Complete shut down w/code C-18

91AOD5.0LX · Sep 26, 2021

1991 5.0 LX stock motor:
I had a no-start issue which started a few days ago. I had the coil, distributor, and ignition module replaced yesterday which solved the no-start problem but now every few miles I drive she loses 100% power, goes completely dead but when I stop and turn the key she fires back up perfectly and drives 100% until the next shut down which is usually within a few more miles of driving and at normal speeds.
I pulled the KOEO codes which reads C-18 loss of Tach input/IDM circuit failure / SPOUT circuit grounded.
I will bring this back to the shop tomorrow that did the above work because it likely has something to do with the ignition module I assume (the module is Ford, distributor is aftermarket).
Also last week my airbag light came on and flashes 10 times then goes off for 3 seconds then back to flashing. Not sure if these electric issues are related or not. Airbag is another issue
Any insight or ideas from you guys is appreciated as it may help me explain to this place tomorrow what may be going on.
Any chance it’s actually the computer?
Any help is appreciated.

Potomus Pete · Sep 26, 2021

Fuel pump will do that.

91AOD5.0LX · Sep 26, 2021

Potomus Pete said:
Fuel pump will do that.

Fuel pump was changed a few months ago. That fixed my first no-start issue (lol).
I’m thinking it has to have something to do with the TFI, distributor or coil being that everything was fine up until a few days ago when it wouldn’t start (crank only) and an electrical issue was suspected by the mechanic so once those parts were swapped out it started fine and drove great until of Course I picked up the car to drive it home and she conked out twice but it was to late in the evening to bring it right back.
That code C 18 seems to circle around those parts. Today i tried her again and same issue so I’m bringing it back tomorrow. Perhaps a bad TFI even though it’s a new Ford part??? Could the timing cause something like this? Also curious if it’s tied to the airbag light flashing that started a few days ago which may indicate something hairy is happening with the computer?
Just curious what ideas you guys would have and that may help me talk to the machanic about tomorrow to explain things being that he’s not strictly a fox mechanic. The place is great but I always like to talk things over, provide wire diagrams, etc. lol

Potomus Pete · Sep 26, 2021

As you probably know, most of us have been through what you are dealing with. In my case after getting all those same ignition parts I needed a PIP. You may want to take out your noid light, and check the power going to your injectors. Usually the PIP is a no start thing..

91AOD5.0LX · Sep 26, 2021

Potomus Pete said:
As you probably know, most of us have been through what you are dealing with. In my case after getting all those same ignition parts I needed a PIP. You may want to take out your noid light, and check the power going to your injectors. Usually the PIP is a no start thing..

Thanks for this info Pete. The distributor is also new so I assume it came with a new PIP but there is a chance the new distributor/PIP is faulty. I will mention this and maybe they can try another distributor. He did mention it’s the only non-Ford part installed so maybe it’s a crap aftermarket. I will mention this and leave it in their hands. Good for me to know. Thanks Pete!

KRUISR · Sep 26, 2021

Related to fuel pump issues. I had an issue I though was the fuel pump relay. It turned out to be the connector in the driver kick panel (if you bumped the connector the right way it would cut out the fuel pump). The pin in the connector that fed the fuel pump was loose in the connection. Female pin had opened up enough that the corresponding male pin did not make enough contact at times.

Potomus Pete · Sep 26, 2021

91AOD5.0LX said:
Thanks for this info Pete. The distributor is also new so I assume it came with a new PIP but there is a chance the new distributor/PIP is faulty. I will mention this and maybe they can try another distributor. He did mention it’s the only non-Ford part installed so maybe it’s a crap aftermarket. I will mention this and leave it in their hands. Good for me to know. Thanks Pete!

You got yourself a mystery now.

Mustang5L5 · Sep 26, 2021

To be honest, the modern electronics offered these days by vendors are really not all that good. Wouldn’t surprise me to see a brand new PiP or TFI fail in a new distributor.

As much as I hate blindly firing the parts cannon at things, this wouldn’t be a bad shoot-from-the-hip suggestion.

Short of those parts being bad, or could be bad wiring as well causing the ECU to lose the signal momentarily over a bump which then allows it to fire up. Give the age of the wiring and the possibility of brittle wiring existing, this can’t be ruled out either.

91AOD5.0LX · Sep 26, 2021

Potomus Pete said:
You got yourself a mystery now.

Hate mysteries! They end up being expensive and make me lose sleep. Lol

91AOD5.0LX · Sep 26, 2021

Mustang5L5 said:
To be honest, the modern electronics offered these days by vendors are really not all that good. Wouldn’t surprise me to see a brand new PiP or TFI fail in a new distributor.

As much as I hate blindly firing the parts cannon at things, this wouldn’t be a bad shoot-from-the-hip suggestion.

Short of those parts being bad, or could be bad wiring as well causing the ECU to lose the signal momentarily over a bump which then allows it to fire up. Give the age of the wiring and the possibility of brittle wiring existing, this can’t be ruled out either.

Im going to see about swapping out the distributor and TFI again although they are new because I agree, these new electronics can be inferior. It’s definitely possible so I will see if they can swap those out again before looking for other issues in the wiring, etc.
At the end of the day though, I will leave it in their hands and leave them alone because they know a lot more than me and have the right tools/guages for trouble shooting. My talents only go so far with this stuff. I try to get as much info as possible to try stuff on my own or at least be able to talk and understand about it when I go for service.
I will keep you guys posted with hopefully the fix in a few days. I appreciate all the input from everyone.

91AOD5.0LX · Sep 26, 2021

This is good to know!

Potomus Pete · Sep 26, 2021

Hope you saved your Motorcraft distributor. It's been proven to be the best, and could be rebuilt.

