When you click on links to various merchants on this site and make a purchase, this can result in this site earning a commission. Affiliate programs and affiliations include, but are not limited to, the eBay Partner Network.
I came across this dangling off the wiring harness and not connected to anything toward the rear of the engine on the passenger side on my just-acquired '78 Toro. It looks a like a coolant temperature sensor or something like that, but there already is one of those at the front of the engine where you'd expect it to be. Plus, this is made of plastic. The business end of it has definitely seen better days.
I might be able to figure out what it is by poring over the manuals, but I thought I'd ask here first to see if anyone could recognize it right away. Thanks in advance!
Might be a cylinder head temp sender. They get threaded into a blind hole on the head(Doesn't contact the coolant) I know Cadillac used them back then. It's possible Olds did also.
The connector and location are consistent with the freon pressure switch in the A/C, however that doesn't look like the factory freon switch. What colors are the wires? Wipe them off with lacquer thinner to get the real colors.
I was thinking it might be part of the A/C system as that's what's in the same area. But you would think there would be gaping, 1-inch threaded hole somewhere in the vicinity of this thing, or at least withing reach of the length of the wire it's on, but I don't see anything.
I did find that, if you squeeze on the knurled part of the black plastic cap, the sensor comes right off, leaving another cruddy little piece inside. I've attached photos.
There is only one wire to this, and it sheathed in black plastic. Right where the wire enters the thing, the sheathing is pulled back a bit, and the wire is white.
There are two "numbers" (one has a letter) on the part I removed. There is a 6322 just below what I'm calling the top (opposite the threaded end), and there is a 7H17 just below it on one of the six facets you would turn a wrench on. The threaded piece is 1.75 inches in length.
I did find that, if you squeeze on the knurled part of the black plastic cap, the sensor comes right off, leaving another cruddy little piece inside. I've attached photos.
There is only one wire to this, and it sheathed in black plastic. Right where the wire enters the thing, the sheathing is pulled back a bit, and the wire is white.
Now I'm confused. The freon pressure sensor has two wires, but that same connector body. I suspect that the yellow part that remained attached to the connector really belongs to the threaded part and only came out with the connector because the other end of the assembly is broken off. Try pulling it out of the connector.
I don't think so. That sensor is in the radiator, correct? That looks to be in place on this car, and the wire isn't anywhere near long enough to reach the radiator.
Originally Posted by joe_padavano
Now I'm confused. The freon pressure sensor has two wires, but that same connector body. I suspect that the yellow part that remained attached to the connector really belongs to the threaded part and only came out with the connector because the other end of the assembly is broken off. Try pulling it out of the connector.
OK, I pulled on what was still left attached to the connector housing, and this came off. It does have two prongs, so it seems there should be another wire attached to the connector.
I looked more closely at the top of the connector, and it does appear that there was another wire attached to the side (yellow arrow) that is now gone.
Originally Posted by joe_padavano
Does this car have the MISAR crank trigger ignition?
I don't know. How would I tell?
Originally Posted by joe_padavano
Does it have any fiber optic systems? Could that be a fiber optic cable and not a wire?
I don't know that it does, but I'm still learning about this car.
Speaking of the coolant temperature sensor, that should be located behind the oil fill tube, correct? At least, that's where it is on my '67 Delta. This is what's there now. Do I need to find a six-sided something-or-other to stick in that six-sided hole and turn what's left of that fitting out? If so, good luck to me!
OK, perhaps in the future I should read first and ask questions later. I think I've tracked down what this is. This car apparently has (or maybe I should say "had") what is called the Electronic Spark Timing Ignition System. See the figure below, which is from the '78 CSM.
Note the lower left corner of the diagram. There's a coolant sensor there that looks very much like the one in question here. It's located at the left rear of the engine. So what I see at the normal coolant sensor location is correct. That port is just blanked off. Note at the bottom of the diagram a white vacuum tube. I did see that and wondered what it was. It looks like a white electrical wire, and I wondered why it was attached to a vacuum port.
But now here's why I say the car "had" the EST system. This diagram shows where this coolant sensor should attach. Right in front of the distributor on the intake manifold (the CSM reference to this figure says the sensor is located "left rear of intake manifold"). Well, there is no location in front of the distributor for this to screw into. Not a chance. So I'm wondering if the intake manifold on this car has been changed to one from an engine that did not have the EST system. That would explain why this connector is no longer connected to anything and why I can't find a location for it. I'll have to get with the seller and see what he can tell me about this.
OK, Joe, here's the 64 million dollar question. Will the car run without the temperature sensor? I'm assuming yes.
I sent an email just now to the prior owner and asked about all of this. He replied quickly said that, as far as he knows, the engine has never been altered. He says the car ran fine up to the point that it was parked, and I have no reason not to believe him. As I recall, he said that his family did not buy the car new but that his father bought it in 1980 or something like that. I'm wondering if the first owner might have had the manifold changed to one for a non-EST engine. Maybe the system was giving too many problems, so the manifold was changed? Did this system have any kind of negative reputation? But a change of the manifold and the disconnecting of this sensor would seem to be a minor change compared to all of the other aspects of the EST system that are integrated into the ignition system.
Perhaps this mystery will never be solved. I'll just be happy to one day have a good-running engine!
OK, one last (for now) comment on this. I think I did find the port on the manifold where this attached. It's just to the left of and below the distributor. I saw it earlier but didn't think it could be the port until I saw the blanked off port at the front of the engine where the sensor would normally go and realized that the two blank-offs look identical. Assuming this is the mystery port, that explains why the sensor is not attached and that this is the original intake manifold after all. I wonder why the sensor was not replaced instead of the port being blanked off. Maybe I should try to find a replacement sensor, remove the blank-off plug (which looks like it could be a hell of a job as it looks thoroughly rusted in there), and reinstall the sensor? Or should I just let sleeping dogs lie?
