'97 Explorer popping PCM MAXIfuses

[whobub]

I’ve read through the other threads and found all things AROUND my particular issue, but nothing directly. Here’s the info:

1997 Ford Expedition 4.0L

Symptoms:

1. Wife took off for 1st run of the day @4:00 p.m., got 5 blocks from the house and stalls going up slight hill
2. Engine turns over fine (engages, turns over engine), but no start
3. Runs battery down trying to get restarted
4. There was approximately ½ tank of fuel

After reading other threads surrounding the “fuel pump issues”, I’ve taken a look at those things covered:

1. Checked out “fuel inertia valve” (under dash, at passenger’s foot area). Checked out okay—button pressed down.
2. Turned ignition to “On” position, listened for fuel pump sound – I immediately didn’t notice this “priming” sound as it has done before
3. Thinking “ah ha!” I’m onto something, I continued to search for fuse issues
4. Found the “PSM Power Relay” (MAXI fuse #2 according to ’97 Explorer Owner’s manual, page 154)

Steps after replacing blown fuse:

A. After these findings, figured most obvious tack was to replace the blown 30A Maxifuse at the aforementioned #2 position.
B. Attempted a start, listened first (again) for the sound of the fuel pump priming, but still no sound.
a. Attempt start again anyway, but was getting dead battery sounds with what I thought was a fully charged battery.
C. Checked #2 slot for the MAXIfuse, and it appeared BLOWN again!!!
a. Luckily I have ONE more, but I don’t want to continue until I get a grip on why I now have a subsequent blowing of this fuse—at $3 per fuse, it’ll get expensive fast

Here’s my question(s):

1. Am I looking at a possible short?
2. At the fuse PDC (is that Power Distribution Center) at that position only? I’m ruling this out as remote. . .
3. Can fuel pump cause the PCM fuses to burn out?
4. How about the fuel pump relay/fuse?
5. How to test for a bad relay for the fuel pump? PCM relay appears in this area too—all have same part #s and codes, so might swap some of them around, but at $8 per, need to use caution as well.

That’s it for now to keep it as short as possible but still giving a good overview of the issue(s). Anyone with a clue I’d appreciate your insight and input.

Thanks in advance

[theoldwizard]

Originally Posted by whobub

1. Am I looking at a possible short?

Probably

3. Can fuel pump cause the PCM fuses to burn out?

Not typically. More likely a shorted wire somewhere. It takes a lot of power to blow one of those fuses.

[whobub]

I'm not making much progress on this Power Control Module (PCM) fuse blowing, although here is some additional notes and follow-up question(s):

1. Disconnected battery (of course )
2. Took PCM off of mount on fender well on driver's side under hood
3. Removed bottom of PCM
4. Tested continuity between top of position #2 maxifuse and bottom of where it’s connected (cont=yes)
5. Checked for obvious bare wires, solid ground connection at PCM/block, all seemed well
6. Took the PCM Relay (the actual RELAY as labeled) and swapped it with the adjacent one with same part/module # (since I might get only one chace)
7. Reassembled, connected newly charged battery and had the wife turn key to “On” position
8. After the wife turned key to “On”, I observed the 30A maxifuse blew AGAIN, but was delayed approximately 45 seconds.

After fuse blows, it still turns over fine, but obviously (still) no power past the point of getting power to the rest of the PCM/block, hence cannot “hear” fuel pump sound.

Would a code reader pick this up??? Any idea on WHICH code reader to get/rent?

So again, the attached graphic from owner’s manual of the PCM fuses/relays. . .I’d truly appreciate any educated “next steps”. Thanks in advance to one and all for your time.

Jesse

[theoldwizard]

Code readers will likely not help you find this short.

[whobub]

But might there be a code for what is possibly "over-amping" in the event it is another circuit or device?

[BroncoJoe19]

whobub,
Stay online, adn we will be able to go back and forth a bit

[BroncoJoe19]

You ahve done a great job explaining what the issue is and what you have done... this thread should be used as an example of a good/great initial post! Good job!

I have some exceptional documentation for your car, and will post diagrams as needed as educational.

In most cars, the PCM relay powers the fuel pump relay (and other components). Is it possible for a relay to short? I don't think so. However it tracking down a short you want to eliminate sections of the circuit.
so pulling the relays, can narrow down the short.

You may want to see if you can obtain a 30 amp circuit breaker, that you can use for testing rather than blowning fuses. OR see if you have access to an amp meter.

[BroncoJoe19]

took a look at some diagrams. We are goning to have a lot of work to do.
Gonna stop for dinner, but will be back tonight.

[whobub]

Thanks for the complement 'BroncoJoe' My angle on writing is that you have to list the things as they occur or were covered, otherwise others have to read between the lines and that helps nobody.

You mention "...take a look at some diagrams..." Did I miss something? Or did you forget to attach in the hurry to make it to dinner .

Thanks again for the assist and to all others that chime in.

Jesse

[BroncoJoe19]

I should have said.. I took a look...