'90 740 running rich and getting TERRIBLE mileage. Ayudame!

Have you cleaned the throttle butterfly and throat area? This can get very coked up and should be cleaned every two years along with the AMM (MAF) and IACV.also make sure that the PCV system is thoroughly clean and operating correctly. It takes almost a whole can of carb fluid to clean the throttle block assembly. Also check on the Brickboard FAQs.

Code 213 = Throttle position switch signal faulty at full load. Codes 231 &

Suggestion is to read and clear the codes indicated then see if any of them return subsequently. Also check the Ignition codes (pin 6 of Diagnostic unit). Code 1-4-3 = knock sensor signal absent or faulty. This code corresponds to the poor performance and high fuel consumption and lack of power.

All the best, Peter.

Have you checked very carefully for leaks in the flex hose to the intake manifold?

Note: In regards to cleaning the flame trap, PCV, and thottle body, i've done all that. Just forgot to list.

So I took it to a one man volvo specialist who claims that the problem with my running rich is due to the ECU not properly interpreting the TPS signal (which i measure to be correct). Is this true or possible? He is wanting $800 for a new ECU and claims he needs to personally install it (when i mentioned me doing it instead) because the ECU's need for calibration. As far as I can tell, the ECU is a plug and play device that will adapt and learn. No calibration needed.

Is this guy full of it on both counts? (1. needing ecu, 2. calibration)

You're right; he's wrong - on both counts. At least you learned somebody to stay away from.

Mike

Getting back to the start...

Anybody disagree that the symptoms come from running excessively rich, at least at cruise and at wide open throttle? (I'm assuming the ignition timing is correct - the sensor in the '90 looks at the flywheel IIRC.)

The big problem is that most of the usual suspects have been eliminated - fuel pressure regulator, AMM, vacuum leaks.... The ECU knows the mixture is way off, as evidenced by the codes, but the mixture is nowhere near being in range so it can't compensate. The only other thing I can think of is the head temperature sensor - on my '85 turbo it is located under the intake manifold, around branch #3, way up. The connection to mine has been intermittent since I replaced the engine harness, and it produces lack of power under boost when it doesn't make contact. Maybe in a non-turbo the symptoms show up at lower throttle? Anyway, I suppose you could unplug it and make sure you see a corresponding code show up. It probably won't get you any closer to a fix, but at least your arm will be oily ;-)

Did this just start out of the blue one day?

Mike

He's full of it, not only is a new ECU dead easy to install with no adjustments or calibration whatsoever, but $800 is a ludicrous price. That's a 15 year old car, there's zillions of them in junkyards, a good used ECU should be $30-$100 tops, any more and you're getting ripped off. Find another mechanic or keep poking around until you solve the problem yourself.

I have suggested that he checks the ignition codes as well. One code (1-4-3) gives the same symptoms as the two fuel codes (2-3-1 & 2-3-2). Regina system does not come up with any of these codes. The ignition code is for the knock sensor and/or wiring. He has not touched these as far as I know. If he has not seen or read the message please pass this on.

All the best, Peter.