I need to confirm that my PCM is causing my problems. Any help or suggestions will be greatly appreciated. I have a 99 f-150 with a 4.2L V-6.

Here it goes...

-I have a non-starting truck and when it does start(very rarely) it runs like crap. The few times that it has started, it runs decent, other times it barely keeps itself going.

-I have no check engine codes

-Fuel is not an issue. I have fuel pressure and every injector is spraying fuel fine.

-I have good compression in every cylinder

-When I do have spark, it is very weak.

-I have replaced the coil, plug wires, plugs, crank sensor, and cam sensor with no help

-I have 12 volts of power going to the coil

-The primary and secondary resistance of my new coil checks out fine

-I have checked the negative wires going to the coil as someone cranked the engine over and I do have a signal pulse in all three of them. It did seem a little weak though, but I am not sure. I was using one of those incandecant test lights and maybe the signal was too fast to light it up fully? (Thats what my manual told me to use)

-Assuming that the signal IS strong enough, the next thing to check is the crank sensor and I had just installed a new one with no results

-All of the wiring in the truck is in very good condition. I haven't taken all of the bundles apart to check, but I have no reason to believe that they would be bad.

The only thing left that could be my problem is the PCM right? I want to make sure this is my problem before I send my unit away for repair and reprogramming. I would really prefer to save the money I would spend to take it to a dealer. I imagine the whole job would be at least $800-$1000. Just trying to save some much needed money

 

Had a similar issue with a mustang. Would intermittently start but run real bad. I would check your harmonic balancer. It is aluminum and will wear out at the keyway slot and throw the crank sensor off, trigger is part of balancer. Can check it by trying to spin the engine over by hand at the balancer. See if it moves independent from the engine. Mine had like 30 degrees of slop or better. Remove the belt too. Had take the balancer bolt loose on the mustang then you could spin it. Still had to use a pulled to get off the crank. Worth a peak. Easy to get at.

 

I have felt around down there and used the crank pulley bolt to rotate the engine. I never noticed anything out of the ordinary. I will give it a closer look first chance I get. Thank you.

 

I am liking the post from TRD-toy, loosen the crank bolt and try turning the engine over by hand as he described. I have never seen this happen but it is believable. Did you use the cam position tool to set the cam sensor? Don't forget to look at all the grounds.

 

You wouldn't have to reset anything to replace the cam sensor. Only if you replaced the cam synchronizer. Not saying there is a problem with the balancer but worth a check. PCM is very uncommon problem. Check the pins at the coil connector for any problems. Just fixed a dodge with pin fit problems at coil. They just had a PCM swapped and still same problem weak spark from coil. Different system but same concept at the coil. Constant power and PCM pulses the ground.

 

I just checked and everything down at the crank is okay. I also checked the pins/connector at the coil and everything checks out there too. Thanks for the ideas. Would a weak ground pulse from the pcm more likely be causing my problems or should I go back to focusing on the coil? Any ideas about anything else? I'm just shooting in the dark at this point.

 

I have confirmed today that all of my wires going to the coil and the crank sensor are good. I did a voltage drop test and they all checked out. I also checked out the related wiring over at the fuse box and all is good.

I am still seeing some spark with my spark tester but not really anything with my plugs.