One of my switches came off looks like I need to solder or replace. What is this used for? Anyone know what it is called? Pictures attached. Thanks!
It’s a pretty standard microswitch. You should be able to get one at any decent electronics shop. Take the old one with you to compare the arm length etc.
The old ones used to come apart, so you could swap bits around to make up what you needed. They’re usually riveted together nowadays.
Thanks Andrew. What is the function of this micro switch?
Transient enrichment under hard acceleration from what I can see.
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JamesLove,
That is the Throttle Switch ( Jaguar Part Number C35509). When you are at or near Wide Open Throttle (WOT) the switch closes and provides a very important signal to the EFI ECU to enrich the mixture to prevent melting pistons. That function is so important that Jaguar also installed another sensor in parallel, the Throttle Control Valve (Jaguar Part Number JLM473), that senses intake manifold vacuum and closes to send a signal to the EFI ECU to enrich fuel mixture when operating at low vacuum levels, like those found at WOT but also other regimes.
There was a recent thread by “Dave the Limey” about some of this, pointing out that the Throttle Control Valves get out of tolerance or broken over the years and may not provide this important protection without you knowing that it isn’t working properly. I found this true with the valves in both of my V12 equipped Jaguars.
I suggest that you check to make sure that the Throttle Switch and Throttle Control Valves are both working as they should and if they are not, get replacement ones and make sure that they work properly before driving the car a WOT or anytime you have vacuum between 0 to 4 inches HG. Otherwise cylinder head temperatures may get too hold and melt your pistons. A very bad thing to happen.
Regards,
Paul M. Novak
1990 Series III V12 Vanden Plas
1990 XJ-S Classic Collection convertible
1987 XJ6 Vanden Plas
1984 XJ6 Vanden Plas
1969 E-Type FHC
1957 MK VIII Saloon
Ramona, CA USA
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Thank you so much very helpful. I understand finally. I will renew these small little things asap. I am glad I have been taking it easy on her. She was laid up for 10 months.
Glad you asked. I just did some work and I have one that is broken too. I was going to ask the same question.
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Would a broken one on the throttle cable cause the engine to run really rough on start up then stall?
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I don’t know but I noticed mine is very difficult to crank over before it finally starts. Once it started it runs fairly well
Frankwills,
No. The Throttle Switch only comes into play at full throttle settings.
Rough start up and stall could be caused by a lot of things. To eliminate fuel delivery as an issue put a fuel pressure gauge in the engine bay fuel lines and observe the fuel pressure which should be about 36 PSI or so. If the fuel pressure drops on start up and when the engine stalls, it could be crud in the fuel tank blocking the fuel strainer or fuel filter.
Assuming that you have a 5.3L V12, fuel delivery issues, improperly set throttle butterflies, or Auxiliary Air Valve (AAV) problems could also cause rough start up and stall. First make sure your throttle butterflies are set properly to 0.002 inches and that the bushings are present and in good shape. The next thing to check is your Auxiliary Air Valve to make sure it is operating properly by removing it and testing it on the stove in a pot of water to make sure it is opening when it is supposed to. I have had problems with all of these things (and a whole lot more) but once sorted out these 5.3L V12 engines run very smoothly and are worth getting set right.
Regards,
Paul M. Novak
1990 Series III V12 Vanden Plas
1990 XJ-S Classic Collection convertible
1987 XJ6 Vanden Plas
1984 XJ6 Vanden Plas
1969 E-Type FHC
1957 MK VIII Saloon
Ramona, CA USA
Frankwills, the one on the throttle cable is transmission kick-down. No effect on the engine.
John’s cars in Texas. …has 'em…really not needed unless you race
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thanks everyone, work keeps getting in the way of my hobby hahaha
I just haven’t had much time to look at it. I did check the fuel pressure before and after the reulator and at the exit of the fuel rail and it tested about 75 psi at all 3 places with the key turned to the on position without trying to start the engine
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75 psi is way too much fuel pressure. You need to investigate further, perhaps for a blockage such as a crushed fuel return line below the car.
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Dave what sort of fuel pressure do you read on yours?
Remember that when you measure feel pressure, it’s a flowing pressure rate. If you dead end the fuel line with your gauge, you’re going to see much higher pressure. A fuel pressure gauge has to come off the line in a T.
On my car I stayed with the original Jaguar design using two FPR’s. They are about three months old.
I have two gauges under the hood- one connected to the fuel line before the first FPR, and the second telling me the pressure in the fuel rail.(I like gauges) The fuel pump was replaced about a month ago. If I turn on the ignition without starting the car, after the pump stops running I have around 42 psi in the line before “A” bank FPR, and 37psi in the fuel rail. After starting the engine , pressures drop as the vacuum starts to control both FPR’s, and, I’ve noticed that the overall fuel pressures will drop a little more as the engine warms up. I’m assuming that as the engine becomes more efficient as it warms up, the vacuum increases in the intake manifolds, and so the FPR’s respond to that change. That’s what happens on MY car, anyway!