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

'90 8v 740 is still getting around 13 MPG. I've been getting the 213,
232, and 231 error codes. Idle still seems jumpy, lack of power, and i
get a strange blip at 1200 rpms whenever the engine is slowing from
2000 rpms. Thus far, I've...

-replaced O2 sensor
-replaced Fuel Pressure Regulator
-replaced sparks, cap, and rotor
-spark cables ok
-cleaned and resecured ground connections
-checked proper voltages coming from ECT
-No vacuum leaks (ACTUALLY, I just found a disconnected vacuum hose at
the charcoal can. Surely this wont do anythign!?)
-No exhaust leaks
-AMM appears to be fine (car nearly dies when you unplug it)
-TPS adjusted properly
-Idle control valve cleaned
-All fuses fine

I'm about ready to give up and am hoping somebody has some guidance or
suggestions.....

 

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 &
232 = fuel supply too weak or too rich in part load stage (231); fuel supply
too weak or too rich at idling (232).

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.

700/900/90 Register Keeper,
Volvo Owners Club (UK).

 

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.

700/900/90 Register Keeper,
Volvo Owners Club (UK).