93 PCM Question

[Blackdr16]

Have a 93 MTX SHO with suspect X2J PCM failure. Current symptoms are as follows:

KOEO - Cannot pull codes
Check Engine Light dimly lit (About half intensity compared to normal. Stays on as soon as key is turned on)
Fuel Pump running constantly when key is on
Fan running constantly when key is on
Tach works - at 500 rpm when cranking
Engine Cranks - no start. Does not sputter

Checked all known ground locations, pulled, cleaned and checked resistance across each one. Usual suspect locations such as back of intake to body (close to PCM), negative to body (by the battery) and other locations close to the radiator to body all cleaned and tested with <.01 ohms.

Prior to issue the vehicle was starting normally. I did change the camshaft position sensor the evening before to correct a 214 code which would happen intermittently while driving. Its possible I stressed a wire while moving harness to get my hand in location. The car did start and run normally after changing the sensor both the evening of and then next morning when I was charging the A/C.

I've checked battery voltage (12.6V - not running) to rule out insufficient power at least from battery terminals. Crank is strong, all other lights and climate control fan runs strong. (ETAC turned off outside of tests to validate other components receiving full power)

I have a spare PCM on order from SHOsource but before it arrives I wanted to see if anyone has insight as to the appearance of the underside of the original PCM. Looks like 3 transistors were repaired at some point (that or something blew out these components, they appear abnormal.) Attached pic shows 2 of them. Not sure what OEM spec should be of these or if there's a good way to test them.

I suppose it is possible the CCRM could have some issue not providing enough power to the PCM but the symptoms appear to point more at the PCM then CCRM. I haven't ruled out anything such as wiring as usually failures of components after recent work point back to what was being worked on / around prior to failure.

Thoughts?

 

[luigisho]

Is this an aftermarket pcm? I haven't purchased one from the box retail stores so I don't know if they use repaired oem units or sell brand new component replacements.

 

[Blackdr16]

Is this an aftermarket pcm? I haven't purchased one from the box retail stores so I don't know if they use repaired oem units or sell brand new component replacements.

It looks factory from what I can tell although I don't know its extended service history. The PCM casing has Ford stamped into it and the warranty sticker was still unbroken (I sliced it open when taking it apart today)

 

[sperold]

Check the OBDI plug. Take a good look at the back to make sure the wires are connected to the plug. Some plugs have 2 wires joining at the plug and one wire can separate, almost unnoticed.

Happened to me, I had the same symptoms.

 

[Blackdr16]

Check the OBDI plug. Take a good look at the back to make sure the wires are connected to the plug. Some plugs have 2 wires joining at the plug and one wire can separate, almost unnoticed.

Happened to me, I had the same symptoms.

I’ll check that out! That would be great

 

[Blackdr16]

All wires in OBD1 port check good, looks like 2 sets of 2 and a single wire in the primary connector then the single wire into the single grey standalone connector

 

[rubydist]

Also, pull the connector off the pcm and check that you really have ground at the pins that are grounded. I have seen too many faults in the wiring harnesses as these cars get older. Its possible your ground locations on the frame and engine are fine but that does not necessarily mean that the pcm is getting grounded properly.

 

[Blackdr16]

Also, pull the connector off the pcm and check that you really have ground at the pins that are grounded. I have seen too many faults in the wiring harnesses as these cars get older. Its possible your ground locations on the frame and engine are fine but that does not necessarily mean that the pcm is getting grounded properly.

I’ll check this out as well and post results. Appreciate the info!!

 

[SHOrod]

I agree that the fault does sound like a ground issue. Like has been mentioned above, I'd suggest really taking a careful look and measurements using the grounds in the connectors to both the CCRM and the PCM.

As for the transistors on the board, I'd suspect that they were installed at the factory following the vapor phase soldering and water wash. Back when the PCM was built they probably didn't have the ability to install the small surface mount transistors in vapor phase, and when installed after wash the boards probably did not go back through wash to clean the flux residue.

-Rod

 

[sperold]

If the back of the plug is OK, then you will be able to get the flashing codes to show up.

That will give you a better idea of what is wrong.

 

[notahemi72]

I have a known good X2J I took out of my 93 MTX a few years ago. I don't know if it's relevant, but the transistors on mine don't have that same fried appearance compared to yours. The attached photo is zoomed in on the black rectangle in the image from your first post.

 

[Blackdr16]

I have a known good X2J I took out of my 93 MTX a few years ago. I don't know if it's relevant, but the transistors on mine don't have that same fried appearance compared to yours. The attached photo is zoomed in on the black rectangle in the image from your first post.

Thanks for this! I'm betting mine is fried but going to check resistance on all ground leads to the connector just to be sure.

Your pic looks like the expected state of transistors, mine looks like something went wrong or was repaired at some point in time.

 

[Irish Pride]

Following this thread. I have a car with the same symptoms that I bought non running. Haven't had the time to mess with it much other than I can confirm mine isn't a bad PCM. That's the only thing I've swapped to this point.

