Volvo 740 Temp Gauge pegged

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psyshrike - 04 Jul 2004 18:23 GMT

Howdy,

87 740 GLE. Had an idle oscilation problem. After reading the comments
here, replaced the flametrap, cleaned the throttle body, idle control
valve, and assosciated hoses. She is running much better. Thanks!

But... The temperature guage is now pegged. Which after reading the
brickboard FAQ, I think means I managed to disconnected the sensor
wire. right?

I took notes, and everything I took apart _intentionally_ is back
together.

Any reccomendations on how to start troubleshooting this?

I am guessing I need to take the idler control valve and its hose back
off and take a look under the manifold for the temperature sensor and
its wiring. It is under there right?

Who else here has done this accidentally and what was the fix?

-Thanks in Advance
-Matt

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Ric - 04 Jul 2004 19:34 GMT

I wonder if you disturbed a wire in your efforts to deal with the flame
trap. Older Volvo's have weak insulation around the engine wiring.

> Howdy,
>
[quoted text clipped - 19 lines]
> -Thanks in Advance
> -Matt

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Mike F - 05 Jul 2004 14:20 GMT

> Howdy,
>
[quoted text clipped - 19 lines]
> -Thanks in Advance
> -Matt

You are correct in the location of the engine temp sensor. Low
resistance = hot, so as suggested you've jostled the remaining
insulation off the wires leading to it, shorting them out. You can see
it from above, close the the runner for cylinder #3. Keep in mind this
won't be the only place the insulation on this harness is bad. You can
tape up the harness by removing the intake manifold, it's not too
difficult, but if you're the kind of person that frustrates easily, get
someone else to do this. If you do attempt this, the only gotcha is the
connectors for the idle valve and throttle switch can be interchanged,
and if you do, it kills a transistor in the idle circuit inside the
computer, so make sure you mark which is which before you start!

Signature

Mike F.
Thornhill (near Toronto), Ont.

NOTE: new address!!
Replace tt with t (twice!) and remove parentheses to email me directly.
(But I check the newsgroup more often than this email address.)

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psyshrike - 07 Jul 2004 22:49 GMT

> > Howdy,
> >
[quoted text clipped - 13 lines]
> > I am guessing I need to take the idler control valve and its hose back
> > off and take a look under the manifold for the temperature sensor and

> > its wiring. It is under there right?
> >
[quoted text clipped - 14 lines]
> and if you do, it kills a transistor in the idle circuit inside the
> computer, so make sure you mark which is which before you start!

Thanks for the heads up on switching the wires. Hope you didn't learn
that the hard way.

You guys were right. The insulation was completely gone from the wires
about 2 inches back from the sensor. I was able to degrease them and
get my fingers in there to tape them up after disconnecting the idler
valve.

Kindof a bodge job. I'll take off the manifold and do it right when I
get around to sending the injectors out to be cleaned.

-Thanks!
-Matt

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