Intermittent crank no start

-
73_swing

73_swing

Member
Joined
Jun 13, 2023
Messages
9
Reaction score
7
Location
New York
Hello Everyone, I'm new to FABO so I'll try my best to present my issue and what I've done so far.

I have a 73' Dodge dart swinger with an automatic slant 6 that was being used as a daily driver until this issue started.

Recently the car has had a crank no start issue. When I do get it started in runs very smoothly and then suddenly dies after roughly 5 minutes. Sometimes it will idle really high but then eventually die the same way.

The battery's voltage reads 12.50v when it's sitting and 13.25v if I get it running. I have re-grounded the ECM and voltage regulator. I used electric parts cleaner and cleaned / brushed all of the connections along the electronic ignition system that I saw. I brushed the terminals in the distributor cap and checked the gap between the reluctor and pickup (only visually, I didn't want to mess with it if I didn't have to).

coil positive to ground key on I get a dim light, crank I get bright light
coil negative to ground key on I get no light, crank no light either

When the car does start up I notice that the spark is very weak. only jumps about a 1/4 inch or so. Coil + reads 6.88v coil - reads 3.10v.

Any help would be much appreciated, I hope this gives you all enough information to help me.
 
The coil NEG seems high. Here is how this works. The ECU switches the coil NEG in the same way that points do--to ground. It might be the ECU is poorly grounded, or that the ground path from block to body is poor. I like to recommend people add a big "ford style" starter to solenoid (eylet to eyelet) cable from the firewall to the block. You can usually bolt it, EG to the master cylinder stud

Also scrape the firewall and mounting ears of the ECU and make sure they are tight.

"Work" the ECU cable connector in/ out several times to scrub the terminals and to "feel" for tightness. Inspect them with a flashlight for corrosion

Did you read the coil + when cranking or with key on/ engine stopped? This creates a different circuit.

With key in "run" and engine stopped, you should measure perhaps 6--10V at coil + but when cranking USING THE KEY, the coil + should read very close to "same as battery".

Don't depend on your spark test if you have resistor wires. Always "rig" a real wire out of the coil tower to test spark, and it should be hot, blue, and at least 3/8 and often 1/2"

Other voltage issues to check is the ignition "run" (IGN1) line through the bulkhead connector, through the ignition switch connector AND THE switch itself.

One way around voltage drop here is to cut the "run" wire soon after it enters the engine bay, use the firewall end to trigger a Bosch relay, and feed the relay contacts off the starter relay. Connect the engine bay end of the cut "run" wire to the switched contact

If voltage drop is the problem THIS WILL also prevent overcharge voltage as well
 
67Dart273 said:
Also scrape the firewall and mounting ears of the ECU and make sure they are tight.

"Work" the ECU cable connector in/ out several times to scrub the terminals and to "feel" for tightness. Inspect them with a flashlight for corrosion

Did you read the coil + when cranking or with key on/ engine stopped? This creates a different circuit.

With key in "run" and engine stopped, you should measure perhaps 6--10V at coil + but when cranking USING THE KEY, the coil + should read very close to "same as battery".

Don't depend on your spark test if you have resistor wires. Always "rig" a real wire out of the coil tower to test spark, and it should be hot, blue, and at least 3/8 and often 1/2"

Other voltage issues to check is the ignition "run" (IGN1) line through the bulkhead connector, through the ignition switch connector AND THE switch itself.

One way around voltage drop here is to cut the "run" wire soon after it enters the engine bay, use the firewall end to trigger a Bosch relay, and feed the relay contacts off the starter relay. Connect the engine bay end of the cut "run" wire to the switched contact

If voltage drop is the problem THIS WILL also prevent overcharge voltage as well
Click to expand...
The firewall and mounting ears have been scraped and have brand new screws

The ECU has been checked for corrosion and cleaned. feels tight

key run coil pos 5.30v coil neg 1.37v
crank coil pos 9.16v coil neg 1.87v

I tested spark coming out of coil with a real wire and it still looks pretty weak

I'm checking the switch connector and switch right now so I'll let you know.

As for the last part I'm a little unsure exactly how that would be done. Are there any other threads where people have done this that I could look at?

Thanks
 
Done what, check the connector? You need to check for voltage drop all along the path. The closest point you can easily pick up the supply point for the key is where the big red wire from the fuse link enters the bulkhead connector, at the firewall. Check this UNDER LOAD in other words with key in "run." Note that voltage

Next would be other side of the that connector in other words up under the brake pedal, but that is difficult. From there the ammeter, but that is difficult

So now, access the ignition switch connector where it leaves the column. You have the wire going "in" is the hot 12V into the key from the ammeter splice, a continuation of where I just started. You have a connection there, so check both sides of the connector, for voltage, and wiggle it, maybe even work it in/' out

Then check the output going OUT of the switch the "ignition run." If that is noticeabley lower voltage than where you measured out at the big red on the firewall, you have found some drop.

