Question: Won't Start - Not pumping gas & no spark
Have a 1987 Plymouth Voyager, with a 3.0-liter, and about 191,000 miles on it. Was driving it the other day and the engine just died, like turning off a light switch, and wouldn’t restart. Had to have it towed back home.
First disconnected the gas line in the engine compartment to see if it was getting gas. Cranked it, and no gas came out. Suspected the fuel pump, so began troubleshooting from that point. Removed the fuel filter, was full of gas, and not clogged up.
Before further suspecting the fuel pump, I wanted to make sure I had power going to the fuel pump. That’s when things got real confusing. There was a separate single conductor I naturally assumed going to the sending unit, then ‘4’ conductors going into a 2 x 2 matrix quick disconnect plug.
Don’t know why there were ‘4’ conductors going back to the fuel pump. Between two Haynes manuals, and some Mitchell Repair Information printouts of the electrical system for this vehicle, none showed or mentioned 4 conductors going to the fuel pump. Basically in the diagrams, a dark green wire going to the fuel pump. There is a dark green wire within that quick disconnect plug.
Reading other information on the Internet, I had seen where the Auto Shut Down Relay was suggested as a potential problem as well. I had found this relay, measured a constant 12 volts going to the relay on a red wire, and seen a dark green wire, which I am guessing is going to the fuel pump.
Then two thinner gauge dark blue-yellow wires tied together, and two thinner gauge dark blue wires tied together. According to the diagrams, the voltage for the coil of that relay comes from those two sources. I verified that with a meter, when the ignition is on, there is voltage going to the coil of the relay, and the relay is switching.
One problem I couldn’t figure out was when I put a meter on the dark green wire and ground, turned the ignition on, there wasn’t any voltage showing on that green wire. In fact, what I eventually found was that there was a ground on that green wire. If I unplugged the quick disconnect connector near the gas tank, and checked for voltage on that green wire again, I would see about 7.5 volts.
From the diagram, I could see that this is a simple relay of a single pole/double throw configuration, with nothing connected to the normally closed side of the relay. Don’t know why I’m getting 12 volts going to the common of the relay, and only 7.5 volts out on the green wire when the ignition is on. Most likely dirty contacts, but the relay is working and switching. Don’t know if the 4.5-volt drop is causing my problems, but went further with troubleshooting before purchasing a new relay.
What really bothered me was seeing that ground on the dark green wire at the relay with the fuel pump wiring connected, and not seeing even that 7.5 volts at that point. The 2x2 matrix quick disconnect plug was easy to access and work with. Not finding any reference to the wiring other than the dark green wire, I attempted my troubleshooting skills, (not very successfully…). I connected one wire in at a time back together, each time checking for that ground on the dark green wire.
I isolated one wire, when connected back together, put a ground on that green wire. I left that wire disconnected, attempted to start the van, with no success. With no diagram or color codes other than a dark green wire going to the fuel pump, I had to try troubleshooting one wire at a time.
I used a 12-volt battery and tested the wires going to the fuel pump, using the dark green as a positive. Put a negative on each of the other connected wires, and didn’t get the pump to operate. Just for the sake of it, I put a negative on the one wire that I had disconnected that was putting that ground on the dark wire and the pump began pumping. And it pumped all the way up to the engine compartment.
Must note that having an alarm system with a remote starter was a ‘big’ help here, as I was able to hit the remote start and have the engine crank while I tested and measured things. At one point, I operated the fuel pump with the battery while the engine cranked, hoping to get it to start, but no luck with that.
So now I began suspecting something else. Reading through comments on web sites I found that the Auto Shut Down Relay not only controls the electric fuel pump, but power to the ignition coil, and fuel injectors. So now I was wondering what else could be wrong.
Don’t know if this is a proper way to test for a spark, but removed the ignition coil wire from the distributor, and held it close to the top of the engine, cranked it, and didn’t see a spark. So it would appear that there is ‘something’ wrong, somewhere in the Auto Shut Down circuit, as it wasn’t operating the fuel pump, or giving a spark.
If I knew for sure that that 4.5 voltage drop at the Auto Shut Down Relay could cause this, I would certainly purchase one and try it. But if the relay contacts were dirty causing this drop in voltage, they must have been dirty for a while, and probably wouldn’t have stopped the van dead in the middle of a street after it’s been running for a while. And if it were a high resistance short somewhere, again don’t know if it would have all of a sudden shut everything down like it did.
And naturally seeing a ground on the dark green wire at the Auto Shut Down Relay, when connected to the fuel pump bothers me. Especially when after disconnecting that wire clears the ground condition, but it’s that same wire, that when putting a battery on it, operates the fuel pump.
Am kind-of familiar with basic electronic circuitry and troubleshooting, but it sure seems like they excessively complicated the electrical systems in vehicles. Don’t know if only having that 7.5 volts, and not the full 12 volts being switched to the dark green wire, is ‘somehow’ showing me that ground condition at the relay. And if there was a full 12 volts there, if that ground condition will somehow change to a positive and make everything work again.
In my years, have seen some really strange circuit designs that makes one wonder why things were designed the way they were, almost seeming to operate backwards. Simple brief example, seen some L.E.D. and diode circuits that had a positive voltage on both leads, and the L.E.D. or diode only turned on when the negative side dropped below the forward bias point of the L.E.D/diode. Don’t know if that in any way relates to what I’m seeing on that dark green wire.
And just have to assume that the dark green wire supplies the positive to the fuel pump as the relay contacts, (according to the diagrams), switches the constant 12 volts from the red wire, directly to the dark green wire.
So I’m stumped, and don’t know what to check next, but got to get my old van going again!