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Lowering frame to change rear HO2S, pull on front head bolts?


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I am about to have a shop lower the frame to change the rear oxygen sensor on my '97 DeVille, and I have two questions:

1) Is there any other way of doing it? Both my mechanic and I were unable to fit the removal tool on the sensor, but has someone done that? How, and with what tool?

2) When lowering the rear of the frame, the instructions in the FSM says to remove for frame bolts (#2 and #3 positions, but I cannot find any diagrams for those references) and lower the frame no more than 3 inches. Then the HO2S sensor can be replaced. If that procedure is followed, what about pull on the front head by the torque struts (dogbones)? And what about push the exhaust pushing on the rear head? If I am overly worried and it is not a problem, I would really appreciate some assurance and explanation -- I really prefer not to do anything that could put any stress on the head bolts.

/Jonas

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Are you talking about the rear one on the back of the engine by the fire wall?I just changed that one and I went from up top ,I rented the tool from advance auto parts.I saw the same thing in the fsm about lowering the cradle but im not sure why cause I did it from up top in 30 minutes.you'll need a few extensions if you do it from up top.just like the crankshaft sensors they say to remove all this stuff in the fsm but there is a way to change the ckp sensors within an hour if you have skinny arms.

sts03

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I changed the rear O2S in my '96 Seville and did it from the top side. I saw the notice in the shop manual about lowering the subframe and decided to try it from the top. Not too bad of a job - less work than lowering the subframe.

Kevin
'93 Fleetwood Brougham
'05 Deville
'04 Deville
2013 Silverado Z71

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I changed mine from the top also, even if you need to use a universal joint, box wrench, etc, I would never drop the carriage unless I had no other option. I would remove the coil/ICM, etc to get at it

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on my 97 Seville the cradle had to be dropped to replace the original sensor. the original sensor body is too long and thick to get but the new sensor is short and skinny. Mine was not doable even with the GM socket. they say some can and some cannot be replaced without cradle being dropped. now the replacement was defective and I was able to replace it myself by using a special o2 sensor socket. (very slender) and a long wobble extension. It was not bad at all to do. Have you seen the pictures I have posted?

GM FAN FOREVER

Nice, clean, luxury= fine automobile

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When we looked at it from the top, there was a pipe (about 1/2") bolted to the engine above the HO2S, which partially blocked the place for the tool. That was the main problem when trying from the top.

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Those pipes are the heater pipes, if that is all that is blocking you, find the heater pipe retainers remove the bolts and move the pipes aside. They are connected on each end to hoses and once the retainers are removed they are no longer ridgid and can be moved easily. I do recall needing to get by the heater pipes. That sounds different than the situation rock is describing above which is shocking that the designers would permit to exist. It is prudent to change an O2 sensor every few years regardless of whether it throws a code and having to drop the carriage each time is mind blowing.

http://www.gm-trucks...howtopic=147890

Oxygen Sensors Don't Last Forever

Here's What Happens As They Age

As an oxygen sensor ages, contaminants from normal combustion and oil ash accumulate on the sensing element. This reduces the sensor's ability to respond quickly to changes in the air/fuel mixture. The sensor slows down and becomes "sluggish".

At the same time, the sensor's output voltage may not be as high as it once was, giving the false impression that the air/fuel mixture is leaner than it actually is. The result can be a richer-than-normal air/fuel mixture under various operating conditions that causes fuel consumption and emissions to rise.

The problem may not be noticed right away because the change in performance occurs gradually. But, over time, the situation will get worse, ultimately requiring the sensor to be replaced to restore peak engine performance.

There is a change recommendation in this article along with the reference credit to the above paragraph

http://www.autohausa...en_sensors.html

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Thanks for that info about the heater pipes, bbf (and thanks to all others also). I will have a look at that.

To go back to one of the original questions: even if it turns out to be possible for me to change the rear HO2S without lowering the subframe, would you be worried at all about lowering the frame with the torque struts connected (and exhaust manifolds)? The service manual does not say anything about disconnecting anything other than the four frame nuts. I still do not feel quite comfortable lowering the frame with dogbones and exhaust connected to the heads, but is there really any reason to be worried about that?

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I dont think I would be worried about the torque struts, but I would probably remove them anyway, its only a couple of bolts.

I would disconnect the steering box connection to the steering wheel, its one bolt, but make sure you tie off the steering wheel so it does not rotate. Mark the connection also and be sure to properly torque that bolt, as the steering gear may be moved and disturbed

I dont think the exhaust would concern me either, although when I tilted me carriage when I did my ISS sensor, I broke the exhaust connection in front of the cat and used a ratcheting come-along to pull the exhaust system back out of the way.

That said, I hope you can get at the sensor without all of this work, if its straight below the heater pipes and you can get an extension straight down on it, you should be good. An 18 inch breaker bar is your friend

Pre-1995 - DTC codes OBD1  >>

1996 and newer - DTC codes OBD2 >> https://www.obd-codes.com/trouble_codes/gm/obd_codes.htm

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Don't worry about the torque struts, steering column shaft, etc. If you have to lower the subframe, you only need to lower it an inch or two using the subframe mounting bolts. It is not as if you're lowering it a foot or more. Remember to properly support the subframe in case you turn out the bolts too far.

