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Well guys rather than continue this discussion on the thread about my new paint job I thought it best to start a new thread just in case we actually find the cause of my problem. That way it will be easier for others in the future to look up possible causes and cures if they have a similar problem.
So let me recap the problem:
Although the 77 Toronado ran fine from time i got it last year it started having problems mid summer. It came out of storage in late April and had a full tank of gas with fuel stabilizer added. Went thru this tank just fine car had no problems. Then filled the tank again and at half a tank refilled it as I was planning a bit of a cruise. Should mention I run only premium fuel in it with NO Ethanol.
That is when the problems started. First the fuel guage would not read correctly so I took it in had the tanked dropped, the sender checked and the guage tested for sweep and the ground redone and the filter replaced. That fixed the guage problem but then the car had starting and idling issues.
First the choke would not kick in and the car would not idle unless I sat there holding my foot on the gas pedal for a few minutes. That would then get it to idle but rather rough and lumpy. Take it for a drive and at stop signs/lights the idle would drop until the engine quit unless I held my foot on the gas. Then after 10-15 miles it started to stutter, miss, hesitate, chug and whatever other similar adjectives one can use to describe the situation. On 2 occasions it actually quit while driving while doing its stutter thing and I could not get it started again. Left me stranded in the middle of the road. So had to have it towed home.
My first guess:
Because of the work on the tank, sender and guage I ruled those out as the source of the problem. I suspected the carb although I also had doubts about the fuel pump. So had the carb rebuilt and while removing it we were convinced by the fact that the bolts were loose, the gasket showed uneven compression on it (but no signs of blow by) that this must be the culprit.
We also tested the fuel pump. Very scientifically we pulled the line, turned the ignition for a few seconds and spit gas half way across my garage just missing my newly painted fender. So we ruled out the pump.
The result:
We primed the carb, fired up it up and viola I had choke action again! Kicked off the choke and it idled very nicely. This must be it! So we went for a drive. Well about 10 minutes in just driving around the block- just in case - it started again pulling away from the stop sign - sputtering, missing, chugging, surging - you get the idea. Did not think I was going to make it the one block to my own driveway.
So now what:
At this point we are reasonably convinced it is not fuel delivery or carb related as we noted that the car would start fine and run again for 10-15 miles after it had cooled down.So we decided to look at the ignition system. What we found is that the coil on the HEI system was extremely hot and the rotor and the resistor brush were a mess. See the photos.
Our theory is that the dirty condition of the rotor and the resistor brush is causing the coil to heat up and the module cannot compensate the timing advance which leads to the misfire, stumbling under load when the engine is warmed up. But I am no expert. Although my research says that the coil should not be hot or at least not that hot.
So I have been running around all day tracking down the parts to replace - 1. the module, 2. the cap, 3. the coil, 4. the rotor, 5. the resistor brush, 6. the dust cap.
Hope to get the parts installed tomorrow and fingers and toes crossed that this cures the problem.
Last edited by ByronF; October 13th, 2018 at 06:50 PM.
I do wonder why you run premium fuel. The engine was designed to run on regular, and using premium fuel doesn't help anything and could actually create problems. The compression ratio on the 403 is only 8 to 1. It was the 10.5 to 1 high compression engines of the '60s and early '70s that needed premium fuel. All you're doing is wasting money. I run regular in my '78 with no problems.
From the U.S. Federal Trade Commission:
“In most cases, using a higher-octane gasoline than your owner’s manual recommends offers absolutely no benefit. It won’t make your car perform better, go faster, get better mileage or run cleaner.”
Last edited by jaunty75; October 13th, 2018 at 08:02 PM.
If the module, coil, cap and rotor do not fix the issue, make sure the choke is staying open when the engine is warmed up. You also have a pick up coil in the distributor that can go bad as well. You can buy a complete HEI off ebay for under $100. Might be Chinese but I understand some are decent quality....what's made in the US anymore anyway?? Hard to diagnose a drivability concern over the computer, but there is not much to these years and should be easy to nail down. Have you checked/read the plugs and have the plug wires been replaced?
