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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?

Reply to
MW
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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

Reply to
G Klein

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?

Reply to
Brick_0

OOPS, SHOULD READ 1988 740 TURBO

Reply to
MW

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

Also hear a slight

Reply to
Brick_0

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

Reply to
MW

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

Reply to
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.

Reply to
Mike F

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