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Discussion Starter · #1 ·
I have a 1992 Seville. It’s a project car I’ve been fixing up the last couple of years. It’s ran fine until recently. I replaced the alternator and battery but it still hesitates to start and sometimes doesn’t start at all. The engine turns over when you turn the key but sometimes will have to try 3-4 times to get it to start. Today for the first time I turned the key and got nothing. Turned it off and back on and it hesitated but started. I also have an issue with the defrost draining my battery if the car is at idle. Heat doesn’t work but defrost does. The heat stopped working when the A/c compressor went this past August. Idk if those things are related or not but I’m at a loss. When I turn on the defrost it makes a knocking sound for a few seconds then stops. Any advice on which direction to go with this is greatly appreciated.
 

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Since you mentioned it's a new battery it sounds to me like it could be a cable connection or a ground. It could also be the starter or perhaps there is something draining the battery. That's where your AC system comments may make sense. I'm not a '92 Seville expert but it sounds like you have an electric actuator which is trying to move the mode door and cannot. If the knock is coming from in the dash it could be that actuator making the noise. The system is probably directing a mode and the door doesn't want to move. I don't know the logic of the actuators but it makes me wonder, if it cannot achieve the position directed, whether it tries to maintain power until it does. If that's true it seems possible that could be draining the battery.

Scott
 

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92 Fleetwood 2dr cpe - FWD, 96 Seville SLS, 02 Seville
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Not sure of a 92 either. . .but some cars auto systems do use the AC at some temps. Have you checked to see if the compressor attempts to come on in defrost - it might be making the nose.
 

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In defrost mode the AC will always run on a GM AC car over around 40F. GM cars will also have at least a minimum percentage of outside air during defrost to avoid a sudden fogging condition.
 

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Hi Ranger,
I was trying to say all GM vehicles with A/C command A/C in defrost mode; defrost is considered an A/C mode. That's regardless of Auto-A/C or manual A/C systems. I can see that I should have worded what I wrote to clarify it's commanded at any temperature but there are other system controls which may prevent the compressor clutch from engaging if certain parameters are not met (despite A/C commanded). The '92 Seville may have additional logic for low temperature but I understood the low temp cut-out in general, including vehicles without Auto-A/C, was because likely the low pressure sensor eventually prevents it.

Thanks for pointing out "all temperatures".
Scott
 

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Discussion Starter · #7 ·
Not sure of a 92 either. . .but some cars auto systems do use the AC at some temps. Have you checked to see if the compressor attempts to come on in defrost - it might be making the nose.
The compressor it totally shot. The man I got the car from told me it was new but he just put stop leak in it. It’s getting a new one installed. It’s just cold where I live and I’ve been trying to push it off until it warms up a bit. Compressor won’t even kick on at all.
 

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Discussion Starter · #8 ·
Since you mentioned it's a new battery it sounds to me like it could be a cable connection or a ground. It could also be the starter or perhaps there is something draining the battery. That's where your AC system comments may make sense. I'm not a '92 Seville expert but it sounds like you have an electric actuator which is trying to move the mode door and cannot. If the knock is coming from in the dash it could be that actuator making the noise. The system is probably directing a mode and the door doesn't want to move. I don't know the logic of the actuators but it makes me wonder, if it cannot achieve the position directed, whether it tries to maintain power until it does. If that's true it seems possible that could be draining the battery.

Scott
I wasn’t sure if any of it was related or if they’re separate issues. Trying to track it down and I’m out of ideas. Heater core is my next option to check but I doubt that’s the issue.
 

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Discussion Starter · #9 ·
Not sure of a 92 either. . .but some cars auto systems do use the AC at some temps. Have you checked to see if the compressor attempts to come on in defrost - it might be making the nose.
The compressor won’t come on at all. I’m about 90% sure it’s the factory part that came with the car in 92. The knocking sound is coming from the dash and only for a few seconds when I turn the defrost on.
 

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You mentioned the heater core but even without heat you would get airflow. If you are getting some, but not much, airflow it's probably the mode door actuator you hear and does not have anything to do with the heater core itself.

If the door is stuck between modes you will likely get some airflow from the heater ducts because even in defrost mode you will generally have some air out the heater ducts. If you have airflow but no heat then maybe it's you temp door actuator making the noise.

