97 Ford Explorer XLT V6 4.0L SOHC P0351 HELP | Ford Explorer Forums - Serious Explorations

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97 Ford Explorer XLT V6 4.0L SOHC P0351 HELP

gwire

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October 27, 2012
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Year, Model & Trim Level
97 Ford Explorer XLT 4.0
Out of no where my engine starts running really rough with less power! When I parked it I looked under the truck and saw the passenger side Cat was cherry red from all the fuel dumped. Naturally I think its a misfire so I Purchased plugs wires and a new coil pack. When trouble shooting I went from cylinder to cylinder Checking for spark. When I got to cylinder 1 there was no spark. OK great! so I changed the wire. Still no spark. Ok great! So I changer the spark plug. Still no spark. OK great so I changed the coil pack. WHAT? Still no spark! WTF? Not only do I have no spark on 1 but also cylinder 5 from the coil pack. I believe the coil pack 1 and 5 are paired from what I read in one of the forums. I scanned for codes and I only got p0351 which I believe is only for cylinder 1. DID I buy a faulty coil pack? Or is it something else? Where do I Go from here $150 dollars later?
Everything was running perfect for the longest time what could this be all of a sudden? I need this fixed ASAP.
 



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From the OBD2 site.


Causes

Potential causes of a P0351 code include:
•Short to voltage or ground on COP driver circuit
•Open on COP driver circuit
•Loose connection at coil or broken connector locks
•Bad Coil (COP)
•Faulty Powertrain Control Module

Possible Solutions

Is the engine misfiring presently? If not, the problem is likely intermittent. Try wiggle testing the wiring at the #1 coil and along the wiring harness to the PCM. If manipulating the wiring causes the misfire to surface, repair the wiring problem. Check for poor connection at the coil connector. Verify the harness isn't misrouted or chafing on anything. Repair as necessary

If the engine is misfiring presently, stop the engine and disconnect the #1 coil wiring connector. Then start the engine and check for a driver signal to the #1 coil. Using a scope will give you a visual pattern to observe, but since most people don't have access to one there's an easier way. Use a Voltmeter in AC Hertz scale and see if there's a Hz reading of between 5 and 20 or so that indicates the driver is working. If there is a Hertz signal, then replace the #1 ignition coil. It's likely bad. If you don't detect any frequency signal from the PCM on the ignition coil driver circuit indicating the PCM is grounding/ungrounding the circuit (or there is no visible pattern on the scope if you have one) then leave the coil disconnected and check for DC voltage on the driver circuit at the ignition coil connector. If there is any significant voltage on that wire then there is a short to voltage somewhere. Find the short and repair it.

If there is no voltage on the driver circuit, then turn the ignition off. Disconnect the PCM connector and check the continuity of the driver between the PCM and the coil. If there is no continuity repair the open or short to ground in the circuit. If continuity is present, then check for resistance between ground and the ignition coil connector. There should be infinite resistance. If there isn't, repair the short to ground in the coil driver circuit

NOTE: If the ignition coil driver signal wire is not open or shorted to voltage or ground and there is no trigger signal to the coil then suspect a faulty PCM coil driver. Also keep in mind that if the PCM driver is at fault, there may be a wiring problem that caused the PCM failure. It's a good idea to do the above check after PCM replacement to verify there won't be a repeat failure. If you find that the engine isn't misfiring, the coil is being triggered properly but P0351 is continually being reset, there is the possibility that the PCM coil monitoring system may be faulty.
 






It is a coil pack, all 6 are together. There is no power to the first two closest to the passenger side which are paired and go to cylinder's 1 and 5. It is the same on the old coil pack as well as the new coil pack. I checked all the connections. Nothing is lose. Like I said I replaced the spark plug wire and the spark plug. I am not that technical and do not want to do a bunch of voltage testing on wires that I do not understand or can not find. Is changing the PCM the next thing to do?
 






Test Results

From the OBD2 site.


Causes

Potential causes of a P0351 code include:
•Short to voltage or ground on COP driver circuit
•Open on COP driver circuit
•Loose connection at coil or broken connector locks
•Bad Coil (COP)
•Faulty Powertrain Control Module

Possible Solutions

Is the engine misfiring presently? If not, the problem is likely intermittent. Try wiggle testing the wiring at the #1 coil and along the wiring harness to the PCM. If manipulating the wiring causes the misfire to surface, repair the wiring problem. Check for poor connection at the coil connector. Verify the harness isn't misrouted or chafing on anything. Repair as necessary

If the engine is misfiring presently, stop the engine and disconnect the #1 coil wiring connector. Then start the engine and check for a driver signal to the #1 coil. Using a scope will give you a visual pattern to observe, but since most people don't have access to one there's an easier way. Use a Voltmeter in AC Hertz scale and see if there's a Hz reading of between 5 and 20 or so that indicates the driver is working. If there is a Hertz signal, then replace the #1 ignition coil. It's likely bad. If you don't detect any frequency signal from the PCM on the ignition coil driver circuit indicating the PCM is grounding/ungrounding the circuit (or there is no visible pattern on the scope if you have one) then leave the coil disconnected and check for DC voltage on the driver circuit at the ignition coil connector. If there is any significant voltage on that wire then there is a short to voltage somewhere. Find the short and repair it.

If there is no voltage on the driver circuit, then turn the ignition off. Disconnect the PCM connector and check the continuity of the driver between the PCM and the coil. If there is no continuity repair the open or short to ground in the circuit. If continuity is present, then check for resistance between ground and the ignition coil connector. There should be infinite resistance. If there isn't, repair the short to ground in the coil driver circuit

NOTE: If the ignition coil driver signal wire is not open or shorted to voltage or ground and there is no trigger signal to the coil then suspect a faulty PCM coil driver. Also keep in mind that if the PCM driver is at fault, there may be a wiring problem that caused the PCM failure. It's a good idea to do the above check after PCM replacement to verify there won't be a repeat failure. If you find that the engine isn't misfiring, the coil is being triggered properly but P0351 is continually being reset, there is the possibility that the PCM coil monitoring system may be faulty.

Hey thank you for your response.

Ok I went and got a multi meter anyway. I tested continuity first. There are 4 wires that connect to the coil pack as follows. Y/B "Yellow w/ black stripe" for coil 1. Y/R "Yellow w/ red stripe" for coil 2. Y/W "Yellow w/ White stripe" for coil 3. The last wire is R/LG " red w/ Light green" I assume is for the ground and is fine because coils 2 and 3 fire no problem. Well sure enough I get perfect continuity for all three coil wire all the way to the PCM connector.
Next I turned the vehicle on and ran the AC HZ test as mentioned above. I didn't quite know what I was doing so don't understand what I was testing. Anyway what I did was set my digital multi meter to AC HZ and while it was running I touched the red probe to #1 output on the coil pack and the black probe to ground and got a reading between 1.6 and 1.9 same for #5 output on the coil pack.

I do not know what that means. this is my setup:

--------------PCM------------Firewall-------------------------------

Coil Pack
1 2 3
5 6 4


---Engine---
3------------4
2------------5
1------------6
------------

--------------------------Front of vehicle----------------------------

1 and 5 are paired with one coil #1
2 and 6 are paired with one coil #2
3 and 4 are paired with one coil #3
3 Coils all together

Spark Plugs and wires are ruled out
Continuity is ruled out
Ground is ruled out since coils 2 and 3 are firing
At this point I think I can safely assume it is the PCM (Powertrain Control Module) Please someone let me know if I am wrong. Thank you
 












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