My 1985 5.0 EFI shows Code 18 which indicates Loss of tach input/IDM circuit failure/SPOUT circuit grounded. I have checked the SPOUT circuit as best I can and found no problem. I am not familiar with what might cause the loss of tach input nor do I know anything about the IDM circuit. Can anyone give me some pointers as to what to check next and how to correct this? Thanks.

 

i have a 86 f150 5.0 efi . and i just got the same code 18 too. i'm sure somebody here knows there stuff to answer this one. i am lost.

 

I'm no mechanic, but I'll try to chip in...

I have a '85 F-150 5.0 EFI and *had* the same code 18. The truck was warming up in the driveway and I was checking the transmission cooler lines (recently replaced the radiator) for leaks. I shut the hood and the truck instantly shut off.

At that point, I did a little poking around. I took the TFI module off and had it tested--passed with flying colors. I put that back on and went probing around the wiring harness.

As soon as I did that, the solution for my problem became apparent. There are two little wires going to the connector for the ignition coil--look just behind the coil. As I recall, one wire is green w/yellow dots (IDM) and the other is orange/yellow with green dots (SPOUT). The green wire on mine was barely hanging on by a strand of copper. It looks like the wiring harness had been rubbing against it for a while. When I shut the hood earlier that day, that probably shook that wire enough to finally break it.

I cut off the orange wire (on it's way to the same fate) and went to NAPA for a replacement "ignition coil connector". I *think* the part number was "ECH ICC1"--the cost was about $14. I installed the new coil connector and the truck started right up.

Based on my experiences, I'd suggest the following:
1.) Look for broken/damaged wires (particularly the green and orange wires) coming off the ignition coil connector and/or TFI module connector.
2.) Take off the TFI module and have it tested at an auto parts store.

Good luck!

 

Thanks for the replies. My problem turned out to be a broken distributor rotor. It was one of the first things I checked when it quit running but I didn't check it closely enough. I pulled the distributor cap and had my wife crank the engine while I checked things over. The rotor looked to be intact and turned with the engine, so everything was okay, right? Wrong. The plastic tab that holds the rotor in place had broken off. The rotor was turning but slipping. Fortunately I didn't start a parts changing crusade hoping to hit the right one...could have been costly. The lesson to all this is, start with the basics and check things thoroughly. Thanks again for your help.