[Lucky Peter]

Hello,
I've ended my search of temperature sensors' resistance in my new service books, but unfortunately I haven't found any information about it. Maybe there are some information about testing these sensors in 'Electrical Troubleshooting' manual, that I don't have yet. Dave, maybe You could look at it, if You have this book?

Even though there wasn't any information about resistance or voltage of these sensors in my service book, there was some other interesting facts, that I'm going to tell You in a moment. When I was looking at some wiring diagrams, I found out that originally both manifold temperature sensor and coolant temperature sensor connectors were looking exactly the same. I don't know if that manifold sensor would cause some troubles, because the car was running fine with it for some time, before it started running rich, so maybe someone put the replacement sensor with a right curve? I've also found an interesting quote about a coolant temperature sensor and its functions, which are not only providing coolant temperature information to the ECM, but also many different ones:

The coolant temperature sensor is similar in function to the MAT sensor and is installed in the right front corner of the engine directly below the thermostat. This sensor provides coolant temperature information to the ECM for fuel enrichment, ignition timing, EGR operation, canister purge control, air management, EFE operation, closed loop fuel control, and modulated displacement.

It is interesting that a seemingly ordinary coolant temperature sensor is so important for the ECM, and have a contribution in so many different processes.

Scott, I'm really impressed by Your knowledge about temperature sensors and its testing. It is very interesting to learn something new everyday. I've got a specification of the coolant sensor that I've bought, so I'll attach a photo of it below. Also I've looked at the intake manifold sensor on RockAuto, and it looks like the original sensor should have indeed the same connector as the coolant one, the only difference between them is the temperature sensing element(?). I think that it would be a good move to remove the intake manifold temperature sensor and see how does it look like. Maybe I'll do it a little bit later today.

- Peter​

 

[1979 Eldorado]

I just took a look at RA and I see that, for the coolant temp sensor, only Four Seasons and Standard are showing the OE connector, and the rest are showing the Delphi connector (in some cases with a wiring harness pigtail) as a replacement. See the capture of most of the options below. Also note that GM doesn't make any parts like this. They are instead buying from a supplier and almost certainly from one of the other actual manufacturers listed on the same page. The "Genuine GM" is not the OE design; instead it has the Delphi connector.

For your car, I suspect someone bought what was likely listed as a "valid" replacement but with the Delphi connector or they bought one which looked the same and assumed it would work. Since your car was running ok let's assume it was close enough that it worked. Since the Delphi connector was your air sensor it's also very likely it has less influence on how the car runs.

The second capture is for the air temp sensors. They are obviously different but they could still be different PNs and have the same sensing element curve... We simply do not know. All we know is that yours seem to be wildly different. It would make sense that the sensing element could be the same because then Cadillac could design a single voltage divider circuit and use a copy/paste for each circuit (air and coolant). The reason the air temp sensor is open is very likely because they felt it would react faster if the sensing element was directly exposed as opposed to through conduction through the housing and through a thermal compound inside. They didn't do the same with the coolant temp sensor because the "open element" likely wouldn't survive long exposed to the coolant loop and if they didn't seal the connector well they would have a coolant leak.

There seems to be no sense in me clinching a Delphi connector for you because, what I suggested, is exactly what most of the aftermarket is already doing (for the coolant temp sensor). So the question still remaining is did the aftermarket copy the sensing element correctly? If they did this reasonably well, and assuming they should be the same curve, then is seems you have a bad sensor. On RA there are inexpensive options from good suppliers especially for the coolant sensor. For the air temp UltraPower, I believe is good, but it looks like they may use a different material housing. For the air temp sensor there are as well zero Delphi connector options. I were you I might buy a couple of different low cost options of the coolant temp sensor and I would check to see if they are consistent. I would compare them to your OE; seemingly original part. I would probably buy the Four Seasons Part and the Standard part but, that said, there's a good possibility that Four Seasons is simply buying the Standard Motors part and "re-branding it" (like GM would do).

I wish the OE connector was something we could obtain because secure contact, when measuring, is important. For the Delphi connector I simply bought an extra pigtail and I cut the lock off so I could test them as fast/securely as possible to not experience temp change from when I removed them from stabilized temp to my measurement. If they had the Delphi connector I would offer to test them for you.