“In most cases, using a higher-octane gasoline than your owner’s manual recommends offers absolutely no benefit. It won’t make your car perform better, go faster, get better mileage or run cleaner.”
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I understand the point that higher octane fuels do nothing in low compression engines of the 70's. However , pumping 87 ethanol blend can't be much worse.
Good question about the premium fuel. My reasoning is based on the fact that the car is just a part time cruiser not a daily driver. So it sits a lot and does maybe 1000 to 1500 miles per season and then sits in storage for 6 months. All the grades of fuel contain ethanol except premium. It is my understanding that ethanol is hard on rubber lines, certain metals in the fuel system and it draws moisture. None of which seems to me like good things to have happen, so I use the premium fuel to minimize the potential problems. With my low annual mileage the extra cost is not outrageous and could well be cheaper than the cost of the repairs that ethanol could cause. Does this make sense or am I just kidding myself?
All the grades of fuel contain ethanol except premium. It is my understanding that ethanol is hard on rubber lines, certain metals in the fuel system and it draws moisture.
Well this is interesting. I don't think this is true in the U.S. I think all grades of gasoline at any particular station contain 10% ethanol unless it specifically says otherwise on the pump. I was googling premium fuel in Canada, and I found that some brands, like Petro-Canada, have ethanol in all grades of fuel, including premium. But other brands do not. It depends on the brand and on where you live in Canada.
Yes, keeping ethanol out of your car's fuel system is certainly a good thing to do. You just want to make sure that you're not trading one set of problems for another. Running premium fuel in an engine not designed for it can cause fuel combustion problems, incomplete combustion, and carbon build-up in the cylinders. Any fuel, ethanol-laced or not, breaks down over time, and the very best thing you can do for your car's engine is to run it regularly and keep the fuel in the system relatively new. Barring that, people often use something like Sta-Bil for long-term storage of a car with gas in the fuel tank. I've never tried it because I've always been able to start my cars and drive them a reasonable amount year-round.
You might consider running regular fuel through the driving season and then filling with premium the last time before storage. Put 50 miles or something like that on the car after that last fill-up to get the premium fuel through the system. It won't replace the ethanol 100% because the fuels are mixed in the tank, but it should come close, especially if you let the tank get pretty close to empty before that last fill-up. Then put in some Sta-Bil and then park the car.
My 71 Delta 88 diesels when the engine is shut off if I use regular, so I use premium.
This is masking the problem, not solving it. The engine didn't require premium fuel when it was new, so something has changed.
A common cause of dieseling is hot spots in one or more cylinders causing fuel vapors to ignite without a spark. Hot spots can be caused by carbon buildup in the cylinder. Causes of that could be a fuel mixture that is too rich, which leaves unburned fuel on the pistons and valves. Other possible causes are the use of spark plugs of the wrong heat range, poor cooling system performance leaving the entire engine running too warm, incorrect timing, or a too-fast idle speed. Given that using a higher octane fuel solves the problem would suggest the presence of too much heat, so carbon buildup or poor cooling are more likely culprits. Constantly paying for premium fuel adds up if the car is driven at all. Might be worth at least a cursory check of the engine's condition.
A way to stop the dieseling when shutting off the engine is to leave the transmission in gear, rather than putting it in Park first, and then turning the key to OFF. The extra drag on the engine from trying to turn the transmission will usually stop the dieseling immediately. I had a '75 Chevy Nova with a straight Six many years ago that would diesel from time to time as the miles piled up, and switching off the engine with the transmission still in Drive stopped it cold.
You should be able to take the HEI module into the local auto parts store and have it tested. I bet that's your problem. I had one fail in the Summit HEI distributor I have in my 71 98.
