Hi guys. Please allow me to add a few comments. That is correct, there is no code 3. I'd be willing to bet that was a misread code 12. That is a very common code and will not turn on the Check Engine light. It just means the computer's memory was erased recently, most commonly by disconnecting the battery. You'll run into that code well over half the time you read the codes.
Chrysler is the only manufacturer that never needed or used a mass air flow sensor. The MAP sensor is the main one for fuel metering calculations.
You mentioned you found 12 volts at the ignition coil, but when was that? The automatic shutdown, (ASD) relay gets turned on for one second when the ignition switch is turned on. That relay sends current to the ignition coil, injectors, and fuel pump or pump relay. That one-second pulse is to insure fuel pressure is up for starting. What can appear to be normal fuel pressure can be misleading. The pump may not be running at other times.
Specifically, the Engine Computer must see signal pulses from the crankshaft position sensor and the camshaft position sensor to know the engine is rotating, (cranking or running). If either signal is missing, the ASD relay does not get turned back on during cranking, and you'll find 0 volts at the ignition coil at that time. Many people see the 12 volts at the coil for that first one second, and conclude incorrectly it's there all the time The easiest way to tell if the ASD relay circuit is working is to listen for the hum of the fuel pump for that one second when the ignition switch is turned on.
The next step should be to determine if those two position sensor signals are showing up. It is quite common to not have a diagnostic fault code related to them just from cranking the engine. That means don't assume both are working just because no fault code is set related to them. They often need more time to set, as in when a stalled engine is coasting to a stop. The best way is to view these two sensors on a scanner under "live data". On Chrysler's DRB3 scanner, they're listed as "No" or "Present" during cranking. When one signal is missing, the sensor itself is responsible only about half of the time. First we look for wiring and connector terminal problems. Aftermarket scanners should have a similar method of saying if those signals are showing up.
A slightly less-reliable method is to check for 12 volts at the ignition coil or the same-color wire at any injector, while a helper is cranking the engine. It must be there steady.
Now here's something you might consider that I'm not sure about. On the OBD2 engines, starting with some '95 models, the Engine Computer looked at the timing between the cam and crank sensors. Even though both signals could be showing up nice and strong, if the timing belt jumped one tooth, the computer turned on the Check Engine light and set the fault code, "Cam and crank sync". If the belt jumped two teeth, the computer shut the engine down by turning off the ASD relay. That was to protect the valves. If it jumped three or more teeth, open valves would be hit and bent by the pistons as they were coasting to a stop. While this engine is not listed an an "interference" engine, I don't know that to be a fact.
For my next comment of value, the camshaft sensor has been replaced, but no mention was made as to whether it was a used one, or how the air gap was set. That's what initially peeked my interest. The sensor's mounting hole is slotted for adjustment. The only way to properly set them is to use a thick paper spacer stuck on the end, then you push the sensor into the hole as far as possible, then tighten the bolt. The first time the engine is cranked, that paper spacer will slide off and be discarded. If that sensor is removed for any reason, you must buy a new spacer for the reinstallation. Being a cheapskate, I can tell you those spacers can be cut into four pieces for four of these jobs. That only saves a few cents, but that could prevent having to wait for the parts guy to deliver one when you're waiting in the shop. If the spacer is not used, it is possible for the sensor to be broken when the engine is cranked. Some sideways engines used this paper spacer on the crankshaft position sensor too. Also, if it is pushed in as far as possible without the spacer, then pulled back slightly, you might get lucky and it will work fine, but on one I did that on, it came back two weeks later with intermittent stalling due to that crank sensor. Was it really a failing sensor or was it due to me not installing it properly?
The Engine Computer should be way at the bottom of the list of suspects. They had very little trouble with them. There is something you should be aware of if you're planning on replacing it. Since the failure rate was so low, a lot of people get a good used one from a salvage yard. Here's where the problem can start. If your car has the factory-installed anti-theft system, you can use any Engine Computer for your application, and there's no need to read any further. Don't worry about part numbers. They change every time there's a revision, but they'll still work just fine.
The anti-theft programming lives in the Engine Computer and in the Body Computer. When you replace either one of them, the new one immediately learns that programming from the other one, meaning that part of the software is activated. That activation can not be undone. If your car does not have the factory-installed anti-theft system, you must install either replacement computer that has never had that software activated. That's what you'll always get from the dealer. If you find a computer in a salvage yard from a car that has anti-theft, and your car doesn't, the replacement Engine Computer will teach that programming to your Body Computer the first time the ignition switch is turned on. At that point the engine will not run because both computers are waiting for the "disarm" signal, but that is never coming.
Chrysler instructors use a car for a few months, then they donate them to Automotive programs for training on. We got a '94 Intrepid and ran into this problem. A student borrowed a computer to verify that was not the cause of a problem with his car. In his car, it learned that anti-theft programming, then, when he put it back in our donated car, we had a crank / no-start. It took most of the school year to convince my tool room attendant that he needed to find both computers from a non-theft system car, and install them at the same time. I ran into this the first time at the dealership where another electrical expert was working on a Dynasty for this problem. The second time was when a friend had rebuilt a smashed Neon in his body shop. The only thing he was waiting for was a replacement Engine Computer since his was broken. He borrowed one from a friend's similar model. The repaired car ran fine, but when the computer was returned to his friend's car, it too was a crank / no-start. Had to replace the Engine and Body Computers because his didn't have the anti-theft system.
The mention of replacing a computer is the second thing that compelled me to add these comments. I'll be waiting to see when you figure this out.
Tuesday, March 16th, 2021 AT 6:50 PM