Coolant temp sensors:

Air Temp sensors:

 

[Lucky Peter]

You're right, Scott - Most coolant sensors on RockAuto have a new 'Delphi' style connectors, but there aren't any connectors available for the intake manifold sensor. There is an old polish saying - "the fool is always lucky", so maybe as You've just said, someone in the past bought this sensor as a "valid" replacement, but it looks like it must have not much different curve than the OE, because the car was running pretty good with it.

Some time ago I've managed to remove this temperature sensor from the intake manifold and now I've got some information about it. First, I can see that this intake sensor's thread is the same as the coolant sensor's one, so fortunately nobody in the past modified intake manifold to fit another type of sensor. Also I can see some markings on this sensor, which are "ACR 12V 1 19" on the metal part, and "PED" on one side of the plastic part, and "81" on the other side.

If we would know if both of these sensors should have the same sensing element curve then definitely one of these sensors would be bad, because I think that there is too much difference in resistance between them. Maybe if Dave or Jay would measure these sensors' resistance in their cars it would give us some reference points? I think that I'll do some more tests tomorrow, and maybe some of You will have some new ideas and information.

- Peter​

 

[1979 Eldorado]

The style of the sensing area is similar to the air sensors listed on Rock. One interesting thing is that air sensor doesn't have the same, most common, Delphi connector. The internal shape is different. I guess that's 3/8in NPT and I don't have that size housings. If I did I could clinch the standard Delphi connector so you would be able to find the pigtail.

The photo on Rock, below, shows the most common Delphi PN under the GM number. I guess all of the rest are the same but since they are so close it's difficult to say for sure. See how it's internally different from yours?

I have another idea but I don't like it. Assuming you coolant temp connector is the same you could move the connector to the air sensor harness position so you can buy an OE style air sensor. You can then get the normal Delphi replacement and pigtail for the coolant sensor. There's one with the pigtail and reasonably priced. If it's the shape of the one pictured below here's the brand/PN I bought recently bought 3 of them.

Other than Dave or Jay testing theirs I don't know how we tell what they should read.

I just noticed something. You need to be VERY careful because that listing I posted for 1981 Seville lists both TX1 and TX3 but TX3 is a PN I just bought to test for Holley Terminator so I have a lot of data on TX3. The main point though is it's very possible NOT ALL of those PNs listed are correct on Rock. I doubt Standard TX1 and TX3 are the same; unless it's only the connector???

I'll also look to see if I tested anything close to the value you measured... You listed 12C and 4.85kOhms. The TX3 replacements I tested would be very close to that value. Maybe the coolant temp sensor is still ok?

 

[Lucky Peter]

Hello,
As You've said Scott, the sensing element on my sensor and OE style one available at RockAuto are very similar, the only big difference between them is a connector. After doing a small research I've found the exact same looking sensor on Amazon, and it turns out that it has the same connector as the one in my car too. Maybe it is even the same sensor that is mounted in my car, but if that is true, then it isn't the right one for sure. According to description, this sensor would be correct for 1985-1993 Seville, so there is a big chance that it isn't correct one for 1981 model. I think that somebody just bought this sensor with its strange connector instead of buying a better one, maybe because of the price, or the availability?

Somewhere else on the forum I found a thread that mentioned some values of these both temperature sensors. According to that, these two sensors must have the same curve, because they're supposed to have very similar resistance. In my Cadillac the difference between these two sensors was somewhere around 8kΩ, so I think that it is too big difference. I also think that there is a big chance that the original coolant sensor is working fine. The intake manifold sensor is definitely the wrong one. Also I'll attach a photo of a table that I've found with resistance of these two sensors at a different temperatures. After looking at my measured readings, I think that it may be a right one for this model (I think that I've found this in some 1984 Cadillac thread).

