Pulled Reverse Voltage Diode - Now Car Won't Start it

I will check to see if there’s voltage going to each fuse. In the meantime, does anyone know if there’s any other onboard computers on a 1998 Contour other than the main ECM/ECU?

There should only be one ECU for the engine. Looking at some data I found on the net I think fuse 11 in panel under hood supplies power to the ECU. The wire color may be orange/yellow going to the ECU. The ECU pin may be pin 58.

Is there any chance that some other wire connections under the dash or under the hood were left disconnected?

I just can’t see how. I did nothing but pull the diode and the car was running fine seconds before I pulled it. Still haven’t had a chance to check the voltage leaving the fuse box but I will first thing in the morning.

Looking at the diagram again I noticed that there is a fusible link that ties to the relay for the PCM power. That relay also supplies power to the injectors and other engine components whenever the ignition is on. With the ignition ON, remove one of the injector connections and verify that power is getting to that injector. If you have no power on either side of the connector then we need to check the fusible link. The wire color on the hot side of the injectors should be green along with a different tracer color to each injector.

Fuses 4, and 13 also supply power that are related to the ECU. I think they are in the dash panel. Fuse 11 may be in there also but it may be in the main panel under the hood. I think it may be for the memory since it has power at all times.

The following are wiring diagrams for the engine, where you can see the fuses that @Cougar mentions. You didn’t specify which engine, so I provided links to both:

ZTEC Engine Wiring

Duratec Engine Wiring

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Kudos to @Bugmenot for the info.

At this point, my best suspect for the issue is fusible link 9 in the upper left of the diagram. I assume this link will be near the battery or the distribution panel under the hood.

oooh nice site !!

Can’t thank everyone enough for your willingness to help. Would have posted earlier but there’s a limit to how many times I can comment on my first day.

Tested all applicable fuses, and they were passing good voltage on both sides. I did find a fusible link right near the battery. Used a shielding penetration needle test (is that the right word?) And it was registering voltage on both sides. However, it then dives into a small wire bundle and I’m not sure if that eventually gets to the injectors. I can’t track wires on either side so essentially I can’t tell if it’s fusible link 9.

I did find a plug at the end of the fuel injector harness, and there was no voltage there. But would there be voltage there when the car is not running or cranking? I may need someone to try and crank it while I test that one.

I have the Zetec engine. Looking at the diagram provided, I don’t see any diodes at all. It appears to be a diagram of only the main components.

Ok, I finally found the solution. it may not end up entirely satisfying, but it will confirm a lot of thoughts on here. The diode had nothing to do with the problem. Turns out, the main power wire leading from the fuse box to the ECM fell out of its connector when I opened the fuse box and pulled the diode. It was barely hanging on by a string, but impossible to see because it was up inside the dash. Pinched the female end down so that it was right and everything is running as it should.

Again, thank you so much for the help. You guys collectively nudged me away from unlikely issues and toward the actual culprit.


Now that you found the problem, I’ll just relate. I had no idea what a reverse diode was. When I quit smoking for a while I pulled the seats out of my Riviera so I could do a thorough cleaning of the carpets. When I put the seats back in the car would not start. Same thing couldn’t figure it out. Finally had to have it towed to the shop. They found a fuse missing. Who knows how that happened but it did. When I said I really felt foolish for not finding the problem, the owner said don’t feel bad it took our best mechanic an hour to find the missing fuse. I think it cost me $100 plus the tow.

Well once again the answer to the problem seems to come down to the simple things in life. Thanks for the update and I’m glad you found the problem. You’re welcome for the help. I see you did find a loose connection, which is why I asked you about that possibility earlier. I couldn’t really see why just removing the diode from the circuit would damage the ECU so I suspected something else may have gotten disconnected and not put back. We still don’t really know what that diode in question is tied to. From what I saw of the ECU diagram that diode isn’t connected to it. It may have something to do with the dash cluster and the warning lights.

I wasn’t aware of these type of diodes until now so I learned something myself with this issue, along with ATO and ATC fuse differences.

I’m tracking what you are saying now. I thought you were speaking of a wire that I had purposely disconnected.

Talked to an electrician with a better schematic and he said the diode was specific to the ignition relay. But he said there was no way it could damage the ECU, so you were 200% right

Well, there went my comment about teaching the wrong lesson. Now I have to warn people about opening the fuse box! Talk about sending me back to square one for more training. Next thing you know I’ll warn people not to drive with the engine running.