Can the VCM-A be tested to see if it's good or bad??

[DelCoch]

Is there anyway to check the VCM-A on a 95 4.3 that won't start? (It has the enhanced ignition system with the plug wires on top of the distributor, there is no module inside the distributor)

There is 12V going into the VCM, 12V going into the coil, 12V going into the crankshaft sensor, and all have a good ground.

The 1-4 volts to the coil driver module from the VCM is not there. Thus, no spark from the coil, and no spark to the plugs.

Also, while cranking there is no return voltage from the crankshaft sensor, which was replaced new and still no return voltage when cranking. Should there be voltage from the crankcase sensor while cranking or only when the engine is running??

It appears the VCM might be bad, but I would like to know for sure before laying out the big bucks for a new one.

Any and all suggestions will be more than welcome!!

[dmbrisket 51]

the crank sencer should send back a signel when the engin is being cranked, a common no start problem on newer chevys is a bad crank signel... ide start with the "enhanced" ignition system, ive yet to see one installed and work correctly on the multiport moters (which i assume is the same on a cpi moter)

[MT-2500]

Originally Posted by DelCoch

Is there anyway to check the VCM-A on a 95 4.3 that won't start? (It has the enhanced ignition system with the plug wires on top of the distributor, there is no module inside the distributor)

There is 12V going into the VCM, 12V going into the coil, 12V going into the crankshaft sensor, and all have a good ground.

The 1-4 volts to the coil driver module from the VCM is not there. Thus, no spark from the coil, and no spark to the plugs.

Also, while cranking there is no return voltage from the crankshaft sensor, which was replaced new and still no return voltage when cranking. Should there be voltage from the crankcase sensor while cranking or only when the engine is running??

It appears the VCM might be bad, but I would like to know for sure before laying out the big bucks for a new one.

Any and all suggestions will be more than welcome!!

No Way to be for sure.
Run all voltage test and get a good engine capable scanner on it and see what all is going on.
I would pitch the enchanced ign in the trash can and go the OEM set up.
MT

[BlazerLT]

VCM-A 4.3Ls come with the horizontal cap and rotor setups.

Sounds like someone put a different distributor in where it didn't belong.

Only the 1995's with the PCM OBDI computers came with the top mounted plug wire connections.

[DelCoch]

Originally Posted by BlazerLT

. . . Only the 1995's with the PCM OBDI computers came with the top mounted plug wire connections.

That’s what I have, 1995 with OBDI and the 16 pin connector. Maybe saying "enhanced" ignition system is the wrong terminology, but I thought that’s what the GM shop manual said.

What will cause the crankshaft sensor not to put out a signal, other than it being bad? It doesn’t appear to be fed by the PCM, or any other sensors, but then trying to read the wiring diagram in the GM shop manual leaves a lot to be desired.

I have an after market scanner but it will only read Generic OBDI, not GM OBDI, and nothing shows up with it except a couple transmission codes. Course, I’ve had the battery disconnected after the no start problem developed. A mechanic friend has a Snap-On scanner that I’m going to try and see if it shows any codes other than the transmission codes. If the codes have been erased do to the battery being disconnected, will any codes show up by just cranking the engine or does the engine have to be running to throw the codes?

Thanks for the replies,