slant six starting problems

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mewk61

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I have a 75 Dart with a slant six that is giving me problems. It was starting fine and when I drove it for a while, I turned it off and it would not start until it cooled down.
Now yesterday, it would not start at all. I changed the coil ater looking at different posts and still nothing. I changed the ballast resistor and it started up but stopped after running for about five minutes. I got it started again and let it run for about ten minutes and it died as if someone shut the motor off.
I had an extra ECU so I changed it and nothing. The same with the voltage regulator as I was getting desperate.
I am getting fuel, spark at the distributor, and now looking for any suggestions.
Thanks in advance.
 
How, EXACTLY are you checking spark?

What does this spark look like?

You must realize that the ignition switch, and depending on how you do this, can give you misleading results.

If example you have a cranking circuit problem, but you check for spark by jumpering across the starter relay, that there is a problem.

"Rig" a spark tester where you can see it and check for spark USING THE KEY. Do not use a resistor coil wire. You should get a nice fat rythmic spark, nice and blue, at least 3/8" and more like 1/2" long.

What shape is this engine in? Lots of miles? Good compression? You checked the plugs?

Check the cap / rotor, for grease, dirt, moisture, damage, and spark "punch through" on the rotor. Check resistance of the coil wire, at least. Check the plugs, condition?

Has anyone been "helping" with what's in the fuel tank?
 
By chance is the carb flooding the engine out because the float could be bad. Or is the choke plate sticking almost shut.
 
Weak fuel pump, bad float (or float out of adjustment). Just ideas to double check.

Does it run hot? could even be a timing issue.
 
Extra ecu may not be a good one. You cant just plug it in to try it either. It needs a good chassis ground before its plugged in, then the battery is connected
 
I had a simple no start problem with mine. I replaced the electronic type stuff only to find out I had a loose ground wire. Pretty simple but very overlooked in the no starts. Change out your old ground cable. Other times the starter relay and it's wires (another ground) were loose and old. Sometimes they shake loose. Hope I helped.
 
How close is the fuel line to the exhaust manifold I was curious if that could effect running (I don't know) after the slants get hot. I have a clear fuel filter that when hot looks like it's boiling. Wonder if that's part of why they don't like to start after they're warm?
 
You might have a bad float or maybe you have moisture in your tank. Add a thing of dry gas to your tank and see if it starts up. I had some water in my tank when i first got my 1974 dodge dart swinger and i added some dry gas to it and it started right up without stalling. It would just cut off at certain points until i added dry gas.
 
Well since it's been a few days, I'd guess he's starved to death by the side of the road by now, LOL

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If it was a ground issue, would it still turn over? This keeps cranking, but no fire.
 
If the ECU (spark box) was not grounded, the starter would still turn the engine over fine, but no spark = no start. Run a dedicated ground wire to a mounting screw on your ECU. Don't rely on a rusty sheet metal screw like the factory did. Buy a cheap in-line spark tester at Harbor Freight and put it in-line with a spark plug next time it won't start and see if the tester is flashing as you crank.
 
thanks I'll try it. I just tore off the carb and put it back on. I don't think that was it. Still turns over, but no fire.
How can I check the ECU or do I just need to replace it? I have a funny feeling this is the problem as it went from not starting when hot to not starting at all and I haven't driven it.
 
Here is a way to seprate the parts of the system so you can start to localize the spark problem:

Remove the wire from the - terminal of the coil. The turn on the ignition to run. The connect a short jumper to the - coil terminal and mometrarily touch it to ground; immediately remove the ground and at that moment, the coil should produce a good spark.

If you get a good spark with this, then the prolbem is in the distributor, ecu or the wiring between them and to the coil -, or in the grounding somewhere. If yo don't get the spark this way, then the problem is in the battery circuit to the ignition switch, through the ballast and to the coil, or in the coil.

This procedure divides the system in half and starts to isolate the problem, rather than just shotgunning and praying.

However, from your original post, if the spark is truly good (please re-read Del's post about how are you testing for spark, and where? ), then you have a fuel problem (duh!). When you say it is getting fuel, what do you mean?

Please answer some of the previous questions; they are aske d for good reason, and it is hard to help you if you don't give good feedback; the questions are being asked for good reason.

Do you have a volt-ohm meter? It is an excellent tool with spark issues.
 
Sorry for the slow response guys. I have limited time that I can work on the car. I really appreciate everyone's help.
I pulled pff the carb and checked the float by checking its condition and seeing if it moves in the bowl by adding fuel when apart. I also removed it and checked it for damage. Everything looked fine. I also checked the fuel pump by pulling the fuel line going into the carb and craned the motor. Looks good.
This weekend I will try some of the ideas you all have given me.I bought a new ECU to try as I want to have one that I know is good even if this isn't the proble this time. They seem to cause problems often. I guess I should have listened to my dad better when I was growing up as he was a forty year Mopar mechanic. He hated replacing parts rather than finding the problem.
Thanks again for the help.
 
Changeneering it is called.
First off, diagnosing with this small amount of info is difficult.
Did you do any work to it recently? Any other symptoms?

With your diagnosis, try to be methodical. You need to determine if it is fuel, electrical or timing related.
First off, try using starting fluid to see if you get any ignition. If so, you likely have a fuel delivery or timing issue. If it backfires, check the distributor timing. If that is ok, maybe time to check valve timing.
If you get no fire at all, a multimeter can be used on the wiring up to the coil input. I am not sure with the ECU's since I have no experience with them, but I believe with the key on, you should have 12 volts coming in to the coil. You may have to crank the engine for the voltage to turn power on to the coil. If not, trace it back and find out which component is getting but not forwarding voltage.
If you have have good spark, is the carb squirting when the throttle is actuated? If not, your carb is fuel starved. Crank the motor and try it again. If no fuel, trace it back to where the fuel stops. Typically a bad float setting, fuel pump or clogged fuel filter etc.
If you have spark and fuel you need to check the ignition timing and possibly the valve timing. These typically wont change unless you have something worn or broken or they were recently adjusted. I would rule out all of the other stuff first unless you made some unreported changes recently to the distributor or valves.
Assuming you have spark, check the ignition timing.
These are some basics to check. Report back and let us know what you find. From there we can dig deeper.
 
