On Sun, 3 Nov 1996, John W. Dean wrote:
> I don't have experience with the system on the TR5, but I have some
> experience with the very similar system used on Maserati 6 cylinder cars
> in the late fifties and sixties. At least if my memory is right, the
> Triumph used the Lucas mechanical system, didn't it?
Yes. But being as early as late fifties, perhaps the Masers used the Mk.1
(same as used in F1 etc.), whereas the Triumphs used the Mk.2? Doesn't
sound as there were any big differences, though.
> In practice, I found the system to be very difficult to deal with. Its
> proper operation depends upon some very precise mechanical parts, which
> must be calibrated using special equipment.
My experience is quite to the contrary. Calibration of the metering unit
is based on an inlet vacuum versus. pump throw chart. I started out with a
sophisticated setup with a vacuum pump and various valves to calibrate it,
but eventually found out that the most convenient way to calibrate it was to
use:
A vacuum gauge
Sophisticated vacuum source (yours truly)
Sophisticated vacuum valve (my tongue closing the tube end)
Sophisticated pump throw gauge ;-) (a set of common feeler blades)
You really must have the Lucas repair book to get the chart, and to find out
what adjustments do what. But it is not very difficult, and the adjustment
seems to last almost infinitely.
Since the system relies on engine vacuum for metering, it depends on valve
timing etc. to be reasonable correct to work well.
> When the units wore out, though, as in most
> mechanical injection systems, they tended to fill the crankcase up with
> gasoline, and they ran very badly.
I've never ever heard of metering units wearing out, they are tough (and
very accurately made) devices. The common problem areas are:
1. The fuel pump wears out, causing problems with starting and
overheating. I overhaul mine every 5 years (30000 miles) as
preventive maintenance. A simple enough job which involves checking
and/or changing the motor brushes, the bearings, the shaft seal
and the pump end plates.
Some fit Bosch replacement pumps, but their pressure is on the
low side, which *might* cause performance problems (I have no
experience with this).
2. The injectors start to dribble, caused by an internal seal
going old and stiff. Other that that, the injectors seem to last
forever.
3. The two injectors connected to the metering unit housing using
90 deg. banjos tend to get pieces of the banjo O-ring stuck in
the valve. Easy enough to clean out, but seems to happen once
every 2 years. I'm looking at a solution with a copper seal to
fix the problem permanently.
4. The pressure regulator valve might get clogged, causing too high a
pressure in the system. Will cause the pump to heat up, causing
vapor locks. Should only be a problem for cars that are left
standing for a long time.
5. Too high resistance in the pump electrical supply. Will cause pump
overheating. (Why: because the surplus fuel will normally be
returned to the tank via the regulator valve, when the pump capacity
decreases, no surplus fuel hence no cooling). Rewiring with heavy
cables and a relay is a good preventive step.
6. Vacuum leaks, causing erratic running (rich mix), esp. in low
power region.
7. Wear in throttle body axle bearings, causing unstable tickover. It
gets impossible to reliably adjust all cylinders for a correct
flow at tickover.
Late (with two tube across) throttle bodies are less critical
in this respect compared to early ones (with one tube across).
An external throttle linkage kit is available to help, but the
standard late system works well enough if it is adjusted correctly
and not worn out.
8. Fuel leaks. I haven't had any problems, but the system DOES carry
around 120 PSI, so do change the rubber and plastic parts of the
piping every (say) 10-15 years.
9. The only problem I've seen with the metering unit is a little
plastic bit connecting the vacuum membrane to the fuel curve
breaking, causing full fuel metering regardless. Easy enough to
diagnose and fix, although "limp-home" mode may cause some
anti-social driving (only runs properly at wide open throttle ;-).
There seems to be a number of people that have problems with vapor locks
in the pump in hot weather. To remedy this, they fit a cooling coil
around the electric motor. This won't hurt, surely, but I have a
suspicion a pump being OK does not really need it.
Another popular myth about the PI is that it relies on lead for
lubrication of the metering unit. All fuel experts I have talked to says
that they can't understand this, because lead as found in gasoline would
only have a lubricating effect at elevated temperatures. And since the
Lucas manual also says nothing about this, I have been running unleaded
for a number of years now, with apparently no bad effects yet.
Compared to carbs, I find the system utterly logical and simple to
diagnose with only a few simple tools:
a. A 1/2 inch wrench to take loosen the injectors. Check the spray
(out of doors!) while the engine is running at tickover.
b. A vacuum gauge to check for vacuum leaks and engine problems.
c. The Lucas manual. The Triumph repair book is not good enough.
d. A high pressure gauge (not really essential).
e. Common sense (essential).
> My opinion is that this injection system is way more trouble than it is
> worth,
YMMV, obviously. For me the immediate response (remember, the Triumph has
one throttle plate for each cylinder, not one common plate before the
plenum chamber as is usual) and the power leaves me with no choice. I've
had the PI on my 150 BHP daily driver for 10 years, and have never looked
back.
You would definitely want a TR5 cam with the PI system.
> In the case of a TR5, I'd bet that the cost of
> overhauling the distribution unit might be about half the value of the
> car.
Yes, it has cost me some $150 over these 10 years. Which is probably half the
value of my car, I'd guess ;-).
If you don't want to do things yourself, reconditioned pumps and
calibrated metering units are available from the UK at approx #150 each.
> And a carburated Triumph runs fine, in my opinion.
Fine, but slow!
Egil
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