Just thought I would post an update. As you have read I had the carb rebuilt and dialed in by my mechanic buddy who has lots of experience on these quadrajets. We then replaced the module, brush, rotor, cap, coil and even sprung for new plugs and wires. We installed everything but the wires on the first go and took it for a test drive. The car started fine, choke works great, it can now hold an idle when I come to stop signs or lights. I hit it pretty good a few times and it got up and went pretty good for a vehicle the size of an ocean liner. But once it got good and warm it started to miss again, intermittently. So we rolled it back in the garage and swapped out the ignition wires for new ones. Took it out again. Modest improvement but again an intermittent miss which then went away at about 20mph. Made no difference whether I pulled away gently or hard. And it did not always happen, just intermittent and only after the car was warmed up. So it would appear that the problem is heat or temp related. So now I am at a loss where to go from here.
Any thoughts or ideas what to try next?
My only thought is that maybe it has something to do with that MISAR (which I think is on this car but not 100% certain) system and it is malfunctioning and can't properly handle the timing advance.
Does this make sense? How does one confirm if that system is on board?
Should also mention that we plugged the line to the EGR valve but that did not help the situation.
Is there any merit in finding an HEI distributor with vacuum advance and swapping it in place of the existing and disabling the MISAR?
If so what distributor would fit and do the job?
Again appreciate any advice.
My only thought is that maybe it has something to do with that MISAR (which I think is on this car but not 100% certain) system and it is malfunctioning and can't properly handle the timing advance.
Does this make sense? How does one confirm if that system is on board?
I would think the '77 Chassis Service Manual would indicate if the MISAR system is on board. I'm pretty sure it is on your car. The system was modified slightly for 1978, which is what I have, and my '78 service manual has all kinds of info on the MISAR system.
I don't know if the following will be any help to you, but it's from the December 2015 issue of Journey With Olds. The latter part of the article describes his problems with his '78. If you want to skip to the relevant part, it starts at the lower left of the second-last page under the heading "MISAR." Based on what this article says, it would seem that changing over to a conventional HEI distributor might be exactly what you want to do.
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Last edited by jaunty75; October 15th, 2018 at 07:45 PM.
If you go to Rockauto and search under 1977 Olds 98 with a 403 engine, you can buy both new (Spectra Premium, Cardone) and remanufactured (AC Delco) vacuum-advance distributors. It looks like you can get an actual AC Delco distributor for your car, at least from Rockauto, if you're will to go the remanufactured route.
Thanks Jaunty. Very interesting article. I note that according to this article a Misar System has a 3 prong module. What I took out and replaced was a 4 prong module. I found a brief bit on the electronic controller assembly under the glovebox in the 77 manual. i would guess someone has already made some changes but who knows. Still puzzled as to what to disable or disconnect if I change to a conventional distributor with vacuum advance. I gather a complete heli distributor with vacuum can be had for $100 to $150. Doubt that I will ever find a replacement electronic controller or if anyone can rebuild one.
The MISAR system is still there on my car, but it's not fully functioning because the temperature sensor is missing. The sensor is apparently unique to these cars and not reproduced (and hasn't been for many years), and when I got the car, the sensor was still connected to its wire, but it was just sitting on top of the engine dangling from the end of the wire. Where it screws into the intake manifold is just blanked off. But the car still starts and runs ok, so I've not touched anything. Temperature is supposed to be one of the things that is sensed and sent to the microprocessor to control the timing, so what the microprocessor does when the sensor is disconnected and apparently indicating a constantly cold condition is anyone's guess. In other words, I'm assuming that the signal the microprocessor gets from the disconnected sensor is that it is always at ambient temperature, or a cold engine temperature, and sets the timing accordingly.
But to be honest, I really don't know for sure. I asked the seller about the disconnected sensor, and he didn't know anything about it. All he said was that the car ran fine when it was last run in 2003, and I have no reason to doubt him because it runs pretty good now. For all I know, this sensor died in 1990 or 1995 and was disconnected then because no replacement was available. As I said, I'm sure this sensor is a one- or two-year thing only, having been used in '77 and '78 Toronados. So once the GM parts service stopped making them available, perhaps 10 years later, that was it. If you needed a new one, find one still in stock at a dealer somewhere or take a used one off another car. Eventually, dealers would run out of supply, and the only choice is to find used, which is probably not a successful long-term strategy as every one of these sensors was made in the late '70s and are just as old as the one on your car, or disconnect it all together. This sensor is not the same as the typical temperature sensor you can get for Olds V-8s all day long at any parts store.
