Rip's New '73 Navajo

[Ripinator]

Some food for thought... Good troubleshooting.

Chrysler Electronic Ignition System

WOW! Thanks again, John.

 

[Boydsdodge]

My money is on ECU. Make sure what ever you replace it with it has a very good ground.

 

[Ripinator]

My money is on ECU. Make sure what ever you replace it with it has a very good ground.

We shall see. . .

 

[saforwardlook]

Dan: Wish I'd known you were so close to us. We coulda had a libation or two.

The museum collection is in the facility where they used to build Vipers. I forget the name. They opened the collection for us only. It was terrific. Unfortunately, they would not allow any photographs. I don't think they want the public to know what is in there. . .

Sounds like the collection is now housed at the former Conner Assembly Plant then..........................

 

[75LandYacht]

My money would be on the pickup coil. Had a car ('73 Plymouth) with the same symptoms many years ago.

They seem to be an intermittent failure point.

My 75 did the exact same thing the RIP is describing, swapped out the pick up coil I never had an issue again.

 

[ceebuddy]

If it is only that the starter won't budge if you try to start the car the starter relais might be the problem. If these are old they are sensitive to a hot and humid environment (as is present if you steam-clean your car after it was driven for a while). At least that's my observation.

A slight tap on the relais might get it going again. It could also be opened and the contact surfaces clened, or replaced entirely.

 

[cantflip]

Some strangeness with the '73 Navajo: Last month, we drove the Navajo from Germantown, MD to Auburn Hills, MI to attend the Chrysler 300 Club, Intl meet. Before we left, I did a quick self serve car wash; when I finished, I tried to start the car in the wash bay, and it would not start. I messed around checking things under the hood and found nothing amiss or wet. Jumped back in and hit the starter. It fired and immediately quit. Went through this scenario a couple more times. I waited a few minutes more and hit the starter again. It fired right up and did not die again, until over eight hundred miles later, after we arrived in Michigan. Tried to start the car in the parking lot, after seeing the Chrysler museum collection. Again - Hit the starter and no fire. Checked around under the hood, looked down the carb throat for presence of fuel. All looked OK. Diddled with it for a while and it would start and die multiple times. Finally, it started right up and did not die again until this past Thursday (many miles after leaving Michigan and returning to Germantown). It died in my driveway and would not start. I pushed the turd into the garage and left it. Started right up the next morning - no issues. BTW, the car runs beautifully and got anywhere from 11 MPG to 17 MPG during the Michigan trip.

I think the problem is electrical, but I'm not sure where / how to diagnose. I replaced the coil yesterday and will drive the car for a while to see if it fails again. I think failing coils are insidious . . . Because they seem to fail only when they get hot, but not always. If it fails to start again, I'm gonna replace the ECU and see what happens afterwards. Do any of the cognoscenti here have a suggestion or two regarding this problem?

Hey Rip, try testing the parts with an ohmmeter... FSM for specs, but you could compare to the replacement part as well. Pickup ohms could be good until hot, no easy way to test that unless you wanted to try to do it at failure... but often will still be out of specs when cold. Ignition coils are similar. Ballast too, but ballast can be easily checked with a voltage drop while cranking/running too.

You already know about setting air gap, if too big it may cause similar symptoms as signal strength is decreased and could cause intermittent issues with high temperatures.

I always feel better about a repair when I know I've replaced parts that tested bad with parts that tested good... there have been occasions that I tested/replaced a number of parts (including replacements) before I was satisfied that everything was in good condition... and there could still be something that ohms good, but fails when hot.

@halifaxhops has been trying to sell a module tester, which a DMM could work in place of... basically it just checks for a on/off signal from the module under test... DMM showing a frequency while cranking, from the module to the coil tells similar information. The module tester is a good option for someone who doesn't want get into learning how to used a DMM and can bench test before replacement. The complexities of an aftermarket tool like this are the adapters for connecting to the common brands modules of the day. It also cant conclusively pass/fail a module that has heat problems unless you catch it hot and failing.

When this stuff was newer, it usually was only one parts to solve a problem... at this age, don't be shocked if everything you test falls outside of spec. It's also possible everything tests good and the heat sensitive piece doesn't show until it does... worst case scenario.

Ignition scopes do a much better job of showing weak parts, but another lesson entirely and few own a working one.

 

[Ripinator]

Hey Rip, try testing the parts with an ohmmeter... FSM for specs, but you could compare to the replacement part as well. Pickup ohms could be good until hot, no easy way to test that unless you wanted to try to do it at failure... but often will still be out of specs when cold. Ignition coils are similar. Ballast too, but ballast can be easily checked with a voltage drop while cranking/running too.

You already know about setting air gap, if too big it may cause similar symptoms as signal strength is decreased and could cause intermittent issues with high temperatures.

I always feel better about a repair when I know I've replaced parts that tested bad with parts that tested good... there have been occasions that I tested/replaced a number of parts (including replacements) before I was satisfied that everything was in good condition... and there could still be something that ohms good, but fails when hot.

