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740 keeps running very rich

I am really starting to pull my hair out with this car. It is an '89 740 (non-turbo), 140,000 miles. Should be a good solid runner, but it just won't stay running. It just belches black smoke from the exhaust and runs a few hundred miles until plugs are so fouled it won't start. It doesn't sound bad when it is running and has pretty good power. I have replaced the air mass meter with a different unit from a junked car. Also replaced the fuel pressure regulator. Should I break down and buy a new AMM just to rule it out as a problem? What other components may be causing this and how easy are they to replace for the do-it yourselfer.

TIA,

Kirk

Reply to
Kirk Grau
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Check the coolant temperature sensor, not the one for the guage but the one for the injection. You can test it with an ohm meter.

Reply to
James Sweet

Thanks for the very fast response. Do you have a site with instructions or know what reading should be?

Kirk

Reply to
Kirk Grau

No, I don't remember what it should read, however if you warm up the engine a bit, clip an ohm meter between the sensor and grounded metal under the hood you should get a resistance reading which changes smoothly as the engine cools. Also how's the wiring harness look? I forget what year this car is but pre-'89 cars had crummy insulation on the engine wiring harness which deteriorates.

Reply to
James Sweet

I have the same problem with my 86 740 were is this ting plased. I want to fix my Volvo too.

James Sweet wrote:

Reply to
Jan-Erik Drangevåg

It's on the cylinder head under the intake manifold, small round sensor threaded into the head. There's two of them, I don't remember which does the guage and which goes to the injection but if you unplug the one to the guage the guage will be pegged. Another option is to simply test both.

Reply to
James Sweet

On my 85, the sensor is somewhere around cylinder #3, under the intake manifold and hidden by the throttle body and idle air control valve. On my turbo, the new engine harness doesn't make good contact with that sensor and it causes the engine to occasionally run very rich under boost until I reseat the connector.

Mike

Reply to
Michael Pardee

Under #3 intake runner.

Bob

Reply to
Robert Dietz

Thanks I'll take a look at it tomorrow!!

James Sweet wrote:

Reply to
Jan-Erik Drangevåg

Thanks wonderful to have so many helpers!!!

Robert Dietz >

Reply to
Jan-Erik Drangevåg

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