If the noise stops maybe it's not the actuator running the battery down but it could be. If you have a service manual and you can determine which actuator is making the noise I would try unplugging it to see if the battery issue is solved. Eventually you need to determine why it's having an issue.

Scott
 

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The compressor it totally shot. The man I got the car from told me it was new but he just put stop leak in it. It’s getting a new one installed.
That stop leak snake oil may be what killed your compressor. The stuff reacts with moisture in the air (or in the A/C system). Most shops will refuse to hook up to their recovery machines if they suspect or find out that the stuff is in the system. Worse yet, it is damned near impossible to flush. You may end up replacing every component in the system.
 

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Discussion Starter · #12 ·
That stop leak snake oil may be what killed your compressor. The stuff reacts with moisture in the air (or in the A/C system). Most shops will refuse to hook up to their recovery machines if they suspect or find out that the stuff is in the system. Worse yet, it is damned near impossible to flush. You may end up replacing every component in the system.
Yea I already planned on replacing the entire system after becoming aware of that. I’m trying to hold off until it’s warmer though if I can. Right now I have to track down this power issue. I have a multimeter I’m going to see if I can narrow things down with that tomorrow
 

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Discussion Starter · #13 ·
You mentioned the heater core but even without heat you would get airflow. If you are getting some, but not much, airflow it's probably the mode door actuator you hear and does not have anything to do with the heater core itself.

If the door is stuck between modes you will likely get some airflow from the heater ducts because even in defrost mode you will generally have some air out the heater ducts. If you have airflow but no heat then maybe it's you temp door actuator making the noise.

If the noise stops maybe it's not the actuator running the battery down but it could be. If you have a service manual and you can determine which actuator is making the noise I would try unplugging it to see if the battery issue is solved. Eventually you need to determine why it's having an issue.

Scott
It’s very likely it could be the actuator. If I turn on heat or ac the dash reads “low refrigerant compressor off” and I don’t get any air flow from any vents besides the defrost vents up on the dash by the windshield. I know the compressor is bad, the water pump and timing chain were replaced last summer and I noticed the compressor was shot and that it hadn’t been replaced like I was told but the guy actually put stop leak in it. I have a multimeter I plan on checking the whole car over tomorrow. I know it has numerous problems with it. It’s 30 years old and most of the parts are original besides what I’ve replaced myself. I’m grateful for this forum, it’s been very helpful in my journey of restoring this old beast.
 

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I don’t get any air flow from any vents besides the defrost vents up on the dash by the windshield.
The system is vacuum operated and defrost is the default setting when vacuum is lost. Check for vacuum at the cabin supply line where it enters the cabin at the firewall on the passengers side. If no vacuum, follow the supply line to the manifold and the vacuum reservoir and look for a disconnected or broken hose. If you have vacuum at the firewall, then check programmer in the cabin under the dash for a vacuum line problem.

P.S.
The parkiing brake auto release is also on that same vacuum circuit and the vacuum diaphragm is a common leak point. You can verify that by pulling the vacuum line off the diaphragm and plugging it. If the HVAC system works, the problem is the auto release diaphragm on the parking brake assembly.
 

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Discussion Starter · #15 ·
The system is vacuum operated and defrost is the default setting when vacuum is lost. Check for vacuum at the cabin supply line where it enters the cabin at the firewall on the passengers side. If no vacuum, follow the supply line to the manifold and the vacuum reservoir and look for a disconnected or broken hose. If you have vacuum at the firewall, then check programmer in the cabin under the dash for a vacuum line problem.

P.S.
The parkiing brake auto release is also on that same vacuum circuit and the vacuum diaphragm is a common leak point. You can verify that by pulling the vacuum line off the diaphragm and plugging it. If the HVAC system works, the problem is the auto release diaphragm on the parking brake assembly.
Would a vacuum leak cause the car to hesitate to start? Or is that a separate issue? I got a multimeter I’m going to run a few tests with to see if I can narrow down the power issue, but I’ll definitely check the vacuum lines too I appreciate the help!
 

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Would a vacuum leak cause the car to hesitate to start? Or is that a separate issue? I got a multimeter I’m going to run a few tests with to see if I can narrow down the power issue, but I’ll definitely check the vacuum lines too I appreciate the help!
Have you tested the fuel pressure at the rail? A failing fuel pressure regulator would make a car hard to start, especially when warm and sitting for a bit.
 