This brought up another issue for me, and that is that, with this sensor disconnected, the engine had no "HOT" light sensor, as this sensor was used for that, too. If the engine were overheating, I would never know it. So I put in a temperature gauge and connected the sensor to a fitting inserted in the upper radiator hose. Not the perfect solution because that location is after the thermostat, but I'll be damned if I can get the blank-off plugs out of the engine. The place were the temp sensor WOULD go next to the thermostat is there as this is the same engine that was used in other GM models which had a conventional temp sensor and idiot light, but the plug has been in there since the beginning and is so in there that I doubt I could ever get it out without drilling. So I've been content to use the setup I have.
I note that according to this article a Misar System has a 3 prong module. What I took out and replaced was a 4 prong module.
I'm wondering if this is because your car is a '77 and the one the article describes is a '78. There were some differences in the MISAR system between the two years.
Jaunty, interesting that yours runs fine with the temp sensor just laying on the top of the engine. Wonder if that would work for me. Mine runs fine when the engine is cold but after 10-15 miles when it is warmed up it will miss. So wondering if disconnecting my temp sensor will tell the little computer that the engine is cool and the advance will work and the other sensors will control the advance and the engine will run thinking it's cool and the miss will disappear. What do you think?
One question. When you turn the key to start the engine, does the "HOT" light or "TEMP" light or whatever it's called on your dash light up momentarily like it's supposed to along with the OIL light, BRAKE light and all the others, to show you that it's working? If it doesn't, I would wonder if your temperature sensor isn't working, either, but is just sitting there stuck in the engine taking up space. Either way, I would disconnect it and see how the car runs. Wouldn't it be nice if getting the car to run better was something as simple as this.
Last edited by jaunty75; October 16th, 2018 at 11:21 AM.
I should also clarify one minor thing. The temperature sensor on my car is gone altogether. All that's sitting on top of the engine is the connector with nothing attached. It was there when I got the car, and I think I did run the engine a few times with the sensor still attached to the connector (but not inserted in the intake manifold), but I removed the sensor and set it aside just in case I ever came across another one that might still work and want to compare it to what came off my car to make sure they match.
BTW, thanks for the article Jaunty. It's quite a story. Early computer controls are definitely archaic by today's standards. I hope Byron can get his Olds dialed in.
One question. When you turn the key to start the engine, does the "HOT" light or "TEMP" light or whatever it's called on your dash light up momentarily like it's supposed to along with the OIL light, BRAKE light and all the others, to show you that it's working? If it doesn't, I would wonder if your temperature sensor isn't working, either, but is just sitting there stuck in the engine taking up space. Either way, I would disconnect it and see how the car runs. Wouldn't it be nice if getting the car to run better was something as simple as this.
Yes it does. When I turn the key to the on position I get GEN and OIL light, CHECK IGNITION on the left side and FASTEN SEAT BELT on the right at top. Then one more click of the key and I get HOT light and something beside it which I can't read because the car starts and all the lights go out. So I am guessing that everything is working at least in the dash module.
OK. I'd still disconnect the temp sensor and see how the car runs.
Also, I think the HOT light going on when you start the car just indicates that the circuit is complete and that the bulb works. I don't think it proves that the sensor is actually working. But I don't know for sure.
Also, I think the HOT light going on when you start the car just indicates that the circuit is complete and that the bulb works. I don't think it proves that the sensor is actually working. But I don't know for sure.
Jaunty, I am no expert but in looking at the schematic for the Misar controller and system ignition wiring it would appear that hot light does run through the controller to the dash based on a signal from that sensor. Do you have the same schematic and do you read it the same way. If so wonder how one would test that the circuit is functioning properly. My sensor looks to be in good shape and I don't want to disturb if I don't have to and don't want to lose the hot light function if it is working.
