Just looking for confirmation the TT switch is failing.

Car starts first turn cold. If I instantly turn off and restart, it wont start unless I crank it several times for 3-5 seconds. Edit - about 70 degrees here in Akron. Engine is cold save a three minute (idle) run seven hours ago.

Test light on CS valve does not light on second turn but lights on first turn.

Resistance on thermotime switch is zero on first turn but 140 after second turn. Takes about 45 seconds for it to crawl back to zero. Then repeat. When I say turn I mean a one second engagement of the starter.

I don't think this is correct. Surely there is not a 45 second wait period between key turns designed into the TT switch.

Thanks!

 

Nothing last forever, so maybe it's time for a new one. Plenty on the internet.

Have a read here: -
Fuel injection and the Jaguar XJ6 4.2 Series 3 / AJ6 Engineering

 

Thanks Fraser.

I own an early 80's 911 that has a Bosch K-Jet system (TT switch and CS - I think the same conceptually as the D-Jet system). All the reads I have seen on the Porsche forums (as well as here) indicate the TT valve works or it does not. I am not aware of it working (Jag or Porsche) kinda-sorta first time then "flaming out" BEFORE an engine block temp increase over 100F.

I agree, it is probably the culprit, but don't want to throw a part at a car without some due diligence.

 

I thought Bosch K-Jetronic was an all-mechanical system.

The Jaguar V12s had D-Jetronic, (which measured air flow using manifold vacuum), and the XK sixes the L-Jetronic (that has a mass air flow meter in the form of a flap valve). All the Jaguar fitments were made by Lucas under licence, I believe.

 

I should have been more "pacific". The K-jet and D-jet have similar cold start systems. That was the comparison I was trying to make. K-jet, as you surely know, has an air flow sensor, big pie tin thingie on an arm that is deflected by intake air (actually manifold vacuum) and the other end of the arm moves a plunger in a fuel distributor and fuel is released continuously through the mechanical injectors. It's mechanical but sensitive to vacuum leaks that bleed down the vacuum sucking on the plate.

Also, I now remember reading the Bosch vs Lucas manufacture of the D-Jet a few years back in a bible a Jaguar enthusiast had written about curing all the V12 problems he ran into with his XJS. I stand corrected.

All that said, I started the car yesterday morning (sat all night) and found the cold start valves worked time after time without incident. They worked like a champ. So me thinks the issue I found originally relates to the gradual taper off of the thermo time switch engagement based on the engine temp. I had run the car for a few minutes in the morning day before yesterday and there must have been enough heat in the block to allow the TT switch to close/engage for a second and that was it. After sitting it had a longer duration. So the CS systems K-Jet/D-Jet are similar but the (my 911 - not sure about other K-Jet systems) K-jet does not have the taper off of the TT duration. It just works when starter sends it juice - if cold enough.

Side note. My pal who owns the car has been starting the car w/o the cold start injectors working for years. 3-4 long duration cranks of the engine to start. I wiggled the connectors on the CS valves and they started working.

Makes me wonder how many other "tasty treats" can be found by cleaning the electrical contacts everywhere.

 

Plenty to read on this site. Roger Bywater, (who worked at Jaguar as a development engineer), says the cold start system with its TT switch shortens crank time, but if there is no separate cold start injection the engine will eventually start as the normal injectors are at maximum pulse time anyway.

http://www.jagweb.com/aj6eng/index.php