REPAIRS PAGE 100
FIRE RISKS
WARNING! flash fire – cause AND cure
It is with an unhappily regular frequency that
members report significant failures, and certain modes dominate these tales of
woe!
This particular one is of potentially sufficient
significance to warrant simple and cheap preventive action - it is fuel injector
O-ring failure, not at all nice. I have written about this danger before, but as
ever ‘what goes round comes round’ and it has.
First the symptoms of this failure mode, usually zero
warning (really helpful this isn’t it, but it puts it into ‘dangerous’
failure territory’)
It is nearly always on the slip road off the
motorway or into a motorway service area that this happens – just as you
decelerate after a good run where the car was ‘on song’ and you are thinking
about the next coffee or toilet visit. The sight in the mirror of flames
erupting from the engine bay soon changes that!
The injectors are obviously at the top of the
engine, but petrol can get sprayed everywhere, so flames out of the underside
can also occur - all very dramatic - and potentially very dangerous to
the occupants. I know of MK1s that have literally burnt themselves out, and
rapidly.
The key is obviously to take steps to minimise the
chance of it happening in the first place, dealt with below – but
crucially prompt action with a fire extinguisher can literally make the
difference between a relatively minor fire (if there can be such a thing) and a
major conflagration.
And if you don’t have a £15 extinguisher to hand
at this point, you are going to look and feel somewhat embarrassed for a good
while.
If you’re sick of my nagging, just talk to our
Chairman, he’ll verify it.
I’m no firefighter – but what I’d do is first
get the car to a safe halt as quickly as possible, cut the ignition, grab the
extinguisher, jump out, rip the safety seal off, pull the engine lid release
catch – hoping that it still works, and start aiming the extinguisher into
that small gap between the lid and the body - from as close possible that still
seems safe. Sounds simple, but in the panic I’m sure its no fun.
I wouldn’t try to immediately whip the engine lid
up, in the first place its probably bloody hot, and more to the point it just
allows infinitely more oxygen for the petrol – it could create a
mini-fireball.
As soon as possible ease the lid up slightly with
whatever is at hand (pen, comb, long screwdriver or the like), at the same time
discharging the remaining extinguisher contents over the top of the engine.
Now I’ve probably told you how not to tackle the
fire properly, but at least I hope I’ve got you to first base - a
decent fire extinguisher to a hand is a must.
If we have any firefighter members – please advise
on a better response - and please –standing back and ringing 999 is not what I
had in mind!
These extinguishers are hardly expensive at around
£12-20. I would say that if in doubt don’t go for very smallest size, get the
next size up.
If there is one slight problem the current
‘environmentally-correct’ auto extinguishers are (to my knowledge) ‘dry
powder’ - which I think is dosed-up sodium bicarbonate.
The bottom line is that being a powder it doesn’t
penetrate as well as gas such as Halon (the best that I know of, but now banned
due to CFC’s etc ) or Co2, which has insufficient ‘smothering power’ to
suppress petrol.
It does however work as a best compromise, but makes
a right mess, lets face it – it’s baking powder (which releases Co2 on fire
impact and smothers the area with residual sodium carbonate solid). Luckily its
water soluble and can be hosed off, at the risk of shorting-out important
electrical connections on any later ‘power-up’ attempt.
Despite these drawbacks it is really an essential,
and way above the likes of Autoglym or new alloys on the ‘buy next’ priority
list.
They are readily available from the likes of
Halfords, Argos, Index, car accessory shops to name but a few.
Having got one – so where to put it?
Yes, I know they are somewhat big, bulky and
pig-ugly, so ‘in your face‘ in the cockpit is hardly attractive, but on the
other hand just chucking it into the boot or front compartment means you’ll
never find it quick enough when its urgently needed (as if these things are ever
needed slowly!) My compromise is to keep it in the glove box, not perfect but at
least not unsightly.
Right, that’s got rid of the condescending fireman
‘holier than thou’ lecture, now onto the real meat – why does this happen
and what can be done to minimise the chance of it occurring?
Starting from scratch, the fuel injectors are
high-speed electro-mechanical valves, which open to spray petrol into the intake
valves. The opening time is controlled by the ECU according to demand, but is
typically as short as 20 milliseconds per ‘squirt’. In order to inject
sufficient fuel in such as short time requires a fairly high pressure into the
injector. This pressure is provided by a fairly powerful ‘canned’ pump,
which resides inside – yes inside the fuel tank.
Everyone knows that electric sparks, friction and
petrol are a bad combination, but in this case the pump bearings are actually
lubricated by the petrol itself!
This might sound risky in the extreme, but nowadays
it is the norm and pretty well fire proof.
Well, at least that’s the theory, of which I am
not entirely convinced, but it seems to work and explain the high cost of these
canned pumps.
Right, so this pumps job is to provide petrol at
around 60psi or 4 bar to the inlet of the injectors, as that’s their design
point. Sounds simple enough but a fixed speed pump serving a variable petrol
flow demand whilst maintaining a fixed pressure just won’t happen without a
regulator valve.
This set-up requires a pump that is permanently
providing the maximum power fuel flow and pressure, but at lower demand settings
the regulator bypasses this surplus petrol back to the tank.
