The light you found under the hood is called a "noid light". It is used to quickly show if the engine computer is firing that injector. It's made specifically for that purpose. Regular bulbs won't respond fast enough.
I know a lot of mechanics pierce wires to measure voltages, but this causes a real big problem later with corrosion from moisture getting in. I would recommend putting a tiny dab of RTV silicone sealer on the hole to prevent that. Rather than buying a whole tube, I would drive to a repair shop where the folks know you, and ask a mechanic for a little bit of this sealer and explain what you're doing with it. Every mechanic has a half-used tube of the stuff, and they might even just give it to you. Once opened, the better stuff cures right in the tube after a few weeks, so it's wasted.
A little dab the size of a finishing nail head is more than enough. Chrysler has two RTV sealers, (room temperature vulcanizing). The black stuff stays more rubbery but will not bond if there is any oil or transmission fluid residue. The gray stuff gets a little harder and will bond even if the surfaces aren't perfectly clean. Either one will work fine. There are other brands of this stuff with other colors. They all will work fine for sealing a wire.
Rather than piercing the wire, he could have easily back-probed the terminal in the connector with a paper clip. That's what I taught my students to do. I made a really big deal of inspecting my prepared broken cars for signs of pierced wires to impress on the kids how important is was to follow professional procedures. They were required to remove any sections of wire they pierced and replace them before continuing on with troubleshooting exercises. Sealing the hole later is fine to prevent problems, but it is not acceptable in my class because it is treated as a quick fix for unprofessional conduct.
It sounds like the guy who did this to your car was expecting it to come back into the shop, so he might have planned on sealing the hole later. Still, ... There's a better way to measure voltages.
As a point of interest, since the mid '70s, a lot of GM cars used aluminum wire to save weight. The insulation was translucent and you could see the wire inside. I worked on a few of those where someone had pierced the insulation and corrosion had caused a break in the wire. Usually that only took a few weeks to occur.
I think there has been some confusion in my interpretation of the symptoms. By "stalling" I took it to mean the engine stopped running due to engine rpm too low when pulling up to a stop sign, and it would easily restart. Now it sounds like you mean it quits running while you're driving and won't restart. If that's correct, and you have a code 54, try a different distributor. There are actually two different sensors in it. I can't remember if they each operate at different engine speeds, or if one identifies which cylinder is getting ready to fire and the other one is for precise spark timing.
Many years ago, Toyota had a bunch of trouble with this type of optical sensor. When the PVC system plugged up or stopped working, pressure built up in the bottom of the engine from normal blowby. The pressure forced engine oil vapor past the rubber seal around the distributor shaft. The vapors condensed on the optical sensor. I can't remember what the symptom was, but I don't think it was as simple as stalling while driving.
This sensor is not a common failure item, but you're well beyond looking for something common.
As for buying a scanner, the investment won't break the bank, but in this case, I would recommend a Chrysler tool. There are a lot of aftermarket units out there but none will ever do everything the manufacturer's unit will do. Some of the better ones are the Genysis and various models by Snapon, but they work on many brands of vehicles, so you'll be paying too much for things you don't need. They both include so much unnecessary stuff that they cost more than the two Chrysler scanners. The Chrysler DRB2 has cartridges that work for '94 and older vehicles, but mine work just fine on my '95 Grand Caravan. I sold one for $600.00 at the nation's second largest old car show swap meet about 50 miles from my house, and I have one more that I no longer use. I also have a Monitor 4000 that I bought new and updated once for '92 models. It was made by the same company that made the DRB2, but it does fewer functions but on all three domestic manufacturers. Cost was a lot lower because of the decreased functionality.
Now I use Chrysler's DRB3. It really does a lot of stuff, but because it's a newer model, it only works on vehicles back to 1998. I will never own anything that new, so I use it with two plug-in cards that lets it work back to '94 or '83 models. The '94 card also gives it the capacity to work on the engine / emissions systems of any '96 or newer brand and model car sold in the U.S. This complete kit can be purchased over the internet for a little over $6200.00, but it includes way more stuff than you'll ever need. It has cables to connect to any Chrysler car or truck back to 1983, (but you would need the extra cards), a huge carrying case, books, etc. If you go through the dealer's parts department, you can order just the scanner, the needed card to do '94 to '97 models, and one cable for around $3900.00.
Besides reading fault codes from any of the many computer modules, you can watch sensor values in real time, actuate things like the fuel pump or radiator fan, observe inputs such as brake light switch and neutral safety switch, and there is a record / playback function. That is really useful for intermittent glitches such as momentary sputtering that doesn't last long enough to troubleshoot. When a problem occurs, you press "record" and it will record all the sensor values beginning a few seconds before the button was pressed.
Another dandy function you won't find on any other equipment is "last cutout" for the cruise control. How do you find the cause of a cruise control that stops working for an instant, but within seconds, you can press "resume" and it's fine? The recorded reason could be "brake light switch", "ignition switch", or "something similar. For "ignition switch" for example, you would look for an intermittent problem in the power wire for that circuit. You obviously didn't turn off the ignition switch while you were driving. For the "brake light switch", you would check its adjustment or suspect pitted contacts.
The DRB2 does all these things too, but you have to have the right cartridge. The latest '94 cartridge works on all domestic Chrysler vehicles up to that year, (and most '95s), but older cartridges only work on the few model years they were made for.
Holler back for more information on scanners if you have an interest in finding one.
Monday, March 1st, 2010 AT 6:36 AM