Next, measure that same line---the IGN1 "run" wire--out at the firewall connector in the engine bay. If it has dropped any from the ignition switch connector reading, then you have a poor connection in the firewall connector for that wire

So the functional path is sort of this:

BATTERY, FUSE LINK, BIG RED TO FIREWALL CONNECTOR---through connector to AMMETER on RED, through ammeter and out BIG BLACK to WELDED SPLICE, branch off and feed to IGNITION SWITCH connector--through the connector and TO AND THROUGH THE IGNITION SWITCH.....out the switch on the IGN1 "run" wire----THROUGH THE IGNITION SWITCH CONNECTOR--to and THROUGH THE FIREwALL CONNECTOR, and BRANCH OFF and feed the ignition system, alternator field , VR, electric choke if used, etc etc.

Now your coil+ readings aren't that bad, but some low, and the CRANK voltage is rather low.

So now you need to check the path for drop for the CRANKING circuit, here is how that works. The ignition system has TWO power sources. The IGN1 "run" wire IS ONLY ENERGIZED with the key in "run." That goes DEAD when you twist the key to "start."

HOW DOES the ignition circuit get power in "start?"

You have a SEPARATE switch contact/ circuit, marked IGN2 which is ONLY energized during cranking. This is DIFFERENT and SEPARATE from the "start" circuit to the start relay, but works the same--it is "hot" in "start."

This contact only goes one place---via (usually a brown) wire out through the firewall to the coil + side of the ballast.

THIS IS WHY it is important to do testing by twisting the key rather than jumpering the start relay, because you have different situations.

So same deal---check for voltage drop, and take your readings WHILE cranking the engine WHILE twisting key to start.

This is COIL +-----to firewall connector BROWN (look that up or post back)---through connector, IGN2 wire goes from firewall connector to IGNITION SWITCH CONNECTOR where you can measure that as before-----through switch and out switch and to SWITCH CONNECTOR to the BLACK supply which is hot.

EACH OF those switch contacts and wire terminal/ connector points is a place for corrosion, damage, and voltage drop

AND THE SWITCH ITSELF

To fix voltage drop in IGN1 you can install a relay in the "run" wire where it leaves the firewall, and if necessary, you can also "fix" the IGN2 bypass circuit also with a relay.
 
Here's the thing. It IS a gamble. After you have checked everything, you still might have a "weak" dist. pickup or poor connection in the pickup connector. You might have a poor connection in the ECU connector. Those are difficult to get to and difficult to evaluate.

Along with that, check the reluctor gap in the distributor., We've had discussions and some of us believe that the dist. pickup magnet can become weak. There is no way to test for that other than to try a different one. And there is a possibility that something in the ECU is actually causing this, and THAT is a gamble.

I built myself a box with a complete coil and HEI module that I use to fire engines and had intended to carry for a spare ignition.

I just connect the distributor, the green wire to ground, and the yellow to a hot battery connection (starter relay stud) and go

4pin-jpg-jpg.jpg


hwlcfa-jpg.jpg
 
Yet another idea: Do you have a workable breaker points distributor lying around. The coil/ ballast wiring for breaker points is same for electronic. All you need to do to swap in a points dist. is.........

Disconnect the ECU box
Drop in points dist. Connect dist wire to coil NEG in place of wire now connected
 
67Dart273 said:
Yet another idea: Do you have a workable breaker points distributor lying around. The coil/ ballast wiring for breaker points is same for electronic. All you need to do to swap in a points dist. is.........

Disconnect the ECU box
Drop in points dist. Connect dist wire to coil NEG in place of wire now connected
Click to expand...
Unfortunately I don't have a points distributor around.

I'm going to start by checking both functional paths for voltage drops and go from there.

Then I'll try some of your other suggestions.

I really appreciate the detailed instructions, this is just what I needed. I'll keep you updated.
 
I intended to mention this and someone else did earlier. Have you tried simply jumpering 12V direct to coil +? You don't want to run it this way very long, but doing so might give you an idea of where you stand, IE if it cranks right up and runs, you know you are headed down the right track of low voltage.

Also, "I think" that I know that a .177 caliber rifle brush (same as bb/ pellet) will fit and clean the connectors such as flat trailer connectors, the distributor pickup connector, and the connector on the ECU. You might investigate that.

(EDIT:) Just checked, and yes, a .177 pellet fits snug right into the female terminal of those connectors
 
Last edited:
The other day I tried but I didn't have long enough wires on me. I'll get my jumper cables and give it a try. I don't have a rifle brush but I found this tiny plastic bristle pipe cleaner type thing that's been doing the job haha.

So if the 12v jump to coil positive does get it started the assumption is that something upstream from the coil is causing voltage drop?
 
Basically, yes. Once you learn to check voltage drop, you will learn more. Just follow the diagram, like a map.

