CATransplant
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- Sep 4, 2012
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- St. Paul, MN
Easy Replacement of Crankshaft Position Sensor - Volvo 740
Like many owners of older Volvo 740s, I've just been through the process of fixing a no-run problem. After replacing the fuel pump in my 1991 740 Volvo Regina non-turbo wagon and the fuel pump relay, the intermittent dying and no-start problem did not go away. Finally, it became permanent with no spark. Research here and elsewhere on the Internet narrowed the issue down to the coil module or the crankshaft position sensor, so I ordered both parts. The coil module I bought used from a running Regina system 740, and I ordered the sensor from an eBay dealer.
Replacing the coil module didn't solve the problem, so it was time to replace the sensor. On another internet site, someone had written up the process of replacing the sensor, using a string of 3/8" drive extensions and wobble-joints to access the 10mm bolt that holds the sensor into the bell housing. Very complicated and unwieldy. I've been wrenching on cars for many years, so I decided to take another look at the job before starting. Here's the process I worked out by studying the car and thinking, and it works perfectly. It took only 5 minutes to do:
1. Use a flashlight to locate the sensor and the bolt. You'll have to peer at the thing from the passenger side fender, looking over the air conditioning pipes. It's below the distributor, on the top of the bell housing. The reason for this step is so you can orient yourself to its exact location. While you're removing and replacing it, you won't be able to see what you're doing, so you'll need to visualize it in your mind.
2. Carefully put your left hand between the engine block and firewall, and locate the retaining bolt head and the wire from the sensor with your fingers. Again, this is an orientation process, because you'll be feeling your way through this job. There's only about 3" of space behind the engine block, so it's a somewhat tight fit back there.
3. The only tool you'll need is a 10mm combination wrench with a racheting box end. These are sometimes called combination gear wrenches. You can usually pick up a set of these fairly cheaply, and they have multiple uses. Or just buy the 10mm one. You flip the wrench over to choose between tightening and loosening.
4. Orient the wrench so that it will loosen the bolt, and then using your left hand, with your index finger placed over the ratcheting box, insert your hand and the wrench carefully behind the engine block and place the racheting box end over the retaining bolt head. The reason for putting your index finger over the box end is to make it easier to find that bolt head, since you won't be able to see.
5. Carefully re-orient your hand on the wrench, trying not to pop the box end off the bolt head and then loosen the retaining bolt. You'll be able to move the wrench only about 10 degrees, so keep going until the ratchet won't loosen the retaining bolt any further, then remove the wrench and your left hand.
6. Insert your right hand behind the engine block, thumb down, and use thumb and index finger to finish removing the retaining bolt. Keep one finger on the bolt at all times. You'll only be able to manage a partial turn each time. When the bolt is free, carefully remove it and take it out from the narrow space. Put it somewhere safe.
7. Using your right hand again, thumb down, reach in and wiggle the sensor to make sure it's free. Use your thumb and forefinger to twist the sensor, using the area where the retaining bolt goes for leverage. Normally, this is easy. When the sensor is moving freely, you can lift it out of the bell housing and from behind the engine block.
8. Disconnect the sensor at the connector near the driver's side firewall. Pry the spring clip loose and put it safely somewhere. It's small and easily lost. You can fish the plug through the zip tie on the firewall, but it's not all that easy. Move the other wires, etc. until you get it out. Don't bother trying to fish the new sensor's plug through there. It's a waste of time. Just zip tie the wire to the other wires after installation.
9. After plugging in and securing the new sensor, carefully route it and let it drop behind the distributor, near where it will go.
10. Insert the 10mm retaining bolt in the sensor's extension. Using your left hand, put your index finger on the top of the retaining bolt, grasp the sensor with your thumb and second finger and carefully maneuver the sensor into position, lowering the sensor into the hole in the bell housing. You may have to fiddle a bit, but if you oriented yourself well before starting, you'll find the hole easily with the part by feel. Keep your index finger on the top of the retaining bolt as it rises when the sensor enters the bell-housing. Gently turn the assembly until you feel the retaining bolt find its threaded hole. It's hard to describe, but you'll feel it. Very carefully, move your hand, and work with thumb and forefinger to start the bolt in the threads. If you don't have lots of experience, this will be the most difficult part of the job, since the quarters are so tight and since you can't rotate the bolt much. Don't rush and don't accidentally pull the bolt out and drop it. The bracket is deep enough to keep the bolt from falling out on its own. Just don't raise the bolt.
11. Once you've started the threads with your left hand, switch to your right hand, thumb down, and continue turning the bolt head to tighten it. When you can no longer move it with your fingers, use the ratchet box end of the wrench to finish the tightening job.
If you're lucky, like I was, and the sensor was the problem, your Volvo will be running again.
Note: This sequence applies to a 1991 non-turbo 740 Regina model specifically, but I believe it will work for all 740 models using the bell housing mounted sensor. It may also work for other Volvo Models, and is at least worth a look.
Experienced mechanics have "eyes in their fingers," since so many automotive jobs require doing things where you can't see. I've described this job in much more detail that I would if I were describing it for an experienced mechanic. If you haven't developed those "eyes" in your fingers, this job will be a good way to do that. The other method, using a long string of extensions and universal joints, is a terrible idea, and is sure to result in dropped bolts and intense frustration. This method, while not child's play, gets the job done quickly, with a minimum of fuss.
