Cranks but no start??????

gotta find a new PCM....but what caused the evil burn.

ASD (auto shut down) circuit which controls the injectors, coil, alternator all on the same circuit. when the ASD relay malfunctions, it shuts this system down and the truck will crank but not start. (sometimes it is the coil itself, sometimes the alternator, sometimes a fuse for the injectors) I was not so lucky, the relay is fine...swapped it out with others of the same rating....a spike (caused by SOMETHING PROBABLY GROUNDED) went straight to the PCM after the relay.

Guess what....the voltage regulator is housed INSIDE the PCM....WTF! so if a spike occurs after the relay it fries the PCM????? (alternator internal ground???)

Pin 12 on PCM block (ASD) circuit is a common problem. when I opened up the wiring loom there, it smelled of burnt circuit board and around that pin was all melty and oozy....

I think it may be the alternator....

start up after a long siesta is always interesting....all kinds of noises, squeaks, tappets, belts, smoke from 2 tons of wd40, ect......and it did its share of squawking.

I guess I ll get the alternator tested...but this kinda sucks. (gauge for alternator read in the right ranges and did not show any spikes while I was getting it going again) Some guys have put a 3a fuse at that wire on the PCM and it has helped in most situations. They do this while figuring out what actually causes the spike. Some guys have fried 3 pcms not knowing the cause of the spikes and just trusting the fact that the PCM was the cause and had an internal issue. (This is true, but the cause is usually most always from outside the PCM)

I wonder if I can put another fuse right after the alternator going to the PCM, though it is probably the same wire.


I can buy a whole parts truck for what they want in parts!


argggghhhhh

 

So I traced the wiring back to from the fried computer terminal (ASD pin 12) and that loom goes back under the radiator support and up under the battery tray. So out came the battery and tray (PIA) and then followed the loom up into the relay box on the drivers side fender. I wanted to see if I could find any corrosion under the relays....there was none, but I did find two wires going to the Leak Detection Pump and they were definitely cut and shorting out against a bolt on the fender.

could this be why the computer fried?....the wiring is after the relays and fuses, I think.......


Ill send some pics this weekend.

JP

 

anyone? anyone?.....

so I did find a loose negative battery connection and compromised wiring coming from the Leak Detection Pump as mentioned above.

Did the alternator fry my computer or was it the wiring on the LDP/neg battery terminal.

More closely looking at the computer itself, the 12 pin was so melted that it burnt the potting medium holding the circuit board in suspension, melted the solder and copper traces that attach the pin to the circuit board and even burnt and charred the fiberglass board putting a hole in it below the main connector about the diameter of a pencil.......and made (computer) repair pretty impossible for me anyway.

WHAT CAUSED THE COOKING????


JP