Regarding to Your idea, it isn't all that bad, honestly I've thought about it too. Since You've measured the TX3 sensor, and we know that its resistance is very close to the TX1 type that is originally mounted in this car, then We could replace the old type sensor with a one with 'Delphi' style connector, so We would be able to move old coolant connector to the intake manifold, and then I could buy appropriate sensor. Now there is an interesting question - Why did somebody cut the original connector and installed this strange one? Was is because the connector was falling apart... or maybe the sensor was too expensive and they choose the cheap way to fix it? Another possibility is as You've said clinching a 'Delphi' connector to the correct sensor, but it would also need changing this crappy connector, but I think that it isn't too hard to find, because they're the same as the coolant sensors ones.

There is a one more thing... Even if this sensor doesn't have a correct resistance, the car was running with it pretty decent before, so would it be able to cause this condition? I think that there is evidently problem with the ECM, because of some tested symptoms. Question is what could go wrong in the engine, and caused this kind of troubles? Recently I've read that somebody was experiencing rich running condition in his 81' Cadillac many years ago, and in his car there was a problem with the ECM. If the diagnostic system would be working, I could check values of various sensors that the ECM sees, and maybe that would help to figure something out. I've also read that once there was somebody with a strange problem - These both sensors were working correctly, but the ECM was sending wrong signals, because it "thought" that there was a way different temperature, and I think that this was caused because of some kind of failure in the ECM. I'm not sure, but maybe there is a possibility that the ECM gone bad just from age, and it cannot communicate with sensors/PROMs correctly, so it is running in hard back up mode? What are Your thoughts about that?

- Peter​

 

[1979 Eldorado]

The chart doesn't go down in temperature to show 16.68 kOhms but based on a similar curve I have it would be between -10 and -15C so there's no way that sensor is ok if it should read the same.

Yes, you could still have an ECM issue but in my opinion you need to fix what you know is wrong and then you need to evaluate the situation once again. I don't know how sophisticated the ECM is. Could it recognize the drastic inconsistency between the coolant and air sensors? I don't know. It's possible that the air temp could be -10 to -15 and the engine could still get to the actual ambient (and even warmer). So the combination wouldn't seem to be completely out of the possibility for the ECM to comprehend. But if the ECM thought the air was -10 to -15C then for sure the ECM would try to add more fuel. The feedback would then try to tell the ECM the car is running too rich. Could the ECM be smart enough to recognize that much of a discrepancy and then cause it to go into a default mode; again I don't know.

If you have time to go step-by-step I would deal with the air temp sensor first. If you think the ECM might be impossible to find in the future you could buy it. I have a spare ECU for my car because they go bad. There's an expert who can fix most items on mine but, if the car was down and wouldn't run, I would need something while mine was being fixed. If I were to go on a road trip I might even carry the spare. So my point is it doesn't hurt to have a back-up even if your ECM isn't the issue this time.

As to why your car has the part it has, maybe they just couldn't find the right part, or maybe that part had the correct curve and it has since failed. Just because we don't see one listed now, with the same configuration, it doesn't mean that there has never been a replacement which has a Delphi connector on it. I don't know the history of that version of Delphi connector. It's not the common one today so maybe the sensor with that connection was discontinued at some point but it was an common connection when it was offered.

 

[Lucky Peter]

Scott, You're absolutely right, of course first thing that I'm gonna do is replace the intake temperature sensor and its connector. I think that what I'm going to do is buy an OE-style intake manifold temperature sensor, and a new 'Delphi' style coolant temperature sensor with a new connector included, and then as I've said before, I'll replace the old intake manifold connector, with a correct one from the coolant sensor, so it will be as original.

I don't know how advanced is the ECM, but definitely there wasn't logic correlation between these two temperature sensors, so maybe it could trigger this back up mode, but would it ran that bad also with this sensor's connector unplugged? It would be excellent if all of these problems would be caused by a bad temperature sensor, but I think that the ECM will be bad too, because of some strange things as deactivating cylinders before even starting the car, so maybe by coincidence both sensor and the ECM has failed at the same time? It is really confusing, but with each new idea, We're making a big step towards solving the problem. I'll see what happens when both temperature sensors will be replaced along with its connectors, then I'll be thinking about getting a new ECM if necessary. I'll keep You informed. For me, that's it for today. Have a nice Sunday.