Kevin
'93 Fleetwood Brougham
'05 Deville
'04 Deville
2013 Silverado Z71

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Don't worry about the torque struts, steering column shaft, etc. If you have to lower the subframe, you only need to lower it an inch or two using the subframe mounting bolts. It is not as if you're lowering it a foot or more. Remember to properly support the subframe in case you turn out the bolts too far.

can you tell that my nick name is Mister Safety? :lol:

Pre-1995 - DTC codes OBD1  >>

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I wouldnt worry about damaging anything as long as a jack is kept under to support the subframe. I refuse to change any on my Deville until the light comes on lol. No problems yet.

GM FAN FOREVER

Nice, clean, luxury= fine automobile

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Don't worry about the torque struts, steering column shaft, etc. If you have to lower the subframe, you only need to lower it an inch or two using the subframe mounting bolts. It is not as if you're lowering it a foot or more. Remember to properly support the subframe in case you turn out the bolts too far.

can you tell that my nick name is Mister Safety? :lol:

:lol:

Kevin
'93 Fleetwood Brougham
'05 Deville
'04 Deville
2013 Silverado Z71

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Those pipes are the heater pipes, if that is all that is blocking you, find the heater pipe retainers remove the bolts and move the pipes aside. They are connected on each end to hoses and once the retainers are removed they are no longer ridgid and can be moved easily. I do recall needing to get by the heater pipes. That sounds different than the situation rock is describing above which is shocking that the designers would permit to exist. It is prudent to change an O2 sensor every few years regardless of whether it throws a code and having to drop the carriage each time is mind blowing.

I admire anyone who has managed to loose the heater-pipe retainers... I just had a look and tried to get at it, and it is very tight to get anything in there. The problem is that what makes it so tight is the heater pipes, which I obviously cannot move until I loosen the retainers that I cannot get to. Catch 22... Each retainer (there are two as far as I can see) consists of two pieces of sheet metal, and each such piece forms a very flat U, or something like this:

*| | ....This screw screws into the second piece of sheet metal

.| |

/ . \

| O | ...Engine here

| O | ...Front of car -->

\ . /

.\ \

..\ \

..*\ \ ..This screw screws into the engine block

* = screw.

O = heater pipe.

(The dots don't mean anything - they are only there to get correct spacing, because it is not possible to use several spaces or initial spaces on the forum - this is also the reason the post is edited)

The top one screws right into the right sheet-metal part above. The bottom one screws into the engine block, and the head of that screw points back/down. To make things worse, one of them sits a little to the left of the HO2S, right under the blower motor. I cannot see how I would be able to get to the lower screw, but it is possible to turn the top one (although it is not easy, due to the location). I will have a second go later. I plan to turn bend the two metal parts apart at the top after removing the screw.

I got slightly discouraged earlier, when on top of temperatures in the mid 20s, it also started to snow quite a bit. Oh well, at least I managed to change my air cleaner :). Even when (staying positive, saying "when", not "if") I can move the heater pipes, the blower motor will still be partly over the sensor, so I will have to use an angled extension.

If anyone has any tips for how to make this easier, they are always appreciated. BBF, do you by any chance recall how you moved the heater pipes when you did yours?

Jonas

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I can't see how this could be very different from 96 to 97, I don't recall this job being very difficult, I think I detached the heater pipe retainer on the passenger side of the engine, maybe the HVAC housing is different on the 97 but I dont recall the fan getting in the way. WOW what a pain in the behind this is. Im sorry I cant help more. Working in 20 degree weather does not make it easy

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On mine, it would definitely be the retainer on the drivers side that would have to come loose, because it is very close to the oxygen sensor, and holds the top heater pipe out over the sensor. The passenger side one would have been easier, since it is much easier to reach, although even there, I would have to unscrew the bolt from underneath to remove it properly (as opposed to loosening the top part and bending a bit, as I am planning on doing on the driver's side). Weather permitting, I may be able to make some pics of it tomorrow. Wow, this is annoying right now -- it is so frustrating to be able to see the sensor so clearly, but yet be unable to get it out. Oh well, one way or another it is going to work to work.

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Keep in mind that there are three hoses on the passenger side of the engine that permit more movement of the pipes, you only need a little movement. It will be interesting to see the photos, hang in there

Pre-1995 - DTC codes OBD1  >>

1996 and newer - DTC codes OBD2 >> https://www.obd-codes.com/trouble_codes/gm/obd_codes.htm

How to check for codes Caddyinfo How To Technical Archive >> http://www.caddyinfo.com/wordpress/cadillac-how-to-faq/

Cadillac History & Specifications Year by Year  http://www.motorera.com/cadillac/index.htm

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I recall using a crowsfoot wrench when I did mine a couple of years ago and did not have to mess with the heater pipes. That was on a '96 Seville which would be tighter than a Deville.

