[xj] burn, baby, burn

XJ
1

When this car couldn’t stop me from driving it, by way of ignition, steering rack, exhaust, suspension, brake, electrical, coolant, or head gasket problems, it turned to fire! :open_mouth:

Replaced the head gasket maybe 3-400 miles ago, and all seemed fairly good. Started it on a cool (43 degrees) morning recently and–atypically–listened to it idle (a little unevenly) for maybe 30-45 seconds. Backed out of the driveway, then maybe 20’ later heard or felt a faint ‘whoomp’. A few seconds later saw smoke coming out of the rear of the bonnet. A few seconds later smoke was very black. Opened hood to find a line of flames a good 8" tall, running most of the length of the intake manifold. Closed the hood and ran a couple hundred feet to get the fire extinguisher from home. Put out fire.

Lesson I learned: Not a bad idea to have a fire extinguisher in any old vehicle. Very bad idea to not have one in a FI older Jag!

I’m still not sure how the fire started, but I think it highly likely it was fuel related, and kept burning as the pressurized fuel kept spurting. Don’t really understand how it started so quickly, as the engine couldn’t have been very hot, especially the intake side? Web searches found a few references to these later cars being ‘prone’ to fires but no real documention of such. Archives have almost nothing, that I could find. Any truth to these ‘rumors’?

I had replaced several of the fuel injector hoses, fuel pressure regulator hose, etc., but hadn’t yet done the rear injector hoses. My guess is either one of those cracked, or a new one I put on came off. Afterwards the hose was off the pressure reg. but it was such a gooey mess I don’t know whether it was cause or effect.

Will need pretty much all wiring on that side of the engine, from about the throttle body to the radiator. David has fixed me up with most of the destroyed parts I need, and I’m hopeful I’ll either be able to source a harness he didn’t have, or possibly make it myself? The front 2 injectors look pretty bad and will be replaced. Am thinking I ought to check the other 4 prior to reinstalling them–with new hose. :wink:

On the brighter side, newly rebuilt head still looks good. :slight_smile:

Thon
87 XJ6===================================================
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2

When this car couldn’t stop me from driving it, by way of ignition, steering
rack, exhaust, suspension, brake, electrical, coolant, or head gasket
problems, it turned to fire! :open_mouth:

Replaced the head gasket maybe 3-400 miles ago, and all seemed fairly good.
Started it on a cool (43 degrees) morning recently
and–atypically–listened to it idle (a little unevenly) for maybe 30-45
seconds. Backed out of the driveway, then maybe 20’ later heard or felt a
faint ‘whoomp’. A few seconds later saw smoke coming out of the rear of the
bonnet. A few seconds later smoke was very black. Opened hood to find a
line of flames a good 8" tall, running most of the length of the intake
manifold. Closed the hood and ran a couple hundred feet to get the fire
extinguisher from home. Put out fire.

Prompt action, bravely and competently carried out, Thon…

The ‘whoomp’ certainly imply petrol igniting by adjacent electrics -
probably from a leaking or disconnected hose. Nominally, with a leak and as
the engine and pump stops, ign ‘off’, rail pressure - and the fire is only
sustained by burning hoses and wire insulation. Main point being that with
EI fuel flow stops with the pump stopping - slightly dependent on tank
levels, carb fuel inlet hoses are lower, and may flow on by gravity…

Nasty nonetheless, and you should carefully re-examine the hose remnants for
a possible clue - a fire won’t actually disconnect the hose remnants/clamps
from its attachment. So a likely scenario is indeed that the fuel return
hose at the pressure regulator disconnected - which would not interfere with
engine running. Petrol will then run back along the right side of the
engine, helped by the cooling fan - until the ignition is turned off. Which
would instantly stop return flow, while the rail pressure is contained by
non-leaking injector hoses…

There should be clamps on the rubber hose stub at the return line - you did
not forget to tighten them, I hope…?

Nominally, you need a fairly hefty spark to ignite the petrol - engine heat
has little bearing; it never gets hot enough to ignite petrol, but may of
course cause petrol to vaporise, making it easier to ignite. The reason you
find little documentation of engine fires is that it certainly is uncommon.

While pouring petrol into the engine compartment is not a good idea - the
petrol adds intensity to a fire, but still requires an ignition source. And
principally, with a running engine, there should be none, the ignition
sparking is nominally contained within the cylinders, and firm wire
connections do not create sparks. So you really need both the cause of the
petrol leak and the ignition source to preempt a repeat…:slight_smile:

Sure, electric fires may start in unfused or delapidated wiring, like a bad
connector overheating, or one remaining strand carrying the load usually
shared by several - fire fed by oil or dust or whatever. But common it aint
even on our old cars…

You did well after the fact, Thon…

Frank
xj6 85 Sov Europe (UK/NZ)

Lesson I learned: Not a bad idea to have a fire extinguisher in any old
vehicle. Very bad idea to not have one in a FI older Jag!

I’m still not sure how the fire started, but I think it highly likely it was
fuel related, and kept burning as the pressurized fuel kept spurting. Don’t
really understand how it started so quickly, as the engine couldn’t have
been very hot, especially the intake side? Web searches found a few
references to these later cars being ‘prone’ to fires but no real
documention of such. Archives have almost nothing, that I could find. Any
truth to these ‘rumors’?

