Bjorn and Kim,
Getting to work on it tomorrow (Saturday) I will post tomorrow night or Sunday the outcome.
Heres hoping and fingers crossed.
Best regards,
John
Bjorn/Kim,
Hello guys, just been out in the garage to the "Patient"..... These are the readings that I have taken on the socket end of the Fuel Rail Pressure control valve
Bjorn you were right, this is a screened cable, I measured across the pins to the screen cable and the results are as listed: All readings are in Kilo Ohms.
No ignition on at time of checking.
Pin 1 (White) to Screen 0.4
Pin 2 (Red) to screen 200
Pin 3 (Black) to screen Momentarily it reads 6.1 then goes to 0.4 and holds steady.
I haven't had chance to look at SCV problem yet.
What does the above readings signify?
Best regards,
John
Sorry John, be prepared for one more novel. If you like, just read bold text! Best way to measure the isolation in your case would of course be to disconnect the ECM connector. Why, it is better because there will be nothing in the ECM that can interact with your readings
If we start with pin 3 (GND) that shows a momentarily 6.1kohms reading and then down to 400ohms. Well ... that does not indicate a good ground unless there is a resistor and capacitor from shield to ground inside the ECM. Why you get these 6.1kohm reading is because, when you measure, you charge the capacitor and then it discharges through the resistor – seems like that but 400ohms? This shield, BTW, is there for a good reason and that is to protect the signal wires, as well as ground wire in this case, from interferences IE electromagnetic fields, as there are plenty of them, under the hood.
One thing more, as you probably noticed, all three shields are terminated only at one end to ground inside the ECU through pin 67. Do not try to ground the other end that goes to the sensor because you will most likely get ground potential differences and a so called ground loop – IE ECM ground to the rail or wherever it would be grounded – and in worst case, you will get, even if it is small, a nasty current flow in the shield that you do not want.
Please, check ground from (pin 3) to battery minus, if you get few tenths of an ohm you probably have a good sensor ground. In order to prevent unwanted ground potential differences, that may cause erratic resistance readings even if they are in the millivolt range, never ever KOEO when you measure resistance.
I will have to come back tomorrow about the two other pins, wrote a lot but it was not exactly the truth, to tired
Regards
Bjorn
Last edited by Tronic on Sun Jun 10, 2018 11:02 pm, edited 1 time in total.
Hi John, Kim and all other interested in this case!
Much could be said about these resistance values, but most would be theory because there is to many unknown parameters that, among them and few other, consists of components inside the ECM and therefore, let us stay simple without to much guessing.
Your measurements on the rail pressure sensor in your first post revealed:
Pin 1: 5 volts.
Pin 3: (sensor ground) 4,85 volts. It should absolutely not read 12 volts on pin 3 as Kim wrote. Your DMM should read 0 volts, but wait now … there could as well be some misunderstandings here. If you had your black probe on pin 3 and red on battery plus it would make sense. If so, it is still wrong, it SHOULD read 12 volts and that is maybe what you meant, or? In that case, if you measured like that and look at the two sentences above, you most likely have a bad ground with a resistance to ground of more than 10Mohms.
Just to measure like above – battery plus to pin 3 (ground) – may fool you to believe that you have a good ground. You could have a resistance from pin 3 to ground, lets say 100kohms, and you would still read 11,88 volts and if you are in a rush, you might believe it is okay.
Lets say that the measurements of yours in fact is what you wrote and with that in mind, put up two scenarios:
1. With red probe on battery plus and black on pin 3 – sensor disconnected
If you get DMM readings of 4.85 volt on pin 3 you most certainly have a bad ground connection of more than 10Mohm. Could be the wire, sensor connector, ECM connector or the ground inside the ECM, but as the car obviously sometimes runs okay, it is of intermittent nature.
2. With red probe on pin 3 and black on battery minus – sensor connected
If you lose the sensor ground it may, I am not sure here, pull up the sensors ground pin 3 to nearly 5 volts and of course you will then get high pressure readings because the sensor is lifted above ground. So, with other words, the 4,85 volts can come from the sensor itself because pin 3 is not grounded.
I may barking up the wrong tree and if so, please comment
Regards
Bjorn
Last edited by Tronic on Mon Jun 18, 2018 1:59 pm, edited 3 times in total.