Hello All.

As time allows, with starts and stops, I've been working (to the best of my ability and experience) to get a H20 flooded XKR on the road and I've run into a final issue that I just can't figure out.

If I turn the key to run position the car will start right up. Nicely. Can be driven, all's "normal".

With the key, 1 time out 20 the relay, if placed, will start the car. I just replaced the starter. Known working. Relays are new.

With a DMM, if I bridge the signal side of the relay, turn key, monitor will go from 0v to around 10v and drop off again when key is released... It doesn't seem to be enough voltage to fire the relay? I understand the ECU grounds the signal side of the circuit to energize the relay to kick the starter motor.

It's like I'm losing 2-3volts somewhere...?
I've cleaned all connections I can find.

HOT WIRED.....I have a remote trigger to the high amp side of the relay that ALWAYS engages the starter and starts the car. If I place a relay with the cap removed and pinch the contacts it ALWAYS engages the starter and starts the car.

- What V does it take to trigger a relay on the low end?
- What if I use a 6v 30/40 amp relay instead of the 12v relay?
- Should I be thinking this might be a corroded wire issue and start to try re-wire as much of the wiring in the circuit involved in the start-up process?

Open to any and all questions.
Super open to suggestions.
Thank you

I'm sorry for the quality of the screen shots.


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I'd expect 10V to be sufficient to fire a 12V relay.

What voltage do you see:
1) on the 'hot' side of the relay with the key in the 'start' position (measuring between the green wire in the diagram and a proper ground)?
2) between the ECM switching output (orange wire) with the key in the 'start' position and a proper ground?

It looks like the power for the relay comes from the TCM when the car is in Park or Neutral.

 

See! This is why I need y'all. Thank you Michael.

I was thinking that the (O) for output at em80-41 in the diagram was indicating positive and the (I) was "inputting" the ground at em80-31... I measured both and swear I got B+ at the orange AND the green...

Are you saying the (O) for output at em80-41 is out put of a ground signal?

The car is in a different neighborhood. I swear I wanna run over there right now and try again...

 

Clearly I don't understand what is supposed to be happening.

This seems like bad news as it's an ECM issue...
Bad news.

 

When the shift is in P or N, the TCM outputs B+ (from GB2-10) to the 'hot' side of the relay (green wire). That TCM B+ signal is also fed (i.e. is an input) to the ECM, at EM80-31, So the ECM knows whether the 'park or neutral?' condition for starting the car has been met.

That is what you should see with the car in park/neutral, and the key in position ii (run).

Yes, that's what the ECM should do to fire the relay. In practice, I would expect to find a small voltage (less than 1V) rather than zero. So, I would expect to see B+, less that small voltage, across the relay when the key is in position iii (crank).

So, if you only see 10V across the relay, either the TCM isn't quite outputting B+, or the ECM isn't outputting a full ground signal.

Hope that makes sense.

 

Yes. It does!
Question is now, what am I going to do?

Gotta get back out to the car. Looks like it's going to be a week...

Thank you much!
Sheesh, this thing!

 

+1 with Michael.

Relay: you've got 4 terminals. 2 control, 2 high amp normally open terminals battery to starter.

Now 3 possibilities:
1. Defective relay.
2. Trigger voltage too low.
3. Bad ground.

You are getting 10v to the + control terminal. It is not tripping. Mind if I ask what you are using as ground to measure trigger voltage? The other control terminal or somewhere else on car? If the other control terminal, measure trigger voltage with another ground point. Still 10volt? If not = bad ground to the relay.

Let's eliminate #2. Try to start, relay trips? No. Jump the 12volts battery wire to 12volt trigger terminal. Relay trips yes = as you suspected trigger voltage too low to trip relay.

Relay does not trip = bad relay

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Jay, is this the fuel pump you were working on (ok, battling) when we first met you? If so: CONGRATULATIONS!