Put fuel into an IV bag and let it gravity feed the carb, vapor lock diagnosed! Now figure out how you can do that with what you got. Also pull cap and make sure dizzy is turning. Coukd ave stripped your pastic gear
 
So I changed the ECU and that didn't work. I tried grounding the ECU as suggested and it didn't work. Starting fluid did not work. With key on I got 6.5 volts to the coil and 9.6 while cranking.
 
I pulled the number one plug and turned it over to check to see if I had spark. Nothing at the plug until the key is turned off. That is when it gives a good spark.
I also tried putting on a timing light and I can't get a light to flash while turning the motor over.
 
Somewhere on this site I have written numerous times, a step by step on troubleshooting Mopar systems

Remove the ECU and clean the ECU and firewall and remount with star lock washers. The ECU MUST be grounded. MUST. Remove ballast, ECU and distributor connectors, and examine for corrosion. Work them in/ out several times, especially distributor connector. Examine the distributor pickup / reluctor for rust and debri, and strike damage. Wiggle the shaft and look for play. Obtain a .008 brass feeler (inches not metric) and check reluctor gap. If you hook an AC multimeter to the distributor connector and crank the engine, the distributor should produce about 1V ac. If you turn the key on, and ground one of the two (try both) distributor harness wires going to the ECU it should produce a spark

9V cranking at the coil is too low Try hooking a clip lead from the coil + to the starter relay battery stud and crank the engine.
 
mewk61 said:
I pulled the number one plug and turned it over to check to see if I had spark. Nothing at the plug until the key is turned off. That is when it gives a good spark.
I also tried putting on a timing light and I can't get a light to flash while turning the motor over.
Click to expand...
Hmmmm, that may be the clue needed. It sounds very much like the wire from the - coil to the ECU is grounded between the coil - and ECU. With this wire shorted, there will be constant coil current that is cannot be turned on and off by the ECU as it needs to do to create each spark, and it would tend to overheat the ballast too. Turning off the ignition will interrupt the coil current and cause the spark you see despite such a ground.

To explore this possibility, try a few things:
1) Remove the wire from the - coil terminal. Using a separate jumper to the coil - and with the ignition on, ground the coil - for a moment and then remove the gound; you should get a spark everytime you ground and unground the coil - with ignition on.
2) Examine the wire from the coil - to the ECU plug to see if it is chafed and bare and grounded anywhere.
3) If it looks OK, then have it disconnected at the coil - and have the ECU plug disconnected (so that this wire is disconnected completely) and use the meter to check from that wire to ground to see if you can find any shorts.
 
So here is the latest. I checked the connections at the coil and at the ECU for corrosion and cleaned it all and put it back together. Tested the ciol for voltage and got 1.4 volts AC. Tested the negative side of the coil for spark with the key on and got a spark on and off when I put it to ground. I checked the reluctor for gap and adjusted from .010 to .008. Checked the distributor for rust or damage everything looks good. I do have a small amount of side to side play.
Checked the negative wire from the ECU to the distributor with an ohm meter and tested good with each end removed.
Any ideas? I think I have covered what has been suggested.

Thanks again.
 
So maybe this will help with your troubleshooting. Please note that all voltages are DC volts and not AC. Make sure that you have your meter set to DC Volts.

Good Luck!
 

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OK, please confirm that you got a good fat spark from the coil's spark wire when you manually grounded and ungrounded the coil - with the ignition on, that jumps a gap of 1/4" or more. If so, then your coil, ballast, and ignition switch are probably good. (I say 'probably' because I am not there to see it all!).

Can you explain what you mean by "Tested the ciol for voltage and got 1.4 volts AC." Do you mean the 'tested the reluctor'? Please descirbe the test and connections for this if you were testing the coil; it is not making sense to me.

One more thing to do: Did you remove the coil - wire and check it is around zero ohms end-to-end from the - terminal to the other end of that wire in the ECU connector (when it is removed from the ECU)? Also, with that wire removed from the coil - and the ECU plug disconnected, check that wire to make sure it is not grounded to chassis. You need to make sure that this wire is good and not grounded, or the ECU cannot control the coil to generate the spark. If this wires chekc good with the meter, you should then reconnect that wire end to the coil - and with the ECU connector off of the ECU, ground and unground that wire manually and see if you still get a good fat spark. Be careful to momentarily grornd this wire only! When you do this, you are simulating what the ECU does to cause the coil to generate a spark.

FYI, if the ballast gets hot when the igntion is on and with the ECU connector disconnected, then there is very likely a short in the coil - wire to the ECU.

Sent you a PM
 
Sorry,

Forgot that you had electronic ignition. It sounds like you might have a bad ignition switch because you said that the coil produces a spark when you let go of the key. There are 2 circuits built into the ignition switch, one that provides full battery voltage to the positive (+) side of the coil when cranking (this insures a hotter spark when starting a cold engine) and a second contact that runs the batter voltage through the ballast resistor to the positive (+) side of the coil. This lower voltage (typically around 9 or 10 volts) is used so that the coil doesn't overheat and burn the coil open. You can try, as a test, using a jumper from the battery positive terminal or starter relay to the positive (+) side of the coil. Crank the engine and if it starts you probably have a bad ignition switch. DO NOT leave the jumper connected for a long period as you could burn open the coil.

Good Luck
 
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