OK, Joe, here's the 64 million dollar question. Will the car run without the temperature sensor? I'm assuming yes.
I would assume that the controller uses engine temp to vary the advance curve, though I'm not sure of the exact algorithm nor do I know whether open circuit is read as "hot" or "cold". The bigger question is, does the distributor have a vacuum advance can or not? The stock distributor does not as the advance curve is totally controlled by that controller, just like on the CCC cars. If the current distributor does have a vac advance can, it's been replaced and the EST has been bypassed.
If you want to read some more, the CSM likely has a description of how the system works and should tell you how it uses the coolant temp sensor to determine timing.
I did read through part of the relevant section of the CSM, and I didn't see a mention of how the coolant temp is used, but I'll keep looking.
I did have one more thought as to why this sensor was not replaced. I have to thank good old Occam and his Razor. "Don't multiply the complexities" or words to this effect. The more modern interpretation is "the simplest explanation is usually the correct one."
The prior owner says the car ran fine and that the engine has never been altered, and the car was in his family since 1980. This temperature sensor looks like hell. It is far more corroded than you might expect it to be after only a year or two of use. I did some looking around, and I can't find a vendor for this sensor. The standard temp sensor that was used on every Olds engine from 1897 to 2004? Yes, that one is available and will fit this engine as well. But this special sensor? No.
So now I'm thinking that the sensor failed after perhaps a decade or so of service, which is more consistent with its current condition, and by that time GM had stopped producing replacements. How many years was the EST system used and in how many cars? If he answers are such that total usage was low, there was probably not enough demand by the late '80s or early '90s to keep producing these sensors, and so when this one failed, there was no replacement available, and the only choice was to blank off the port and leave the sensor disconnected and dangling.
Just a thought.
Perhaps something NOS will turn up on ebay.
Last edited by jaunty75; February 26th, 2017 at 12:13 PM.
I've got one on my parts car, no idea if it works or not. But if you want to give it a try let me know and I'll see if I can pull it without damaging it.
John
I'd be interested if it's in decent shape. Thank you. That cap comes off by squeezing the sides as shown in that figure 6D-64 above, and I would need both the sensor itself, which pulls out of the cap once removed, and the part that screws into the manifold.
He may not need the wire, the diagram shows it to be a shielded cable. He can check continuity back to the box for both the center conductor and the shield. The next question is since this has been removed, does the car still have the box installed and does it still have the original distributor?
Jaunty, might you not need the wire and plug as well, as you said yours seemed to have a broken wire?
Good point, but this was before I realized it was a coolant temp sensor. If it works the same as the regular type, there is only one wire. Also, the one John is offering looks to have only one wire coming out of it as well.
The next question is since this has been removed, does the car still have the box installed and does it still have the original distributor?
Good questions both. I'm going to guess yes because the distributor does have that large wiring connector as shown at about the 4 o'clock position in Figure 6D-61 I posted earlier. Also, the seller is insistent that the car was original when the family got it in 1980, and they didn't change anything in the years since.
Good point, but this was before I realized it was a coolant temp sensor. If it works the same as the regular type, there is only one wire. Also, the one John is offering looks to have only one wire coming out of it as well.
The normal temp sensor has a metal body that grounds through the block. This one has a plastic body. It needs two wires - as seen by the fact that your sensor has two terminals. As (other) Eric correctly pointed out, the schematic shows that it is a coax wire. The ground is through the shield. Your harness does not need to be replaced.
I hope John's part works for you. That's definitely as rare as hen's teeth.
It's a historically interesting system, but frankly, at the first sign of a performance issue, I'd drop in a conventional HEI and not look back. Unlike CCC, the EST system is self contained and won't disrupt other systems if deleted.
It's a historically interesting system, but frankly, at the first sign of a performance issue, I'd drop in a conventional HEI and not look back. Unlike CCC, the EST system is self contained and won't disrupt other systems if deleted.
... and that's why I keep a new, regular HEI distributor in the trunk of my '77 - just in case. My MISAR system still runs great, but this is cheap insurance.
It was the first thing tucked up above the spare tire, along with a timing light and my Craftsman distributor wrench when I was packing to drive my car from Florida to Lansing for the Homecoming show last June!
Think about how awesome this site is. A question about an obscure part on a two year, one make and model only system from 40 years ago, and people chime in with answers quickly. Totally awesome!
I wonder if the EST system was used by other GM divisions in 77 and 78?
Not that I've been able to determine. Cadillac offered a system called Electronic Spark Selection, but it was different. The HEI used a five pin module (instead of the three pin module used for EST), and apparently the primary function was to retard spark during cranking to aid starting.
OK, this was easy to pull. The sender has one thread that's gone about half way around. Otherwise it looks good. If you want to give it a try send me your address and I'll drop it in the mail. Also the plug seems to have some kind of blue grease on it. John
I'll PM you my address. Thank you. Your part sure looks a lot better than mine. Let me know if you want anything for and/or for shipping. Thanks again.
The HEI used a five pin module (instead of the three pin module used for EST), and apparently the primary function was to retard spark during cranking to aid starting.
I remember coming across a 5 pin HEI module when I worked at O'Reilly Auto Parts years ago. Apparently, there are also 7 pin modules. I never knew the 5 pin modules were used for that Cadillac system.
I remember coming across a 5 pin HEI module when I worked at O'Reilly Auto Parts years ago. Apparently, there are also 7 pin modules. I never knew the 5 pin modules were used for that Cadillac system.
The seven pin modules are used in the CCC and TBI systems.
February 25th, 2017, 02:39 PM
