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Dodgerench
Dodgerench, ASE Certified Technician
Category: Dodge
Satisfied Customers: 3385
Experience:  30+ years Dodge/Chrysler exp., ASE Master with L1 certification. Driveability/ combustion specialist
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Doodge Ram: I'm having trouble starting my 1985 dodge Ram half

Customer Question

I'm having trouble starting my 1985 dodge Ram half ton with a 318 motor. We've traced the issue down to the electrical start. The coil was not passing the electricity, so we tried a brand new ignition coil but the issue was unchanged. We are thinking that we narrowed it down to a couple of possibilities. There are a couple of relay type plates that are on the driver's side fender wall (one with a three pronged plug, the other silver metal plate, with male ends that protrude to plug in 3-4 female plugs, the other plate is a black square box(H8D) that has three male ends for a three pronged plug to plug into). The other option being a 4 pronged plug that plugs into a plate on the firewall, on the driver's side, that is alongside oval shape both inside a rectangular plate/box on that firewall. I'm looking at the wiring schematic but there are no names of the parts that I can figure. Do you have any idea?
Submitted: 1 year ago.
Category: Dodge
Expert:  Dodgerench replied 1 year ago.
Hi, my name is Ed. Welcome to JustAnswer!. I do have some ideas, but no longer have wiring harness info, unfortunately... so I'll have to wing it a bit.Do you know if your coil maintains voltage on the + terminal when cranking? Does it run OK once you get it fired up? Is this one of those starting problems where the engine seems to spin without spark, then catches as you let off the key?If so, it's probably a dual pickup plate system. Let me know and we'll push on from there. I may not be online much longer tonight (7/24). Talk in a bit, Ed
Customer: replied 1 year ago.
The coil does maintain voltage on the positive terminal when cranking. It won't fire up. No, there is no sign of the engine trying to catch at all, even when letting off the key. I tried changing the black box (which is the female receiver of a 3 pronged plug)that is attached to the left side of the fender, but nothing different. Just crank it until the battery dies. I've gone to pick your parts but can't find the rectangular box on the firewall hat also has electrical wires passing through it before getting to the black box then onto a silver relay with 4 plugs.
Expert:  Dodgerench replied 1 year ago.
Thanks. Let' try something to see if we can generate spark for test purposes. Locate the soft rubber connector at the distributor that has one male and one female terminal, visible when disconnected.Pull the coil wire from the distributor cap and set it in a spot where spark could leap from it to a good ground (about a half inch gap should be good).Turn the key on and then drag the harness side male connector on a good ground surface. This is called the "scratch test", which should produce a virtual storm of spark at the coil wire ... IF this is a single or dual pickup plate ignition system that uses the old ECU type controller. I hadn't imagined that your truck might have a Spark Control Computer (SCC), but in retrospect, this could be the case. If you can locate a black plastic box on the engine or behind the battery that has two push-in connectors (of 10 and 14 pins I think), you have an SCC system. The SCC will also have a vacuum transducer and vacuum hose running to it, which is a dead giveaway. I'm expecting the more common electronic ignition that was basically put into service back in the early 70s, which consists of a distributor with vacuum advance and an ECU that would be located on the driver's side fenderwell or bulkhead. It's a metal box consisting of 4 or 5 wires (likely 4 in '85). Once again, the presence of a vacuum advance on the distributor this time will tell you if it's the old ECU system. I don't expect the SCC system to produce spark in this test, but the ECU certainly should. The second distributor pickup plate (if equipped) is used during engine cranking only, so the test won't produce spark with the key simply turned on. We'll have to wing it a bit once you've gotten me some more information. Carry on!Ed
Customer: replied 1 year ago.
Couldn't find any plastic black box near the battery. There is a hose (6 inch) coming from the fuel injection system that runs along the sidewall and under the battery. We did the SCC scratch test prior to you suggesting it, with no spark. The electronic ignition box is on the firewall in fron6t of the driver and only has one plug with 4 prongs on the inside of the plug.
If I can attach to this email I will send you the schematic for the 85 Dodge. This might make the part designation easier to follow.
Expert:  Dodgerench replied 1 year ago.
Thanks for looking. It's the basic ECU type ignition system (no injection, tho). I think that hose is probably for the speed control servo.
Is this a single or dual type distributor pickup system?
Does the coil have something near battery voltage when cranking?
Do you have the left side of the diagram?
Customer: replied 1 year ago.
Hi Ed
to tell you the truth Ed, you haven't been much help (no offense intended). There are no vacuum systems that I can find. The electronic ignition system box (Which I think you refer to as the ECU) was replaced but with one that had 5 prongs instead of the 4 prongs like the one I removed. The engine actually started after the replacement but could maintain a charge or something because it wouldn't stay running once the key was released. Anyways, thanks for your attempts. I'll send you the other side of the engine wiring system and maybe something I've said has triggered an answer.
Looks like the program won't let me add any attachments/files.
Customer: replied 1 year ago.
This time the program did let me attach. Here's the wiring diagrams.
Expert:  Dodgerench replied 1 year ago.
By the sound of it, you're losing your coil's power source when you let off the key. Check the ballast resistor at both ends if necessary to see if you're getting power to the resistor (circuit J10, 14 gauge red wire) and if it's making it out (J9, pink). You'll get a power bypass from the starter relay when in the crank position, but when you let off, the ballast side should take over. If necessary, you can jumper 12 volts directly to the coil positive terminal to prove whether it's a loss of power problem. You just can't operate it for any length of time because the coil and ECU might overheat. That was a funny thing about those old ECUs -- they alternately had 4 or 5 pins, but none actually used that last pin. They can be interchanged.
Expert:  Dodgerench replied 1 year ago.
A different possibility to explain loss of spark when you let off the key is that some of these ignition systems used the dual pickup plate -- one for starting and another for running. Normal operation involved a relay that switched pickup plate input to the ECU while cranking, then toggled back to the run side when you let off the key. For this to work, you had to have a working relay and a good run-side pickup plate. Since you have spark now at least while cranking, it does appear that the old ECU was part of your problem. You might try the scratch test again to see if your results have changed.
Expert:  Dodgerench replied 1 year ago.
If there are two pigtails exiting the distributor, you'd need to use the one with male and female terminals on each plug. The start side pickup plate (if equipped) had two males or two females on their pickup connectors. Be sure that you're scratching the exposed male terminal (on the harness side connector) to a good ground source. I often used the coil mount bracket for this.