Potomus Pete · Sep 26, 2021

My car was down for a month one time with the same issues you have. Ended up being the PIP. I was very upset for quite a while, but you will get it. You probably have a loose wire after the work done. I would do some wire wigglin.

Mustang5L5 · Sep 26, 2021

That’s not a bad suggestion. Start the car and start wigging the harness.

The distributor harness runs under the intake on the drivers side to the main firewall harness, then it runs across the firewall in the main bundle over to the pass side and into the passenger computer behind the strut tower. Give those a strong wiggle and see if the car stumbles or stalls

91AOD5.0LX · Sep 26, 2021

Ok im Going to do this in the morning. Will Wiggle the entire harness from the distributor all the way around to the computer and see if she dies or if she runs without crapping out after I do this. Thanks for this suggestion! I have the original distributor so if that’s needed I can always revert back to that as well.
Looking forward to trying the wiggle though in the morning and see what happens. Thanks Pete and 5L5!

jrichker · Oct 3, 2021

Code 18 - SPOUT out or wiring fault - look for short to ground in SPOUT wiring going
back to the computer. Possible bad TFI or defective 22 K resistor in the IDM wiring

Revised 24 June 2019 to add comment about the need of thermal paste on TFI mounting surface.

Use a timing light to check the timing: remove the SPOUT and observe that the timing retards at least 4 degrees. Put the SPOUT back in place and observe that the spark advances at least 4 degrees.
This code can disable spark advance and reduce power and fuel economy.

Remove the passenger side kick panel and disconnect the computer connector.
It takes a 10 MM socket to remove the bolt that holds the connector in place..
Disconnect the TFI module connector from the TFI and the measure the resistance between the yellow/lt green wire and ground.
You should see greater than 100 K (100000) ohms.
Check the resistance from Pin 4 on the computer connector (dark green/yellow) and the dark green/yellow wire on the TFI connector. You should see 20-24 K Ohms (20,000-24,0000 ohms).

Resistor location: A big thanks to liljoe07 for this information:

liljoe07 said:
Check over by the brake booster. It’s not in the harness on the TFI, it’s on the main part of the harness over by the plugs that connect to the dash harness. About 6" or so from that, going back toward the EEC.

If I remember right, the resistor is covered in a shrink tubing that is sealed to the wires. So, you won’t be able see any markings. The shrink tubing is labeled though. It's a 22 KΩ, 1/2 watt resistor.

Here is the location.

Next measure the resistance between the yellow/lt green wire on the TFI module connector and Pin 36 on the computer connector. With the SPOUT plug in place, you should see less than 2 ohms.

The following is a view from the computer side of the computer connector.

This diagram is the wire side of the computer connector.

Diagram courtesy of Tmoss & Stang&2birds

If you replace the or remove the TFI, clean the mounting surface off with alcohol and apply a fresh coat of thermal paste to the TFI mounting surface. Fail to do this and the TFI will quit working once the engine warms up.

manicmechanic007 · Oct 3, 2021

I get a kick out of some of you guys saying you needed a pip
The pip is just a signal from the stator in the distributor
So if you need a pip you need a stator because you have no pip signal
The processor uses the pip signal for the fuel pump and to time the injectors and the ignition module feed
When you see the blinking light on the negative side of the ignition coil it's the pip signal you are seeing
Yes always replace your stator in your distributor if possible with a ford part (DU-30C Motorcraft for most of you)
Do not get lazy and put a chinese distributor in it or you will have no idea
Plug a TFI tester into it and road test it again

91AOD5.0LX · Oct 3, 2021

Jrichker,
Thanks so much! Also for liljoe07 information!
I didn’t know about the thermal Paste. The car is still in the shop. I am going to take a swing by tomorrow and show them this information!
Manicmachanic007, thanks for taking the time for me as well! I hope to have the straightened out this week! Thanks guys!

91AOD5.0LX · Nov 16, 2021

I’m still down gents....... it’s been 2 months and problem still not solved. I had several very knowledgeable and competent smart mechanics and fox body enthusiasts play with it as well as myself for what I was able to do on my own but still no luck.
I will have an appointment with a very respected shop thats an hour from my home next month. I have a great feeling about this place and are excited to get someone else’s arms around this pony. I can’t wait to have her back in fine running condition.
I just thought I’d drop a quick update in regards because I’ve been dark for a while now. Be well guys..

General karthief · Nov 16, 2021

manicmechanic007 said:
The pip is just a signal from the stator in the distributor

i'm not here to argue this point, just posting facts:
PIP - profile ignition pickup sensor
This is from a ford distributor parts list.
@91AOD5.0LX has the distributor been replaced (sorry, I didn't go back through the thread)?

Complete shut down w/code C-18

91AOD5.0LX

I have a slight sag in my rear

Potomus Pete

I'm still waiting for the fully nude shots

91AOD5.0LX

I have a slight sag in my rear

Potomus Pete

I'm still waiting for the fully nude shots

91AOD5.0LX

I have a slight sag in my rear

KRUISR

Potomus Pete

I'm still waiting for the fully nude shots

Mustang5L5

That is…until I whipped out my Bissell

91AOD5.0LX

I have a slight sag in my rear

91AOD5.0LX

I have a slight sag in my rear

91AOD5.0LX

I have a slight sag in my rear

Potomus Pete

I'm still waiting for the fully nude shots

Potomus Pete

I'm still waiting for the fully nude shots

Mustang5L5

That is…until I whipped out my Bissell

91AOD5.0LX

I have a slight sag in my rear

jrichker

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manicmechanic007

91AOD5.0LX

I have a slight sag in my rear

91AOD5.0LX

I have a slight sag in my rear

General karthief

wonder how much it would cost to ship you a pair

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