I have still not figured out my electrical problem, but I am trying to look into it a little further. After reviewing the PCM diagrams from shoebox's page, it seems that all my random electrical problems show up in the same sensors that are on the same circuits as the black connector out of the PCM. Watching datamaster, I see random spikes in TPS%, RPM, MAF frequencies (so much that it blows the fuse), IGN VOLTS, and Vehicle speed. There may be a few more but those are the most common ones.
I have eliminated the PCM from the list of possibilities by swapping with another.
I have checked connections and wire continuity with a ohm meter on the brake switch, o2 sensors, and MAF connector and wiring.
Car is tuned in SD mode right now because of the ENG SNSR (MAF) fuse blowing all the time.
Also, I have eliminated the MAF from list of possiblities, along with the alternator voltage regulator (I bought a new alternator).

So today, I unplugged the black connector from the PCM and then removed the black transparent plastic cover to gain access for probing the terminals. I used the pinout from shoebox's page http://shbox.com/1/4th_gen_tech2.html#1995_pcm_pinouts
which does not seem to be 100% accurate for my 97...I had a few pins where the diagram shows blank pins.

My optispark is a brand new MSD. The car accelerates nice and smooth at all RPMs and throttle positions so I have always thought the optispark is good. I contacted MSD as soon as I installed it (in May) because I was blowing IGN (U/H) fuses under full throttle. MSD said the optispark couldn't be the problem. I installed a 20AMP fuse in the IGN and it only did it one time after that, but then my MAF fuse decided to start blowing!
Am I missing anything obvious here? I really need some help because I can't continue to modify the car until I get this electrical issue taken care of.

 

Unless you know the resistance value of the device you are looking at, resistance readings are not going to mean much. The only real reading you can take is that of a bare, disconnected wire at both ends (you will have to ground the wire or extend your meter lead to take a resistance reading after it is checked for any grounding). If there is any voltage on a wire, you cannot take an accurate resistance reading.

Replacing the fuse with a larger one is a big mistake. You can cause damage to the wiring and create problems you never had to start with. You'll end up chasing your tail.

 

Yeah, I was wondering about that, so I went back out with a few other ideas. I unplugged the optispark harness and retested the ohms from the PCM to the connector and got the 0 ohms I was looking for, so it does not seem to be on the PCM side of things...I also found that I was reading the pin numbers backwards.
Shoebox, could this be a problem with my optispark? I tried to watch for plug wires arching with the engine running in the dark, and saw nothing.
What is the next step I should take? Should I just take it to a dealer and pay $85/hr?

 

Day 74:
I am still clueless as to what my car's problem is and I'm out of ideas. I've tested the voltage for every input into that PCM with the key forward and the only "bad" reading i saw was for the VSS. It read about 8.6V when it calls for a 6.X V reading.

Does anyone have any ideas which I have not tried? Could this be some sort of electrical interference between components? Could it be a wire such as a corroded turn signal bulb causing a short which shows up in my engine sensors? Who can figure this out?

 

You said "(so much that it blows the fuse)". What fuse?

Intermittent contact and subsequent loss of contact could cause your problem but it is highly unlikely since the load has to be near the limit of the fuse. There are no fuses in our vehicles that are operated near the limit however.

A fuse typically blows because either the device(s) that it powers are suddenly pulling more power or most likely the wire from the fuse (pink wire) is touching ground. In your case I believe the pink power wire to the PCM is occasionally touching ground. This causes the PCM to show radical sensor readings and blow the fuse. Therefore my guess is the fuse you are having a problem with is one that powers the PCM since there is no common fuse powering the sensors you listed.

To find the problem it is easiest if you remove the fuse in question. Measure voltage at the contacts for the fuse. One has 0 volts and the other side has 12 volts. Use the contact that does not have 12 volts and measure to a good ground for resistance. If it's low, you have to wiggle the pink wires until it goes high. If it is already high, you have to wiggle the pink wires until it goes low. You can use a continuity beeper so you don't have to look at the meter while you do this. Check the pink wire(s) where they go under something or around a corner or thru something such as the firewall.