John

 

After 40 years as an auto electrician, I can tell you a digital voltmeter will always fool you as its resistance is 3 million ohms. It can measure through any corrosion. Use an old analogue meter with a pointer or put a 10K resistor across your meter connections. Automobiles are not the world that digital meters were designed for.

 

Good Morning, John...

Yes about the fueling. Like an epiphany, lol, I suddenly considered the inertia switch as a potential problem. Basically it's a little barrel shaped thing and when the car went under water, the barrel filled up and who knows how long it sat there, pooled. I had hit the button to "reset it" when checking on things over these weeks and months. There are only 3 wires to it. I cut the switch out of the circuit, spiced the wires and BAM, PWMod fueling straight away. I was jumping up and down, lol... It'll be a month of Sundays before I replace the inertia switch - if I ever do... I'll run it (eventually) as is. Can't give up on a Portfolio Edition XKR Convertible. Well, not yet anyways. Know what I mean?

I have tried several relays. Known good relays. That ain't it.

I have replaced the starter. That ain't it. Both old and new starters worked WELL, when jumping the relay to start the car.

I think the ground is switched inside the ECM. Perhaps the overall ECM ground is suffering and inadequate?

I have to get back out to the car with the clarification provided and see what I see.... From memory, with the car not running and key in position 2, battery admittedly low (not tip top since I haven't been driving the car and doing these tests) I swear I remember getting 10-11+ volts at both the green and orange wires in the diagram, key at 2. I guess what I need to do is probe the orange wire, key in position 2. Turn the key with orange wire to chassis ground and see if the orange EM80-41 goes ground to ZERO or 1v round about? I am hoping I don't have an ECM problem. Or a TCM problem. Or both.

I swear I remember B+ voltage at the green wire in the diagram,,, which Michael explained was the 12v B+ source to the relay and the B+ signal to the ECM that car is in Park/Neutral...

In the diagram,,, I see something that says powered ground on the BPM. What does that mean? Also, where in the hell do I find ems29? It doesn't show up in the legend... It's the link in the green wire between the TCM, the ECM and the starter relay...

 

40 years as an auto electrician? Wow... Amazing!
I hear you about the DMM vs Analog - the best I can. Ok...

Any guidance on the issue with the electrics involved with the starter? What needs doing?

 

If the DVM says 10v means nothing ....intended for electronics not cars ..try a bulb even if its only 5w and see if it lights full bright .

 

Please do. It may save your life one day.

Yes - my test #2 above. Definitely <1V, likely ~0.2V, depending on the switching circuitry inside the ECM.

pistnbroke is absolutely correct that the readings from a DMM - and to an extent - analogue mutimeter must be viewed in context of what's being measured due to their both drawing tiny amounts of current from the circuit being measured.
However, the tests above are valid since they are checking voltages under load conditions: we are determining both the relay supply voltage and the efficiency of the switched 'ground' from the ECM during the start event. The voltage on the green wire should not vary when you turn the key from 2 to 3 - does it?

From JTIS: "Both power grounds (high current consumers) and logic grounds (electronic switching circuits) are used throughout the system.". This separation is to mitigate any effect that a controlled high-current item (e.g. a seat motor) may have on the supply to the more sensitive logic parts of the module (random noise, transients, etc.).

I sympathise. EM - engine management. S - splice. 29 - splice #. The harness layout doesn't really offer any clues that I can see, although the ECM and the starter relay are both on the vehicle RHS, so I'd be looking around that area.

 

Thanks Michael! Really.

I haven't done anything, yet.

I have one of these laying around.

The "3w83" ECU is the one laying around. The 4w83 is the OE from the car... Michael, might the 3w83 work, if push comes to shove? I remember you know how to get the inside skinny on parts information like this... Please let me know, if you would...? And what would it take if so? Reprogramming?

 

I wish! I don't recognise the 3W or 4W numbers. On the older ones, there's a sticker with the Jaguar part # that tallies (usually) with JEPC Here's what it shows:



Care to share the last 6 characters of your VIN?