-Chad

 

[Devin]

I'm probably barking up the wrong tree, but with the fuel pump and fan misbehaving that makes me think the culprit could be the CCRM.

 

[Blackdr16]

Got a couple hours of testing in today. Put old PCM back in for the following as I haven't received my new one yet. Here are the results:

Started testing at the CCRM - Followed test procedure listed in this article. https://www.taurusclub.com/threads/ccrm-test-procedure.121857/ Passed every test besides the resistance test between pin 13 and 15. My reader showed open circuit on every resistance setting the meter had. Not sure if that's a clue, passed every other test. Ground has 0.06 ohm resistance at CCRM connector pin 15. 12.3V at each + connection including pins 13 and 24, about 0.5v drop when ignition is on (fan running).

Tried to pull codes once again, no luck. When OBD1 connector is jumped to test mode the check engine light remains dimly lit (no change when jumper is in place vs not)

Ran a voltage check on test light connector on the OBD1 connector - read 5.82 v. CCRM is providing 12.3v to above mentioned pins (not sure if those pins run straight to the PCM connector without looking at an example harness schematic) No fluctuation in voltage while in test mode using test light connector. Check engine light remains dimmly light. No flashing or change in intensity. PCM is getting full 12.3 at pin 1. Voltage at PCM pin 37 - is 12.3V when key is turned on.

Checked resistance for every ground connection listed in this article: https://shoforum.com/index.php?threads/how-to-wire-a-sho-motor-in-something-else.115598/ and each tested within 0.02 -0.04 ohm to negative battery terminal. Positive terminal read at 12.3v at PCM connector.

From the above I'd say something is malfunctioning in the PCM. Does anyone know what the test light output on the OBD1 connector should be at? I did validate 0.00 ohm resistance probing each wire joined at the OBD1 connection. (Measured at 2" below connection probed using small slits from exacto knife in paired wire insulation)

More info noted during tests - when PCM is disconnected and ignition is turned on the CCRM turns the fan and fuel pump on constant. No check engine light. (Expected) Assuming the PCM takes control of the fan and fuel pump when functioning properly once the CCRM provides them with power. (?)

If the CCRM is disconnected the fan does not turn on. No check engine light. (Expected behavior as power to PCM comes from CCRM)

Appreciate everyone's insight - fun solving these!

 

[tracy_s_1993_atx]

A really helpful diagnostic tool at this point would be a break-out box. See if anyone locally has one to loan to you. I found one on ebay a few years ago and it has been very helpful.

Michael

 

[NoSlo]

A helpful diagnostic tool would be another PCM. The symptom of fans and pump on (signals to CCRM) plus no codes has been the PCM before.

Here's pinouts:


The shop manual warns not to probe the unplugged PCM harness, the connector pins can be damaged by normal multimeter probes.

I'd guess in this type of failure, the PCM CPU isn't able to start. Microcode or power regulation might be damaged.

 

[Blackdr16]

A helpful diagnostic tool would be another PCM. The symptom of fans and pump on (signals to CCRM) plus no codes has been the PCM before.

Here's pinouts:


The shop manual warns not to probe the unplugged PCM harness, the connector pins can be damaged by normal multimeter probes.

I'd guess in this type of failure, the PCM CPU isn't able to start. Microcode or power regulation might be damaged.

Thanks for the above info!! Good stuff.

I’m guessing the warning for not probing the unplugged PCM connector would be more for if someone jammed the leads into the female side of the connector vs just making contact with the lead?

Tracking shows my spare PCM will be delivered Saturday or Monday. Should have more answers soon

 

[Irish Pride]

I hope yours ends up being a simple fix.

I found some time to mess with mine yesterday after work and it ended up being really simple. First I swapped in a differnt PCM with no change. Next I swapped the CCRM with no change. Then I started tracing wires and checking grounds. The ground that comes off the battery and bolts to the fender wall was not as tight as I thought it should be so I removed it and cleaned it then re mounted it. From there I traced the two wires back towards the main harness and that's when I found it. The two ground wires going around the strut tower had been smashed by something and were completely severed and neatly tucked away out of sight. I reconnected those two wires and it cranked right up. The engine runs perfect. Let the part out begin!

-Chad

 

[Blackdr16]

I hope yours ends up being a simple fix.

I found some time to mess with mine yesterday after work and it ended up being really simple. First I swapped in a differnt PCM with no change. Next I swapped the CCRM with no change. Then I started tracing wires and checking grounds. The ground that comes off the battery and bolts to the fender wall was not as tight as I thought it should be so I removed it and cleaned it then re mounted it. From there I traced the two wires back towards the main harness and that's when I found it. The two ground wires going around the strut tower had been smashed by something and were completely severed and neatly tucked away out of sight. I reconnected those two wires and it cranked right up. The engine runs perfect. Let the part out begin!

-Chad

That’s great!! Glad to hear it was something easy to fix! And of course having it run perfect is the best part!