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Easy Replacement of Crankshaft Position Sensor - 740

CATransplant

New member
Joined
Sep 4, 2012
Location
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.
 
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Thanks, that was actually very easy. I just did this job and you were right, it only takes about ten minutes and I didn't drop anything.
 
Its a little tighter on a 240 because of reduced firewall clearance. I usually use a 1/4" drive ratchet with a long extention and a swivel to reach them.
 
Niiice!

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.



That right there is some of the best mechanic-porn I've ever read. My hat is off to you!

I've had a bad CPS on at least one of the Volvos and I think I need to do this job on the 740. Thank you so much for the detailed instructions!
If I recall, that's a relatively cheap part I hope.

Thanks!!
 
Another quickie idea/solution related

After reading CATransplant's post, I decided to go out and have a look at my CPS wire and connection.

The wire itself seems OK. I re-routed it a bit around some other wires and also I put some di-electric grease on the connections. I then plugged in and unplugged the CPS connector several times.

BTW, the connectors for the CPS, (just below the windshield on my '92 740) looked somewhat corroded.

Maybe a good first step for troubleshooting intermittent no start condition in a Volvo 740.

Jiggle that CPS wire and unplug/re-plug it several times.

/only 125,000 miles on my '92
//going for a million miles!
 
I will post further details on how my experience with jiggling/greasing the connections for the Crank Position Sensor advance.
 
I'm too old and crippled to do all of that reaching... .trying to use a ratchet wrench to remove that bolt...I wouldn't be able to straighten up without assistance....it's hell to get old.

I've always used a 12" long...1/4" "wobble" extension and a 1/4", 10mm 6 point socket.

You're correct about trying to connect enough extensions together and using a regular "universal" on a 10mm socket. That way is ponderous and hard to manuver.

I realize a lot of people don't have a large tool collection, but owning a few wobble extensions are worth the money.
Buy short ones and then connect them to your longer extensions as needed for length.
I never use regular "universals" anymore.

ps...Dont get me wrong...I do love the ratchet wrenches.

hope this helps
steve
 
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240 Volvo...CPS...hidden away in a narrow passage between the block
and firewall....(see post # * 3 *)
1/4" drive extension about 14" long and a six point "universal socket" driven by
a "flex head ratchet".....the secret??
a dab of 3M weatherstrip CAULK in the socket and a bit of HEATSHRINK tube over
the "joint" in the socket...keeps all the fiddly bits in situ...
mee also too olde and cripped up to do the "gymnastics route" anymore...the geardrive
ratcheting wrenches are a TREAT ( I have both the metric and "SAE" sets...LOVE'EM!)
 
total time to compose post = 3 minutes....* 8 * minutes to load...
auto double post....another five to get to the edit page....:wtf:
 
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New tools!!

I'm too old and crippled to do all of that reaching... .trying to use a ratchet wrench to remove that bolt...I wouldn't be able to straighten up without assistance....it's hell to get old.

I've always used a 12" long...1/4" "wobble" extension and a 1/4", 10mm 6 point socket.

You're correct about trying to connect enough extensions together and using a regular "universal" on a 10mm socket. That way is ponderous and hard to manuver.

I realize a lot of people don't have a large tool collection, but owning a few wobble extensions are worth the money.
Buy short ones and then connect them to your longer extensions as needed for length.
I never use regular "universals" anymore.

ps...Dont get me wrong...I do love the ratchet wrenches.

hope this helps
steve


Thanks Steve! I've been using ratchet sets (not as a pro mechanic) for 30+ years and have NEVER seen a wobble extension. I will be adding some to my kit.

:)
 
Well, after jiggling/re-routing the Crank Position Sensor wire and putting some di-electric grease on the connections. I then plugged in and unplugged the CPS connector several times.

The car starts EVERY time now.

Woot!

Now, time to work on the 240.
 
I'm having the same problem with my 1990 240 DL Wagon...

I *finally* thought to get a 14" extension and a universal joint head with a 10mm socket, and got the bolt out with almost no problem....

**HOWEVER**...the sensor is the original one....it's in there like it's been welded there. just a little bit of wiggle...and my hands are too big to get a decent grip.

Any ideas on how to get this bad boy *out* so I can put the new one *in*? With a flashlight aimed at it from the drivers side, I can *see* the sensor relatively well, I just can't *move* it to remove it.
 
I'm having the same problem with my 1990 240 DL Wagon...

I *finally* thought to get a 14" extension and a universal joint head with a 10mm socket, and got the bolt out with almost no problem....

**HOWEVER**...the sensor is the original one....it's in there like it's been welded there. just a little bit of wiggle...and my hands are too big to get a decent grip.

Any ideas on how to get this bad boy *out* so I can put the new one *in*? With a flashlight aimed at it from the drivers side, I can *see* the sensor relatively well, I just can't *move* it to remove it.

This is a problem. And I can't tell you how to solve it, but just warn you against forcing things. The reason it is a problem is the water that caused the sensor to fail got inside the sensor through the broken sheathing on the cable. It followed the silicone rubber insulated wiring into the reluctor itself causing the magnet to rust and expand, locking the plastic housing to the aluminum bracket.

That bracket not real sturdy. Just sturdy enough to hold the sensor in a stable position exactly 0.030" above the tone ring in normal conditions. If you bend or break it you will be dropping the tranny to replace it.

Some have conquered this with as simple a technique as a drywall screw. It is the easy-out approach, I guess. I have not needed to do this. Just passing on what I've read. The main thing is you don't want to break that bracket, but you need to know the sensor has swelled into the bracket, so it isn't just a matter of old grease.

The 740/940 gives you lots of room to work. The pre-GM ac 240 (89 and 90) are reachable with no problem, but the 91-93 240s are tight because you need two elbows in your left arm or you lay on the motor. (use a board) No point in a ratchet (gear wrench) with an M10 bolt. Once you turn it 90 degrees, it is less than finger tight and won't offer enough resistance to any pawls even snap-on's. My favorite tool for this bolt is a shorty combination wrench. No ratchets. No sockets. No wobble extensions.
 
Nice write up - I used a hybrid of the extension plus "finger-feel" to swap out my 945 Regina CPS. No start issues, just a stumble at 1500 rpm moving from a dead stop (I posted longer about it already). It seemed to make things run smoother for at least a little while.
 
No need for it, that way hack mechanics/owners won't mess with it and screw something up.....

I plan on "upgrading" a B23F with a CPS...so, it means I'd better install that flexplate, place a feeler gauge between flex and CPS, and hope I can nail it with a magnetic drill; otherwise, I will be running a LH 2.0, instead of a Bendix Regina ignition system in 1993 944.

When I remove the B230F, I'll see the mounting details better.
 
M10 bolt.

Happen to have the length for the bolt as well? Or something that is near ballpark - Attempted to do mine today and I dropped it, no big deal --- As I see it, another guy walking through the shop to get something kicked the bolt into oblivion...
 
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