309 temperature gauge error

[309B6D]

Not long ago the XU5 JA was indicating on the second to last bar of the temp gauge even though it was nowhere near overheating. It had been middle of the dial since fitting. I replaced it with another correct part and the gauge sat at midway.
I have run it with no problems for about 1500km, but today the needle flicked straight to the top of the scale on startup.
I wriggled the sensor connection but had no improvement.
Water level was down a bit, but took no more than a cup full.

A 12km drive showed no shift. After stopping I flicked the ignition on and the needle was reading correctly at about middle of the range.
Starting up again soon after had the needle go to the top and I cannot get it to read in the normal range again.

Any suggestions about what might be going on would be very helpful.

Bryan

 

[PeterT]

An earth leak. The gauge has +12V continuously. The sensor varies the resistance to ground. Flicking the sensor wire against the block, grounding it, will normally make the gauge to a nasty full scale deflection.

 

[309B6D]

Thanks for that PeterT. I will have a good look at it tomorrow.

 

[pugwash]

similar but different ,i fitted a new sender as the tab on the old one was broken the guage didnt work , did the peter t check, guage worked ,eventualy i discovered ,i had used thread tape on the new sender and it wasnt earthing ,what was i thinking .

 

[PeterT]

similar but different ,i fitted a new sender as the tab on the old one was broken the guage didnt work , did the peter t check, guage worked ,eventualy i discovered ,i had used thread tape on the new sender and it wasnt earthing ,what was i thinking .

lol, use Loctite 569 or similar.

 

[309B6D]

The orange wire to the sender is only supplying 11v.
I went to Haynes 309 to read the circuit diagram and I am now very confused.
I want to find the other end of the orange and the yellow/green wires so that I can test them for damage. The ECU and instrument panel are not easy to access for a visual inspection.
Two diagrams are "typical for XU5JA/XU9JA" and another loose sheet is a copy that PO has used with notes of various parts such as the sender.
Some show the sender going to ECU while the other shows it going straight to the instrument cluster.

With LE2 Jetronic fitted with SAD does the temp sender signal cause the ECU to alter the fuel ratio? From one of the diagrams it looks as though it is only for the gauge. Most searches mention faulty senders causing very rich running, but mine seems to be running and idling nicely.

Can someone explain to this idiot where the live wire comes from and where the yellow/green wire leads to.

( Yesterday after quite a bit of testing I recharged the battery just to top it up again. I turned on the ignition and the gauge indicated at its usual startup position. After about 15secs running the gauge flicked up to the top. (battery reading 13.1v - feed to sender at 11.1v )