catalytic converter, AMM or something else?

1998 740 turbo w/185K miles. Need a little diagnostic help. This
problem came on very quickly. I can't be sure but somehow I think it
is related to possibly a tank of bad gas. Then again, it may have
been developing for a long time and may simply be age. Owned car
since new. Changed oil and filter every 4K.

Car always starts, stalls a few times then is OK. (in winter it
doesn't stall) Lately, very very rough idle as opposed to normal
rough idle. Also stalls and stumbles at idle. Never a problem
re-starting. Lately, no or very little power below 3,000 then most of
the power returns till 4,500 or so, then peaks. Also hear a slight
backfire/stumble when at idle and I blip the throttle. Gas mileage is
worst ever.

Added techron several tanks ago. Didn't really help. Tried again,
still no real help.

Had annoying little oil leak (one of many over the years)which I
traced to either the valve cover gasket or cam shaft seal. Replaced
gasket and now get lots more oil dripping onto water pump and being
blown everywhere by the fan.

Pulled intake hose off turbo and found very slight lateral movement
with almost no axial movement. I could spin turbo with my fingers.
Expected little or no friction and it to just continue spinning, but
it didn't.

Checked fuel injectors, ballast resistor pack, temp sensor, knock
sensor, air valve, throttle switch, AMM. All tested good per Volvo
service manual. Plugs (platinum) all were uniform in light color. No
signs of oil. Replaced dist. cap, tested wires, replaced air filter.
checked hoses for air leaks.

At this point in time I suspect either the catalytic converter
(original) or the AMM. I doubt I can get the bolt out of the header
pipe (also original)to test the pressure and I hate like hell to start
replacing parts considering the 185K miles.

One other observation. Over the past several months I did notice that
under heavy accelleration the boost gauge readings were kind of
sluggish. Any thoughts?

 

Do you mean 1989 740T from what you are describing it
possibly could be a bad turbo check for any engine
codes in A2 & A6 post back with what codes if any come
up

 

What is your vacuum when you first start the car and what happens to it over
the next few minutes. Normal running vacuum is 16-22. What you describe
sounds like some major vacuum leaks. Is the engine behavior different
between a cold engine and a hot running engine.

I would suspect the seal behind the timing gear on the front of the cam.
There are also seals behing the intermediate shaft and the crank.

A turbo that's starting to go bad or a partially blocked cat can cause this.
Has the fuel filter been changed lately? Is the behavior different if the
tank is low on fuel?

 

OOPS, SHOULD READ 1988 740 TURBO

 

It doesn't happen very often but your timing belt could have jumped a notch.



Also hear a slight

 

TIME. DON'T NOTICE ANY CHANGE IN PERFORMANCE RELATED TO FUEL TANK
LEVEL. THOUGHT IT MIGHT BE PRESSURE REGULATOR BUT THAT SEEMS TO CHECK
OUT. AS FOR VACUUM LEAKS, REMOVED EACH LINE AND PLUGGED FITTING IN
MANIFOLD, NO CHANGE. USED WD-40 ON ALL VACUUM CONNECTION, ON INJECTOR
SEALS, THROTTLE VALVE SEALS AND INTAKE MANIFOLD, NO LEAKS FOUND.

DID THINK ABOUT TIMING BELT JUMPING A COG THOUGH. CHECKED IGNITION
TIMING AND IT WAS AT 10 BTDC THOUGH I GUESS I SHOULD CHECK THE BELT
ANYWAY.

COMMON SENSE SAYS I SHOULD GET RID OF THE CAR, ECONOMIC SENSE SAYS I
SHOULD GET RID OF THE CAR, MECHANICAL SENSE SAYS I SHOULD GET RID OF
THE CAR, BUT THE WIFE WANTS IT SINCE SHE HAD IT SINCE NEW.

MY CURRENT THOUGHTS ARE A COMBINATION OF PROBLEMS. AS I MENTIONED, THE
TURBO SPUN BUT I WOULD HAVE THOUGHT MORE FREELY. MAYBE THIS IS OK AT
IDLE BUT WHEN GIVING GAS, THE ROTATIONAL FRICTION IMPEEDS THE FLOW OF
AIR AND IT STUMBLES UNTILL IT GAINS ENOUGH SPEED TO ALLOW FOR THE
PROPER VOLUME OF AIR FOR COMBUSTION. THEN, POSSIBLY DUE TO A CLOGED
OR PARTIALLY CLOGED CAT, THE SPEED/POWER MAX OUT AT THE REDUCED
CAPACITY OF THE CAT.

I CAN DEAL WITH THE $100+ FOR THE CAT WHICH I WILL INSTALL, BUT IF IT
IS THE TURBO ALSO, ITS COST DOESN'T MAKE SENSE. AND WE ALL KNOW IT
MIGHT NOT END THERE.

MITCHEL

 

The crank and intermediate shaft (distributor) could be correct but the cam
gear could be off by one notch. That would mean the ignition timing would be
correct. Other than that I would strongly suspect the cat. A shop with
computer diagnostic equipment would be able to diagnose your problem, then
you could take if from there.

Brick_0

 

Look at the hoses between turbo and intake manifold. The hoses at the
intercooler often fail on the bottom, where oil sits, and the rip is not
readily obvious until you actually remove the hose. Even if the turbo
completely seizes, the engine runs perfectly smoothly (well as good as a
B230 ever is), just with little power. A plugged cat inhibits boost
production as well, but really doesn't make the engine run poorly.