Thanks for the info guys. I wonder what the computer uses for "feedback" regarding the SPOUT signal. If it thinks there is a failure in that circuit yet it's functioning then the feedback must be faulty. I would assume that a change in RPM upon timing advance would be one way it could detect this, ie PIP signal. Maybe the IM is sending back information about this. It revs really high when you first start it up cold in the morning, it comes down in RPM pretty quickly but it never used to rev so high when you started it. IAC, TPS everything is brand new, I wonder if this is an indication of the SPOUT signal not registering with the computer. As I mentioned before the only check of the wiring harness that was off was the SPOUT wire at the shorting bar connector to ground having a resistance of only around 6K, haynes said it should exceed 10K. Same values at the IM connector as well so I know it isn't the shorting bar coupler at fault. I noticed that there is an RF grounding wire and foil wraped around this wire in the harness in an attempt to make it a "shielded cable" maybe it's not isolating the RF comming from the AC in this circuit, getting feedback from the other wires or something. The engine seems to run pretty good other than the EGR, bucking and hesitation I'm experiencing, but I think that's because of the aftermarket EGR valve I bought for it. That problem goes away when the EGR is blocked, when I tried the other EGR valve for that engine, the problem is worse so I think it's an EGR valve calibration issue. I wonder if the two are related, ie. the admission of EGR should be affecting RPM change which the PCM would interpret as SPOUT signal modulation.

 

SPOUT is an output from the PCM, not an input. The PCM does not interpret anything from observations of SPOUT. (Although it may feed SPOUT back to check if it is shorted). SPOUT does not set the timing of the fuel injector pulse, it only controls the ignition system firing. (SPOUT does reflect the thinking of the PCM, and in doing so reflects the position at which the PCM will fire the coil and fire the injectors, but SPOUT has no electrical connection to the injector circuit).

The PCM gets its information on RPM from the PIP input.

I suspect you are right about how it detects EGR is working. It opens the valve and watches PIP for an RPM drop. Same idea with the IAC motor.

For checking timing advance (and therefore the continuity of SPOUT) it could use IDM. This directly tells the PCM when the coil has fired. The PCM gets PIP in, generates SPOUT, and looks for IDM for confirmation. Nice direct feedback. The strange thing is, from observations of my truck, it doesn't seem to use IDM for this, or much of anything other than to set code 212. (My truck is a 91 302 V8 with the TFI mounted on the distributor. Your 93 may be different.)

The reason I know this is that I inadvertantly broke the 22K ohm resistor in my wiring harness in my zeal to track down a different problem. This open circuited IDM. After clearing up the original problem, everything ran normally except for the code 212.

Tracing the circuit revealed the damaged resistor, so I cut open the harness and replaced the resistor. This fixed code 212. But the truck didn't run any differently.

So I think the PCM checks the effectiveness of SPOUT as you say, by advancing the timing and watching for an RPM change via PIP, at least during the KOER test.

When you measured 6K ohms from SPOUT to ground, was the PCM or the TFI module in the circuit? It would be normal for there to be a non-infinite resistance if anything is connected to the harness. If you isolate the wire on both ends (pull both connectors off), then the resistance to ground should be infinite. If it isn't, SPOUT may be shorted to some other signal in the harness, which could cause some "interesting" behavior.

Make sure your spark plug wires do not come anywhere near the fuel injection wiring, especially the branch that goes to the TFI.