- Peter​

 

[1979 Eldorado]

If a sensor is unplugged it will be an open circuit, infinite resistance, and since the sensors are NTC type it means the ECM would likely give the maximum enrichment it could. I'm sure there is a limit, but it would seem it would go to the cold limit.... Anyway step by step and let's see. It would be great if it was only a sensor but sometimes multiple things need to fail before we notice there's a problem.

 

[Lucky Peter]

Hi,
Today I've managed to order a new coolant temperature sensor with a new connector, along with a intake manifold temperature sensor. Estimated delivery date is June 9th. Now there is nothing left to do, but wait patiently.

Since I had some free time today, I decided to try cleaning the wires under the hood that was unintentionally painted black with the engine when it was painted by somebody in the past. I'm really amazed by the effect, but unfortunately I haven't took a photos of the worst wires, but trust me that they turned out as fantastic as these ones at the attached photos:

Also I've removed some leftovers of a remote start that somebody in the past installed in this car. Now I'm just trying to figure out - where these vacuum lines were supposed to be? There was only a one sensor(?) left from the remote start with a short vacuum line that was connected to the other vacuum lines. I believe that somebody put a "T-joint" (I don't know what to call it) and plugged it in the existing vacuum line. By any chance, do anyone know what these vacuum lines are for? If I don't messed up anything, there are two lines going from the engine (1), somewhere under distributor (2), one of them goes up to this "T-joint" connector (3), then to the intake manifold (4) and to the old sensor (6), a second one is connected to a metal line that goes somewhere down at the end of the engine (passenger side) (5). Now I think that somebody just put a "T-joint" connector in existing vacuum line, and I just need to remove it and replace these vacuum lines. By the way, the vacuum line that was connected to this old sensor (6) was broken, so I think that there was definitely some leak. The longer I look at this car, the more new problems I find, but it isn't a bad thing, at least there's something to do. If anybody have some knowledge of how it is supposed to look, tell me If I have a right idea.

- Peter​

 

[1979 Eldorado]

Nr 1 looks like the type of connection normally going to an air cleaner. That line running near the valve cover, nr 5, looks like the type of line they normally use for the vacuum canister and/or the main vacuum going into the car for HVAC vacuum controlled items. If it is that same type of tubing it gets EXTREMELY brittle and often a portion is missing.

The one light colored "T" is open in the photo. The bottom line is vacuum leaks can cause any car to run differently. Vacuum leaks can also make your MAP sensor think that you are accelerating (so it would tell the ECM more fuel is needed). Now we potentially have two items telling the ECM the engine should have more fuel; one bad sensor and the vacuum leak(s).

Nice job on the clean-up

 

[81 BENY Biarritz]

Hi Peter, I just went out to see if I could get some pictures of one of mine and I couldn't really get anything that would be of use to you as it is so tight to get the phone in a good position. Yes you are correct that the outboard line from the vacuum switch(?) should be connected directly to the intake manifold (remove the Tee connector). Also from the emissions labels on both my car with the first generation ECM and one of the others from the second generation they show the second line connecting to the metal tube that runs to the back of the engine for the EFE valve. I have attached both Emissions labels from my Fleetwood and my Eldorado that should be located on the top of your radiator fan shroud. Not sure if they are actually different but they have different Part #s for some reason.

 

[Lucky Peter]

Scott, You're right that this "T-connector" is open - it is because I've unplugged some kind of sensor from remote start, but even with it installed, there still was a massive vacuum leak, because of the vacuum line severe damage.

Thank You Dave for providing me these photos and some information. Now I'm sure that I need to remove this "T-connector" and replace these vacuum lines, along with inspecting the others, which may need to be changed too. By the way, I've got this emission label on my Seville too (not in as good condition as Yours), but since I've covered the front of the car while working on it, I forget about it's existence.

