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Old 08-22-2008, 04:54 PM   #1
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Default Where is the ECM/PCM in a '93 F150 4.9L?

I originally had starting problems in my 1993 F150 4.9L because of the aftermarket Viper alarm system which I completely removed. Sometimes the truck would immediately start up five or more times in a row. I drove it 5 miles, when I turned the engine off it wouldn't restart and still won't. I am getting 12V at the coil input but it doesn't pulse when the engine turns over (subsequently no spark). This problem has been intermittent but is a constant problem now and is driving me crazy.

I thought I'd replace the ECM unit but can't find it (the chilton manual calls it a PCM also). The Chilton manual (not a good manual by my estimates) claims it is on the drivers side of the engine firewall. I can't find it, help I am becoming suicidal.
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Old 08-22-2008, 07:17 PM   #2
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Never mind! I searched and found the information I needed.. It isn't simple though!

http://www.ford-trucks.com/article/i...Detailed_.html
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Old 08-22-2008, 08:31 PM   #3
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The 12v wire to the coil isn't supposed to pulse. That is the red wire with a light green stripe. The one that does pulse is the tan wire with a yellow stripe. Check the computer for codes before you go buying a computer. Description how in the maintenance section under "Diagnose trouble codes".
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Old 08-23-2008, 12:04 AM   #4
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Thanks, that is the one I meant (tan wire with a yellow stripe). I pulled the PCM out and it was easy enough to do. Tomorrow I'm going to try and find a place to test it or hit the junk yard and find a replacement. I am less suicidal now.

Sean, I don't get a trouble code with the wire in the diagnostic connector.
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Old 08-23-2008, 12:15 AM   #5
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The tan wire with a yellow stripe comes from the ignition module and goes to the coil and computer. Test the ignition module. If it's not the module it probably is the sensor in the distributor.

Check the computer for codes instead of buying parts you don't need. If the battery has been disconnected you need to try to start it a few times and then check for codes.
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Old 08-23-2008, 12:16 AM   #6
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Also, the tan wire with the yellow stripe is negative, so it pulses negative. To test it the curcuit tester needs to be hooked up to power and the ground hooked to that wire.
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Old 08-30-2008, 10:36 PM   #7
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Solved! Once again. I replaced the ignition control module ( it was on the inside of the left front fender and easy to get too) and it fired right up. I thought I had fixed the starting problem once before, but this time I feel really good about it being solved. Only time will tell...
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Old 04-26-2009, 10:06 AM   #8
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Default 1993 Ford F150 - No Spark - Finally SOLVED (bad coil)

I had intermittent problems starting for several months (usually when it was humid or raining). Finally, after replacing the rotor/cap/wires/plugs, it stopped having any spark at all and wouldn't fire.

After reading these forum results, I first tried replacing the ignition control module on the left front panel ($50). That didn't make any difference. Next, I tested the resistance for primary and secondary poles on the coil. For my TFI-IV model, the specs call for a range of 8,000 to 11,500 ohms on the secondary poles. (measure between the main spark plug connector on the coil and a ground). My reading was 7,410 ohms... just barely below the acceptable range. Though doubtful, I replaced the coil anyhow ($20), and VOILE! It started and ran perfectly!

I hope this helps someone else. My advice is to replace the coil first since it's cheaper. Both the coil and the ignition control module are easily accessible (though the ignition control module requires a special tool to reach the bolts holding it to the heat sink)

-Justin
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Old 04-26-2009, 05:40 PM   #9
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ha i had a 95 with the 4.9L and went threw all this process and it ended up bein the timing gears!! it was hard to find out what it was but once i did i took it to a real good mechanic i know and he fixed it right up
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Old 03-29-2010, 07:33 AM   #10
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I have a 5.0 same year, I'm guessing there is no way to read the code off the computer without pulling it out? I need to stop by the junkyard and find a new one I think
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Old 03-29-2010, 07:33 AM
 
 
 
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