Like many owners of older Volvo 740s, I've just been through the process of fixing a no-run problem. After replacing the fuel pump in my 1991 740 Volvo Regina non-turbo wagon and the fuel pump relay, the intermittent dying and no-start problem did not go away. Finally, it became permanent with no spark. Research here and elsewhere on the Internet narrowed the issue down to the coil module or the crankshaft position sensor, so I ordered both parts. The coil module I bought used from a running Regina system 740, and I ordered the sensor from an eBay dealer.
Replacing the coil module didn't solve the problem, so it was time to replace the sensor. On another internet site, someone had written up the process of replacing the sensor, using a string of 3/8" drive extensions and wobble-joints to access the 10mm bolt that holds the sensor into the bell housing. Very complicated and unwieldy. I've been wrenching on cars for many years, so I decided to take another look at the job before starting. Here's the process I worked out by studying the car and thinking, and it works perfectly. It took only 5 minutes to do:
1. Use a flashlight to locate the sensor and the bolt. You'll have to peer at the thing from the passenger side fender, looking over the air conditioning pipes. It's below the distributor, on the top of the bell housing. The reason for this step is so you can orient yourself to its exact location. While you're removing and replacing it, you won't be able to see what you're doing, so you'll need to visualize it in your mind.
2. Carefully put your left hand between the engine block and firewall, and locate the retaining bolt head and the wire from the sensor with your fingers. Again, this is an orientation process, because you'll be feeling your way through this job. There's only about 3" of space behind the engine block, so it's a somewhat tight fit back there.
3. The only tool you'll need is a 10mm combination wrench with a racheting box end. These are sometimes called combination gear wrenches. You can usually pick up a set of these fairly cheaply, and they have multiple uses. Or just buy the 10mm one. You flip the wrench over to choose between tightening and loosening.
4. Orient the wrench so that it will loosen the bolt, and then using your left hand, with your index finger placed over the ratcheting box, insert your hand and the wrench carefully behind the engine block and place the racheting box end over the retaining bolt head. The reason for putting your index finger over the box end is to make it easier to find that bolt head, since you won't be able to see.
5. Carefully re-orient your hand on the wrench, trying not to pop the box end off the bolt head and then loosen the retaining bolt. You'll be able to move the wrench only about 10 degrees, so keep going until the ratchet won't loosen the retaining bolt any further, then remove the wrench and your left hand.
6. Insert your right hand behind the engine block, thumb down, and use thumb and index finger to finish removing the retaining bolt. Keep one finger on the bolt at all times. You'll only be able to manage a partial turn each time. When the bolt is free, carefully remove it and take it out from the narrow space. Put it somewhere safe.
7. Using your right hand again, thumb down, reach in and wiggle the sensor to make sure it's free. Use your thumb and forefinger to twist the sensor, using the area where the retaining bolt goes for leverage. Normally, this is easy. When the sensor is moving freely, you can lift it out of the bell housing and from behind the engine block.
8. Disconnect the sensor at the connector near the driver's side firewall. Pry the spring clip loose and put it safely somewhere. It's small and easily lost. You can fish the plug through the zip tie on the firewall, but it's not all that easy. Move the other wires, etc. until you get it out. Don't bother trying to fish the new sensor's plug through there. It's a waste of time. Just zip tie the wire to the other wires after installation.
9. After plugging in and securing the new sensor, carefully route it and let it drop behind the distributor, near where it will go.
10. Insert the 10mm retaining bolt in the sensor's extension. Using your left hand, put your index finger on the top of the retaining bolt, grasp the sensor with your thumb and second finger and carefully maneuver the sensor into position, lowering the sensor into the hole in the bell housing. You may have to fiddle a bit, but if you oriented yourself well before starting, you'll find the hole easily with the part by feel. Keep your index finger on the top of the retaining bolt as it rises when the sensor enters the bell-housing. Gently turn the assembly until you feel the retaining bolt find its threaded hole. It's hard to describe, but you'll feel it. Very carefully, move your hand, and work with thumb and forefinger to start the bolt in the threads. If you don't have lots of experience, this will be the most difficult part of the job, since the quarters are so tight and since you can't rotate the bolt much. Don't rush and don't accidentally pull the bolt out and drop it. The bracket is deep enough to keep the bolt from falling out on its own. Just don't raise the bolt.
11. Once you've started the threads with your left hand, switch to your right hand, thumb down, and continue turning the bolt head to tighten it. When you can no longer move it with your fingers, use the ratchet box end of the wrench to finish the tightening job.
If you're lucky, like I was, and the sensor was the problem, your Volvo will be running again.
Note: This sequence applies to a 1991 non-turbo 740 Regina model specifically, but I believe it will work for all 740 models using the bell housing mounted sensor. It may also work for other Volvo Models, and is at least worth a look.
Experienced mechanics have "eyes in their fingers," since so many automotive jobs require doing things where you can't see. I've described this job in much more detail that I would if I were describing it for an experienced mechanic. If you haven't developed those "eyes" in your fingers, this job will be a good way to do that. The other method, using a long string of extensions and universal joints, is a terrible idea, and is sure to result in dropped bolts and intense frustration. This method, while not child's play, gets the job done quickly, with a minimum of fuss.
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