I'm still having a big problem with my car. I've been trying all week to figure it out.

I totally replaced the interior harness from the C200D connector and in with a spare and it didn't help. So it's between the C200D and the firewall, or the engine compartment.

What it's doing is when I turn on the car the rpm gauge bounces around and sometimes the fans flicker on off, and the pcm sometimes keeps resetting.

If I unplug the injector fuses and just let it crank then the rpm gauge goes crazy.

The symptoms are exactly like if I take the pcm ign. fuse and pull it in and out quickly with the key on.

I checked the pink power wire from the ignition to the injector fuses and it's fine. I also checked the pink one from the ignition switch to the C200D connector.

I know it's not the ignition switch itself either.

I also checked grounding straps and the power and ground at the block right by the battery.

I also checked the pcm pink power wire that goes through the blue connector.

I just need more ideas and things to check because I'm making zero progress and have been at it for a week straight.

 

First of all, there are four 12 volt supply lines going to the PCM. 2 of them go through the ignition switch and C200. And you only looked at one of them. Second, the one you did check, on the blue connector of the PCM also goes to the black connector AND goes to the MAF. If the MAF had an intermittent short, it would pull the 2 lines down to the PCM. BUT

There are also 2(unswitched) orange wires bringing 12 volts to the PCM on the black connector. The orange wires are supplied with 12 volts from the #4 fuse in the I/P fuse panel, 10 amps. They travel to the PCM through connector C210 (black 4 pin behind right kick panel from the I/P fuse panel.

The pink wire you looked at on the blue connector comes from the I/P fuse panel, thru C230 (10 pin blue connector) behind the right kick panel.

Third, any sensor powered by the PCM like the IAT, MAP, TPS etc that has an intermittent problem shorting the reference to ground, can cause a problem. BUT another point is, how do you know your PCM is resetting? Does it keep going thru the instrument panel lamp check?

One last issue, if you are looking for a power interruption to a device (in this case the PCM) you have to look across the power line(s) and the ground line(s) to the device. For example, if you have one meter lead on the power line but have the other lead of the meter on a ground such as the frame, you will not see the power drop out if the device has a ground problem. Understand. You must look at the power AND ground at the device on the associated wires.

Just put the meter on the pins at the PCM with paper clips as back probes if necessary. Put the meter on BOTH suppy and ground pins and see what is happening when the problem occurs. You will have to try it possibly 16 different times as there could be 16 different combinations.

The PCM has 4 wires for ground. They are either tan/white or black/white and are located on the red, white and blue connectors. The tan/white are on the red and blue connectors. The black/white wires are on the red and white connectors. If you don't see any problem on the 12 volt lines, you coulc have a problem on the 5 volt lines I mentioned, that go to sensors.

You were asked to post specific information about your vehicle before. Folks will get tired of asking and therefore will not respond in the future. Put up your signature.

 

Sorry, this is just one of those things where I'm no longer operating on all my mental capacity. I've been at this until almost 1am every single night and exhausted to no end.

I figured anyone that's following this would know what car I had. I did post it in the last one. '94Z.

Anyhow, I checked all the power wires at the pcm and they seem to be good.

I did just now find that when I was messing with the wires I seemed to get the biggest reaction when I mess with the C200C connector or possibly the big one right next to it. C200B I think. I will check on that and keep posted.

 

Here's an update.

I wiggled the fusible links and the car went nuts. I wiggled them some more and replaced two of the wires with a spare I had. The problem got a little better. The rpm gauge just goes crazy now when I crank it. So I had my wife out there to turn the key while I messed with the wires. She said when I started playing with them the gauge stopped bouncing around and when I messed with them again it started back up.

So... it would really seem like it's right in the wire just before or after the fusible links. I need to find where to get something like that so I can replace it and rule it out as a possibility.

 

Perhaps you have a half-fried fusible link.

 

Is that something that can go partially bad? I thought they just go out completely.

The problem has to be on these wires because every single time I messed with those wires the problem happened, and those are the wires that feed the whole ignition circuit and pcm etc. So at the least it's right at or below the link. I'm goign to try and patch in some links from my parts car and see if that does it.

Also, could I wire in a replaceable fuse instead of a fusible link. That way if it pops again or it's just one wire I can replace the fuse.

I think the main problem was the previous owner had some type of remote start system hooked up to the ignition circuit and it had crappy connectors.. either it put too much resistance on the circuit or it drew too many amps through the wires and messed up the fusible links. Of course it could also just be age, but the wires looked to be in good shape just below the links.

 

It might be possible that the fusible link is hanging on by a hair and giving intermittent proper voltage. Trying the fuse thing would be your call.

 

I did read that they can slowly fail and that the wire doesn't get messed up but you can tell because it becomes sort of stretchy like a rubber band once they are no good. In any event I'm going to go home now and try and wire in a couple extra links I have off my parts car. If that doesn't do it, I may just try an inline fuse like you would on an stereo amp or something. I figure if they use them on those which have high and constant amperage then I could use it on the car. Just as long as I weatherproof it well.