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From: Irwin Armstrong <armstrong@btinternet.com>
To: David Hill <David_J_Hill@email.msn.com>
Subject: TR6 PI System Pt 1&2
Date: 05 April 1998 23:26
This is about 10% and may take a little time as the original is multi
faxed and almost impossible to read never mind OCR!!
Irwin
Dave Hill adds: Irwin very kindly sent me this info and will be sending
more. Perhaps he'll send copies of the rest direct if you ask him nicely.
Cheers.
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So how does it work? Intricate though It may appear, its really fairly
straightforward as you can see from the illustrated system Figure A.
Fuel from the tank is gravity fed to a high pressure electric pump,
found on the left side of the boot. Some early systems will have the
pressure relief valve return feeding back to the filter unit, the
diagram shows the Mark 2 TR6 version feeding back to the petrol tank.
The pressure relief valve should maintain fuel pressure at 106-110 psi
in the main line to the metering unit. This unit is driven by the
ignition distributor shaft, and controls the timing of each fuel
injection, and the amount of fuel delivered.
In Fig. B we have a simplified metering unit for 2 cylinders A
6-cylinder unit simply has two additional pairs of outlets. The rotor is
driven at half engine speed, and the shuttle is free to slide back and
forth. The whole assembly is surrounded by petrol under pressure and, as
the rotor turns, the port at the top left-side aligns with the inlet
port and petrol enters the sleeve, pushing the shuttle to the right.
This causes petrol to be discharged through the bottom right hand port
to number 2 cylinder. Turning the rotor through 180Ί allows fuel to
enter via the top right port and, as the shuttle moves right to left, it
is discharged via the bottom left port to number 1 cylinder.
So, we can see that the distance the shuttle Is allowed to travel,
controls the amount of fuel injected and this distance is controlled
by an adjustable moving stop. The position of the moving slop, and the
amount of fuel injected, is controlled by manifold vacuum.The higher
the vacuum, the smaller the quantity of fuel.
In Fig, C we see the control unit, As the vacuum varies with the
throttle opening, etc, the diaphragm moves up and down, taking with It
a pair of links, which have three rollers sandwiched between them. The
outer, larger pair of rollers move the cam follower, as prescribed by
the centre smaller roller moving upon the datum track, and the cam
follower controls the position of the moving stop. The springs which
surround the cam follower counteract the force which would otherwise be
applied to the rollers and datum track by the 106+/- psi fuel pressure.
Thus metered doses of fuel pass to the injectors, which are
spring-loaded valve that open at 60 psi fuel pressure. The shape of the
nozzle causes fuel to be finely atomised, as It leaves the injector, in
the form of a 60 degree hollow cone.
Before we attempt to make any adjustments to the system, there are a few
points we must check as many minor troubles often attributed to the PI
system are caused by poor engine tune.
1 set contact-breaker points to 0.015in.
2 clean and gap sparking plugs to 0.025 in.
3 before replacing plugs, set valve clearance to 0.010 in cold The
engine can be rotated by means of a socket spanner on the alternator
pulley nut.
4 set static ignition timing to 11 degrees before TDC on number 1
cylinder firing stroke, as indicated on crankshaft pulley.
Now to the pi system Itself. which may have had, no attention for
several years -so most of these checks will be long overdue The more you
can complete, the greater your chance of success.
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to be continued with diagrams to follow.
The only expensive part to fix is probably the fuel pump unless your PI
unit is worn so don't give up yet.
If your problem is general lack of response. see the graph on timing the
metering unit. For the more usual trouble of misfiring, running rich,
and excessive fuel consumption, proceed with checks as follows.
Cylinder compression must be fairly even and at least 150 psi or low
manifold vacuum will result and the system will never work properly.
Check the pipe from the inlet manifold to the metering unit for leaks.
Also, the small pipe from lower front end of the metering unit which
returns petrol leakage to the tank, if kinked or blocked, a pressure
build-up will occur, causing rich mixture.
The over-fuel lever, equivalent to the choke on carburetor see Figure
C - may be sticking. There should be 8 thou clearance between the lever
and the cam on the throttle linkage. Incidentally if your engine won't
start, but the pump is running: the problem is rarely caused by the
injection system. To check, release the clamp that holds the injector
pipes together on top of the valve cover, and feel the pipes whilst
turning the engine over. Distinct pulsations should be felt in each of
the pipes.
Synchronisation of throttle butterflies is extremely; important, if an
over-rich mixture on any the cylinders is to be avoided. Synchronisation
is best carried out using an air-flow meter as normally used on
conventional twin-carb installations remove the air-box. Check rubber
balance-pipes between air Intakes are not leaking. Start engine,
increase tickover speed by turning the adjusting screw adjacent to the
throttle return-spring, clockwise until a reading can be obtained on the
air-flow meter . Now. decide which pair of intakes will be used as a
master set. Each butterfly is adjusted by a rod on the linkage. Slacken
base locknut. The rod can then be screwed in and out with a screwdriver,
to alter the flow, by means of a slot in the top end. When tightening
the locknuts, hold the screwdriver in the slot to prevent the rod
turning, and thus altering the flow readings. Reset tickover by
returning the adjusting screw to its original position - just touching
the lower bracket.
Fuel line pressure. There is no alternative but check this with a
suitable gauge having a maximum scale of 120 psi. Connect the gauge, via
a T-piece, to the petrol inlet to the metering unit. The correct
pressure at both tick-over and revving should be 106 to 110 psi. The
pressure relief valve can be adjusted a quarter of a turn at a time
clockwise will increase the pressure Take great care that there are no
leaks. A high-pressure spray of petrol, will act like a flame thrower.
The electrical consumption of the pump 3.5 to 5 amps when pumping. If
the correct pressure cannot be found, either the pump, or the pressure
relief-valve, may be at fault. see paragraph on pump failure.
It is a good idea to remove the spark plugs after a run- to check if
there is any uneveness between cylinders the insulator noses should
all be the same light tan to brown colour. Light tan to white indicates
to weak a mixture.. brown to black sooty colour indicates to rich a
mixture. If only one cylinder is rich, it could be a sticking or worn
injector, a faulty seal between pipe and metering unit, or metering unit
adaptor seal.
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To be continued !!!!!
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