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Oct 28, 2017 | 11:51 PM

#31

m-chan68

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From: Woodbridge, Ontario, CA

Quote:

Originally Posted by barrucuda

Im looking up where the pcm diode would be. Im not clear as to what it really is.

Battery junction box. Looks very similar to a fuse, except it's black and it has a diode symbol on it instead of an amperage rating.

Oct 29, 2017 | 12:09 AM

#32

barrucuda

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Thanks guys. Looks like im off to the store in the morning to get fresh ones. I have no way nor the knowledge to test these.

Oct 29, 2017 | 01:52 AM

#33

m-chan68

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From: Woodbridge, Ontario, CA

To test the diode properly, simply remove the diode and connect an ohm meter to the terminals. You should have continuity with the leads connected one way. Switch the leads around, and you should get an OL reading.

In other words, it allows current flow in one direction, but not the other.

Oct 29, 2017 | 07:23 AM

#34

projectSHO89

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From: St Louis

To test a diode with a meter, make sure you have one with a diode test setting.

In any event, simply look at your check engine light and turn the ignition switch to RUN. If the light comes on, the PCM is, at least powering up and there is no issue with the PCM diode. In any event, I've never seen a PCM diode go bad, even from crossed battery cables which is why it's there - prevents the PCM from getting reversed polarity power.

It's unlikely you'll find a diode in your local store anyway.

Oct 29, 2017 | 11:19 AM

#35

m-chan68

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From: Woodbridge, Ontario, CA

Quote:

Originally Posted by projectSHO89

To test a diode with a meter, make sure you have one with a diode test setting.

Very good advice I should have added above.

Quote:

Originally Posted by projectSHO89

In any event, simply look at your check engine light and turn the ignition switch to RUN. If the light comes on, the PCM is, at least powering up and there is no issue with the PCM diode. In any event, I've never seen a PCM diode go bad, even from crossed battery cables which is why it's there - prevents the PCM from getting reversed polarity power.

It's unlikely you'll find a diode in your local store anyway.

I vaguely recall an instance years ago, was when one particular vehicle I had as a no-start, also no communication with PCM pulled my hair out. It was a 2000 F-Series 7.3L diesel (similar vehicle to OP but with different engine, not that it matters in this particular instance), which I nearly submitted a quote for a PCM replace, ended up being the PCM diode that repaired it successfully. Given the fact that the OP has been attempting to repair his vehicle for quite some time now, I figured something small and simple like this, should not be overlooked before dumping even more money into it like he already has, by the looks of things so far. We all know that electrical problems can be very frustrating to diagnose, and for the most part always ends up being something so simple and dumb as the cause of the issue.

For what it's worth, the PCM diode is located in fuse cavity number 37 of the battery junction box, adjacent to the A/C compressor clutch diode which is number 36.

Oct 29, 2017 | 12:10 PM

#36

projectSHO89

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From: St Louis

Quote:

For what it's worth, the PCM diode is located in fuse cavity number 37 of the battery junction box, adjacent to the A/C compressor clutch diode which is number 36.

I'd bet they're he same part number... FWIW, back before Radio Shack went out of business, you could walk into one of them, buy a 1N400x diode and improvise a replacement from one of them.

Oct 29, 2017 | 02:23 PM

#37

barrucuda

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I appreciate the tips guys. I still haven't been able to test those diodes. I did notice the fuel pump is actually turning on now, before it would not. A new problem is it won't turn off. So now i suspect the pressure switch in the pump is damaged on top of the obvious other problems.

Oct 29, 2017 | 02:33 PM

#38

barrucuda

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I just read up on the pressure regulator. Thank god that seems to be an easy R&R

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Oct 29, 2017 | 03:14 PM

#39

barrucuda

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I must have gremlins. I went out to turn the key to the on position to verify the check engine light came on. It did. How ever upon trying to crank the engine it wont crank now. It did this morning. Now i just hear a noise, something like a pop. Just once every time i turn the key. The odd part is i haven't made any changes since the last time i cranked the motor a few hours ago.

Oct 29, 2017 | 03:41 PM

#40

projectSHO89

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From: St Louis

Quote:

A new problem is it won't turn off. So now i suspect the pressure switch in the pump is damaged on top of the obvious other problems.

There is no "pressure switch". The PCM simply turns the pump on or off via the FP relay according to its logic.

Quote:

I just read up on the pressure regulator.

The PR cannot cause your issues. It simply maintains a minimum of fuel system pressure depending on whether or not there is vacuum applied to it or not.

Quote:

How ever upon trying to crank the engine it wont crank now.

Now you have a problem in the starter circuit. Probably a cable or connection that was damaged when the original incident occurred has now given up the ghost. Troubleshoot this as a stand-alone, first priority since there's a fair chance that this hard failure is likely what's been causing your gremlins before it failed completely.

I'd be looking at primary battery power and ground circuits followed by the starter circuit.

Mar 4, 2018 | 07:00 PM

#41

barrucuda

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Well i been slowly trying to narrow down my issues. All fuses have been replaced and the pcm was repaired by SIA electronics. It cranks but still no spark. The fuel pump wont shut off now unless i pull the relay. Any Ideas? I even sent the pcm back to be reevaluated and to make sure it is not the pcm. And the obd2 port still does not work. Could the power distribution box have been damaged?