manifold vacuum and modifies the fuel pressure at certain areas of the rev range.
Of course the ECU doesn't know what injectors it is firing, or what the fuel pressure is. You can only increase the fuel pressure so far before you run into other problems (such as the injectors can no longer close because the fuel is keeping them open!), so you then look for some 'fatter' injectors that flow more fuel in a given time, for the same pressure.
Or you go down the hotwire route...
Ian
The job of the fuel regulator is not to keep a constant pressure in the fuel system, it is to keep a constant differential between the fuel in the injectors and the manifold. So that if the injectors are open for x milliseconds then y amount of fuel passes through under all engine conditions. There is either close to atmospheric (throttle wide open) or a partial vacuum (throttle closed). So when the throttle is wide open the fuel pressure (if read with a gauge outside the manifold) will rise. Rising rate regulators change the speed that the regulator works and thus give more richness immediately after the pressure has risen (throttle open).
The diaphragm at the rear of the plenum chamber should only open on the overrun otherwise a hunting idle will result. All air going through this diaphragm (and the extra-air or cold start valve) comes past the flap so the fuel mixture is correct.
The above applies to flap injection as I have no knowledge of hot-wire.
The diaphragm at the rear of the plenum chamber should only open on the overrun otherwise a hunting idle will result. All air going through this diaphragm (and the extra-air or cold start valve) comes past the flap so the fuel mixture is correct.
The above applies to flap injection as I have no knowledge of hot-wire.
, thanks for the great reply , only played around with "Hot wires" before on the old Chimaera and MrsH's 400 . Going to save that info for future reference . 
Rus Wood said:
The diaphragm at the rear of the plenum chamber should only open on the overrun otherwise a hunting idle will result. All air going through this diaphragm (and the extra-air or cold start valve) comes past the flap so the fuel mixture is correct.
The above applies to flap injection as I have no knowledge of hot-wire.
You're on about the over-run valve: that's not connected to the fuel pressure. The standard V8 fuel reg is fixed pressure, the adjustable one as used on 390SE etc has a vacuum link to the manifold. As you say the rising-rate type is a further enhancement (the 'power boost valve' as it's often advertised).
The way I thought the over-run valve worked is (although I'm happy to be corrected) that with the throttle closed, the depression causes the ORV to open. Crancase fumes are then pulled from the flame trap, mixed with some of the air coming through the flap meter and sucked into the plenum via the ORV, to be burnt off. Hence the ORV is often oily, due to the suspended oil in the fumes. There is a vent to atmosphere on the lefthand rocker cover; I presumed this was to allow air back in to the crankcase (it's only a small orifice so wouldn't admit enough air to upset the mixture).
You can't help thinking that a lot of the ancillaries on the Lucas (and K-Jetronic etc) were added on as afterthoughts as they found problems they didn't anticipate...
Ian
The inlet to the overrun valve is taken before the throttle and is there to limit the vacuum in the manifold to prevent condensation. It doesn't have anything to do with crankcase ventilation.
You are right that there is a small orifice on one of the rocker covers to permit air in to allow crankcase scavenging. Then a larger flame-trap on the other rocker that connects to the air intake before the throttle to burn the oil, this limits the sucking power. Don't try to set the mixture with the filler cap off (or the dipstick out).
By the way the action of the regulator is to let the fuel pump keep going at full chat, the regulator allows any excess fuel back into the fuel tank. This helps to keep the fuel cooler.
You are right that there is a small orifice on one of the rocker covers to permit air in to allow crankcase scavenging. Then a larger flame-trap on the other rocker that connects to the air intake before the throttle to burn the oil, this limits the sucking power. Don't try to set the mixture with the filler cap off (or the dipstick out).
By the way the action of the regulator is to let the fuel pump keep going at full chat, the regulator allows any excess fuel back into the fuel tank. This helps to keep the fuel cooler.
.....and....
....
get thee behind satan
Pinch the thread ......... at the moment you can pinch the damn car !!!!!!
