Inertia Switch ('85 EFI dual tanks)

ArdWrknTrk wrote

C118 is only identified as a brown 2 wire connector located near the inertia switch.

Under dash picture of Inertia Switch location.
There are two bright-yellow wires that go to the Inertia Switch. The wires are wrapped in electrical tape and the resultant harness goes to another harness where both are then wrapped in electrical tape. There is a nylon clip that attaches both of them to a support. What is interesting, is that where they come together the diameter is larger than both of them for about 2 to 3 inches. It wouldn't surprise me but if the connector is inside that larger harness.

ArdWrknTrk wrote

(I wanted to attach the page from the EVTM, but the forum will not open the "insert image" window for me today... )

Thats a computer problem. *sigh*
Thank you for the additional information. That looks like the location and will be helpful when I tear into it.
-= John =-

Hi Jim,

ArdWrknTrk wrote

Wires get crispy after 30+ years.
I spent yesterday afternoon chasing a bad wire in my parking lamp circuit.

After changing out the switch and pigtail I ultimately ran a jumper from behind the fuse panel to the new socket.  😖

Unfortunately, electronics don't seem to be forever.

ArdWrknTrk wrote

I hope you can figure out if 97 is seeing ground and pulling in the relay when you first turn the key to 'Run'
Back probing that relay socket with a test light you can see from the driver's seat seems the easy way to accomplish that.

If the ECM isn't responding and you have some soldering skills replacing the capacitors on the board is inexpensive and worthwhile since those caps go bad over time, even just sitting on a shelf!

There is a backyard electronics guy locally that likes to work on old audio / stereo gear and I've got a couple items I'm going to talk to him about: A Dual 701 that doesn't maintain it's RPM and a Pioneer RT-909 reel-to-reel deck (no problem but just to check out). He changes out transistors and capacitors so if it comes to that I think he'll be a good resource.
Back in high school I built the first stage of a one-tube Ham Radio receiver but never got it to work. It only had standard electronic items like resistors and capacitors with a home-made coil and a tuning capacitor. Battery for power supply and Headphones for output. Todays stuff is much more technical. Hopefully it won't lead to that!!!
-= John =-
P.S. Still own my first two cameras, a 120 Box cameral and a 35mm Argus C3. No electronics and they still work. Life was a bit simpler back then.

If the engine runs fine and you just have a problem starting I don't think there's an issue with the inertia switch or fuel pump relay.
The battery ground cable should first tag the front crossmember and then attach to the corner of the engine block.
The smaller wire is the ground for the engine computer.

Aft of the battery is likely the MAP sensor and perhaps relays for EGR/TAB?
I'm not entirely sure about this 1st year EFI, and don't want to lead you astray.

Is your problem only cold starts, or all starting?
I'm wondering if it isn't something as simple as the coolant temperature sensor (NOT the sender)

Connectors won't be wrapped up in the harness. I'd imagine the 'lump' you've noticed is a splice, which should be noted in the EVTM.

Jim - this is just a quickie reply ... gotta head out.

If what you wrote is a possibility, what I'd like to do now is deal with some of the "loose ends" with troubleshooting and dual track my other major, and important, work item ... installing new fuel tanks with new in-tank fuel pumps.

There are so many outside projects I have to work on before fall, then winter sets in, and the fuel tanks is one of the must-do indoor projects. The rig is in the garage and the driveway slopes downhill. The tanks will have to be changed inside the garage with the water heater and HVAC turned off and all the doors open. I'll start a new thread about this project.

meantime ... gotta run!
Thanks very much for this input!!!

-= John =-

If it is only a problem with cold starts and a spritz of gasoline in the intake will get the truck started, my logic says the computer doesn't realize the engine is cold and enrich the mixture.

The sensor (separate from the gauge sender is responsible for this function)

Bill Vose is much better at EFI diagnosis, and probably has a more concrete answer.

Have a great day at work!  

The wiggly button is normal. It isn't physically attached to anything inside the switch. It only pushes the contacts closed if the ball comes off of the magnet.

myrl883 wrote

The wiggly button is normal. It isn't physically attached to anything inside the switch. It only pushes the contacts closed if the ball comes off of the magnet.

Really like this reply!!!
This solves a puzzle. I think. The engine does run, after a fashion.

Due to several days between running it, a squirt of gas into the throttle body helps.
After running, it runs at a fast idle, warms up, gradually slows down the RPMs until it reaches a slow idle. Once there, the RPMs start to vacillate then it dies.

From idle the engine can be goosed with the throttle to speed up the RPMs, can be done a few times, but then it ultimately dies as it drops below the slow idle. Perhaps it runs out of gas in the line?

Don't want to run it any more until the fuel tanks are removed and new ones installed because I don't want to risk any rust getting to the injectors. There isn't much rust showing in the filter but there is some rust color.

The next thread will be a list of steps to go through to drop the fuel tanks, for "public comment".
Once new tanks, pumps, and lines are installed, with fresh gas, I'll see how it runs again.
Thats the plan I'm thinking of.

This continuing Heat Dome and forest fire smoke isn't helping anything, either.

Your description of the wiggly button is exactly what it acts like so it really appears the Inertia Switch is okay. Still plan to make up a couple test wires, though. Thank you for your input!
-= John =-

Unstable idle is a classic symptom of a bad MAP sensor in vehicles of this vintage.  (just saying)

Jim - Thanks for the post about the MAP.

While searching for the MAP location I found comments on-line about the failure modus operandi that corresponded with your description, the electrical schematic that shows where it is in the system: 1985 EVTM: ELECTRONIC ENGINE CONTROL, bottom of Page 61 http://www.garysgaragemahal.com/electronic-engine-control1.html 
Found pictures of what it looks like, sources to buy it (fortunately not expensive), and then finally ... where it is located! Aft of the battery on the right side of the engine compartment. Looks like a comparatively easy fix to replace (for once). Note to self: Big engine compartment helps.

Question: Put dielectric grease on the contacts?
Will see what is there when its disconnected.

With this Heat Dome with lots of wood smoke from the forest fires (Yuk!) that has been over us the past few days, forecasted to start diminishing a bit tomorrow (Whew!), I've noticed a bit of gas smell in the garage. Thought this might be coming from the gas tank vents. Pilots old saying: "Trouble comes in bunches"

I'm honestly not sure what values this MAP should have (how to test frequency or pulses from the component itself) but I do think you should check for codes using the blinking check engine light procedure where you ground the test plug and write down the flashes.

That is, if you can get through the KOER tests with your truck. Not many people have the proper Rotunda test equipment to grab the codes.
I used to refer people to the oldfuelinjection website for polling the ECA, but the site has been down for a long time.

I certainly think having clean contacts in the socket is way better than corrosion or oxidation changing whatever the computer is expecting.  Bulb grease or silicone isn't going to hurt anything.

Hope you see a break in the weather. Even here in the Northeast it's been pretty oppressive the past few days.
At least we don't have fires or flooding.  Hard enough to work with the heat index around 110. I can't imagine adding thick smoke to that.
Stay safe!   🤞

Edit: I did find this,. https://troubleshootmyvehicle.com/ford/4.9L-5.0L-5.8L/how-to-test-the-map-sensor-1
I'm not one to go swapping parts unless something is observably bad.
I think it just makes further diagnosis more difficult.