400se Guage issue

400se Guage issue

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Discussion

AM400

Original Poster:

1,196 posts

272 months

Monday 14th November 2022
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I recently had some work done on my 400se, since picking up the car the petrol guage and temp guage are acting differently. Before they used to creep up to their current reading. Now when I turn the ignition they shoot straight to the reading almost bouncing off it. Any ideas what could have caused them to do this?
The only work I really had done was the injectors refurbed and a new valley gasket in the process. My first thoughts would have been earth but the main earth's have not been disturbed. I have been told there could be an earth to the fuel rail but I cannot see one.
Thanks

jon haines

953 posts

255 months

Monday 5th December 2022
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I would have said an earth wire has been disturbed but was not aware the fuel rail had an earth.

wild rover

448 posts

190 months

Tuesday 6th December 2022
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Disconnect the temperature connection at the front of the engine. If there is no difference check for chaffing on the wire.

AM400

Original Poster:

1,196 posts

272 months

Tuesday 6th December 2022
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Thanks both. There is no earth on the fuel rail, I didn't think I had ever spotted one. The other earths are all ok so I will check the temperature connection/wire as suggested.

ElvisWedgeman

2,715 posts

174 months

Tuesday 6th December 2022
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I would check the gauges themselves. Easiest one to check would be the temperature gauge. Put the ignition on and touch the temperature gauge sensor wire under the bonnet to an earth and watch the gauge. If it shoots up like an amp meter would, then the gauge is suspect as it should creep up slowly to the maximum mark. Same applies to the fuel gauge. If they disconnected the battery during the work they carried out, maybe they’ve shorted something out and damaged them somehow.

Edited by ElvisWedgeman on Tuesday 6th December 15:28

Adrian@

4,390 posts

291 months

Tuesday 6th December 2022
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Q. Smiths or VDO gauges? (I have a SEAC interior '86 280DH with VDO which jump into life), then as said, Smiths versions (hot wire, earth dissipate) will slowly go to full if the wire is shorted down to earth. A@

AM400

Original Poster:

1,196 posts

272 months

Saturday 17th December 2022
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ElvisWedgeman said:
I would check the gauges themselves. Easiest one to check would be the temperature gauge. Put the ignition on and touch the temperature gauge sensor wire under the bonnet to an earth and watch the gauge. If it shoots up like an amp meter would, then the gauge is suspect as it should creep up slowly to the maximum mark. Same applies to the fuel gauge. If they disconnected the
battery during the work they carried out, maybe they’ve shorted something out and damaged them somehow.

Edited by ElvisWedgeman on Tuesday 6th December 15:28
I was thinking they may have done something like that. Next check is the gauges themselves.

AM400

Original Poster:

1,196 posts

272 months

Saturday 17th December 2022
quotequote all
Adrian@ said:
Q. Smiths or VDO gauges? (I have a SEAC interior '86 280DH with VDO which jump into life), then as said, Smiths versions (hot wire, earth dissipate) will slowly go to full if the wire is shorted down to earth. A@
I am pretty sure they are Stuart Warner although they do look like Smith's gauges.

Polly Grigora

11,209 posts

118 months

Saturday 17th December 2022
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Somebody has got to ask

Why didn't you take it back to whoever did the work?

AM400

Original Poster:

1,196 posts

272 months

Saturday 17th December 2022
quotequote all
They didn't want to know and suggested it was just coincidence and nothing they did would have affected the gauges.

Edited by AM400 on Saturday 17th December 22:09

Polly Grigora

11,209 posts

118 months

Sunday 18th December 2022
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Ok then, difficult innit

Earths missing from the gauges springs to mind, burnt out earths is another one

The thing is, burnt wiring leaves a smell behind for a long time and you would have noticed it

AM400

Original Poster:

1,196 posts

272 months

Sunday 18th December 2022
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Yeah, I'm positive it's something they have done but finding it is difficult. This was a TVR specialist as well. I guess the next check is to have a look at the gauges themselves....when it gets a bit warmer in the garage!

Adrian@

4,390 posts

291 months

Monday 19th December 2022
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From memory SW gauges were only fitted as OE to 81-83 cars (might even be 82, I do not remember having them in either my A or B reg 280's back in my childhood), but VDO do hit almost instantly to the gauge point.
The 400SE should use TVR's (canted to one side) Smiths version (which must have an integral voltage stabiliser as I cannot see one in any diagram I have).
Historically gauges have suffered from poor earth to the dash, which in turn have the indicators giving a drama effect to the gauges when operating ...my (presuming your car is running TVR's gauges as expected for a 400SE 5 gauge version dash) thoughts are that you have had a poor earth and that now you don't and things are working reasonable better than they were. Obviously, TVR were still using VDO in '86 (as my 280DH is) but I have not seen them in a 400. (there is nothing saying that different gauges have been retro fitted ATM). A@

Edited by Adrian@ on Monday 19th December 08:36

adam quantrill

11,584 posts

251 months

Wednesday 21st December 2022
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I've not looked on the 400SE (SX) but the earth on the 350i came to the dash via the bonnet cable. There's an earth strap in teh engine bay to (probably) back of the engine.

Quite likely if they did the valley gasket they have disturbed the earths to the rear of the engine usually drivers side cylinder head.

You could try running a temporary (thick) cable from there through the bulkhead grommet to dash earth, to see if that clears it up.
Also double check battery -ve still attached properly.