1986 740

After thinking I had a fixed, next moring car ran as if on one cylinder. Pulling 3 plug wires made no difference. Pulling one specific plug wire stopped engine (as well as pulling AMM wire). Plugs wet.

While messing around the engine warmed a bit and started running better, until normal running. Hard to believe a sensor could make it go from running like crap (would not run when in gear) to near perfect.

I have 240,000 miles without changing a sensor since its been running great, but now looks like its time. After looking at FAQ, not sure if temp sensor would cause symptoms.

Any feedback appreciated.

Thanks,

Gary

It sounds like an ECT sensor.

Works via resistance ... if it not working correctly though, it will tell the computer it is -684F and dump lots of gas into engine.

I will qualify this by saying I've never had the problem myself but read lots of posts about this issue.
--
Norm Cook Vancouver BC; 1989 745T 204,000KM

Thanks,

That was my suspicion, but like you I never had one go bad to know exact symptoms. Not certain if it could cause such a ratical change in performance. However, if flooding engine, then that would explain it and why no firing (liquid rather than mist/gas drowning spark).

Gary

Many of the folks here are knowledgeable about ECT failures.

Anyone else care to chime in? I know John Sargent has had this problem before.
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Norm Cook Vancouver BC; 1989 745T 204,000KM

ECT sensor disconnected or with broken wire will signal rich as if the engine is cold. It will start and run perfectly normal but when warmed up will idle slow, maybe stall, little power. Doubt that is the problem.

Plugs, wires, dist cap, rotor all in good condition?

If your wiring harness are detiorated be carefull rooting around, you may just create more problems.
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David Hunter

That car is old enough to have wiring issues. My 87 745T has a really deteriorated wiring harness, as bad as the 86 245 was before rewiring. Could be wiring instead of sensors, the same symptoms apply.

Regards,
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Will Dallas, www.willdallas.us, www.willdallas.org, 86 245 DL 205K miles, 93 940 250K miles, 88 765 GLE 149K miles, 87 745 , 86 244 DL 200K Miles

I'll follow the wires in the engine compartment and check their condition.

Thanks

Make certain to check and clean (or replace)the connectors. Volvo ran their grounds through the connector bodies. A little corrosion or slippage and you don't have a ground, you have a resistor. With multiple sensors sharing a common ground, a grounding failure can look like many different things.

Regards,
--
Will Dallas, www.willdallas.us, www.willdallas.org, 86 245 DL 205K miles, 93 940 250K miles, 88 765 GLE 149K miles, 87 745 , 86 244 DL 200K Miles