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Car Forum / Volvo Cars / May 200789 760 Turbo engine shutting down!
My 760 Turbo will be running along fine, then suddenly the engine just stops! In a few moments, it will start again and run for weeks without problems. Could it be the fuel line, or perhaps an electrical problem? Many thanks! Bass Man > My 760 Turbo will be running along fine, then suddenly the engine just > stops! In a few moments, it will start again and run for weeks > without problems. Could it be the fuel line, or perhaps an electrical > problem? > Many thanks! > Bass Man I think '89 is new enough that the engine wiring harness will be fine, but it's worth checking for rotting insulation, if you find some, there will be more in hidden places. When it shuts down, does the tach drop like a rock or does it drop slowly with the engine RPM? If you try to start it immediately afterward, does the tach twitch or just lay there dead? If you get tach activity then the ECU is getting a signal from the hall sensor, that will help narrow things down. Ignition power stage and fuel pump relay are both reasonably common failures. > My 760 Turbo will be running along fine, then suddenly the engine just > stops! In a few moments, it will start again and run for weeks > without problems. Could it be the fuel line, or perhaps an electrical > problem? > Many thanks! > Bass Man It is vital to determine whether it is the ignition or fuel that is quitting. Look at the tach the next time it dies; if the pointer has already dropped like a stone even though the engine hasn't come to a stop the problem is in the ignition. If you missed the moment, watch the tach while you crank. If the tach doesn't twitch every second or so, the ignition is the problem. Also, usually fuel delivery problems have a softer fail, like the power sags away in a second or so, while ignition failures are typically abrupt as though you turned the ignition off. There are a few causes of each problem area - fuel or ignition. Your description has me thinking it is the notoriously hard to diagnose Crank Angle Sensor, though. It affects the ignition (and fuel, too, but the ignition is obvious) and comes and goes as it pleases. Others will weigh in with more ideas and some troubleshooting will help narrow the search. One quick item: does your battery have a ring terminal fastened to the bolt on the positive post as my '85 does? If so, it's worth your while to clean the battery terminals, including scraping both sides of that terminal to shiny metal. When it corrodes the ignition cuts out at odd times. Mike On May 8, 8:46 pm, "Michael Pardee" <michaeltn...@cybertrails.com> wrote: > <geo...@ontherightside.com> wrote in message > [quoted text clipped - 26 lines] > > Mike Many thanks guys. I'll check out your ideas and will get back to you. I didn't look at the tach, but the engine cuts out instantly which leads me to believe it's an ignition problem. The battery terminals are already super cleaned. You can plow fields with a Volvo, but their electrical sytems are often a nightmare! BTW, where is the Crank Angle Sensor located? Is it something I can locate and replace? George > Many thanks guys. I'll check out your ideas and will get back to > you. I didn't look at the tach, but the engine cuts out instantly [quoted text clipped - 4 lines] > locate and replace? > George It's on the bellhousing, I don't believe it's difficult to replace. >> Many thanks guys. I'll check out your ideas and will get back to >> you. I didn't look at the tach, but the engine cuts out instantly [quoted text clipped - 6 lines] > > It's on the bellhousing, I don't believe it's difficult to replace. That makes it sound difficult, but it's right at the top where it's only aggravating rather than maddening. The truly maddening part of crank angle sensor failures is tracking it down. The failures are often so random and so short-lived it's hard to get the goods on it. Sometimes they fail suddenly and completely (like mine did last year), but that is the luck of the draw. Mike > That makes it sound difficult, but it's right at the top where it's only > aggravating rather than maddening. The truly maddening part of crank angle [quoted text clipped - 4 lines] > > Mike My cars don't have them, but I suspect some freeze spray might make tracking down the failure easier, or you could just take the gamble and replace it. If that wasn't the problem, at least you then have a spare which you'll be glad you have should it ever fail. I'm curious if it's a hall or VR sensor, the VR type is just a coil of wire on a magnet and rarely fails, perhaps engine compartment heat is hard on them though. >> That makes it sound difficult, but it's right at the top where it's only >> aggravating rather than maddening. The truly maddening part of crank [quoted text clipped - 13 lines] > wire on a magnet and rarely fails, perhaps engine compartment heat is hard > on them though. Mine is almost certainly a Hall sensor. It has three leads: power, ground and output. I can see the output with a voltmeter. In my '85 it is mounted in the distributor, so I can hold the assembly in my hand to test it. After replacing the sensor I could also turn the distributor shaft and see the spark. When I worked in component level electronics I learned to dread intermittent coils. They were rare enough, but they failed just like the crank angle sensors do: open when they want to be, working when they feel like it, and no temperature sensitivity. It always came down to luck to catch them in the act. Mike |
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