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Misfire/no spark

Tiny
BIGLIP
  • MEMBER
  • 1997 FORD THUNDERBIRD
  • 33,500 MILES
There's no spark on paired cyl's 4 & 7, I replaced the coil, still no spark, swapped ignition wires and they're good. Check for signal input, none to coil for 4 & 7.I assume it'd the Powertrain Control Module but I have no way to test it and I can't afford to spend $200 for a new one if it's not the problem. Is there anyway to be sure?
Thanks
Biglip
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Friday, May 24th, 2013 AT 10:47 AM

11 Replies

Tiny
KHLOW2008
  • MECHANIC
  • 41,814 POSTS
Test the wire for continuity between PCM and the ignition coil. If continuity exists, check the crankshaft wheel for crnkposition sensor, if it turns out good, there would be no other possibilities except a faulty PCM.
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Friday, May 24th, 2013 AT 11:33 AM
Tiny
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  • 6 POSTS
Sorry it's been so long, the continuity checks out but I don't follow you on the crnk position sensor, I was under the impression that was only 1 point, not seperate points for each "firing position". Long and the short of it, I replaced the PCM and it made no difference.
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Thursday, June 13th, 2013 AT 9:33 AM
Tiny
KHLOW2008
  • MECHANIC
  • 41,814 POSTS
2 cylinders share the same point of reference for the cranksensor and there are 4 separate pickup points in total.
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Thursday, June 13th, 2013 AT 11:08 AM
Tiny
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  • 6 POSTS
How would I check that out? The manual talks about voiding the A/C system and removing the compressor yada yada!
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Thursday, June 13th, 2013 AT 11:29 AM
Tiny
KHLOW2008
  • MECHANIC
  • 41,814 POSTS
Yup, not an easy job. The front cover has to be removed to gain access to the cranksensor pulse wheel, which would mean a host of components to remove.
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Thursday, June 13th, 2013 AT 11:36 AM
Tiny
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  • 6 POSTS
Sorry but "Test the wire for continuity between PCM and the ignition coil. If continuity exists, check the crankshaft wheel for crnkposition sensor, if it turns out good, there would be no other possibilities except a faulty PCM."
Sounded a bit easier than your last statement, not your fault or mine, it's very frustrating to have this kind of problem with a "babied car" with less than 33,500 miles. Too much for a disabled old goat, guess I'll save my money and take it to a mechanic, thanks for tryin'.
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Thursday, June 13th, 2013 AT 9:24 PM
Tiny
KHLOW2008
  • MECHANIC
  • 41,814 POSTS
A lot of things are easier said than done and sorry I could not be of a better help than this.

Good luck.
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Friday, June 14th, 2013 AT 10:52 AM
Tiny
BIGLIP
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  • 6 POSTS
I'm sorry to "beat a dead horse" but I'm grasping at straws here. I decided to redo all my tests and while doing the test with a neon lamp to show the "pulse" to fire the coils, I noticed that one wire is pulsing as it should, the wire for cyl 4 &7 glows faintly, which could mean? I know the center wire of the 3 supplies the 12 vdc.
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Monday, June 17th, 2013 AT 9:35 AM
Tiny
KHLOW2008
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Which wire is glowing faintly?
Did you try comparing with other cylinders?
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Tuesday, June 18th, 2013 AT 5:47 AM
Tiny
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  • 6 POSTS
I used a "LED with 1 leg going to the battery positive and the other going to the "signal wire for 7&4 cyl. The 3 wires going to the "spark coil" the left wire is for 7&4, the right wire is for cyl 2&8, the center wire supplies 12 vdc. When I connect the LED to the 2&8 wire and crank the engine the LED flashes as the 12 vdc is sent to fire the 2&8 coil, when I change the LED to the 7&4 wire it doesn't "flash, just a low glow". Sorry to be so long winded but I want to be accurate.
Thanks
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Tuesday, June 18th, 2013 AT 2:13 PM
Tiny
KHLOW2008
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From the schematics, I believe the coil drive circuit # 4 is the one that is faulty. From the coil, check the wire ( I believe is Red/Yellow) for continuity to the PCM terminal # 104. If continuity is available, the PCM is most likely faulty.
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Wednesday, June 19th, 2013 AT 6:06 AM

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