How JustAnswer Works:
  • Ask an Expert
    Experts are full of valuable knowledge and are ready to help with any question. Credentials confirmed by a Fortune 500 verification firm.
  • Get a Professional Answer
    Via email, text message, or notification as you wait on our site.
    Ask follow up questions if you need to.
  • 100% Satisfaction Guarantee
    Rate the answer you receive.
Ask Zaphod Your Own Question
Zaphod, Diagnostician, Trainer
Category: Car
Satisfied Customers: 33
Experience:  14+ years on an automotive technical hot line; Top Gun Diagnostician award
Type Your Car Question Here...
Zaphod is online now
A new question is answered every 9 seconds

XJ6: Jag..throttle body gate opening test because ive lost my keys

This answer was rated:

!986 Jag XJ6 Thanks for your answer on the thotle body gate opening. However, I haven't even been able to test the used CPU uniit I bought or the throttle body gate opening test because I've lost my keys. Crazy, but too true! BI have another set but without the black elec. pwr door and ignition lock/button.
Question: could you tell me how to override this electronic ignition lock so I can turn the car over and how/where to get a new electric key box. And how to repair the pwr door locks ?

Hi, I’m a moderator for this topic and I wonder whether you’re still waiting for an answer. If you are, please let me know and I will do my best to find a Professional to assist you right away. If not, feel free to let me know and I will cancel this question for you. Thank you!

Customer: replied 5 years ago.
Yes, thank you, I'm still looking for an answer.

Customer: replied 5 years ago.
Can somebody help me override my electronic keychain-black box button so I can turn the engine over??
Hi Mr. Russo, Jeff here to assist you with your starter problem. Your electronic remote on the key chain is for a system that is not original equipment. It may have been installed by the dealer where it was first sold, but because there is no published wiring it would be virtually impossible to work on. Even if you had the wiring diagram we don't know where the installing technician made his connections-though this diagram would help us to bypass what it controlled from the module connector(s). If you're really fortunate, the multi-function module [MFM] that was installed will be readily visible under the dash and it will have the name of it's manufacturer on it. If you're really lucky as well, presuming this was a dealer installed system, they'll still be in business. If the stars are shining brightly over your Jag, they'll be able to get you another remote. From experience though, I wouldn't count on it. Your starter circuit is very simple and there are two locations where the circuit is fairly easy to access. The first image is the system wiring diagram; it shows us what color wires we're going to look for.

The line labeled WY [white with a yellow stripe] represents the wire going from the Ignition Switch to the Starter Relay, and this is usually where the circuit is interrupted by alarm systems/anti theft systems and remote start systems. We'll go after the relay output which goes directly to the starter, a circuit hardly ever cut into. This wire is labeled WR [white/red stripe] and should be visible at the relay, which is located for us in the next image:
This will be on the firewall, and the wires might still be taped up. There will be two that are much larger than the others, the WR will be one of them. To jump the starter you will need a remote starter switch -or- a heavy 10 gauge jumper wire with good alligator clips. A remote starter switch is a hand held momentary button style switch mounted in an easy to hold handle, with a length of paired wires and clips at the ends. One clip goes to the WR wire -make this connection first using either method- the other goes to battery positive at the battery. If you can get the clip on the wire without touching the other terminals that's great-otherwise we'll need that wire removed from the relay. If there's still some insulation around the terminal at the end of the wire that connects to the relay, you can insert a small screwdriver and attach the clip to that; be careful not to spread the connector open or it will have to be squeezed a bit when you reconnect it to the relay. We're jumping about 10 amps to engage the starter solenoid, and the clip on a jumper wire might get hot really quickly when you touch it to the battery terminal-if you use this method I'd suggest taping it up or otherwise protecting yourself from a burn. Once we're connected at the WR wire, either press the button or touch the battery positive terminal; the solenoid should click and the starter motor should spin the engine. This will happen even if the key is out of the ignition switch. If the circuit was interrupted between the relay and the starter then this won't work, so If you get no reaction, move the clip at the relay right down to the starter [or you could go here first, it's a bit deeper in the engine bay where things get incredibly dirty and it involves leaning over which can be strenuous]. The starter has only two wires, one that's huge and our little [in comparison] WR friend. The connection at the starter may be a spade terminal or a screw; clip to the screw or pull the wire off and clip onto the spade. If the key is in the ignition in the RUN position, and the MFM isn't wired to kill anything else, the engine should start; at the very least it will turn over.
Watch out for moving parts.
I hope I've helped with your starter issue. Please let me know if you need further assistance, I'll be waiting for your reply.
Zaphod, Diagnostician, Trainer
Category: Car
Satisfied Customers: 33
Experience: 14+ years on an automotive technical hot line; Top Gun Diagnostician award
Zaphod and other Car Specialists are ready to help you
Thanks very much for the accept, Mr. Russo, I hope the rating is positive as well as that's the only way I get paid here.
More importantly, how is your starter issue? I should note that if you're really in love with the remote control features, there are high quality technicians who could replace your existing system with a newer version. If you ask the service managers at a few dealers who they use for installations you'll have a few to choose from. It's surprising to many people that many new car dealers don't install aftermarket equipment.
Again, I'd really like to hear how your project is going. Perhaps you could tell me why you are swapping the controller? I've only swapped one in a Jaguar and it was at the owner's request; the new unit behaved exactly the same way which was as it was designed to. The real problem was a faulty temperature sensor.
Thanks again, I'll be waiting for an update.
Customer: replied 5 years ago.

