94 ATX low voltage at CCRM pin 24

[apanthropy]

Hello

After the excellent help here in getting my girlfriend's recently acquired 94 ATX SHO running, she's been driving it about with no additional issues, but now I finally have time to track down the latent problems it had which weren't directly related to being able to get to work: A/C wasn't working, the battery charging light comes on at idle sometimes and the ABS light is on.

Worth noting: at one point after I had reassembled everything from repairing earlier engine problems, and cleaned the engine compartment with simple green and water, there were 3 or 4 run cycles where the ABS light was NOT on.. I wasn't able to clearly identify why.. but then it came back on and I have not performed further diagnostic.

So: today I had an A/C shop perform basic diagnostic service on the A/C refrigerant circuit. They evacuated the system (it was empty, no pressure) and refilled with refrigerant/dye/lubricant, and pressure tested it. It holds pressure but the compressor clutch does not engage. There is no power at the compressor clutch connector when MAX A/C is selected. I have not tried manually jumpering power to the clutch since I have already determined no power at the connector.

So, the shop offered to continue repair at who-knows-what expense but also understands my financial paucity and suggested I troubleshoot the electrical problems on my own to save money.

I took it home and per the troubleshooting steps in my factory service manual;

• Battery voltage >12.5V
• Jumpered A/C cyclic switch on receiver/dryer (no change, A/C magnetic clutch still has no voltage)

Here's where I stopped for the evening (it's 11pm and I work at 7am) - I began to check the CCRM connector (unplugged, cleaned, applied dielectric grease for good measure, replugged, rechecked operation, no change) and was trying to back-probe the pins/wires on the CCRM to check for a short on pins 16 and 23 but due to lighting conditions and maybe my own frustration I wasn't able to get anywhere on that... but, here's the part that struck me as weird: I only have 9.40 to 9.49 volts at pin 24 of the CCRM.

I verified 12.69v at idle on battery terminals and between 13.5 and 14 volts on the battery terminals when I rev the engine, but when I backprobed pin 24 on the CCRM and referenced to chassis ground and to engine block, I got between 9.4V and 9.49V with the engine revving, that's it. I re-checked several times and re-probed to make sure I was getting good contact in there.

That doesn't seem right, pin 24 is a large gauge, red wire and is labeled "VEHICLE POWER" in the factory service manual. I have also found a reference online that indicates this is circuit 361(R) which appears to be the hot side of MANY things under the hood... though I have not yet put a volt meter to those things.

While I do have the big factory service manual I do not have the EVTM supplement.

Anyone have any tips for that? I should have >12v there, right?

Thank you for any insight.

 

[apanthropy]

A bit more reading... this circuit appears to be fed by pins 37 and 57 of the PCM... does all the current for this pass THROUGH the PCM?

 

[SHOdded]

Battery voltage is on the low side. It should show around 13+ V at idle, 14+ V when charging at speed. Maybe you have an unaccounted for amp draw somewhere?

 

[rubydist]

check pin 37 of the pcm to see if you have 12V there - that is what feeds to pin 24 of the ccrm - along with several other underhood sensors.

I agree that less than 13V at idle is bad, and that is what is causing the alternator idiot light to flicker. from my experience, it is most likely due to a sick voltage regulator in the alternator. the only replacements that I have gotten to survive are the NAPA lifetime guarantee ones, and even if one of those dies you can get it replaced free.

 

[apanthropy]

Can the regulator be replaced independent of the alternator or is it an all-together deal?

(edit) holy crap the regulator assembly is $140 which is barely $50 less than the whole alternator...


Even though I agree <13V with the engine running seems pretty low, that wouldn't account for the <10V at the supply end of the CCRM - sadly, I'm at work still and won't be able to poke around more at the SHO till after 5..

 

[apanthropy]

Update: after some major googling about and reading the FSM and a borrowed electrical supplement, I came to the conclusion that no matter what, I need a new alternator and there's just no way around it.

