'78 XJ V-12 Fuel Injected -- Hot Shut Down
#1
11-25-2016, 11:00 AM
'78 XJ V-12 Fuel Injected -- Hot Shut Down
Hi All!
I've bought a "pig-in-a-poke" '78 XJ V-12 to add to my stable of a Series 1 XJ6, Triumph Stag, and RR Silver Shadow. I've got a good British "aptitude," mechanically speaking, but have never dealt with a fuel injected V-12.
The car seems extraordinarily well maintained, however, the former elderly owner states that at temperature, the car will shut down.
Ignition is largely ruled out, as it's had a recent Pertronix conversion.
He believes it's one of two sensors that screw into the left and right thermostat housings. The left one is cheap and available anywhere, called the "Water temperature SENSOR" (Not the gauge sender) While the one on the right bank is the "Thermo Time Switch" and this one appears to be absolutely unobtanium.
QUESTION #1: Is this fault diagnosis speculation on his part? Or will either (or both) of these sensors interrupt fuel delivery if they work improperly once the vehicle hits operating temperature?
Question #2: If in fact the "Thermo Time Switch" could be a culprit, any ideas on where to either cross-reference or find one?
thanks so much!
Brian
I've bought a "pig-in-a-poke" '78 XJ V-12 to add to my stable of a Series 1 XJ6, Triumph Stag, and RR Silver Shadow. I've got a good British "aptitude," mechanically speaking, but have never dealt with a fuel injected V-12.
The car seems extraordinarily well maintained, however, the former elderly owner states that at temperature, the car will shut down.
Ignition is largely ruled out, as it's had a recent Pertronix conversion.
He believes it's one of two sensors that screw into the left and right thermostat housings. The left one is cheap and available anywhere, called the "Water temperature SENSOR" (Not the gauge sender) While the one on the right bank is the "Thermo Time Switch" and this one appears to be absolutely unobtanium.
QUESTION #1: Is this fault diagnosis speculation on his part? Or will either (or both) of these sensors interrupt fuel delivery if they work improperly once the vehicle hits operating temperature?
Question #2: If in fact the "Thermo Time Switch" could be a culprit, any ideas on where to either cross-reference or find one?
thanks so much!
Brian
#2
11-25-2016, 01:06 PM
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I'm not an authority on the earlier V12 FI systems, but.....
On later models (and probably your earlier models like yours) the Thermotime switch is part of the cold start system and is operational only when the key is turned to 'start'.
IOW, even if inoperative, a Thermotime switch wouldn't cause a *running* problem such as you've described
The coolant temp sensor is a key player in fuel mixture on a cold engine and *can* cause running problems....particularly if it doesn't tell the ECU that the engine has warmed up....thus over-fueling a warmed-up engine. Easily checked with an ohm meter.
Cheers
DD
On later models (and probably your earlier models like yours) the Thermotime switch is part of the cold start system and is operational only when the key is turned to 'start'.
IOW, even if inoperative, a Thermotime switch wouldn't cause a *running* problem such as you've described
The coolant temp sensor is a key player in fuel mixture on a cold engine and *can* cause running problems....particularly if it doesn't tell the ECU that the engine has warmed up....thus over-fueling a warmed-up engine. Easily checked with an ohm meter.
Cheers
DD
#3
11-25-2016, 08:55 PM
The way it "cuts out' will help me, and maybe others.
1) Does it stop as if a switch is flicked?
2) Does it cough and splutter and belch black smoke?, PreHE are BAD for that one.
3) Does it cough and wheeze as if running out of fuel?
4) Does it happen only at idle, or does it shut down when driving along the roadway?
Fuel Infected V12's are simple beasts, really.
1) Does it stop as if a switch is flicked?
2) Does it cough and splutter and belch black smoke?, PreHE are BAD for that one.
3) Does it cough and wheeze as if running out of fuel?
4) Does it happen only at idle, or does it shut down when driving along the roadway?
Fuel Infected V12's are simple beasts, really.