QuestionQUESTION: I have had this problem for awhile.The car has 235k on it and a newly installed used engine (the old one was leaking from the head gasket)that ran fine for a month. Then a recurring intermittent problem resurfaced (probably after the computer setting reset after the new engine was installed). The problem has been around for at least 18 months. The car stalls while moving at any speed and can't be easily restarted. You have to wait 2 minutes or more before it will restart. Then the problem tends to recur within 5 minutes several times until it disappears. he car can then run well for a few weeks before the symptoms disappear. Recently, the problem got worse with more frequent stalls (especially when damp) and now it will crank but not start, even with extra power. I have asked Volvo and they thought it could either be a small switch, the fuel pump, or the harass. The car had another stalling problem when it stopped two years ago which was corrected with a $250 part which modulated the idle. After that the intermittent stalling began. I am about ready to give up since sinking more money into this car makes little sense. Your thoughts would be appreciated
ANSWER: Ignition module or Hall sensor in distributor. Are you losing spark when it's no start? I'll bet you are.
Mark
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QUESTION: I asked the dealer about this problem and they believe the more likely problem is the fuel pump since this problem has been going on for so long and the fuel pumps on this 740s have this slow die characteristic, especially given something has too cool off before it can restart. If it were the Hall Sensor or the Ignition Module (which they admit is possible), it would not have lasted so long. They also think it is not lightly to be the harness. It could be both problems since it also is worse when it is raining (a recent development).
Since the car is not working now, when it is brought would the cause between these possibilities be evident? What do you think about the fuel pump cause and what would be a reasonable price to fix it?
Answer Frank, do you want the simple answer or the correct way to test now that it's dead? VBG
My guess, 90% is that the pre pump in the fuel tank is shot or the pickup tube hose is rotted and fallen off. A fuel pressure test would tell you very quickly.
History, the pre pump in the tank feeds/primes the main pump which can produce much greater pressure and volume than the pre-pump. Because it's designed to be an efficient pressure device, it cannot "suck" for crap. That's why it needs the helper pre-pump. Sometimes when the helper is weak or intermittent the main pump can hold the siphon from the fuel tank until the tank level gets real low or until the main pump gets too hot from doing all the work. The heat in the main pump "percolates" areates the fuel. Now that the fuel is not a solid liquid, (hydraulics) not enough pressure and volume can be created for proper injection. Whew!
You can try filling the tank to the very top to see if you can get it started to save yourself a tow.
Cycle the key on for a few seconds, then off. Do this five or six times before turning the engine over and trying to start it. When you turn that key on, you should hear a "buzzing sound under the car for 3-5 seconds. That sound is your main pump. If you don't hear that, either the pump is bad, or the fuel pump relay. The relay is the more likely culprit of the two. Components in order of likely pattern failure with this scenario are: Pre-pump, pump relay, main pump, and out of gas.(Bad guage,inattentive operator)VBG
Let me know what fixes it or if you need more help!
Merry Christmas!
Mark
P.S. Oh, if that pre-pump has been bad long enough, it's not uncommon for the main pump now to be bad also. Start with the pre and see how it goes. The replacement procedures are unrelated so you are not redoubling any efforts.
