Volvo: rich/lean running, vacuum leaks, lambda sensor

Question
QUESTION: hi there, i have a '93 240, with the b200f engine, running what i believe to be lh 3.1 ignition.

some time ago, it started running extremely rich, pouring black smoke on accelaration, and single figure fuel economy.

the throttle body has been cleaned, and the switch tested and adjusted. it seems to work fine.

the air mass meter has been replaced, as has the o2 sensor.

since i changed the lambda sensor, it will now start with the air mass meter connected, but after driving a couple of miles, it will start running rough, and backfiring into the intake.
if you then disconnect the AMM, it will run, but is underpowered, and occasionally cuts out, sometimes on speed humps, or potholes
i don't have a fuel pressure meter, or have access to one.

temperature sensor resistance increases  as it cools, and decreases when hot.

if the crank sensor is disconnected, the engine stops.


starting to go round in circles now, and rapidly running out of patience, and funds !!

please help !!
thanks,
bob

ANSWER: Bob,
Not knowing the fuel pressure is not good. Are there some fault codes to follow up on and repair? How about does the pressure reg leak, from the vac line? You maybe overpressering and running rich. If all that fails, seek help from a Volvo tech who can make some tests, drive the car and inspect the engine.

---------- FOLLOW-UP ----------

QUESTION: the only fault codes we got were

system compensating for rich/lean mixture at cruise,

system compensating for rich/lean mixture at idle.

it did bring up a fault in the injectors, but that has been cleared, and not reoccured.

interestingly tho, the system will not let me clear stored fault codes ?

wondering if there's maybe a problem with the ecu itself ?

cheers,
bob

ANSWER: Bob,
Yes possible the C/unit is bad. Do you have access to another known good one to try? How well will it run with the HO2S unplugged? Any vacuum leaks? Brake booster maybe?

---------- FOLLOW-UP ----------

QUESTION: by ho2s, do you mean the lambda sensor ?
it seems to run ok until it's warm enough to go to closed loop, i had wondered if disconnecting the lambda would force it to stay in open loop.
the last one i believe went faulty, and replaced it. prior to the replacement, it ran extremely rich, so much so you could smell fuel from the exhaust !!
when i changed the sensor, and the airflow meter, i reset the codes, and it ran perfectly for about 20 miles. (and the lambda light was out for the first time in 3 years !!)
it did occasionally misfire, and was still maybe a little heavy on fuel, but i hoped that might clear, as i'm guessing the bores will be pretty sooted up.
i stopped it for 10 mins tro get some shopping, and since then it has never run properly unless the air meter is disconnected.
sadly i don't have a spare brain to try.

considering the idea of picking up an earlier car for spares and changing it to carb, i don't really like injection anyway.
do the carburretted cars still have the 2 fuel pumps, or would the tank need to be changed too ?

cheers,
bob

Answer
Bob,
HO2S same as Lambda. Here in the States we  do not have Carburated cars, so I do not how the fuel system is set up. I would say that a small pump with 4 to 6 psi would supply the carbs. Possibly just a turbo feed pump in the tank would be enought fuel pressure.