Driving back home yesterday on the motorway, making " Steady" progress , loud pop, followed by clouds of white smoke ( no I'm not Catholic) .On to the hard shoulder to discover one of the pipes from the power steering pump had blown .
So unless I get it fixed soon , by the time BBWF comes along , should look like Schwarzenegger !
. Mind you , it does stop MrsH having a play
Driving back home yesterday on the motorway, making " Steady" progress , loud pop, followed by clouds of white smoke ( no I'm not Catholic) .On to the hard shoulder to discover one of the pipes from the power steering pump had blown .
So unless I get it fixed soon , by the time BBWF comes along , should look like Schwarzenegger !
. Mind you , it does stop MrsH having a play
rus wood said:
The inlet to the overrun valve is taken before the throttle and is there to limit the vacuum in the manifold to prevent condensation. It doesn't have anything to do with crankcase ventilation.
You are right that there is a small orifice on one of the rocker covers to permit air in to allow crankcase scavenging. Then a larger flame-trap on the other rocker that connects to the air intake before the throttle to burn the oil, this limits the sucking power. Don't try to set the mixture with the filler cap off (or the dipstick out).
By the way the action of the regulator is to let the fuel pump keep going at full chat, the regulator allows any excess fuel back into the fuel tank. This helps to keep the fuel cooler.
Not wishing to labour a point; I accept your description, but as the flame trap feeds the throttle body before the throttle plate, virtually opposite the tap for the aux air reg/ overrun valve, then surely the 'suction' through the open ORV must act on the flame trap to some degree? Otherwise, under what conditions is the crankcase purged?
Also, your point about the dipstick is a valid one: when searching for air leaks, don't forget there's an O-ring around the top of the dipstick tube to help seal the crankcase...
Ian
Ian Said:-
"Not wishing to labour a point; I accept your description, but as the flame trap feeds the throttle body before the throttle plate, virtually opposite the tap for the aux air reg/ overrun valve, then surely the 'suction' through the open ORV must act on the flame trap to some degree? Otherwise, under what conditions is the crankcase purged?
Also, your point about the dipstick is a valid one: when searching for air leaks, don't forget there's an O-ring around the top of the dipstick tube to help seal the crankcase... "
I agree with what you are saying but it is all a matter of degree. The fumes would be sucked in by the over-run valve but the fumes would also be sucked in by the main inlet under normal running. It is only the resistance of the air-filter that will cause the crankcase to be purged - unless the crankcase is at a positive pressure (ring blow-by etc.).
We can find a level of agreement over a pint someday perhaps. I hope to be able to get to one of the days of BBWF but I am waiting to see if the car survives Zolder first.
Russ
"Not wishing to labour a point; I accept your description, but as the flame trap feeds the throttle body before the throttle plate, virtually opposite the tap for the aux air reg/ overrun valve, then surely the 'suction' through the open ORV must act on the flame trap to some degree? Otherwise, under what conditions is the crankcase purged?
Also, your point about the dipstick is a valid one: when searching for air leaks, don't forget there's an O-ring around the top of the dipstick tube to help seal the crankcase... "
I agree with what you are saying but it is all a matter of degree. The fumes would be sucked in by the over-run valve but the fumes would also be sucked in by the main inlet under normal running. It is only the resistance of the air-filter that will cause the crankcase to be purged - unless the crankcase is at a positive pressure (ring blow-by etc.).
We can find a level of agreement over a pint someday perhaps. I hope to be able to get to one of the days of BBWF but I am waiting to see if the car survives Zolder first.
Russ
Rus Wood said:
I agree with what you are saying but it is all a matter of degree. The fumes would be sucked in by the over-run valve but the fumes would also be sucked in by the main inlet under normal running. It is only the resistance of the air-filter that will cause the crankcase to be purged - unless the crankcase is at a positive pressure (ring blow-by etc.).
We can find a level of agreement over a pint someday perhaps. I hope to be able to get to one of the days of BBWF but I am waiting to see if the car survives Zolder first.
Russ
Fair comment.
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