Just rechecked AC Voltage from CPS, registers 1.034V AC while cranking. This is higher than I had when the Jag started the first time (see post 132). Voltage at the battery 12.95V, voltage at Ignition Module pins 1 & 2, 12.14V, voltage at Coil + & -, 12.16V. Coil Primary Resistance 5.4 Ohms, Secondary Resistance 7.4K Ohms.
I found a test I have not performed before and it may be telling (see below). This is on pg 65 of the Jaguar Diagnostic Guide, Ignition Primary and Secondary.Circuits
Measure voltage between EMS/ECM Blue Connector pin 1 and Ground, I registered a reading of .025V.
Crank engine, Voltage should rise from near 0 upon cranking, I registered a reading of .465V, just not sure this is enough of a rise, less than .5V rise. If voltage now rises, replace Ignition Module.
Now here’s the rub. How does this test determine the Ignition Module is bad when it is not connected?
I ran this same test with the Ignition Module connected and there was no rise in voltage. This is not correct, my back probe was not engaging.
UPDATE Looks like I didn’t understand the test. Where it says “Expected Measurement” V4 When the engine is cranked voltage should rise from near 0 to approximately .3 Volts. My reading with the connector engaged is the same as when it is disconnected.
Thanks exMBman, I updated the above post, turns out my back probe was not fully engaged when testing while hooked up. Reran the test and got the same readings while connected or unconnected.
Well I’m clear you guys are sick of reading this thread but I can assure you not half as sick of it as I am. Unlike all of you, I don’t have an option, I have to get it running.
OK, here’s what I’ve narrowed it down to. Below is a matrix of Suspected Problem Area as presented in the official Jaguar AJ6 4.0L Engine Management System (EMS)/OBD I Diagnostic Guide.
What I have done is try to narrow it down to symptoms I have experienced.
First and foremost is, Engine Cranks/Does Not Start , this is the most prevalent symptom.
Second, Stalls After Start , this has happened 2 maybe 3 times.
Third, Stalls While Driving , this happened several times but not recently.
So, I have done two things here.
First, I eliminated those Suspected Problem Areas which I KNOW are not an issue, these are outlined in GREEN .
Second, of the remaining Suspected Problem Areas, I have narrowed it down to those issues common to ALL three symptoms, namely EMS ECM POWER/GROUND . (Blue highlight)
And third, those issues common to two of the symptoms, IGNITION PRIMARY CIRCUIT . (Yellow highlight)
Battery voltage to EMS ECM POWER Blue connector Pin 14 = 12.53V
Battery voltage to EMS ECM POWER
Yellow connector Pin 1 = 12.26V
Blue connector Pin 10 = 12.24V
Blue connector Pin 22 = 12.24V
EMS ECM GROUND*
Yellow connector Pin 18 = 00.6 ohm
Blue connector Pin 11 = 00.6 ohm
Blue connector Pin 23 = 00.1 ohm
Blue connector Pin 24 = 00.1 ohm
= Ground connection resistance from a component to a known good chassis ground point should be less than 1 ohm .
Moving on to the IGNITION PRIMARY CIRCUIT , here’s what the Diagnostic Guide says, “A fault in the Ignition System Primary circuit will cause stalling or a “No Start” condition. If there is no spark, use the diagnostic procedure on the next page (page 65 of the Diagnostic Guide).
Following the diagnostic procedure, here are the results:
Test 1 = No Spark
Test 2
V1 measured @ Battery = 12.29V
V2 measured from Ground to Coil Pos terminal = 11.99V
V3a measured from Ground to Coil Neg terminal =11.99V
V3b measured from Ground to Coil Neg terminal = 11.87V after disconnecting wire
V4 This measurement is confusing to me, it states that “if Incorrect check ground connection to Ignition Module and Heat Sink Plate”, how else can you check the V4 voltage? The reading I received = 00.8V (which appears higher than their 0.0 to 0.1V)
Test 3 This too is confusing to me. If you look at the “Test 3” box on the diagnostic it states “Crank engine, voltage should increase from 0.0 upon cranking”, however, it goes on to tell you if the voltage does increase, “Replace the COIL” . My test results = .584V , when cranking = 1.265V . Because it increased I replaced it with a New Coil I had on hand. New Coil test results = .441V , when cranking = 1.126V . As a result of this test I believe the information is faulty, I believe it is the other way around, if it increases it’s good, if it does not increase, Replace it.
Still working on the No Spark issue. I never received a response to Test 3 above and re-posted below.
The box for Test 3 reads “CRANK ENGINE. VOLTAGE SHOULD INCREASE FROM 0.0 UPON CRANKING”. What I’m having a problem understanding is what it tells you to do if the voltage does increase. The box or information to the right of the Test 3 box tells you what to do if your test is Incorrect, however, in this case it is telling you to REPLACE IGNITION COIL IF THE VOLTAGE INCREASES and to move on to Test 4 (i.e. the coil is OK) if the voltage DOES NOT increase.
Jag.Man, I’m afraid I cannot shed any light on this. But you have replaced the coil, which shouldn’t hurt anything even if not the problem. And you have also.replaced the ignition module (amplifier), correct? And applied the goo between the ignition module and the base plate?
Hi Mike, yes the coil was replaced with a new one. I swapped out the Ignition Module with another purported to be good module and that did not resolve the issue so I placed the original back in the Jag. I did removed the module from the plate and cleaned both surfaces then reassembled with thermal paste between the module and plate before reinstalling.
Robin you hit on the reason for my question about the thermal paste / grease (goo). My understanding is there are both conductive and non-conductive (electrically insulating in fact) types.
A high-grade thermal paste is 8.5 W/mK, and the heat conductivity of copper is 385 W/mK, or for aluminum 205 W/mK. … With that said, some thermal pastes can be conductive , but the majority of them are not. I believe the main reason for the paste on the ignition module is heat dissipation and not conductivity. That’s why it’s mounted to a large chunk of aluminum. However the question remains, in Test 2 (above in photo) how do you check if the ignition module is grounded?
To be honest I don’t know and that’s why I said “purported”. So unless you have the ability to see or remove the module from a running car yourself, you pretty much have to take the sellers word for it.
Agreed. It is unfortunate we Jag owners are relatively few and far between. Ideally there would be someone local with a compatible vehicle that we could swap parts with for test purposes.
Hi Robin, “Are you sure the ignition module is grounded?”, excellent question and one I am trying to get an answer to. For sure the aluminum plate it is attached to is grounded and the bolts that hold the module to the aluminum plate are also grounded but I really don’t know how to check the module itself. The module housing is plastic, as you know, and the metal (alum) plate under the housing that touches the large aluminum heat sink it is attached to is not accessible. that leaves the connector pins of the module. What else is there on the module to check for ground???
From memory the unit grounds through the base, not via any grounding wire hence the query about the paste, jus try cleaning off all the gunk and give that a try?