Hello Zap, I gave you a positive rating but the easiest way to disconect the pwr.button keychain system which I asked about was to go right to the source of it's power- Under the dash on the drivers side in and around the factory fuses. I simply followed the wire from the engine compartment, through the fire wall and upto the power source- near the driver's side fuse box under the dash.
Looked for a fuse tie-in where it met up with a bunch of factory wires and pulled the amp fuse.


Optional Information:
Make: Jaguar
Model: xj6
Year: 1986

Already Tried:
Car still doesn't get fuel to the jets. Tried testing light to the electrical junction at the fuel injector and it merely stays lit once you crank the motor. Tester light's supposed to flash on and off and it just stays light with barely a dimming. I've replaced the ECU with a used one, changed the fuel pump and regulator. I'm getting spark to the plugs. I checked the throttle body electronic air intake and opened the gate. (was told this gate opening sends electricity to the fuel injecto

Hi Mr. Russo, and thanks for the positive rating, I really appreciate it. Now, let's see if we can get your Jaguar running. Someone has misled you in the operation of this system. I don't know what your level of expertise is, or how much you know about your vehicle systems, so I'll go slowly. Please tell me if I'm breaking things down too much or perhaps not explaining things well enough. I'll start with the basics. Besides the ECU, relays, wiring and fuel pump, the Bosch L-Jetronic system contains the following parts:
I'll briefly describe each of these - the thermotime switch is a temperature and starter-cranking-time sensitive device. It's job is to allow extra fuel for cold starts to be sprayed inth the large open area of the intake manifold by the cold start injector. Inside the switch is a bi-metal strip wrapped with a heating wire. The end of the bi-metal strip, which bends with temperature changes, opens and closes the contacts that feed battery voltage to the cold start injector. The circuit is only powered while the starter is actually engaged; this is to prevent flooding a cold engine that isn't starting. The colder the initial temperature, the longer it stays closed. Typically these fail open, rarely do they short. The injectors are supplied with battery voltage any time the ignition is turned on. The voltage goes through the injector to the ECU, where a momentary ground based on RPM, engine and air temperatures and measured air flow opens the injector for it to deliver fuel. Injectors are never just turned 'on', they are always pulsed. The auxiliary air valve provides extra air necessary for cold starts. Inside the long extension that protrudes from the disc shaped section is a large bi-metal strip wrapped with a heating wire. The end of this bi-metal strip contacts the flat, spring-loaded 'gate'. This device is powered only when the engine actually runs, and electrical power as well as heat from the engine [in case the electrical part fails] will cause the strip to bend and gradually close off the valve's opening. The VAF [Volume or Vane Airflow Sensor] is a spring-loaded door that informs the ECU of the amount of airflow the engine is taking in. {Trivia: the L in L-Jetronic is for luftenmessing, the German word for airflow measurement}

Hi there Mr. Russo; I'm terribly sorry about the delay. I see I left off at the VAF. The overrun valve opens under deceleration if manifold vacuum breaches 22.2"Hg. The throttle switch is actually two switches; one switch is closed at idle and the other closes at nearly full throttle.
Now we get to check some basics. The L Jet ECU is connected to the ignition system, from which it receives a pulse each time the coil creates a spark. This is the RPM signal, or trigger, that the ECU needs to get in order for it to start pulsing the injectors. The coil's negative terminal is connected directly to the ECU at pin 1. The following is a wiring diagram:
With the ECU disconnected, the harness connector should look like this:
Carefully probe pin 1 with a plain test light that's grounded-we don't want to distort the connector. You can do this from the visible pins, although it is possible to remove the rear of the connector and backprobe the terminals. If you do remove the rear cover, there are locking tabs that hold the pins in their proper positions. I can tell you it's not fun putting all those pins back where they belong. While the key is on it should light up, and if there's activity in the primary ignition circuit while the starter's engaged [if you have good spark] the test light will flash brightly. I don't know what type of test equipment you have - perhaps you could let me know. This input signal along with the power feeds and grounds [we're about to check those] will get the injectors to pulse. There should be one injector pulse, on all six injectors at the same time, for every two coil trigger pulses. Each injector has it's own connection to the ECU, and they are powered by the main relay via a resistor block. Each injector has it's own power supply circuit running through individual resistors; this limits the current going through the ECU's transistors. There is one power transistor for each injector inside the ECU, and a ground circuit via individual pins for each power transistor. The main relay powers the ECU at pin 10. Probing this pin with a grounded test light should get you a bright light; a voltmeter will show battery voltage. This voltage must remain present at all times the key is on or while cranking [though it will dim/drop voltage when cranking]. Pins 5, 16, 17 and 35 are critical grounds for the ECU. All system grounds go to the engine, which is grounded to the battery via heavy gauge cable. With the test light clipped to battery positive, each of these pins should get a bright light; a meter will show battery voltage. Each of these grounds, as well as the power supply, should be able to handle higher current than a meter or test light will allow-a favorite high current power/ground test is to use a low beam headlight. This checks the wiring to see if it will allow 4 to 5 amps of current to pass through. The Main Relay is often faulty, the contacts get pitted and don't allow enough current for the system to operate. It is also grounded at the engine with all the other grounds. The circle labeled Engine Connections in the next image indicates the ground location area is at the rear of the engine; usually on the cylinder head. There will be several wires going to the same location.