Definitely these vacuum lines will be fixed before the new temperature sensors will arrive. I must admit, that this progress that We're making together really satisfies me. By the way, yesterday was exactly 2 years from the day that I've bought this Cadillac. It amazes me how far the progress is going with You guys... I'm really thankful for all of Your help that You're giving me. I'll attach a photo of my Seville from the day that I've bought it, because You don't even know how this car looks. Maybe from the outside it doesn't look the best, but underneath it is so solid, and since this is a Canadian-Spec (Dave, are Your Cadillacs Canadian versions too? Maybe You know some facts or some changes for the Canadian versions? This might be an interesting topic for the future, isn't it?), I am really amazed how this car is holding up after all these years. When I've decided to buy this Cadillac, I rented a trailer and drove over 430 kilometers (267 miles) in one side, just to see this car, and if it would turn out to be rusted out, I would go back home with an empty trailer. The "towing machine" was my father's '14 GL350 Bluetec, and it was a pleasure hauling it home, because everyone on the road was looking and smiling, so it is definitely great memory, worth sharing with You. Maybe I went a little bit off-topic, but I think that's worth it, because You all now have a great contribution in making this car running again.

- Peter​

 

[81 BENY Biarritz]

Peter, our cars are twins! I am assuming yours is an Elegant model also by the nameplate on the C-pillar. Have you found the build sheet for yours by any chance yet? Have a look behind the right side inside trunk liner panel to see if it might be taped on there. It will tell you which dealer your car was sold to and all the options on it.
My picture is from Feb 2022 when it first came home from a cross Canada trip as it was a west coast car. I still have had enough time just yet to work on mine to get it licensed for the road. It is also in very good condition underneath and doesn't have too many miles on it either.

 

[levcole59]

Hi Peter, I have three 81's with the V864 engine and have gathered lots of info on them to help me in future if they have any issues. I have read a number of posts over the past few years that have the same issue with only displaying "..". I have also read somewhere in the past that it is a serial communication issue with the ECM. I have attached a scan of two pages from the "1981 Cadillac Digital Fuel Injection and Computer Command Control Diagnosis Manual Supplement" that you may not have. Hopefully it will be of some help. I also have all the Electrical Drawings so if you do not have them I can scan appropriate pages for further information. I also know of another 81 Seville owner who happens to be in Polland and can contact him to see if he might of any help to you. As for the PROMs my suspicion is that your issue will be with the ECM and not the PROMs. I have never had to change ECM's in any of my cars but do have some original spares that I can open up, as Scott suggested you do to yours, to compare for burnt components. I will watch for your reply and hopefully we might be able to get your car running decently again. Dave

81 BENY Biarritz this is not about this post I couldn't find a different way to message u so I'd like to get info on my 864 I have a coupe deville it ran okay then had a major problem I'm hoping u can help point me in the right direction on how I should go about fixing it thank u for your time my email is Levcole59@yahoo.com if we can connect and see from there how we can discuss this problem thank u for your time

 

[Lucky Peter]

Dave, Your Seville looks fantastic! Unfortunately mine isn't Elegante version (I wish it was). I think that somebody in the past wanted Elegante version so much, that he made one himself... kind of... If You look closer, the nameplate on the C-pillar (obviously this was not visible in the photos) in fact says "d'Elegance", which is wrong for this model. The two-tone paintjob that I really like isn't factory too, because this Seville was originally painted in a Bordeaux Red Irid (paint no. 76). That's the main reason why I need a complete paintjob. If I see correctly, Your Seville's lower paint is maybe the same as mine? I've looked for a build sheet in the trunk, as You've said, but unfortunately it wasn't there. I've also read some time ago that a build sheet could be taped on a headliner, but since the headliner in my car was messed up so badly, it of course wasn't there too. In future I'll be looking for either only a headliner board, or an used headliner to make a correct one for my car. Someone instead of fixing the old headliner the right way, just cut the rectangular pieces of foam and glued old headliner material on it... I've also read somewhere that a build sheet can be obtained by contacting General Motors and buying it from them - Do You by any chance know if this is possible? I'm really curious if all the equipment is factory or not. I do really like the burgundy cloth interior of my Seville, because it is so soft and nice to touch, also there's a reclining passenger seat, which I believe was an option along with 'Symphonic Sound System' and wire wheel covers which it has. It would be interesting to know some more information about this car. I don't know very much of its history, but I know for sure that it has a clean title, and it has been in many places in its life. My Seville started its life in Ontario, then it moved to British Columbia in 1994, and then to Alberta in 2012, and finally before I've bought it, it returned to Ontario in 2022. It is also interesting that CARFAX says, that there was only one owner change reported in 2022, but I think that maybe because it is such an old car the report doesn't have much information. Dave, maybe You could attach a photo of Your Seville's interior, because I'm curious how nice it looks like, the Elegante model in my opinion is really gorgeous.

