1981-1983 Imperial Automatic Shut-Down Module

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Tip from Dick:

The question about the importance of the ASDM needs an answer, and I will see if I can help here;

The ASDM is a device whose sole purpose in life is to decide whether or not to supply power to the EFI system. It takes the 12 volt supplied via the ignition switch and passes it through to the power module in the HSA if and only if it "thinks" conditions are such that it should turn on the system. The components in the main assembly (the HSA and the CCC and their accessory devices) accept the 12 volts when it is supplied, and use it to power everything in the system, via the 23 volt power supply, which is part of the power module. The sensors are supposed to be bypassed (ignored) for the first few seconds of cranking, while the fuel system is purged of vapor and the pressure comes up to 20 PSI at the pump output, but as soon as the car starts, the designed function comes into play.

There are a few different reason why the ASDM may "decide" not to supply power. If the Engine RPM, which it monitors, drops below 150 RPM, it shuts the system off. If the fuel pumps stay on too long without the engine firing, it shuts the system off. If fuel is flowing, for whatever reason, with the engine not turning above 150 RPM, it shuts the system off.

Unfortunately for the mental health of the drivers of these cars, the ASDM sometimes "imagines" things are not right. If one is driving along a 65 MPH on the freeway, and the ASDM gets a wild hair, it will shut the car down, and no amount of cranking will restart it until the driver cycles the key completely to "off" to reset the logic circuit in the ASDM. This is why, sometimes, the car will refuse to start no matter how long you crank, but if you cycle the key to off and then on, it will restart immediately.

The logic circuit that monitors the sensor inputs to make its "decision" is unfortunately a poor design in that it is very sensitive to any disturbance on ground or other connections. (For the Tech Types on the list, it is a TTL tied back NAND type of bistable or "Flip/Flop", with no decoupling on either the Vcc or ground lines, and no filtering on the logic inputs.) This means that if there is any deterioration at all in the grounding at the fender well, it is likely to suddenly shut the car down on a bump, or with a temperature change, or just because because.

Incredibly, there is no ground wire on this circuit; the engineers relied on the sheet metal screw which fastens its case to the inner fender to ground it. That is why the service material from Chrysler recommended that a wire be added to connect the case of the ASDM to the system ground, preferably at the master EFI ground point at the rear of the right head, but also, and nearly as good, more conveniently at the alternator case.

There are many EFI cars still working OK without this wire, but generally, it is just a matter of time before it begins to cause trouble of the most irritating kind, mysterious stalling and cutting out, which comes and goes without rhyme or reason.

I would add to the suggested fix, that the ASDM should be deliberately insulated from the fender, which is likely to pick up static discharge or other contaminating signals as the car ages and the mounting bolts get crud under them. When the added wire is put on the ASDM, it no longer needs the potentially troublesome connection to the body sheetmetal.

Tip from Bob:

Re the ASD Module grounding - prior to the grounding of the device, you probably saw the rust that accumulated under the ASD module, this because of the galvanic corrosion that occurred as the module case tried to seek its own ground, the electrolysis caused the corrosion. The added ground strap provides a good path to return electricity to the source while avoiding the rust; the path of least resistance. From what I hear, the two braided ground straps at the Radiator to Condenser also avoid an electrolytic reaction within the cooling system - apparently this is due to a reaction of the particles travelling in the coolant as a result of a reaction of the dissimilar metals which the radiator is made of and assembled with; nothing new here, just an added life enhancer idea. The latest Popular Mechanics has a fine story about coolants/antifreezes that is important because of the problems newer engines with aluminum castings had with the older coolants. If you've disassembled some of those engines with iron blocks and aluminum heads you'll often find the steel bolts rusted to half the original diameter and they often break upon removal. So the Imperial ground straps were a beginning attempt to retard the damage caused by this electro/chemical reaction. the reason for the spacers under the ASD Module is to prevent contact with the wheelhouse metal and have rust.

Tip from Dick:

This sounds like the Automatic Shut Down Module (ASDM) is acting up. You can verify this by unplugging it and bypassing it with a jumper between the two #12 wires in its harness plug (see below for further details.) This device is present to shut down the EFI system when it detects something out of the ordinary as to running conditions, and is the source of many EFI system troubles. It does not cause any drivability problems to bypass it, but for safety, be sure you never leave the car with the key in the on position without the engine running, it would cause the throttle body to inject fuel, which would be a safety hazard.

If you have a service manual for this car, you will see the diagram which shows the location of the ASDM. Just in case you do not, the module is on the passenger side inner fender, about directly across from the alternator. It has a 5 wire plug going to it, which is held into the module with a center screw. To bypass it, remove this plug and jumper between the two largest wires in the harness with a short piece of bare wire. If you decide that this is the offending part, try running a separate ground wire from its case to the alternator ground terminal, often the problem with these is that the factory, in its penury, decided to allow the circuit to be grounded only through the mounting tabs, and with age and moisture, many of these cars have poor grounds here. The circuit is especially sensitive to poor grounding, thus these problems are common.

Tip from Bob:

On the other hand if there is a lack of fuel then the problem might lie in the ASD not signaling the pump to run at full speed to purge air out of the line. If your ASDM is the problem you can test it by bypassing it.

What you were saying about the ASDM capacitor makes sense. If it discharges fast then you would be able to start it again without any delay. The 23 volts comes out of pin #3 on the front of the hydraulic plate, according to my 82 manual it should be a pink wire. If you want to stick the wire with a pin that'll work. I can't really see any easier way to check , the engine has to be running. 23v goes to the CCC, throttle pot., airflow meter and fuel flow meter.

Question from Kurt (1981):

I saw a reference on the archives a while back about running a seperate ground lead from the ASD module housing to the ground stud on the intake manifold. What do you do? Tap a new screw into the ASD box and attach the lead to the screw? Also, how would one isolate the ASD from the fender to prevent "noise" from the frame? How about running the screws through rubber grommets and then attach to fender? What's the success rate on improvement of ASD function?

Reply from Dick:

The separate grounding wire is essential on these cars, as there is no provision for ground in the electrical plug for the unit, and the logic circuits are very poorly designed TTL logic, notorious for noise vulnerability. I isolate the ASDM from the inner fender with insulating washers and add a #14 wire to the ground lug on the alternator.

Follow-up question from Kurt:

Did you just ground it attaching the wire to one of the existing fender bolts over to the alternator?

Reply from Dick:

I don't think it matters where you connect to it, as long as you are making metal to metal contact to the case of the module, and you have insulated it from the inner fender.

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