Volvo 740 Turbo Problems

THIS LOW MILEAGE TURBO VOLVO COULDN'T GET OUT OF ITS OWN WAY.

This is a problem that I received from one of my readers. The story is in three parts, his problem statement, my suggestions, and his solution. There is a lesson here - you have to look with your mind as well as your eyes. Sometimes the apparently difficult problems have the simplest of solutions.

PROBLEM

Symptom = Starts fine, runs at idle fine, very slow acceleration is fine; however, terrible performance and black smoke occurs when going up grades or trying to accelerate in a normal fashion. Also, on highways, top speed is pretty much 60 mph, with black smoke and rough running nearly constant companions. I must mention that this is exacerbated whenever the turbo kicks in, the turbo pressure is there, just no boost in acceleration, although I have been told the turbo is "fine." Thanks for any thoughts you may have!

SUGGESTIONS

Well, the good news is that you have a myriad of things from which to choose to attack the problem. The bad news is that you have a myriad of things from which to choose to attack the problem. Where to start??

It's obvious that the engine is running rich. We can start with one hypothesis that the injectors are dumping much too much gas into the cylinders. Is it because the injectors are hanging up and sticking open?? (pressure clean the injectors) Or is is because the computer is telling them to stay open much longer than they should. Next is the computer making a bad decision (bad prom) or is it getting bad information from some of its inputs, namely the oxygen sensor?? Is the fuel pressure way too high causing entirely too much fuel to inject while the injectors are open (bad fuel pressure regulator)? Is it simply a clogged air filter or a birds nest in the inlet tube?? [don't laugh - I had one last week which was similar and it turned out to be a squirrel's's nest in the grille in front of the air inlet!!] (see http://www.misterfixit.com/nuts2u.htm)

Next assume that all is normal in fuel land and the spark is either not strong enough to fire the plugs under load (bad coil) or that the spark is not getting there at the correct time (bad computer or bad information getting to the computer aka crank position sensor or distributor [which ever one you have????])? Is the problem with the high voltage wires? Bad coil wire or spark plug wires?? Bad spark plugs (you did change them but ya never know) Next, is the engine breathing correctly? Is the catalytic converter clogged or partially clogged? Do a backpressure test by measuring vacuum at idle and at 2200 rpm and see if it is lower at 2200. Like I said in the beginning you have your work cut out for you. Let me know what you find. You'll want to get it sorted as soon as possible so you won't have to get roadside assistance any time soon.

Bob

SOLUTION

Dear Bob: Thought I would let you know that I got off easy on repairing the acceleration problems I wrote you about this weekend. It was nothing more than a cracked rubber hose. This hose, rather a coupling, was located between the device that resembles a radiator (which, in fact, sits behind the radiator) and an air induction "barrel" that connects to the engine. This radiator device has another barrel which leads to (or from?) the turbo. I would swear that unless I had happened to bump this barrel with my arm and noticed how loose it seemed, that I might have not found this. The crack was on the underside of an otherwise very new looking piece of rubber. Replacing it resulted in a very peppy car!! Thanks so much for your quick response, maybe this is something I should have checked before I contacted you, but in any event, wanted you to know about it.

Regards, Steve Sloan

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