Now there's time for something more on-topic. I've managed to check all the vacuum lines around the one that I need to replace, and they're looking fine, so I don't see any problems. Today I've came up with an idea about 'hard back-up' mode engaging just after turning the key. Maybe there is a possibility that something in the engine bay is making some kind of short that is causing ECM to enter this mode instantly? Maybe it isn't a thing, but I thought that it could be worth checking. I thought that unplugging some of the connectors could eliminate this short, so theoretically the car should not enter 'hard back-up' mode right away after turning the key, but maybe without signal coming from these devices it will also enter this mode? I'll check it a little later, because it's very simple to do, but I think that it won't change anything.

- Peter​

 

[1979 Eldorado]

Regarding the headliner: I haven't done one in the Seville. The Eldorados had "hard urethane" (but VERY brittle) backing. Some cars used pressed cardboard which was a much more robust material. You need to remove the trim/headliner and then carefully but thoroughly all of the deteriorated foam. A stiff bristle brush works the best. Then you get foam backed cloth made for headliners and you use professional spray adhesive on the hard shell or cardboard... but at that point follow the instructions because a local interior place applied my fabric and I only did all the rest of the work. He could sell me the material, applied to my prepared shell, for less than I could buy the material and do it myslef because I was only doing one car at a time. I have done several though all together.

Edit: You may have a build sheet on top of your gas tank. I did.

 

[81 BENY Biarritz]

Hi Peter, I was looking through the black book to find out what defines a "hard back mode". I can't find this as a defined condition however I did see a page that defines when the ECM will stay in fail soft mode. Have a look at pages A137-139 (if you haven't found it already). Maybe this will be helpful if you want to disconnect various inputs to the ECM.
Thanks for the pictures of your interior, I actually like the red velour better than the leather interior in mine. Yours looks to be in very good condition too! I will send you some other pictures by direct messaging later so that it doesn't clutter up this topic.

 

[Lucky Peter]

Scott, the main problem with headliner in my car is that it doesn't really exist. There was only multiple pieces of white foam glued straight on the roof, and then original material was glued on top. That's why I need to buy a new/used headliner, because I don't have a board/base of it. I don't know what do You mean by top of a gas tank, do You mean under the carpet in trunk above fuel tank? I have all trunk carpeting disassembled for now, and unfortunately I haven't found out a build sheet anywhere.

Dave, I haven't found any information about a "hard back-up mode" too, besides the one on the internet, which I believe was taken from a certain service bulletin. You're right that these pages might be helpful, my plan is to use them while I'll be doing some tests, probably tomorrow.

- Peter​

 

[1979 Eldorado]

Headliner: It's difficult without even a template but I would probably attempt to find some of the dense pressed cardboard. I know what it looks like but I don't know if I even have the proper term in English. That's what my 1983 Olds Delta88 has and it's a lot better solution that urethane.If you can find some I would take as accurate measurements as you can and then try to cut something from a large sheet. You can then test fit it. Once you have something which fits get the fabric to adhere to it.

Build sheet: No, not in the trunk. Mine was literally taped to the top of the gas tank itself. Mine was a central Texas car where it's generally warm and pretty dry. My tank was basically like new when I had to drop it to replace the soft fuel hose... and if you replace that hose be aware that there is a specific standard for submersible fuel hose; normal FI and normal fuel hose is not sufficient.

 

[JayArr]

My build sheet was above the headliner.

Speaking of which, I had an 83 with a Skytop moonroof, likely a dealer installed aftermarket item. They took out all the original headliner and put in a new one that wasn't glued to anything, It was secured around the perimeter of the roof by the trim and then around the perimeter of the sunroof with that trim and then there were two strips of cardboard sewn into it that clipped into brackets that ran lengthwise along the roof between the sunroof and back window. The cardboard strips were only about 6 or 8 inches long but everything stayed up OK and it looked great.

So... if you have a sunroof with a little ingenuity you can install a headliner without the need of any urethane or cardboard form.