I had replaced several of the fuel injector hoses, fuel pressure regulator
hose, etc., but hadn’t yet done the rear injector hoses. My guess is either
one of those cracked, or a new one I put on came off. Afterwards the hose
was off the pressure reg. but it was such a gooey mess I don’t know whether
it was cause or effect.

Will need pretty much all wiring on that side of the engine, from about the
throttle body to the radiator. David has fixed me up with most of the
destroyed parts I need, and I’m hopeful I’ll either be able to source a
harness he didn’t have, or possibly make it myself? The front 2 injectors
look pretty bad and will be replaced. Am thinking I ought to check the
other 4 prior to reinstalling them–with new hose. :wink:

On the brighter side, newly rebuilt head still looks good. :-)-----Original Message-----
From: tb
Sent: Monday, December 16, 2013 10:48 AM
To: xj@jag-lovers.org
Subject: [xj] burn, baby, burn

===================================================
The archives and FAQ will answer many queries on the XJ series…
FAQs: http://www.jag-lovers.org/xjlovers/xjfaq/index.html
Archives: Jag-lovers Forums - Jag-lovers

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3

In reply to a message from Frank Andersen sent Sun 15 Dec 2013:

You lost me here, Frank. With the ignition off, the pump
stops, but the system is still under pressure, on both sides
of the regulator, right? With a small leak, that could take
quite a while to drop the pressure enough to stop it ‘spraying’?

After the fact–the fire looks to have been hottest in the
area of the front two injectors, but the flames looked about
the same, most of the way back down the intake side of the
engine. That’s what made me suspicious fuel was spraying,
plus the fact it was just as intense when I returned with
the extinguisher.

I’m very certain I tightened all the hose clamps–I’d read
numerous cautions about this prior to doing the work. Seems
unlikely but I’m wondering if I may have overtightened a
clamp, and cut through a hose?

Which brings up a question: Is it important to have smooth
clamps rather than the normal kind (like I have)?

I agree a stray spark makes the most sense, but have no clue
from where.

Assuming I get this thing running again, I may be so gun shy
I’ll be driving with an extinguisher between my knees, for
the first 1000 miles. :slight_smile:

Thanks.

Thon–
tab a
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===================================================
The archives and FAQ will answer many queries on the XJ series…
FAQs: http://www.jag-lovers.org/xjlovers/xjfaq/index.html
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4

In reply to a message from Frank Andersen sent Sun 15 Dec 2013:

You lost me here, Frank. With the ignition off, the pump
stops, but the system is still under pressure, on both sides
of the regulator, right? With a small leak, that could take
quite a while to drop the pressure enough to stop it ‘spraying’?

My take was the return hose jumping off at the pressure regulator, Thon…

As soon as the pump stops the regulator closes off the return line, as no
further fuel is delivered from the pump. Rail pressure is then retained,
courtesy of the non-return valve - but unless injector hoses are also
leaking; no fuel will leak out of the rail. The amount of fuel under
pressure, between the non-return valve and the pressure regulator, is
limited to the filter volume and the very small volume in the rail itself…

I do suspect the return hose as if detached it would have no effect on
engine running - while any detached injector hose, except the CSI, would
give some engine reaction, and you had none. Another point is that the
return hose is nearest the front injectors, which shows the worst fire
damage - though petrol would spread backwards from fan action. When you
returned with the extinguisher the fire was likely sustained by burning
hoses and insulation - and to some extent by rail fuel leaking out of burnt
off injector hoses.

There is very little pressure at the return hose - the fuel is free to run
back to the tanks. Basically; if hose remnants are still clamped to the
regulator return exit pipe, the hose failed - for whatever reason. If the
hose slipped off due to insufficient clamping, there is nothing left on the
regulator - though with the burning there may be nothing anywhere.

As an aside; the safety feature of the AFM reed switch is that a major leak
between the pump and the regulator will drop fuel pressure - and the engine
will stop. Which will open the reed switch and the pump will stop -
preventing further fuel spraying. Point is that a fire sustained by pumped
fuel would be virtually uncontrollable…

I don’t think you should be unduly worried about a repeat - engine fires are
very unusual, but sure are dramatic when they do occur. Regular inspections
are required as a first line of defence, one slip-up is enough, and a fire
extinguisher is then a good second line - and useful for a lot of
purposes…

Frank
xj6 85 Sov Europe (UK/NZ)

After the fact–the fire looks to have been hottest in the
area of the front two injectors, but the flames looked about
the same, most of the way back down the intake side of the
engine. That’s what made me suspicious fuel was spraying,
plus the fact it was just as intense when I returned with
the extinguisher.

I’m very certain I tightened all the hose clamps–I’d read
numerous cautions about this prior to doing the work. Seems
unlikely but I’m wondering if I may have overtightened a
clamp, and cut through a hose?

Which brings up a question: Is it important to have smooth
clamps rather than the normal kind (like I have)?

I agree a stray spark makes the most sense, but have no clue
from where.

Assuming I get this thing running again, I may be so gun shy
I’ll be driving with an extinguisher between my knees, for
the first 1000 miles. :-)-----Original Message-----
From: tab a
Sent: Wednesday, December 18, 2013 7:39 PM
To: xj@jag-lovers.org
Subject: Re: [xj] burn, baby, burn

===================================================
The archives and FAQ will answer many queries on the XJ series…
FAQs: http://www.jag-lovers.org/xjlovers/xjfaq/index.html
Archives: Jag-lovers Forums - Jag-lovers

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