You cannot reliably check for drop in the harness with an ohmeter. The resistances are too low for a meter to be accurate, and the situation often changes due to current, IE current through a bad terminal can heat up and worsen the situation, etc.
 
73_swing said:
Recently the car has had a crank no start issue. When I do get it started in runs very smoothly and then suddenly dies after roughly 5 minutes.
Click to expand...
And then how long before you can get it to start again? This doesn't act like a dirty or faulty connection sounds a lot like a failing electrical component in your ignition system which works marginally, heats up quicker than it should, and then quits working at all til it cools back down. Suspects are the ignition box (ICU/ECU, mounted over on the driver's side at the rear of the engine bay), the pickup coil (inside the distributor), the ignition switch, and the ignition coil (not as likely, especially as it's been replaced recently).

If you want to try some diagnostic work rather than just shotgun-replacing parts, fetch a hairdryer and some basic tools. Start the car to verify it will start, then shut it off. Remove the distributor cap and aim the hairdryer, on a hot setting, at the pickup coil for a few minutes; get it good and hot. Snap the cap back on and try to start the car. Does it start? If not, replace the pickup. If it does, then shut it off again and heat up the ignition box with your hairdryer. Get it good and hot. Try starting the car. No go? Your ignition box is faulty. Yes go? It's something else.

Much more difficult to heat up the ignition switch to test, so this diagnostic technique has its limits, but you can also do the opposite: engine stops running on its own, remove the ignition box from the car and put it in the freezer for half an hour. Put it back in the car; does it start?

Also, watch your inbox for a PM.
 
slantsixdan said:
And then how long before you can get it to start again? This doesn't act like a dirty or faulty connection sounds a lot like a failing electrical component in your ignition system which works marginally, heats up quicker than it should, and then quits working at all til it cools back down. Suspects are the ignition box (ICU/ECU, mounted over on the driver's side at the rear of the engine bay), the pickup coil (inside the distributor), the ignition switch, and the ignition coil (not as likely, especially as it's been replaced recently).

If you want to try some diagnostic work rather than just shotgun-replacing parts, fetch a hairdryer and some basic tools. Start the car to verify it will start, then shut it off. Remove the distributor cap and aim the hairdryer, on a hot setting, at the pickup coil for a few minutes; get it good and hot. Snap the cap back on and try to start the car. Does it start? If not, replace the pickup. If it does, then shut it off again and heat up the ignition box with your hairdryer. Get it good and hot. Try starting the car. No go? Your ignition box is faulty. Yes go? It's something else.

Much more difficult to heat up the ignition switch to test, so this diagnostic technique has its limits, but you can also do the opposite: engine stops running on its own, remove the ignition box from the car and put it in the freezer for half an hour. Put it back in the car; does it start?

Also, watch your inbox for a PM.
Click to expand...
It's hard to say. Everyday I work on it I'm cleaning / testing something different based on this thread and other ignition troubleshooting threads. I generally get it started after testing some of the components with the key in the run position for a few minutes - I don't know if this means anything. It runs smooth and will start right back up if I try it again the same day but if I try the next morning it's back to crank no start.

I'm actively trying to avoid part replacement until I've found probable cause. I'm out of town right now but when I get back I'll try that hairdryer/freezer trick you mentioned.

I just read your PM. Thanks for the reading suggestions ! I'll check those mods too!
 
Don't know if its been mentioed, but have you chrcked the connections in the bulk head connector,??. They are notorius for causing intermitened start problesm.
Just a thought.

Dave
 
barracudadave67 said:
Don't know if its been mentioed, but have you chrcked the connections in the bulk head connector,??. They are notorius for causing intermitened start problesm.
Just a thought.

Dave
Click to expand...
I did, I gave them a thorough cleaning and inspection.

Thanks for the suggestion
 
67Dart273 said:
I intended to mention this and someone else did earlier. Have you tried simply jumpering 12V direct to coil +? You don't want to run it this way very long, but doing so might give you an idea of where you stand, IE if it cranks right up and runs, you know you are headed down the right track of low voltage.

Also, "I think" that I know that a .177 caliber rifle brush (same as bb/ pellet) will fit and clean the connectors such as flat trailer connectors, the distributor pickup connector, and the connector on the ECU. You might investigate that.

(EDIT:) Just checked, and yes, a .177 pellet fits snug right into the female terminal of those connectors
Click to expand...
I just tried cranking with jumper wire from battery positive to coil positive and it didn't start.

So now would the assumption be that that something downstream is the problem such as the coil, distributor pickup or connections?
 
Id like to see how this turns out. I'm having the same issues. Something is intermittently losing contact in the start circuit. Then when I shut off the key it tries to fire. I've checked everything in the run position. It's a bit harder to do the same while starting without another set of eyes and hands. Don't want to have to go back to points ignition but I could for now.
 
You must log in or register to reply here.
-

Back
Top