Hey guys... I have a 92 F150, 4.9l, 5spd, 4x4 that has had its share of problems, but I love the truck and have a lot of parts into it over the past several years. For a while I was chasing a never ending set of codes, including multiple egr, fuel system, and ignition faults. The entire ignition system has been redone (even the pcm and icm), the weak fuel pump, filter, and relay were replaced, the egr and its components. At one point I had a problem with it running rich and stalling when warm, and the coolant temp sensor fixed that (info I got from this forum!). Now I have two codes left and the truck is struggling. Runs good at startup but after a few miles things fall apart. Here is a video of the biggest problem, the erratic tach and the stalling:


Bouncing tach and stall



And here is the other, seemingly related symptom which is the high idle thst occasionally surges too:

Idle:



The big code that it throws is this:


212 (Ignition TACH signal was erratic (module/wiring) or SPOUT circuit fault – Ignition Systems


And the other code it throws which may just be another symptom is


173 - single, right, or rear o2 sensor not switching or rich


All of the small vacuum lines have been replaced too, and the canister holds pressure even after the truck has been sitting for a bit. Removed the throttle body and it looked good. Cleaned and lubricated it, replaced the iac and tps, and threw in a map sensor for good measure as it was cheap.


The only other nagging problems with the truck are some belt squeak (idler pulley, maybe), a missing set of wires going to the transfer case (only prob I've seen is that the 4x4 light doesn't come on) and a power steering reservoir that occasionally boils over and leaks (it has already been replaced, as has the alternator, battery, etc.).


I've had a pro look at it and he didn't have any more ideas than me (the tb and iac were his idea, then he suggested a crank position sensor, which I know is a prob on some vehicles but hadn't heard about it on this one, so I came here instead), so I'm asking for any insight you guys might have.


Thanks for anything you can provide... it is appreciated (as I'm losing the battle here)!

 

I’ve got same symptoms without the code however. Do you have a Haynes Manual? Chapter 5 goes through ignition testing procedure- it will ask you to crank your truck with DVOM on your Spout in AC Volts. Will tell you if it’s a problem. Mine is; will be testing a jumper wire from spout to EEC in hopes it clears it up. Research shows Spout code can be an ignition problem OR an EEC problem. Get the Haynes book and follow the ignition testing procedures. Report back what values you get.
This link is extremely helpful read through all of it

 

I don't think they came out with a crank sensor till 96 at least not on the 302, so it could be that that was just a guess on the part of the mechanic - which they shouldn't be doing.
If the mechanic doesn't know the vehicle well enough to diagnose the problem accurately and correctly he should say so and refer you to someone who does know how to diagnose your truck. Parts and labour are too expensive to guess at what might be the problem.
In my humble opinion anyway.

Without seeing all the videos I will mention that when I changed my y-pipe I didn't have the right O2 sensor. Truck would run great for about a mile or two but as soon as the engine got warm enough (and switched from open loop to closed loop when it reads the emissions sensors) it would fall flat on it's face and barely run.
A new O2 sensor fixed that.

 

 

If it’s an odd electrical issue, I’d always say to start with inspecting and replacing old grounds. There’s a ground coming out of the ignition wiring harness that goes to the block on my I6-300, it was not only covered in oil but the exposed sections were completely frayed. Replacing it helped me get spark every time

 

Also take a look at your ignition switch to verify power to systems with key on engine off etc- could be a bad key cylinder

 

Just a definitive note for everyone re ICM's. 93 and previous takes a grey ICM. 94 and later takes a black ICM.

Having the wrong one in there would have had you chasing ghosts so disregard the codes you pulled when that black ICM was installed and start over.
On a 4.9 one I bought the 12V power plug for the coil was bad; sometimes it connected and sometimes it didn't. Bought a new one of those and cleared up that one.
If you have power to the coil (key on) on the other side of the plug you should have power as well. The power goes through the coil (and builds energy) and then that power is disrupted, causing the coil to fire.
This disruption happens inside the distributor at the PIP (works the same as points used to work inside the distributor). The PIP is a common issue for failure. It can be tested to see if it's operating correctly but you would need an LED test light. A normal test light won't flash fast enough to detect a PIP signal.
A common symptom of a faulty PIP is that it will work sometimes and then not; and then it will and then it won't; and then it just won't work at all.
If everything else like connections, faulty parts etc, power going everywhere it's supposed to have all been eliminated, the PIP would be a prime suspect for a no spark situation.

 

 

I MAY be wrong, but the wire your describing is the radio interference wire- it looks like a cylinder going into the block. Symptoms do sound like a ground issue, the hard one to track is the open wire ground running basically through the wiring harness and exits near the EEC (still unwrapped and exposed wire). It attached to driver side upper fender adjacent to brake master cylinder kind of near the relays and EEC tester. There’s another ground going from the wiring harness near the distributor harness to the block, just put your multimeter in continuity and test points until you hear a faint sound or signal or even one that cuts out while making good contact.

 

So she is running again, at least! Turns out the yellow wire, the pulsing signal, was nearly broken (hanging on by a thread) right at the connector, but seemed solid between the metal female connector and the insulation. That was probably why I was showing 10.x volts once in a while.