Bit of technical support please

Bit of technical support please

Author
Discussion

STE VR

Original Poster:

498 posts

205 months

Tuesday 6th August 2019
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Having already started a topic on my erratic dash water temp issues I’d thought I start this one as it’ll likely be a bit more in depth.

Water temp readings very erratic on dash. ECU fine and stable. Fans ok. Cooling system ok. Everything is brand new. (Major restoration).

OCD won’t let this issue lie so need help.

I’ve injected the plug that fits on the water temp sensor with a calibrated resistance. 86 ohms gives me 95 degc. When engine off dash reads very stable throughout the range. Start engine readings jump +\- 4 deg. (Thus eliminating the two new sensors I bought!!) This is consistent across most readings except when temperature is low (60 deg) the jumping is less. The higher the reading and therefore the lower the resistance the jumping is much higher. It looks like interference somewhere.

I want to eliminate the loom but can’t find where the engine loom wiring meets the dash pod. With tracing the loom it seems to me that it goes to the ecu???

I’m being a bit lazy asking here but I want to inject straight into the connection directly before the wiring hits the dash.

It’s a big job to trace so any knowledge out there would be very, very helpful.

Thanks.

Edit: 2003 T350c 3.6

Edited by STE VR on Tuesday 6th August 21:15

leerdam23

606 posts

260 months

Saturday 10th August 2019
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Mines exactly the same and bloody annoying...

STE VR

Original Poster:

498 posts

205 months

Saturday 10th August 2019
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I’m getting there slowly. Hopefully have an answer either way over the next few days. Injecting straight into the dash ecu has same effect. Must be picking ‘noise’ up from somewhere.

leerdam23

606 posts

260 months

Saturday 10th August 2019
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yhm

leerdam23

606 posts

260 months

Tuesday 13th August 2019
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Any update?

STE VR

Original Poster:

498 posts

205 months

Tuesday 13th August 2019
quotequote all
Unfortunately not a definitive answer yet. Had added additional main earths just for test purposes but still no joy. Steady up to 91deg then starts jumping after that.

Still haven’t completely worked out how the sensor is wired. Looks to be split between main ecu and dash ecu.

Might borrow a dash ecu and see if the problem still exists.

Penelope Stopit

11,209 posts

108 months

Tuesday 13th August 2019
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STE VR said:
Unfortunately not a definitive answer yet. Had added additional main earths just for test purposes but still no joy. Steady up to 91deg then starts jumping after that.

Still haven’t completely worked out how the sensor is wired. Looks to be split between main ecu and dash ecu.

Might borrow a dash ecu and see if the problem still exists.
Have you got all the electrical info that's needed for checking the circuit through?

leerdam23

606 posts

260 months

Wednesday 9th October 2019
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Any luck sorting or improving this?

Penelope Stopit

11,209 posts

108 months

Wednesday 9th October 2019
quotequote all
leerdam23 said:
Any luck sorting or improving this?
Seconded

STE VR

Original Poster:

498 posts

205 months

Wednesday 9th October 2019
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Hi, unfortunately not yet. Did try two other dash ecu units but both were faulty (given to me as suspected faulty so no surprise) Also noted that the oil pressure and battery voltage were not exactly steady either but they just seem to be ‘live data’ changes rather than the jumping of the display.

Need a properly proven dash Ecu first to rid that suspicion. That Ecu has to come from a car with a known steady temp reading above 90 degC though.


s6boy

1,613 posts

224 months

Wednesday 9th October 2019
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Could be a noisy output from the alternator. Mine stared with erratic temp and went to the whole pod flickering/weird readings.

nawarne

3,088 posts

259 months

Thursday 10th October 2019
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On the Tuscan forum - some years ago (Google search) similar problems.

One responder advised that checking and tightening the earth - Battery -VE to chassis at rear of battery box/pass' footwell was the culprit.

Nick


Basil Brush

5,060 posts

262 months

Thursday 10th October 2019
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Apologies in advance if this is a stupid question as I'm not sure if I am understanding your posts correctly. You know there are 2 temp senders, one feeding the dash and one for the ECU? I'm only asking as you were saying you couldn't trace back from the sender to the dash.

Penelope Stopit

11,209 posts

108 months

Saturday 12th October 2019
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Any joy?

STE VR

Original Poster:

498 posts

205 months

Monday 28th October 2019
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s6boy said:
Could be a noisy output from the alternator. Mine stared with erratic temp and went to the whole pod flickering/weird readings.
Yep, looking very possible. It’s a brand new alternator but doesn’t mean anything when fault finding. Been there before!

nawarne said:
On the Tuscan forum - some years ago (Google search) similar problems.

One responder advised that checking and tightening the earth - Battery -VE to chassis at rear of battery box/pass' footwell was the culprit.

Nick
Thanks, yes seen that. Again all brand new and looks good. Tested out ok and even threw an additional earth to it just in case.

Basil Brush said:
Apologies in advance if this is a stupid question as I'm not sure if I am understanding your posts correctly. You know there are 2 temp senders, one feeding the dash and one for the ECU? I'm only asking as you were saying you couldn't trace back from the sender to the dash.
Thanks, yes aware of the two. The ECU one is fine, the dash one is erratic. They both seem to have their signal return going to the ECU but the dash sender seems to have its ‘positive’ wire to the dash ECU. The ECU and dash ECU must be linked somewhere for the signal return.

I’ve probably cocked up somewhere in the tracing of the wires.


SergSC

508 posts

161 months

Friday 1st November 2019
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Hope this helps you as it did me, if it does it will be the easiest fix ever.

In the passenger's footwell behind the cover, there is an earth connection nut and a fuse next to it. In my case, half a turn of tightening that nut cured all of my erratic sensor readings.

Some people have reported it may need to be tightened from the other side in the battery compartment as well.

edit: ah seems that was already checked.