I am working on a '92 Dakota 5.2 auto for a friend. No spark but cranks. I have checked the triple splice and it is fine. I get battery voltage to prong 30 on both the fuel pump anjd asd relays. If i push in on the Fuel Pump relay the pump runs (cap removed). However I get no codes from the PCM. In fact the check engine light never comes on even momentarily when the ignition is switched on. I checked the bulb and it is good. So where do I look next? Or could the PCM be bad as the check engine light never illuminates? All help is appreciated!

 

the pcm could be bad, I don't know much about the 5.2 in those. Does the distributor have the plastic pickup in it like the v6 does? If so that could be bad like i said don't know much about that year but it's something to look at.

 

Yes the PCM could be bad. But I truly think it is the splice issue since the splice supplies power to the fuel and ASD relays and computer all of which has no power.

 

Thanks for your help, but I have spent 2 hrs checking the splice. No corrosion, all wires well fused at splice. Measured voltage across splice (by sticking pins into wires), at both terminal 30's (ASD and FP relays) and at red/ yellow battery wire (pin #3) on pcm. Got good voltage at all points even loaded the circuit by connecting a headlight (for load) and it worked (voltage between ASD terminal 30 and battery ground). Actually depressed the ASD relay by hand (took off relay cap) and still got no voltage to coil. What bothers me the most is the Check Engine light never comes on. On all other cars I have worked on the light comes on momentarily when you power up so that you can make sure the light bulb is good. Even this does not happen when I bypass the splice with a jumper. I have checked ground continuity between all grounds and the PCM which was good. I checked terminal 87 to ground on start and I never get a ground connection to that side of the relay coil, as if the PCM is not working.
I was hoping for a bad splice, but so far cannot fault the splice. I have reviewed the wiring diagram to see if there is another interface between the asd relay and the pcm and cannot see one. Could a bad crankshaft or camshaft position sensor keep the PCM from coming on?

 

Forgot to say the fuel pump runs fine when I depress the fuel pump relay by hand. I even cleaned the splice and soldered the jouint. Still not getting ground signal from PCM.

 

Final check, depressed the ASD relay and checked for 12 volts at pin 57 (B+) on PCM. Got the voltage and then loaded the circuit with headlight and it lit up fine. Still no coil voltage and no negative at terminal 87.

 

Is your PCM receiving the Key On voltage from the ignition?

 

Yes it is, but it still does not seem to have any output to send a ground signal to the ASD and Fuel Pump relays (terminal 87).

 

Crazy RT, thank you for your help. I replaced the PCM this morning. As soon as I turned the key on both the ASD an FP relays pulled in and it immediately started. Now I am wondering what killed the original PCM. In addition this thing really needs a tune-up. It has 120,000 miles on it with original plugs, plug wires, dist cap and rotor. I will run for awhile and see if I pull any codes. I drive a rusted '83 s-10 Blazer, 5sp. 2.8. People ask why? It is not computer controlled and in 320,000 miles has never let me down except for 1 time when the fuel pump (mechanical) failed. I keep an extra ignition module in the console but have never installed it. Not bragging on it, but it is a lot easier to trouble shoot and fix. I have been working on cars for 40 years and hate a black box that I can not troubleshoot in itself. Signals & power in, electrons work their magic and signals out, but I can't see the magic work.

 

Think I have figured out the cause of the PCM failure. An interior light under the rt. side of dash would not shut off, so to keep the battery from running down the owner was pulling the POSITIVE cable off the battery each time after driving the truck. As we all know if disconnecting the power we should remove the NEGATIVE cable first. Pulling and replacing the positive will create voltage spikes which electronics do not like. They drove the truck, pulled the positive and after reconnecting it the truck was dead. I will bet a spike killed the PCM. Good lesson to remember, ALWAYS remove the negative cable first! I took the bulb out of the offending light, but will fix properly later. After running the only code I pulled was 12 and that is normal.