So, thankfully that was easier to physically perform than afford... these alternators aren't cheap! And, don't cross-reference to many other vehicles... ( Lincoln Mark VIII and 3.8 t-bird.. ) - I would have thought a mitsu alternator would cross reference to, i dunno, a Mitsubishi vehicle or a forklift or something anyway, why did they feel like they had to reinvent the wheel here?

That aside, new alternator in, now I have 13.1V at the battery at idle and 12.59V at the power supply pin 24 of the CCRM. Good enough to proceed.

I again measure >12v at the a/c cycling switch, so I proceeded to measure the WAC pin which I think was #22 (not looking at the book right now) which provides 1.1~1.14v DC and which does not affect anything when removed from the CCRM plug thinger. So, it is not preventing the a/c from engaging, simple enough.

This narrows us way down; the instruction to engage IS being sent to the CCRM, (from the EATC and through the A/C Cycling Switch) and the instruction to not engage (from the PCM's WAC output) is NOT being sent, and the CCRM IS being supplied with >12v, therefore the CCRM itself should be producing >11v at pins 16 and 21 or 23 or whichever, the ones that directly feed the a/c clutch. Since it is not providing that power, the CCRM is dead. Now we're in business!

But, that doesn't get me going exactly; I next proceeded to remove pins 16 and 23(21? sorry, still don't have the book in front of me as I type this) from the harness and supplied battery voltage directly to them, so I can determine status of the clutch and compressor and you know, feel a bit of cool breeze from the vents to encourage me to spend yet more money on replacing the CCRM secure in the knowledge that it will resolve the non-working A/C issue.

No luck. Battery power supplied directly to those pins at the CCRM end (pulled out from the harness) did not engage the clutch, and when I finally decided to get smart and measure resistance across the pins I got an open circuit. Several four letter words later, I found that one of the wires feeding the a/c clutch coil had been cut or otherwise broken for no good reason and nothing I was going to do elsewhere would cause the clutch to engage. Since there's no room to work on the harness and cutting open 20 year old harnesses is an awful job in any case, I'll be buying a new plug and running a new wire up to the CCRM, and then of course find a new CCRM.

 

[SHOdded]

Progress! Did you gap the clutch? Be sure to get the right (used) CCRM, either by posting here, or off of http://rcmautomotive.com/id32.html or http://www.shosource.com/catalog/product_info.php?products_id=42.

 

[apanthropy]

(hopefully) final update?

My replacement harness plug showed up and I had time this morning to work on this - first thing was to look inside the socket on the A/C clutch with a mirror to clear debris if there was any - surprise, one of the pins was bent over! And, not a lot of room to work in there, I found a tiny flat screwdriver, closed my eyes and spent a few minutes gently poking around in there to learn the landscape by touch, then teased the pin straight. That job actually sucked a lot.. no part of it was fun. I couldn't even curse under my breath, I wasn't even frustrated - just... not a fun job.

Anyway that sorted out, I ran my replacement cable up to the battery and touched the wire ends to the battery terminals - bam clutch clicked! So I started the car and clamped the cables with alligator clips, turned on a/c and the clutch stayed engaged, and I got cold air!! EFF YEAH!!!! - ran the wire up and cut out the wire harness off the CCRM, separated the A/C pins and connected those to the new cable, crimped weathertight butt connectors, heat shrunk it, rubber taped all of it neatly and ziptied it in a careful route to avoid too much heat or any mechanical rubbing.. again started the car and still had a/c - which means my CCRM does work!

Soo.. I'm in business. The factory service manual earned its keep, for sure - as did this forum! Thanks guys!

 

[SHOdded]

Cool! I guess bent pins are not just computer problems

 

[apanthropy]

Cool! I guess bent pins are not just computer problems

Got that right!

The a/c is still working well... so far so good! I want to get in and do a 60k on this car in the next month or two - but convincing the girlfriend that it's important to fix something that presently works so that it will keep working is an uphill battle. I can suggest it, and she will agree it's a good idea, but somehow never make time

Battle of the sexes aside, this forum's been immensely helpful as have the factory service manuals. I'm not yet experienced enough to contribute much to the discussions but hopefully documenting my repairs helps the knowledge base for future owners anyway.