My thinking is if I can prove that this sensor and the hot light is working correctly then it would suggest that my timing problem probably centres around the crankshaft sensor. Have no idea and can't find any information on how to test it. Either way can't repair or get replacements for either of these units. For the temperature your approach would do the job.
So I am now looking at switching to a regular vacuum advance distributor and bypassing the whole Misar system. Still trying to figure out how to disable it but without losing any of the dash light functions such as the HOT temp indicator.
Any thoughts or suggestions on how to disable the Misar system?
I am no expert but in looking at the schematic for the Misar controller and system ignition wiring it would appear that hot light does run through the controller to the dash based on a signal from that sensor. Do you have the same schematic and do you read it the same way. If so wonder how one would test that the circuit is functioning properly. My sensor looks to be in good shape and I don't want to disturb if I don't have to and don't want to lose the hot light function if it is working.
Here's the relevant diagram out of the '78 service manual. I don't know if it's identical to the '77 diagram, but I'm guessing it's close. Yes, the output of the temperature sensor, which is on the lower left in this diagram, is connected to two terminals on the controller, and two wires come off of different terminals on the controller and connect to the hot light through the "I. P. Extension Harness Connector" whose location is given as the left side of the radio. It doesn't look like there is an easy way to just disconnect the sensor and hot light wires from the controller and connect them directly together to bypass the controller and connect the sensor directly to the hot light, at least without the likelihood of messing something else up.
Originally Posted by ByronF
My thinking is if I can prove that this sensor and the hot light is working correctly then it would suggest that my timing problem probably centres around the crankshaft sensor. Have no idea and can't find any information on how to test it.
I would think you could test it in a straightforward way. The manual describes it this way: "It is part of the ignition system and resistance in the sensor changes with changes in coolant temperature. (Resistance lowers when temperature rises.)" Why couldn't you disconnect its connector, remove it from the engine, and immerse the sensor end in a pot of water on a stove with an Ohmmeter attached to the two leads. See what resistance is measured, and then see if it decreases as you heat the water. I don't see a specification anywhere indicating what the resistances should be specifically, but at least you could verify that there's no open circuit and that the resistance does change with temperature. If it checks out, put it back on the engine and assume it works. If it doesn't check out, well, there you go. A possible source of your problem.
Originally Posted by ByronF
So I am now looking at switching to a regular vacuum advance distributor and bypassing the whole Misar system. Still trying to figure out how to disable it but without losing any of the dash light functions such as the HOT temp indicator.
Any thoughts or suggestions on how to disable the Misar system?
I would frighten me to death to attempt it without knowing what I'm doing. In looking at the diagram above, everything connects through the controller. How you bypass that, I don't know. I do note that it says in the center of the diagram "DO NOT USE 4 TERM. MODULE." You said your distributor has a four-terminal module while the article I posted above says the module has three terminals, and that was for a '78. What these terminals all do and there were four in '77 but only three in '78, I don't know, but apparently there was a change from 1977 to 1978. If the controller CAN be bypassed, maybe you could leave the temperature sensor connections undisturbed, and the HOT light would still work.
Did you ever try just disconnecting the temperature sensor and driving the car? If that cured the problem, I would leave the MISAR system alone and find another way to get a temperature warning system in place. Put on an aftermarket gauge like I did and screw a conventional temperature sensor into the same port where the current sensor is, and then just run a wire. The goal here, after all, is not to change to a conventional HEI distributor. The goal is to get the car running smoothy. If that can be done in some fashion while leaving the current ignition system in place, that would seem to be the better solution. Any side-effects can be worked around.
Here's what the situation was with the temperature sensor on my car.
This is what it looked like when I got the car. Still connected to the wiring harness at one end and just sitting on top of the engine passing the time of day. Corroded beyond recognition.
I was able to get a replacement from one of our moderators who is parting out a '78 Toro. The sensor on his car was intact. Here's mine and his side by side.
