1997 Ford F-150 voltages or pcm?

Tiny
FANTUM48
  • MEMBER
  • 1997 FORD F-150
  • 6 CYL
  • 2WD
  • AUTOMATIC
  • 172,000 MILES
My truck is in a start/no run situation. I Rebuilt the 4.2L and have put 2000 good miles on it when it just bucked, coughed and stalled out last week. Checked the mechanics of the motor. Fine(timing, compression, all good). Fuel delivers a static 35psi to the rail and is being injected into the cylinders and there is spark. No code has been thrown out by the PCM. All sensors I have checked(TPS, IAC, IWT) are good. I am having issues finding out what voltage I should be seeing going into and out of the Cam Angle sensor and the Crank position sensor. The Cam angle is new from the rebuild. I am at my last resource here before I say its the PCM that quit. So some voltage knowledge and where to go from there would help me greatly. Thanks
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Wednesday, August 4th, 2010 AT 9:41 PM

10 Replies

Tiny
KHLOW2008
  • EXPERT
Hi fantum48,

Thank you for the donation.

You mentioned start/no run condition, does that mean it can be started?

The voltage of the CMP is less than 5 volt and with engine running, it should not vary more than 0.1 volt.

Crankshaft position sensor is Hall effect so it is 12 volts.
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Friday, August 6th, 2010 AT 7:22 AM
Tiny
FANTUM48
  • MEMBER
It cranks over only, sputters and coughs occasionally, but does not run. I have replaced the CMP and CKP. I am at a loss with it, can't figure it out and am very hesitant to get a new PCM. No codes to retrieve. Help!
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Sunday, August 8th, 2010 AT 5:24 PM
Tiny
KHLOW2008
  • EXPERT
Since it is sparking with compression and fuel getting to the cylinders, it should be running.

When sparks are available, it is not likely to be a problem with the PCM, cam or crank position sensor.

Are the sparks bright blue or orange? If it is dull orange, the sparks could be weak resulting in the non starting. Were the spark plugs checked? Are they clean or sooty?
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Monday, August 9th, 2010 AT 6:32 AM
Tiny
FANTUM48
  • MEMBER
I have replaced the plugs. Then old ones did have carbon build up on them, but I figure that's part of the break in period for a rebuilt engine. The Coil pack primary side was around 700ohm, and the secondary side was around 13k ohms, which I think is just outside of spec. I have not actually looked at at the spark myself, so I dont know if its blue or orange.
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Tuesday, August 10th, 2010 AT 1:48 PM
Tiny
FANTUM48
  • MEMBER
In addition. The cam angle sensor(CMP) is seeing.6V under battery voltage, and the Crank Position Sensor(CKP) I cannot get a voltage reading either front or backprobing. These readings were taken key on engine off because of the no start condition
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Tuesday, August 10th, 2010 AT 6:04 PM
Tiny
KHLOW2008
  • EXPERT
Something is wrong with the coil pack. The specifications indicates the primary coils should be 0.5 ohms. You are getting 700 ohms. That is way out of specs. Reconfirm the resistance. If it is out, then you need to replace it.

Weak sparks would not fire easiyl and with prolonged cranking flooding would occur resultng in even more difficult starting.
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Wednesday, August 11th, 2010 AT 9:09 AM
Tiny
FANTUM48
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Sorry, the coil pack primary side is at.6 to.7ohms. Cam angle senso is seeing battery voltage and the Crank position sensor I can't find any voltage going to it, both tested KOEO.
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Thursday, August 12th, 2010 AT 11:18 AM
Tiny
KHLOW2008
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).6 0.7 is slightly out of specs. They wold firee but the sparks could be weak.

I could not find any information on testing of the crank position sensor.

Both CKP wire goes to the PCM.
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Thursday, August 12th, 2010 AT 12:56 PM
Tiny
FANTUM48
  • MEMBER
Replaced the coil pack and sill no start.I guess the hunt is on for a bad wire, then replace the PCM. Is this logical?
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Monday, August 16th, 2010 AT 5:16 PM
Tiny
KHLOW2008
  • EXPERT
Reconfirm that there is sparking and fuel is being injected into the cylinders.
Ensure the engine compression is within specs.

Since engine has not started for quite some time and if fuel is getting into the cylinders, it could have caused the compression to drop.

Remove the spark plugs and squirt some engine oil into the cylinders and crank the engine briefly to bring up the compression. Do this with the fuel pump or inijectors disconnected to prevent flooding.

Reinstall the spark plugs and retry.

With sparks and fuel being injected into the cylinders, it is hard to accept a PCM fault.
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Tuesday, August 17th, 2010 AT 7:16 AM

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