A quick search brought a result that the 3w83 is for a 2003 car, and some mention of immobiliser programming. I can't offer much help here, although I'd be wary of introducing another variable at this stage.

 

I would suspect the B+ from the transmission module, maybe a corroded P/N switch?
If you measured B+ on both sides of the relay with the relay in place that is correct. The voltage will come from the transmission module and go through the winding in the relay.
Disconnect the B+ from the relay and make a jumper wire from a known good B+ to the relay (or from Battery power just to test)

As I see it it only can be one of two things; either B+ from TCM or ground from ECM. Just eliminate one or the other and you know where the problem is.

 

Hey! Good Morning, Michael.
Thanks for this... I do.

I have always been a little puzzled as to the dates on the VIN and the exact year & make of this machine. Here's a photo of the full VIN.

 

Hi - that makes it a Model Year 2004 car - built August 2003. The 2004MY intro was June 2003. See the 'Points of Interest' in the attached Heritage doc.

 

Got it Michael, thank you...
I've been using a 2003 ED (just my luck) and honestly I haven't found anything that doesn't match up,,, yet. This whole thing has been tough, that's for sure, and I'm getting tired.

I have a few hours tomorrow and am wondering about something. I'm going to try to do some tests on the ECU/M ground trigger for the starter relay. The orange wire EM80 - 41... If I were to source B+ voltage off the main feed for the fuse box in the RH false bulkhead area for instance, clipping one probe there, and the second to a pin back probed into the back of the ECM main plug - EM80-41 - then turn the key - is this a good way to test for whether or not the ECM is switching to ground to crank the engine... And, how do I know it is a "good" and solid grounding by DMM test?

I would love some suggestions for how to test this ground circuit. The switch to ground.

There are a TON of grounds built into this ECU plug and loom. Which is for what function of the ECU, ya know?

In the diagram attached, there are two "power grounds". EM80 4 and 5 (I've seen and remember them)... Can these be double or redundantly grounded with the hope of creating a BETTER ground for the ECM which will hopefully help with the grounding and triggering of the starter relay at EM80-41? I get totally nervous when messing around with the ECU wiring. If I splaced in a wire and ran it to ground points in the false bulkhead space used by the O2 sensor ground, for instance...? Would that help the overall grounding of the ECU/M?

Also, even though the orange wire to the starter relay seems to go INTO and pop back OUT of the wire loom in the area of the false bulkhead, there doesn't seem to be anything (any other connections, plugs or splices) between the ECM and the relay. Would it make sense or would there be any great danger in just replacing most of this wire - between the ECU/M plug and the relay?

I mean, the solution to this problem has to be right there!? Right? If not, I guess it could mean the ECU has lost its ability to "switch" to ground in that circuit...

I am allllll ears and open to suggestions.

 

Thanks Nor...

The P/N switch on the shifter assembly I tested, and it works. The P/N switch in the TCM I believed was inside of the transmission, I'd guessed. Is there one outside of the trans on the 6hp26? That's an honest question.

I thought the TCM that I had out when I swapped the separator plate and solenoids was where that P/N "switch" lived...? Are all these electronics in the innards of the mechatronics unit?

You're right. I do need to ISOLATE this problem once and for all. Hopefully tomorrow before I go away on vacation.

 

The 2003 edition is the latest issued by Jaguar, AFAIK. I believe there have been some additions (at least to DTCs) since then, but I haven't seen them documented.

The best way IMO is to attach one lead of your DMM to a ground point, and the other to EM80-41, then measure the voltage in the 'crank' key state. You should see less than 1V. I'd expect around 0.2-0.5V.

It's always a challenge when the problem is intermittent, and you can be sure that everything will check out OK when you measure it

I'm thinking that the problem is more likely the feed to the 'hot' side of the starter relay. Can you make up a bridge wire with a low value (say 1A) fuse inline?