I would gladly have tried to install the replacement in my engine, hook up the connector, and see what happens. But there is a big problem with this. Below is a photo of the port on the engine where the sensor is supposed to be screwed in. That's the distributor right behind it. It looks like it has been in there since the time of Christ and only a nuclear explosion would loosen the screwed-in plug.
It looks like a large hex-head wrench is supposed to be the tool to use, but it is so rusty, and the hex opening is already partially rounded, that I don't think any amount of soaking in PB Blaster or anything else would have a chance of loosening it. I suppose hitting it with a torch might break the rust, but then I'd probably blow myself up in the process. Given that the engine has always run OK without the sensor, I've never been inclined to pursue this. It's a sort-of don't fix what ain't broken, discretion is the better part of valor situation.
When I went to install the aftermarket temp gauge, I originally wanted to put the sensor in the port where it would normally go on a non-MISAR Oldsmobile engine. But THAT port, which is right next to the oil fill tube, was blanked-off at the factory and has apparently never been removed. While it doesn't look quite as bad in terms of rust, and while it looks like the hex opening is undamaged, it still looks like it would take a team of horses to loosen it. I have not had any success doing so, and that is why I went to the sensor-in-the-radiator-hose option.
Here's the temperature sensor setup currently in the car. Mounted in the upper radiator hose.
Here's a photo of the dash. The temp gauge is mounted down low. You can see it between the brake and gas pedals. Works very nicely.
Jaunty, thank you for all the great pictures and the schematic for your 78. I am uploading the schematic for my 77 from the manual. It would appear that the major difference 77 to 78 is that the crankshaft sensor on the 78 is within the distributor where on mine it is mounted below the ps pump and wired back to the controller.
I have also uploaded a picture of my temp sensor which is mounted at the front of the engine and as you can see it is plugged in and appears to be in good shape. Although if i remove it i might discover something different.
I tried to crawl under the dash and take a picture of the controller box but that did not turn out so well. It will take days I am sure for the the aches and pains to go away after twisting myself into a pretzel to get into there. But what I think I did capture is the plug that holds all the wires that plug into the controller. What I could not get a picture of is the 2 vacuum lines at the top of the controller.
Again I am no expert and am probably dumber than toast most days but my reading of the schematic suggests that when switching to a vacuum advance distributor it simply is a matter of disconnecting the connector from the controller to distributor (circled in red on the schematic and shown in the photo) and this should by my theory disable the misar from trying to change the timing but still leave the functionality of the other parts particularily the temp sensor and light.
Does that make sense to you?
There are definitely a few differences between the '77 and '78 systems. Among other things, the controller for '77 looks to be simpler in that it appears to have fewer terminals. Also, it appears that for '77 they had TWO vacuum hoses coming off the controller, one connected to engine vacuum and one routed back under the hood and left open to atmosphere. For '78, they didn't bother with that second hose and just left the port open right at the controller. Atmospheric pressure is atmospheric pressure, right? Whether we're sensing it under the hood as in '77 or under the dash as in '78? I guess they figured there was no reason for that second hose.
What you suggest is what I would try. I can't see that you would damage anything if what you want to try doesn't work. Disconnect what you have a circled in red, remove the distributor, put in a conventional one, wire it up, and see what happens. If we notice a large black cloud off to the northeast, we'll know it didn't work and we'll send our condolences to your next of kin!
LOL! I am sure they will appreciate your kind words and would look forward to getting the old girl out the garage.
I did more checking on this site and found a couple of old posts regarding the 403 motor and misar in particular.
There is a gentleman by the name of Joe Padavano who appears to be rather knowledgeable about these systems so I sent him a pm and asked for his advice an input.
Hopefully we hear from him before the big boom.
Here is a link to the article if you are interested.
Here is the picture of the Cardone vacuum dsitributor that I am planning to go with. It fits the 1977 Olds 98 with the 403 engine and according to the folks at Summitt it will physically fit all olds 403's including the Toronado. Also works on the same engines used in Pontiacs and Buicks.
