Re: 4.7 no start help PLEASE!

From: David Gersic (
Date: Wed Aug 29 2012 - 08:18:48 EDT

On Tuesday, August 28, 2012 10:03:32 PM you wrote:

> PCM's are both Refurbs, 1st was junk, but
> last two do exactly the same thing, so unless it were the issue of the
> security system shutting it down, I doubt it's that

Whoever refurbed them should be able to tell you if the security system is
active, at least from what I can read about it in the FSM. I'd think they'd
turn that off unless you told them you have the security keys, and even then,
they'd have to have programmed it with the key codes.

What was wrong with the original PCM that it needed to be replaced?

> god 1w2v at
> injectors, will run a test on the side going to the PCM to ground, but i'm
> pretty sure there is none... question is why?

Having not done this myself, I'm only guessing from the schematics. The PCM
would have to have a good connection to ground for this circuit to work. But
it looks to me like the PCM would have to have a good connection to ground for
other stuff to work, too. Still, if the +12V side is good, then the problem
would have to be on the Ground side.

> i've unraveled the
> engine harness looking for any sign of melted/crossed wires, will confirm
> connection on the lines going to the PCM, but doubt it's that cause they
> are ALL dead, if only 1 cyl was dead i'd say 1 bad wire...

Yeah, that's what I was thinking too. If you had one dead, it'd seem to be a
problem in the wiring to that one. But all dead seems unlikely, unless, as you
said, the PCM just is refusing to fire the injectors because it doesn't think
the engine is running or something like that.

You mentioned replacing the cam and crank sensors. Were they bad, or was that
just a shotgun attempt? I'm assuming the PCM uses them to decide if the engine
is spinning and whether (or not) to fire the injectors. Is the wiring from
these two making it back to the PCM ok as well?

Does anybody know what else the engine uses to decide if the engine is

> I see the
> cap's on the 12v line too? prob. to stabalize voltage, if bad prob go to a
> short...

If it shorts, I'd expect it to go up in smoke, or for you to have no +12V. I'm
not sure what would happen if it failed open, but I can't see how that would
shut down the injectors if it did. But I also don't understand what it's doing
in the circuit.

> truck has no security system, just a door lock
> clicker, but as I had been reading online, somehow there can be an issue
> if you get a PCM that has security turned ON, and install it into a truck
> w/o it???

>From the "SKIM" description, yeah, if the PCM is expecting security key
information from the sensor, and doesn't get it, the engine would start, then
quit after a couple of seconds. I don't think that's your problem, though,
since you're not getting the "start" or "run for a couple of seconds" parts of
that description.

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