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Old 10-07-2011, 07:34 PM   #1
96 birdman
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PCM/CCRM grounding issue?-fuse #13 blows

96 t-bird V-8 4.6l LX: this is an intermittent problem. Here is what happened--
Turning a corner, car just died. Checked around and found fuse #13 was blown
Replaced fuse and when key was turned to just "run" position the fuse would
blow again. Towed it to Ford dealer and was told the fuel pump was bad, had
it replaced and it ran fine for about 2 weeks. Then, driving on freeway it died
again--fuse #13 blown again. This time I replaced the fuse and it started right
up. Then 2 days later it died again but this time when I replaced the fuse it
wouldn't start but it would crank over fine. Checked the fuel pump and it was
bad. Got a new fuel pump and new wire harness connector for it (replaced both
sides of connector). Hooked it up out of the car and it worked fine so I put it
back inside the tank. Ran great for another 2 weeks, then died again. Sure
enough fuse #13 was blown again. Replaced the fuse and it started right up.
Two days later it wouldn't start but the fuse was ok. Tried to start it the next
day and it started. Then 2 days later it wouldn't start. Next day it would start.
Then next day it wouldn't and it hasn't started since (fuse #13 still ok). So, sometimes the fuel pump would prime and sometimes it wouldn't. Took the CCRM
out of the car and it worked properly (12 Volts on pins 12,24 & 5 on CCRM) but
when I put it back in the car there is no voltage on those pins. I know the PCM
supplies the ground (PCM pin #80 to CCRM pin #18) for the fuel pump relay (pin 85 on relay). 12 volts to pin #11 (pin 30 on relay itself) is supplied from battery via
fuse #13 (the fuse that blew). The other 12 volts for the fuel pump comes from
the EEC power relay when it is activated by the ignition switch. When this happens the fuel pump gets it's 12 volts which I get with the CCRM out but nothing when it is in the car. So I'm thinking it is either a bad PCM or a short to
ground somewhere from something. Anyone have any idea how I could find out.
Also, there were no codes being generated but my scanner will not communicate
with the PCM now. Please help, it's going on 1 year now. Thanks
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Old 10-11-2011, 07:08 PM   #2
97Bird
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Re: PCM/CCRM grounding issue?-fuse #13 blows

Welcome to the forum 96 birdman. Maybe the 96 is a little different then a 97 because I see no connection from the PCM power relay output to the fuel pump circuit unless it is coming through the PCM pin 40 , which is supposed to be a monitor signal (in 97). In 97 the CCRM pins 12 and 24 are the PCM Power Relay outputs whose relay coil gets it's power from fuse 3 and it's low side goes directly to ground through pin 15. If you have no power on pins 12 and 24 with the key in start or run then either the relay is bad, you have a poor or no ground connection at pin 15 or no power on pin 13. I would check all of the ground connections on the PCM also. Use an ohmmeter between all of the PCM grounds and the ground connection on top of the radiator support in front of the battery.
Are you using an aftermarket fuel pump? They have been known to be problematic. I hate to say it but you might want to start tracing the fuel pump power wire back to be sure it isn't rubbing on something and shorting out because the insulation is worn off.
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