New Member 1986 F150 4.9L

I have a hand-me-down 1986 F150 4.9L, 4 speed manual with Feedback Carburetor, EEC-IV ignition and California Emissions. While trying to resolve a smog issue (too much CO) I replaced the EGR and after that the truck would not start.   No Spark! Can’t find a wiring problem and  the coil seems OK, but when checking the ICM cable I am getting 12V between the Run signal and engine ground (key in Run position) but only 7+ V between Run signal and ICM ground. There is 5 V between ICM ground and engine ground. Note ICM cable was disconnected for these tests. So I think either the computer is shorted or there is a missing ground to the computer. (Floating ground)

Does anyone know how to get the computer assembly out of the truck? Local mechanic says there should be a single screw on the back of the computer to release it but I haven’t been able to find it.   Cable comes off easily.

Welcome to the forum. Unfortunately I don't know the answer to your problem or how to trouble shoot your EEC-IV ignition system. There are others here who should be able to help but you need to post a new topic about your truck and about the problem.

Welcome!

Yes, welcome to the forum!

Like the others I don't have specific answers about the TFI ignition.  However, we have these two documents that should help:

On the page at Documentation/Electrical/Ignition there is the factory shop manual section on ignition systems.

On the page at Documentation/Literature you'll see a link under 1982 for the Engine Emissions Diagnosis document.  Click the On Site link and you'll be taken to that.  Scroll down a bit and you'll see Ignition Systems.  Click that link and you'll be taken to the diagnostic section for the ignitions.  And scrolling way down in that document to Page 5-64 you'll get to the TFI section.  Note that the bottom of the webpage you can choose what zoom level you want, or you can click the "fullscreen" icon on the right to open the document in another browser window.

Hope that helps!

Also, where's home?  We have a map (Bullnose Forum/Member's Map in the menu) and we'd be happy to add you.

Welcome, 1985F150CA!

It has been a long time since I removed the computer from a 1986 F150, but it was not too complicated. It is mounted vertically in the area to the right of the steering column, near the ash tray. It seems like there was 1 bolt holding the wiring harness to the computer and then just wiggling the computer while pulling/tugging downward.

Regarding the "no power" issue, you said this began after replacing the EGR. Usually, when something just happens after working on something else [EGR], the issue is something having been moved or damaged in that same area. There are numerous wires in that area. Most are in wiring looms. Years ago, I was driving my son's 1984 4.9L with the feedback system. When hitting bumps on the road, the truck would miss or cut out. I stopped with the engine idling, popped the hood and began to grab parts of the wiring harness and give that part a shake. I found the wire which goes from the alternator to the choke heater. It had numerous cracks in the insulation and when shaken, would short out causing the engine to momentarily drop RPMs. I wrapped the wire with electrical tape and the problem disappeared.