There are definitely a few differences between the '77 and '78 systems. Among other things, the controller for '77 looks to be simpler in that it appears to have fewer terminals. Also, it appears that for '77 they had TWO vacuum hoses coming off the controller, one connected to engine vacuum and one routed back under the hood and left open to atmosphere. For '78, they didn't bother with that second hose and just left the port open right at the controller. Atmospheric pressure is atmospheric pressure, right? Whether we're sensing it under the hood as in '77 or under the dash as in '78? I guess they figured there was no reason for that second hose.
What you suggest is what I would try. I can't see that you would damage anything if what you want to try doesn't work. Disconnect what you have a circled in red, remove the distributor, put in a conventional one, wire it up, and see what happens. If we notice a large black cloud off to the northeast, we'll know it didn't work and we'll send our condolences to your next of kin!
I did notice that about the vacuum hoses but I dont think it is a big deal just to leave them as long as they dont leak and diminish vaccum pressure. In order to provide vacuum to the new distributor I was thinking of using the line that runs to the EGR valve, as I doubt it is working as someone somewhere has plugged this line. I am not keen on teeing in another vacuum line as there must be 16 miles of vaccum hose under that hood already. Any thoughts on this idea.
Looks good about the distributor. Keep a detailed record of what you did and post it here because I might want to do this some time down the line.
As far as where to get the vacuum, yes, you just need a source of manifold vacuum. There are ports on the engine you can use as well as several on the carburetor.
I looked back through earlier chassis service manuals to see where they show the vacuum advance getting its vacuum.
Here's the vacuum hose routing for 1975. Note that the vacuum advance is connected to a four-port connector which is in turn connected to manifold vacuum and to the bottom port on the CTVS (choke thermal vacuum switch). I looked through the manual for 1973 as well, and it shows something similar, but the connection is to a different thermal switch. But the general idea is that, when the coolant reaches operating temperature, the switch opens and allows vacuum to the advance to advance the ignition. The idea is to keep the engine running cooler at idle. I don't know that you would have a problem if you didn't use a switch. Just watch your engine temperature when it is idling and fully warmed up to make sure it's not running too hot.
What I'd do if I were you is look through your '77 service manual and find the vacuum hose routing diagram for the 403 engine when it's not in a Toro. Look at the diagrams for 88 or 98 with the 403. Those should show where the vacuum advance is connected on a non-MISAR engine, and you can do the same thing.
Thanks again Jaunty. For the record I am posting the vaccum routing from the 77 manual that covers the 403 engine except Toronado. Marked with a red star the one I think should be followed.They hook into an SAVM Spark Advance Vacuum Modulator. Wonder if I need to track down one of those?
Here's the equivalent diagram for 1978, and notice what the distributor vacuum advance is connected to. Directly to manifold vacuum! No intervening vacuum switch of any kind.
I think you might just try it this way and see how things go. This is certainly what I would do with my car given that it's a '78 and this the diagram in the '78 manual.
I've been on business travel, so I'm late to this party. Yes, the 77 and 78 MISAR systems are different. The 77 used the crank trigger, the 78 used a distributor-based trigger. The 78 is actually much closer to the ignition part of the CCC system used on the 307s.
The easiest way to bypass the system while retaining the HOT light function is to replace the original temp sensor with a conventional single wire temp switch and run a new wire to the feed for the HOT light. I would simply replace the MISAR temp sensor with one from a same-year Olds 98. That would be a single wire sensor, which closes to ground when the coolant exceeds the sender set temperature (usually around 258 deg or so). Run a wire from this new sender to the wire that formerly operated the HOT light from the MISAR controller, as shown in this diagram.
Joe, thank you for the advice and input on how to bypass the system and salvage the hot light. Just hope I can find a replacement sender unit and more importantly get the old unit out.
Jaunty the part number on the vacuum distributor that I have ordered Cardone #841893. This is a complete unit with cap, coil, module, rotor and wire connector.
Cardone also makes a unit with just the module and connector #301893.
October 13th, 2018, 06:43 PM
