Hey all,



I recently swapped the engine on my van with an identical 5.9 long block. I swapped the quadrajet carb for an edlebrock 650. I removed the air pump and EGR system. I went to turn it over for the 1st time and I’ve got no spark. With the key on I tested the ignition coil and it’s got roughly 4 volts which is way too low. However, when I unplug the ECU the coil reads the same as the battery, 12 volts( as it should).



What could possibly be happening? Why would the ECU being in the circuit bring the voltage down on the coil? All the electrical worked fine before I did the engine swap. It’s a carb engine. Do I even need the ECU?



-dune

 

The ecu is your brain box for the electronic ignition. I think. 1988 is when Chrysler was going from carbs to TBI injection. Did you check your ballast resistor? Those reduce the voltage so the brain box can work but they are really prone to failure. I always carried an extra back in the day in my tool box wrapped in a towel.

 

I haven’t checked the ballast resistor. How would I go about doing that? Could it also have something to do with the ignition condenser?

The 5.9 in ‘88 was still carbureted but it calls it an electronic ignition. So a carb with an ECU module.

thanks for your response!

 

Electronic ignition became an option in 1972 and was so good, it was on all Chrysler products in '73. It did away with points and condensers as well as a twice a year tune up. So you don't have a condenser in your ignition The ballast resistor is about 1/2 an inch by 2 inches, usually mounted on the firewall although I've seen them on the inner fender too. It's a white piece of porcelain with either 2 or 4 electrical tabs. Power goes through it to your brain box. It reduces 12 volts to 6 for the ignition to work properly. You can TEMPORARILY jump across the ballast resistor to see if it works. Do NOT leave it like that as it will eventually fry the engine controller. (Actual name for the part, I prefer brain box because I'm strange that way. )

Now, I'm assuming you have regular electronic ignition. In the late 70's for emissions reasons, Chrysler came out with a lean burn ignition. Instead of a box on the inner fender, it's a module on the side of the air cleaner. I've seen them work okay but every car I've had with it I converted to regular electronic ignition.

 

For whatever reason mine does have a condenser on it, though someone may have added it aftermarket (I’ve owned the van for 5 years).

Bought a new ballast resistor that I will try tonight. Which direction does it decrease the voltage? My chassis manual says I should be reading within one volt of the battery at my ignition coil leads. Without the ECU plugged in I do, when it’s plugged in, it decreases roughly 6 volts.

My ECU is on the center of the engine bay side of the firewall beside the ballast resistor. See photo (ECU unplugged in photo)

 

The perspective of the carburetor was messing with my head then I remembered you have a van. That white block is probably your ballast resistor. Your control module looks a bit sketchy. They do go bad. The resistor on the controller itself is rusty (round and bolted to the controller body itself) and I've never seen one like that before.. Before replacing it, I'd clean it good and make sure it's got a clean ground as it grounds out through the body where it bolts on. The power comes from the battery to the ballast resistor.

I'm thinking your issue is either in the ballast resistor or the controller itself. If you can find a good one in the bone yard, that will all interchange unless you have lean burn. You don't.

 

Replaced the ballast resistor and still no luck. It definitely drops in voltage across the resistor as it should.

Just to triple check, I should see full battery power at the ignition coil in the key is on, correct?

I guess it must be the ECU then? Though it worked fine before the engine swap. Is there anything in that process that would cause an ECU to malfunction?

Any chance it would be the starter relay? I hear it click but not everytime. The two hot wires going into it, 1 reads 12 volts and the other 6volts.

Thank You so so much for going back and forth with me on this. It’s super helpful

 

Chrysler had two different designs for the electronic ignition one with two wires and one with four, You have the two. they both work the same cut the battery voltage down during run. You have two wires coming from the ignition switch, "run" and "start/crank". You should have power to one or the other during run or crank. Here is a diagram.

 

Ya I do have power coming from those wires at the right time. I talked to some friends today and we came to the conclusion that maybe it is as simple as the ignition coil. It sounds like I should only see 6ish volts at the coil when the key is turned to run.

just to pick your brain, I have 6 volts at ignition coil on both positive and negative terminals with the key in run. Engine turns over but produces no spark. Does that just leave the ignition coil as being the offender?

 

I've replaced several coils to run a hotter spark but in 55 years, I've only replaced one because it had failed. They are about as fool proof and it comes. I'd suspect the brain box before the coil. I have replaced those because they failed. Make sure the box is grounded and if the problem persists, replace it. I don't like the look of the box. It looks pretty rough. Snag a couple out of the junk yard and swap one in. If you can find one. They went away when Fuel Injection came in. They all look alike and will interchange. just don't bother with the lean burn engine. You're looking for 1973 to early 1988 vehicles.