Kevin
'93 Fleetwood Brougham
'05 Deville
'04 Deville
2013 Silverado Z71

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The Devilles I am sure have more room, and as I said, I dont recall having much trouble, I cant remember 100% whether I had to remove the heater pipe retainer, I do know I removed the retainer when I replaced my heater pipes.

Craftsman sells an offset box wrench, I would see if I could get something like that in there and muscle it out laying across the engine

Pre-1995 - DTC codes OBD1  >>

1996 and newer - DTC codes OBD2 >> https://www.obd-codes.com/trouble_codes/gm/obd_codes.htm

How to check for codes Caddyinfo How To Technical Archive >> http://www.caddyinfo.com/wordpress/cadillac-how-to-faq/

Cadillac History & Specifications Year by Year  http://www.motorera.com/cadillac/index.htm

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I made another unsuccessful attempt at the rear oxygen sensor today. I started in sunshine and 20 degrees with a hot engine to warm my hands, not to bad. Three hours later, it was dark and an icy 10 degrees. At the moment it is about 0 degrees, and it is supposed to stay cold tomorrow. I think that mine requires more movement, maybe because my tool is differently shaped compared to the one you used. Just a little bit bigger would be enough to make it much harder. After loosening both retainers, and trying to move the upper heater hose (that one was the one in the way, since it was sticking out more than the lower one) both towards the engine and upwards, it was still not even close that the tool would be able to come onto the sensor. The only possibility I can see now is to grind away some of the tool (the opening on the side of the tool is just a tad to tight for the oxygen sensor to go in sideways, like it is supposed to), and maybe it could work then. I might have to take away a little bit at the bottom and top as well, to get the tool to protrude less towards the heater pipes. I have some pics of the oxygen sensor coming, but it is late here now, so I will upload tomorrow.

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I recall using a crowsfoot wrench when I did mine a couple of years ago and did not have to mess with the heater pipes. That was on a '96 Seville which would be tighter than a Deville.

That is a good idea. I will see if I can find and buy one of those.

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Gm has a rounded version of the o2 sensor tool. it is supposed to be easier but it did not work on mine. Is your sensor the original large one or has it been changed already?

Also the clearance on the Deville and Seville is identical under the hood. it looks identical on all 3 models, eldo, deville, andd Seville. I have all 3 and they all are the same that I can see

GM FAN FOREVER

Nice, clean, luxury= fine automobile

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Success!

Thank you all for tips and support!

The crow's foot wrench did the trick. Thank you Kevin for enlightening me about that tool, which I did not know existed. It was about 4 degrees today, but the work was quick, so the engine was warm enough to keep my hands warm. I used a 22 mm crow's foot with extensions and a breaker bar. First, I could not get it to move (although I had ran the engine to heat the manifold), but after running the engine for the second time to heat up the manifold some more, it actually came loose without too much force. Even with the crow's foot, I still had to use a flexing joint between the crow's foot and the extension. I used some duct tape to prevent the parts from disengaging, since I had to move them 6 times for every one turn of the oxygen sensor (the old, fat one). When threading the new (thinner) one in place, I could go 1/3 or ever 1/2 turn before having to move the crow's foot.

I checked the codes immediately after installing the sensor, and was surprised to see P0135 CURRENT. That is the code I used to have with the old sensor, and sets if the oxygen sensor is too slow too start working after a cold start. I cleared it, and it has not reappeared after a few restarts with the car sitting for 30-40 minutes in between. Later, after 20 minutes of driving, the SES light came on, and code P0138 was CURRENT. I pulled of the road, and P0138 was then HISTORY. I cleared it, and drove for maybe 40 minutes, and the code did not come back. P0138 indicates that the sensor is giving a rich signal. Maybe it was just that the PCM had not adjusted its long-term fuel trim values yet, and it was therefore still running a little rich (assuming that the old sensor caused the engine to run rich). What do you think?

Some pictures from yesterday (with the old sensor in place):

The links go to versions with higher resolution.

(Let me know if there are any problems with the pictures, or try using the links to the high-res versions.)

IMGP0716.JPG

https://lh4.googleus...00/IMGP0716.JPG

This is what it looked like a week ago after the snow storm. The hood was in place the whole time, and it must have blown in through the grille or from below. I wiped some of it off, and then drove the car until it was all evaporated and the engine was dry. It did not seem to cause any problems.

IMGP0728.JPG

https://lh5.googleus...00/IMGP0728.JPG

The old oxygen sensor from the front manifold (top) and the new one that has now finally gone into the rear manifold.

IMGP0742.JPG

https://lh4.googleus...00/IMGP0742.JPG

Close-up of the location of the rear oxygen sensor.

IMGP0743.JPG

https://lh4.googleus...00/IMGP0743.JPG

The rear oxygen sensor again, but with some perspective.

IMGP0748.JPG

https://lh6.googleusercontent.com/-i_nFiBN6gWY/UMTuQXjcGHI/AAAAAAAAAOw/spANbM2MTXs/s1600/IMGP0748.JPG

The tool that I used (breaker bar, extensions, joint and crow's foot). The black duct tape held things together when moving the tool around, and also made the joint a bit more rigid, thus making it easier to position it on the oxygen sensor.

Edit: the last picture of the tool was added.

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