Hopefully these tests will reveal one problem or another, and we'll be able to correct the condition and get the engine running.
Again I apologize for the delay, I'm on Long Island in New York and rush hour traffic isn't pretty.
Please let me know how you're doing, if you need more help or information.
Zaphod, Diagnostician, Trainer
Category: Car
Satisfied Customers: 33
Experience: 14+ years on an automotive technical hot line; Top Gun Diagnostician award
Zaphod and other Car Specialists are ready to help you
Customer: replied 5 years ago.
Hey Jeff, I wish I could say your good info helped but it didn't. There seems to be juice and power coming from the ecu. I did your suggested test with the test light- both negative battery terminal and possitive. All test proved light . Wasn't able to test the amps or volts. but I do have a volt meter. I believe, like others, that the L Jtetronic system rarely goes wrong.
I took out the relay and emory clothed it clean- still nothing.
I couldn't understand if you said the Thermotime switch and or the cold start injector could also be the culprit by themselves.
In the meantime, with all the attempted starts now the starter wont shut off once you turn the key. So I have to pull the battery positive post wire.
Could my problem be coming from the ignition switch- because now I have to figure out how to fix it from keeping the starter motor turning. Uggggggggh!!

Any further words of wisdom would be deeply appreciated. Chris
Customer: replied 5 years ago.
It's not your fault, it's the stupid car. Three years I have this car and never a problem other than general maintenance.

I just don't know what to do?
Hi Mr. Russo, cars can certainly be frustrating things, and fascinating when it all works like it was designed to. There have been times when I've had to lock up my hammers. We certainly can't do much testing if the starter is running amok, so let's get to that new issue first.
The starter issue: It might be a sticking starter solenoid, possibly a combination of age and recent activity. To differentiate between the switch and starter as the cause, disconnect the small wire at the starter and use a jumper [or starter button] to B+. If the starter stays engaged then the solenoid contacts are pitted, which limits the contact area between the two surfaces. The starter motor doesn't give a fig about pitted contacts and wants it's normal amount of current; this energy going through a smaller pathway causes the contacts to overheat and at times weld together. If jumping the starter manually causes no problems, run a grounded test light to the wire [that you disconnected from the starter] and operate the switch while watching the light: it should always turn on and off sharply. Hangups in the switch from weak or broken springs can usually be felt at the key; melted solder from contacts can cause intermittent malfunctioning. Switches that are coming apart inside usually don't misbehave for long before failing completely.
Other culprits: The thermotime switch and cold start injector are powered by the same circuit that turns on the starter, they can't supply power to anything and they are not related to getting or not getting injector pulse. The L-Jet needs to be 'tapped on the shoulder and reminded' every time it's supposed to pulse an injector, and it needs two taps to pulse the half dozen injectors once. The ignition system's primary [low voltage] circuit does the tapping, the ECU does the pulsing. All of the other sensors can only cause the ECU to increase or decrease the pulse width [the amount of time the injector is turned on]. If your ignition system isn't creating a really hot spark, which can be verified with a spark tester, the electrical pulse may not be enough to trigger the ECU. Your ignition system is actually controlled by a General Motors High Energy Ignition module mounted inside that box. This isn't a module from an Oldsmobile that GM sold to Lucas, it was specifically designed to use the extra circuitry you see in this image:

Lucas had these made by GM because GM had the manufacturing in place, and those HEI modules were incredibly reliable. Jaguar found out that techs were swapping in GM parts and issued a bulletin:

Many GM modules were built with current limiting circuits that wouldn't work well with the Jag's coil. L jet has been connected to more than a dozen different ignition systems in the various vehicles it's been fitted to.
Let me know what goes on with the starter. Jeff