97 FORD E 350 V 10 CLUB WAGON -- Cylinders 1 thru 5 have no spark. Each coil has 12v on one side and good continuity on the other coil side to the PCM pin for that coil. A scope check shows no pulse on the PCM coil side of each of the 1-5 coils (as measured at the coil). The good bank shows good pulses on each coil side going to the PCM. Is this pretty conclusive that the PCM is the problem, or is there something else that can cause only one bank to have no pulse at the coils? There is good continuity from the negative side of the coils to the actual pin on the PCM connector and there is good 12V at each coil. All harness plugs have been checked for good condition at the PCM as well as the intermediate harness plugs to the coils.

 

Just to touch all the bases , is the PCM getting the signal from the cam sensor for that bank? I believe the cam signal comes from the cam sensor in the distributor housing. A thorough check of that sensor and wiring that goes to the PCM to fire the coils could hold the answer. Could be a shaft problem ,but I would check all that out before condemning the PCM.

 

I assume you are referring to the "Cylinder Identification Sensor", correct? That is what is referred to in a schematic for the 6.8L engine. I will check that, but I don't see any bank 1 or bank 2, ie, there is only one sensor and I would logically expect failure of it would not single out just one bank, but I may be in error.

 

If you check the firing order for your 6.8L you will note that you are missing every other cyl. Hook up the scope and see what is going on with the cam synchronizer regarding its timing with the crank sensor. I think you may find something missing there.

 

Scoping the camshaft sensor and the crankshaft sensor showed good pulses on both. Shape and amplitude looked good. Continuity wiring harness checks from the sensors back to the PCM plug were confirmed good. I was unable to confirm the two pulses exact relative timing relationship because of the type scope being used, so can not say for sure that the pulses are synchronized exactly as they should be. Any other thoughts on what I could try next would be appreciated.

 

The timing relationship of the camshaft signal to the crankshaft signal is critical in this application. I gather you may be using an analog scope when you should be using a 2 channel digital scope to detect this.
I could be wrong, but I suspect something has changed with that cam sensor signal which is supposed to signal the PCM to initiate the correct synchronizing of the sequential injection and coil firing. If this synchronizing signal is "off" the coil sequencing is off also. If you decide to check into this further, be sure to mark the cam sensor synchronizer housing relationship to the engine block for correct installation on assembly. Mark and keep a record of the position of everything relative to that housing and the shaft inside it. There are tools available to insure the correct installation should anything inside it need to be replaced. Among the possibilities are the housing has moved,the pin in the drive gear may have sheared or something got in there that shouldn't be there. Look the entire unit over carefully for anything unusual.

 

We had an opportunity for an off duty Ford service technician to look at things and his test brought him to the conclusion that the PCM is bad. I will report back here with the results once a PCM is obtained.

 

Thank you for the update. Will be waiting for the results.
What kind of tests did he perform to confirm this?

 

He had a Ford touchscreen diagnostic laptop size computer that plugged in to the vehicle and gave extremely detailed readouts of all engine aspects. Obviously this is what is truly needed to efficiently and rapidly pinpoint problems, but it is probably too expensive and well beyond what individuals would normally have available. He stated the PCM is probably the problem, but may have been initially damaged by some other fault yet to be discovered. We shall see.........

 

I suspect he may have used the Ford IDS. (Integrated Diagnostic System).
They run in the area of $2500-3000. Lets hope it told the whole story. The equip is only as good as the man behind it. When you have the best equipment available and your diagnosis is "probably" I get the jitters because those PCMs are expensive too.
Thank you for keeping us informed.