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I have a 1992 Seville. It’s a project car I’ve been fixing up the last couple of years. It’s ran fine until recently. I replaced the alternator and battery but it still hesitates to start and sometimes doesn’t start at all. The engine turns over when you turn the key but sometimes will have to try 3-4 times to get it to start. Today for the first time I turned the key and got nothing. Turned it off and back on and it hesitated but started. I also have an issue with the defrost draining my battery if the car is at idle. Heat doesn’t work but defrost does. The heat stopped working when the A/c compressor went this past August. Idk if those things are related or not but I’m at a loss. When I turn on the defrost it makes a knocking sound for a few seconds then stops. Any advice on which direction to go with this is greatly appreciated.
1.I would look at all fuse boxes, (under the dash, & under the hood),
2. Check wiring harness under the hood, for frayed or split wire(s).
3. It could also be in the steering collar/ignition switch
4. Heater controls could need replacing
5. Pay the 200/250 for diagnosis, this will be faster/more efficient to figure out the exact problem for your car.....it will be cheaper in the long run,
 

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Would a vacuum leak cause the car to hesitate to start? Or is that a separate issue? I got a multimeter I’m going to run a few tests with to see if I can narrow down the power issue, but I’ll definitely check the vacuum lines too I appreciate the help!
Sounds like you have 2 main issues, the HVAC and no start

As to vacuum and MAP, the engine for a OBD-I car is the ECM breaks down all engine conditions into 16 blocks
From 0 to 15 cells (like a matrix)
The ECM decides on how much fuel and timing and what cell is being used by what the RPM is and what MAP ( inverse or what vacuum reports)
As example if at warmed up (closed loop) idle, the ECM expects the RPMS to be like 600-700 RPMs then MAP would be reporting about 35 KPA (depending on the elevation car is at)
That would be like cell 16 and the ECM then looks at what the stored date is for fuel, timing and assumes engine is at idle

IF there is a vacuum leak then MAP would be reporting higher then 35 KPA and think the engine is not in idle and adjust as example car is moving at low speed and is now reporting a different cell block and is incorrectly commanding different amount of fuel and timing

That would effect how engine then functions
Also if battery is low, the ECM does what is called adaptive strategy, which is over time of driving it adjusts those cell values and when voltage is low the ECM stored information in all those cells is flushed out and each time this happens the ECM has no learned values and is functioning incorrectly and has to relearn all over again

IF and should be known IF as example the vacuum hose has a leak or the MAP sensor (or wiring to it) itself is faulty or the hose to HVAC is leaking or off then that leak causes a loss in vacuum which then means MAP reports higher value and fools the ECM into thinking engine is in a different engine mode (cell) and incorrectly commands timing and fueling needs.

I suggest you first check the vacuum hose from intake to HVAC doors and assure zero leaks
Assure wiring to MAP sensor is good, then check MAP itself either by a multimeter as MAP functions from 0 to 5 volts
Or better is with a full OBD-I scanner as then you would see what cell is reported for cold start, timing and fuel commands
If you can get engine started and stay at idle wait until engine warms up, and it should then report it is in closed loop and if so what MAP reports. If seeing MAP at high reading values then it would be clear there is some type of vacuum leak and must be corrected

You could do is find where HVAC hose connects to engine,
take the hose off and then block that male fitting on block would then remove HVAC functions to doors out of the equation and see how that does for engine start/idle
 

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I have a 1992 Seville. It’s a project car I’ve been fixing up the last couple of years. It’s ran fine until recently. I replaced the alternator and battery but it still hesitates to start and sometimes doesn’t start at all. The engine turns over when you turn the key but sometimes will have to try 3-4 times to get it to start. Today for the first time I turned the key and got nothing. Turned it off and back on and it hesitated but started. I also have an issue with the defrost draining my battery if the car is at idle. Heat doesn’t work but defrost does. The heat stopped working when the A/c compressor went this past August. Idk if those things are related or not but I’m at a loss. When I turn on the defrost it makes a knocking sound for a few seconds then stops. Any advice on which direction to go with this is greatly appreciated.
How many miles on the fuel pump? Have you ever changed the gas filter?
The heater control switch is failing.
 
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