You are currently viewing our forum as a guest, which gives you limited access to view most discussions and access our other features. By joining our community, at no cost, you will have access to post topics, communicate privately with other members (PM), respond to polls, upload content and access many other special features. Registration is free, fast and simple, so please join our community today!
I am referring to a '93 Factory Service Manual. Power is applied to pin A of the ASD relay from the ignition switch. Ground is applied to pin C by the computer (PCM) under the following conditions: for appx two seconds after the key is turned to start and thereafter if a signal is detected from the camshaft position sensor (aka; distributor pick-up).
If the computer is not seeing the signal and therefore not furnishing Ground, you should still see 12 volts at pin A and pin C (both sides of the ASD coil). The preceding is true for the 2.5 and 3.9/5.2 liter engines. These two wires are dark blue/ yellow for pin C and dark blue for pin A on the 3.9 liter. For the 3.9/ 5.2, the same pin on the PCM that grounds the ASD relay (pin 51) simultaneously grounds the fuel pump relay coil. Failure to see a pick-up signal may generate a code 11 or code 54 (camshaft signal missing/ camshaft sensor circuit failure).
This help any?
Yes, this does help. I'm terrible when it comes to wiring but I'm quickly learning. My theory is the ASD isn't grounding properly so it's not letting the power pass through the relay into the ignition circuit.
Are there any tests I can conduct to verify if the PCM is bad?
I don't think it's from no pickup signal reference. My manual states that if I have power at coil for 1 or 2 seconds at cranking then it drops off to 0, I'm looking at the distributor. However, I get NO power period during cranking or when I switch it to ON. According to my factory service manual, that leaves me with three options. Bad ASD relay, bad wiring in that circuit, or the PCM is shot. I've replaced the ASD. I'm pretty positive the wiring is good because if I jumper 12v to the positive side of coil, I hear my fuel pump come on and I get 12v on my injector power wire. That tells me power is getting to everything through the splice that I initially thought was the culprit. When I test at the relay no power is getting through it to the ignition system. I'm 90% sure it's the PCM but I'd really like to test it before I buy a new one. I might just bite the bullet and get the computer.
OK, before you commit to buying a new PCM, be sure the chassis grounds are good. I am not looking at a Manual right now (at work) but there are three pins on the PCM connector for power ground. Figure that out and see if they are 5 Ohms or less back to the chassis. One connection is right above the driver side headlight, another is in the vicinity of the ballast resistor for the blower on the passenger side firewall. Incidentally, the OBD1 connector is found dangling from the wire harness in this same neighborhood. The fact you recorded at least one code for the EGR indicates the PCM is at least somewhat functional. If you have a scanner, can you communicate with the PCM and clear the code? This would further indicate the state of health of the PCM. You may want to go ahead and replace the EGR soon. When the EGR fails, its often the vacuum transducer diaphragm that quits, allowing hot exhaust gas to leak into the vacuum system which can cause other mysterious problems. Also make sure the engine ground strap is sound and free of corrosion. The various grounds are common sources of gremlins and if you plop a 2-300 dollar "remanufactured" PCM down in that mess you'll still have all the same problems. The PCM can't furnish power ground if it doesn't have a sound connection to work with. You can also swap the fan clutch relay with the ASD relay(never mind this suggestion, I see you've covered that). Check from the return side of the ASD coil to pin 51 (or whatever for your year) of the PCM connector. Finally, I presume you've already eliminated the "Splice", right?
I will inspect those PCM grounds tomorrow. The chassis ground strap near the coil was roasted. I've already replaced it with a new one. Also, the wires running into the positive and negative terminals were a bit corroded. I cut the corrosion out and redid the connections.
I haven't checked the splice you mention. I'm not sure but I think the '90 Dakota doesn't have the same problem with the splice that I've read about on this site. If it was on my truck, where is it? Directly under the ASD relay? I've checked there and all the wiring looks solid.
The FAQ stickey has the low down on the "Splice". It is located in the bundle of wires that pass under the box (PDC) that contains the relays. Generally, the section right next to the battery. I lied, there are two power grounds (pins 11 and 12) and one signal ground (pin 5) in the sixty pin PCM connector.
i heard the ignition switch can be a problem to but in that splice of wires on the left fender there are quite a few splices that can go bad. i found them wen i was diagnosing my 91 which had almost the same problems as you except i had power on both sides if the coil and no fuel pump or injectors. when i fixed those splices all of the sudden my fuel pump turned on as did my injectors but my pcm was shot s they wouldnt shut off.
hope this helps
R.I.P. my brother Andrew O. 12/12/1990-9/26/12
R.I.p. love of my life Sarah G. 4/12/1990-8/3/2012