So far so good but the MK1 regulator valve is a
touch undersized, it has a tiny
diaphragm, just look at it – go to the RHS of the TVIS box and look down to
the fuel rail and there it is, a glorified thimble!
OK – so what does this matter – well actually
quite a lot in the wrong circumstances.
Now for these very circumstances, just imagine a good motorway cruise.
No real problem for a MK1, and the injectors will
naturally be injecting a fair old fuel flow to provide this level of power. This
in turn requires a goodly amount of the fuel pumps capacity, so the regulator
valve is nigh on shut as its bypass capacity is not needed to dump the pump
surplus flow back to the fuel tank – there simply isn’t much pump surplus
flow to dump!
Next the tricky bit, the slow-down into the service
area, sounds innocuous enough but potentially fraught with hazards.
That’s exactly when the O-ring gremlin bites you,
the fuel demand drops to very little but the little regulator diaphragm can’t
open enough to dump the unwanted petrol back to the tank.
Result - the pressure in the fuel rail ‘spikes’,
and if the injector O-ring seals are past their best they can burst under the
pressure. High pressure petrol sprays over the hot surfaces, and bingo the fire
starts.
Bear in mind these injectors should be removed and
spray-tested every 30K miles. (Admittedly this is not official Toyota
data, but it is injector manufacturer information.) Whenever this is done the
O-ring must be replaced.
The design life of the injectors is also 60-75K
miles, after which they should be replaced.
OK, who amongst us is that conscientious?
Right, so that’s none of us, including me and I
don’t even have the excuse of ignorance that others members could claim!
(In mitigation, at least my SC is only 55K miles and
I have the good intention to ultrasonically back-flush them at 70K, more on this
in future issues if there is a demand.)
I the meantime though I’ll have that fire
extinguisher to hand as a form of ‘comfort insurance’.
It also helps to keep the transition from sustained
throttle-on to zero throttle from being too sudden – i.e. ease the car back a
bit before the exit and don’t do an F1 replica pit lane brake. (In a certain
fair Lauren’s case ignore that advice - as if she wouldn’t anyway! Just
order a new injector seal kit as soon as possible, and buy a big extinguisher!)
All of which brings me on to new seals, and as usual Toyota
don’t appear to stock injector O-rings per se – a fuel injection kit has to
be bought which costs ca £30. Yes, admittedly a bit pricey when you only want
four O-rings, but still cheaper than the smallest fire damage.
Clearly, there would seem to be a case for finding a seal
trade factor source for these O-rings, size measuring is easy, but material
specification is a bit trickier. I couldn’t possibly recommend chucking any
O-ring in that just happens to be the right size, some of the cheaper rubbers
might expire all too quickly against petrol, heat, pressure pulses etc.
Any one got any knowledge on the best materials?
Well, as usual, that seems to have talked the legs
off what started as a simple short article, was it ever thus.
The summary though is - At least be aware of the
problem and its potential for a dramatic fire. Don’t be panicked, it is not
absolutely essential to rush out and get new seals fitted tomorrow as long as
you keep it in your plan for ‘near-future’ action.
Do – as a MUST – make that insurance investment
in a fire extinguisher - and keep it close to hand. They cost relatively so
little compared to their ability to minimise dangerous occurrences.
You knowit makes sense – so get out now and buy one.
ALAN JONES
FIRE WARNING 2
The car was pulling well, and handled like it was on
rails on the slicks. Then on what was probably my last lap of the session I went to change
down from 4th into 3rd for the chicane at the end of the main straight and felt
the clutch pedal hit the floor. I just managed to make it through the chicane,
because of the extra grip of the slicks and saw a puff of smoke in my rear view
mirror.
As I pulled off the track onto the run off area I was thinking "crap the
clutch must have let go on the down shift, wonder how long it's going to take to
get home". Next minute there’s a marshal shouting and waving at me to get
out, whilst running towards me with an extinguisher. Either the oil cooler
lines, or maybe the clutch line must have cracked and sprayed onto the manifold
and caught light, and the engine bay was dripping flames. Supposedly they'd seen
a trace of flame under the car as I'd passed the pits the last time round and
were about to pull me in, but it was too late, I'd driven more or less a whole
lap with flames lapping round the underside of the car.
We used up about 7 or 8 big extinguishers up trying to get it out, but it must
have been on top of the gearbox or something and kept relighting on it's own.
Eventually I was forced to stand and watch as 18 months of development and God
knows how much cash in imported parts from Japan and replaced new suspension and
brake parts went up in smoke in a matter of 2 or 3 minutes. The fire brigade
turned up and managed to put what was left out after about 15 mins of soaking it
with foam and water, and luckily the fuel tank didn't go up, but the rest is
just gone.
The car is literally a twisted shell of melted metal, with maybe if I'm
lucky a salvageable front end.
If you do track days or aim to compete in your car in the future, I would
seriously consider getting a fully plumbed in engine bay extinguisher fitted.
Once a fire has started in the engine bay it's too dangerous to pop the lid to
get at it, and the SC has no access through the sides like the MK2. All you
can do is spray in through the intercooler area on the lid, and from underneath,
which just doesn't work. Gutted.