pcm b fuse blown
 

hi all, drove my 1999 sw1 last week. went to start it today and it cranks but doesn't fire up. checked fuses and found pcm b fuse blown. went to put in a new fuse and it blew instantly. apparently there was/is a problem with a wire chafing issue in the harness at the firewall according a tsb and another forum but no exact location. i checked the harness boots thru the firewall and on the left side under the dash but all looks good there. anybody have this issue and were you able to find where the wire grounding problem was occuring? thanks for all the help!!

Not from me, never heard of or had the problem.

I've never heard that either, but I'd try removing the fuse box and checking under it for a bare wire. You've got one going direct to ground that shouldn't be.

Looking at outdated schematics, I think you're looking for an orange wire leaving the underhood junction box at that fuse and heading straight to the pcm.
Might want to pull off the underhood junction box to make sure there's not corrosion on the low side of that fuse forming a ground to somewhere.
Otherwise, ya gotta start tracing.....

i did a search and came up with nothing. i unbolted the uhjb from the inner fender flipped it over, opened it up and did not see any problems there. i looked at the harness under the dash and did not see any problems that were obvious. i fear that the short may be in the harness....ugh...

sounds like tracing of the orange wire is in order (unfortunately)
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oh, the other (worst case) possibility is that the pcm input that this circuit feeds has internally fried to ground. I suppose you could test this by determining which pcm pin the orange wire is feeding and testing for resistance to ground/continuity.

I sure hope it's not that.

i hate tracing wires...ugh...internal short in pcm....double ugh with #@% sigh....

Well, whatever has happened, until he gets that problem fixed, he ain't going anywhere. Here's one thing to try --> disconnect the PCM, replace the fuse, and turn the key to RUN. If the fuse holds, the problem is inside the PCM

most excellent idea

The PCM-B fuse is power directly to the PCM. There are 2 connections on the UHJB to the PCM, A-1 on the Brown 68 way plug and E-1 on the black 68 way plug. A-1 connects to the Lt. Blue 24 way plug at the PCM J-2 B-12 orange wire. E-1 connects to the Lt. Blue 32 way plug at the PCM J-1 D-13 orange wire. Disconnect the 2 Lt. Blue plugs from the PCM and see if either of these wires are shorted to ground. Usual problem is a bare wire at the firewall. There is a TSB on this...

ok....now i'm really scratching my head... traced wires according to directions from oldnuc(thanks) using an ohm meter from uhjb to the blue plugs...no shorts....left blue plugs disconnected from pcm and installed another 10 amp fuse. plugged in blue plugs one at a time and fuse blew each time. installed 15 amp fuse and it blew. unplugged blue plugs from pcm and installed another 10 amp fuse. plugged in blue plugs to pcm and low and behold...pcm b fuse did not blow....pcm 1 fuse blows!!!! unplugged blue plugs from pcm, installed another 10amp fuse in pcm 1 slot and it is good. so now all fuses are good but car still cranks over but no fire. checked for spark...there is none. sooooooo........any ideas?