And do as Rob said and don't use a larger fuse.

 

The fuse which blows is the ENG SNR fuse and also the IGN fuse, both located under the hood.
I tried checking the fuses in question before and wiggling every wiring harness I could find. However, I barely knew how to use the Multi-meter at the time, so maybe I should try again.
When you say to check for resistance, "low" and "high"--what is actually considered "low" or "high?"
Oh and when the ohm meter reads "OL," am I correct assuming that translates to "open circuit?"

The dealer told me the ignition switch could be the problem (or the wires running from it). This is interesting because wire 3 PINK happens to go to INJECTOR FuSE 9, ENGINE SENSOR FUSE 10, and IGNITION FUSE 11. Note both of my blowing fuses are listed there.
I remember Dad having to pull all that apart and finding a wire causing the car (my brother's 95 Formula) to completely die on left hand turns so maybe that is also my problem.

Thank you for the help.

 

All your mentioned sensors run B+ on the pink wire's and they all join together. I suspect a short to ground on one of the pink wires as your blowing the MAF fuse. Easy check at least, disconnect the battery, use a continuity tester and check the pink wire at the MAF with one lead and the other to ground, there should be no continuity, if there is you have a short on one of the pink wires, if there is no continuity, then reconnect the battery, turn the key to run (without starting the engine) and set your test meter to VDC, check how many volts are running to the MAF pink wire (terminal C on the MAF plug) as its a direct feed from the ignition. Also the A terminal (yellow wire) is a 5 volt reference from the PCM and you should only have 4 to 6 Volts. Measure between B & C this should read 12 volts.

 

The eng sensor fuse powers all 4 O2's, the MAF and the brake switch. The first place I'de look is the O2 wires possibly burned or rubbed thru. Particularly if you have headers.

The ignition fuse powers the coil, ICM and CKP. It's true these 2 circuits are both powered by pink wires but that's were the commonality ends.

Since the ignition switch is powered by the battery and then powers the fuse. The only way it could blow a fuse is drop out and come back quickly causing spikes. But if that were to happen, you would notice a loss of power or funky things happening before the fuse actually blows. A short from the switch to ground (if such a thing could exist) is before the power even gets to the fuse, so that couldn't be the problem. You said brother had a problem with left hand turns. Sounds like it would come and go. That is true that power will drop out from a bad switch. But he wasn't blowing a fuse. See where I'm coming from.

By low and high I mean large swings in resistance. However when ever you are dealing with coil windings, there will be low resistance even though there is no short. It would be best to unplug the devices while you "ohm" for shorts. And yes the OL means open circuit and stands for Over Load. Be careful if you have selectable ranges on your meter. OL when the meter is set to 2K can be just slightly over 2K ohms. If that same example is viewed at say the 200K setting, it would appear as 2. So when you see a circuit that shows OL when say the meter is set at 2K. It should then be checked at higher settings to see if it is some number or actually an open. Understand? In other words, change the dial when you see OL in a low scale (which is the scale you want when you are looking for shorts).

One last item if I could. I noticed that the 2 circuits in question pass through 2 different connectors that are in the same general location.

The engine sensor fuse supplies thru C105. It's a black 8 pin connector located on the RH firewall near the PCM. The ign fuse supplies thru connector C100. It's the black 10 pin connector also located near the PCM. Coincidence ???????

 

I have already carefully checked all the o2 wires and also checked the brake switch.
I have checked 5V referance at the MAF but I have not tried the continuity test with the battery unhooked as kingslam mentioned.
What you pointed out about C105 and C100 is very interesting. I am going to inspect those connections next trip out to the garage.
I really appreciate everyone's help thus far. I am going to keep you posted on my findings.

By the way, I turned the MAF back on today and drove around. No fuses were blown in the 45 miles of city driving but spikes continue to be present while viewing Datamaster.