@halifaxhops has been trying to sell a module tester, which a DMM could work in place of... basically it just checks for a on/off signal from the module under test... DMM showing a frequency while cranking, from the module to the coil tells similar information. The module tester is a good option for someone who doesn't want get into learning how to used a DMM and can bench test before replacement. The complexities of an aftermarket tool like this are the adapters for connecting to the common brands modules of the day. It also cant conclusively pass/fail a module that has heat problems unless you catch it hot and failing.

When this stuff was newer, it usually was only one parts to solve a problem... at this age, don't be shocked if everything you test falls outside of spec. It's also possible everything tests good and the heat sensitive piece doesn't show until it does... worst case scenario.

Ignition scopes do a much better job of showing weak parts, but another lesson entirely and few own a working one.

Thanks a lot, Jeff for taking the time to discuss my problem. Why does this all seem like a black art ?!?

 

[Ripinator]

If it is only that the starter won't budge if you try to start the car the starter relais might be the problem. If these are old they are sensitive to a hot and humid environment (as is present if you steam-clean your car after it was driven for a while). At least that's my observation.

A slight tap on the relais might get it going again. It could also be opened and the contact surfaces clened, or replaced entirely.

Thanks for this insight. However, the starter is fine. It spins the engine really fast. Damn thing just won't fire during this particular episode. . .

 

[Ripinator]

My 75 did the exact same thing the RIP is describing, swapped out the pick up coil I never had an issue again.

Thanks, John. The P/U coil is next on my list to try. . .

 

[halifaxhops]

Hey Rip, try testing the parts with an ohmmeter... FSM for specs, but you could compare to the replacement part as well. Pickup ohms could be good until hot, no easy way to test that unless you wanted to try to do it at failure... but often will still be out of specs when cold. Ignition coils are similar. Ballast too, but ballast can be easily checked with a voltage drop while cranking/running too.

You already know about setting air gap, if too big it may cause similar symptoms as signal strength is decreased and could cause intermittent issues with high temperatures.

I always feel better about a repair when I know I've replaced parts that tested bad with parts that tested good... there have been occasions that I tested/replaced a number of parts (including replacements) before I was satisfied that everything was in good condition... and there could still be something that ohms good, but fails when hot. A scope gives you a visual of the ignition pattern and is great for certain things also.

@halifaxhops has been trying to sell a module tester, which a DMM could work in place of... basically it just checks for a on/off signal from the module under test... DMM showing a frequency while cranking, from the module to the coil tells similar information. The module tester is a good option for someone who doesn't want get into learning how to used a DMM and can bench test before replacement. The complexities of an aftermarket tool like this are the adapters for connecting to the common brands modules of the day. It also cant conclusively pass/fail a module that has heat problems unless you catch it hot and failing.

When this stuff was newer, it usually was only one parts to solve a problem... at this age, don't be shocked if everything you test falls outside of spec. It's also possible everything tests good and the heat sensitive piece doesn't show until it does... worst case scenario.

Ignition scopes do a much better job of showing weak parts, but another lesson entirely and few own a working one.

Wow Jeff you nailed it. There are a ton of ways to test it, just how much do you want to learn? I totaly agree the environment make a big difference a part can be fine cold then not work hot. When I bench check ECU's I throw them in the fridge and then heat them up, they fail usually heated up around 130 F.

 

[Ripinator]

Wow Jeff you nailed it. There are a ton of ways to test it, just how much do you want to learn? I totaly agree the environment make a big difference a part can be fine cold then not work hot. When I bench check ECU's I throw them in the fridge and then heat them up, they fail usually heated up around 130 F.

Thanks a lot, Ray. Funny. . . I was thinking of you the whole time I've been messing with this thing. . .

 

[halifaxhops]

Call me fast way easier. Sent you a pm.

 

[cantflip]

Thanks a lot, Jeff for taking the time to discuss my problem. Why does this all seem like a black art ?!?

Its not... any coil is a hair-like strand of copper, insulated by varnish and wound x# of times. Used to create an electro-magnet or to build voltage. Testing with an ohmmeter can tell you if there is high resistance from micro fractures in the wire (high resistance), or shorts from the varnish overheating (low resistance). Temperature naturally affects the resistance of the coil, so most specs are set for 70*F. FSM ohmmeter tests are easy and good, but leave out some failures. If you get familiar with your DMM and it has the appropriate ranges and functions, lots of mind bending problems can be diagnosed with it.

The ECM or module is basically just a transistor... an electronically activated switch... and testing that it still turns on/off is easily done using the frequency setting, but caution that some DMM's can only measure frequency in AC voltage and this will be DC. the ballast is a simple resistor... GM's of the era used a resistor wire... same idea.

None of this is hard, but our cars were built when this stuff was in its infancy for automotive use... no other appliance gets exposed to as much vibration or environmental conditions and those are the leading cause of failures over time.