QuestionHi Howard,
I have the same problem as you posted an answer to in 2009. (Question
Hi i have been fortunate enough to have had another jag towed to me after being several other places.I have proper fuel pressure 38 psi at filter,have real strong and consistent spark(passes ST-125 test)when ignition is turned on pump runs for 2 second prime and when motor is turned over pump relay is energized again,also falsely triggered ignition and circuit works.I have battery feed to power side of injector's,i disconnected ECU and checked harness integrity to injectors OK,I can trigger injectors at ECU.If i manipulate throttle around 12-34 i notice injectors give a brief trigger this happens when cranking and with key on,i have tested both throttle switches working properly and consistently,check throttle position sensor for proper and consistent reading threw out throttle travel OK,vehicle will run if i introduce fuel from outside source.I don't know how the power resistor works,i also don't know what the inhibit switches the wiring diagram shows actually due,we have an extensive resources for information and a fare bit of knowledge working on mostly European autos,but would be help full to know what impact some of these items have on the system and how they operate before proceeding. thank you
Answer
Hi Jim,
I believe the injection system will trigger (ground in groups)injectors when the ECU sees an ignition trigger signal and all of the other sensors only change the pulse duration to change fuel mixture. I would check the throttle switches because I know other injection systems do cut injection pulse off on deceleration, I don't know if this one does or not. I worked on some of these cars but not many and I don't have a book on it.
Howard)
My throttle swiches and TPS are in working order. Do you know what the final solution was?
AnswerHi Mark,
I don't remember getting any feed back from that problem. so I don't know what that guy found. I believe you have the "P" injection system on that car. I am not sharp on the earlier "D" nor "P" systems used on the "XJ-S". I did work on a few "D" Jetronic systems but left Jaguar dealerships and started traveling around the country teaching the "L" jetronic system used on the XJ-6. Over the years I have looked at most of the other brands of injection systems and noted that they for the most part operate the same. They power up the injectors and the ECU grounds the injector or injectors or in the "D" and "P" system ground the injectors in groups. Some ground the injectors in the firing order and others (Like the "L", "D" & "P" systems) ground the injectors two times per cylinder firing.
All injection systems just supply fuel as per what an engine needs and they control the amount of fuel by the pulse duration which is controlled by the amount of air entering the cylinder, the engine temperature and engine load and RPM. All of the other sensors are just fine trimmers to fine tune the mixture. For example, I would not expect to see an 0-2 sensor to stop injection as it is only a feed back trim. I would expect to see a ignition signal to cause a stop or a coolant temp sensor and a signal from either a throttle position sensor or a air mass sensor or air flow meter to stop injection. Your "P" system is not a "peak & hold" system meaning the injector is opened by a full 12v and the voltage is dropped by the ECU to a lower voltage to just hold the injector open. Your system uses a resistor pack to operate the injectors (in packs of 3) at a reduced voltage. Most injection systems look at only a few items to operate and they consider these "Major In-Puts" Ignition signal, power, grounds, start signal, coolant sensor, Engine air (air flow or air mass or throttle setting)
All of the other sensors just supply trimmers for mixture after it is running like 0-2, Air temp, etc.
In your case, you say that you have power at the injectors so that means that the ECU has powered up the resistor pack to power the injectors. You did not tell me if you had ignition signal at pin #18 at the ECU (white w/slate tracer wire) when the engine was spinning. (best to use a logic Prob so as not to alter the signal) Pin #26 at the ECU should receive power from the Starter relay to tell the ECU the starter is engaged. The "full throttle" switch is connected to the coolant sensor so I would want to see that received at the ECU. The throttle pot is three wires and you will have to ohm that to see that it is working.
The inhibit relay is just the inhibit for the starter in neutral or park of the gear lever.
I have a good diagram of just the injection system if you want it. I will post it on my web site for you to copy. Check your VIN # to see that it falls in between 133461 and 139052 and let me know and I will post it for you.
Howard
