Can't pull codes. KOEO test does nothing

[jbserra]

Hello,

I forgot the car info:
1995 3.2L MTX. Originally an auto car. The wiring diagram seems to line up with the MTX.

I started my car over the weekend. Almost immediately after it started, I smelled burnt electronics inside the cabin (the vent was on), the engine ran for 2-3 seconds and then died. I'm thinking something arc'd or a circuit board fried, versus plastic/rubber melting on something hot (plus the car just started). I tried to pull codes, but it never runs the test. I tried using both a reader and the jumper CEL setup, but it doesn't energize any relays and no codes come out. The car electrically turns on (interior lights, radio, climate control) and even turns over, but never starts.

The fuel pump runs when I ground the pin on the test connector. With the fuel pump running, it still does not start. I pulled a plug and no spark. I think the key issue I have to get past is the no codes and then see if I have other issues. I think the no codes is a sign that the computer isn't getting power and I'm not sure how to fix that. Is it the RCM that needs to turn on the PCM or is the PCM powered elsewhere? Can I directly power it to further my testing? Any help would be appreciated. Thanks!

Side notes on what I've done and what hasn't worked:
tested the inertia switch and fuel pump
repaired a cap on my old RCM (no burnt traces)
swapped the RCM
inspected my old PCM (nothing burnt that I could see)
swapped the PCM
checked that the DIS is grounded
jumpered a fuseable link that didn't pass a continuity check
tested all fuses in the engine bay
tested all fuses in the fuse panel under the dash
pulled out a Viper alarm that I didn't even know was installed (removing the start disable relay)

Wire testing:
pnk/yel RCM->PCM (continuity ok)
tan/org RCM->PCM (continuity ok)
pnk/blk RCM->PCM (continuity ok)
Yel = 12v
tan/lt grn RCM->PCM->Data Link Connector (continuity ok)
(pin 41 PCM was open, but that didn't cause problems before)
red RCM->PCM (continuity ok)
gry/wht (TPS 0V)
Brn PCM to STI Data Link Connector (continuity ok)
Brn/Wht (TPS .43V)
Lt Grn/Blk (TPS .4V)
Pin 40,60,20 PCM all connected (Blk, Blk/lt grn)

Oxygen sensors are warm (not sure if that indicates 100%?)
I included TPS voltages in case they could cause any issues.

Are there any sensors that would prevent the computer from coming up? CPS?


I think that about covers it. I'll kick back to the forum if anyone can help me out! Thanks!!

 

[rubydist]

it sounds like your pcm is dead. But you are on the right track to make sure it has power - there is a thread on here by OffRoadSHO that details how to wire a SHO pcm into another vehicle - it tells you which 2 or 3 wires need to have power for the pcm to operate.

 

[Devin]

If you smelled it inside the car, odds are that it is the PCM, as it is in the glove box just above the plenum.

 

[jbserra]

I agree that it feels like it should be the PCM, but I've swapped in what I thought was a working PCM, but no joy. Is it possible that any of the sensors could be open or shorted that would cause the computer not to come up, or should the computer still be able to come up and then just throw a code?

 

[Devin]

Oops, didn't notice that you swapped the PCM

 

[jbserra]

Ok, using my old CCRM, I determined that power to the PCM was supposed to be returned on pin 24. 12+ was not present, so I soldered in a wire to put 12v to the computer. Computer came up and complains about the power steering sensor and the fuel pump relay (CCRM). I think both the CCRM and the PCM smoked originally, probably one led to the other. I'm not convinced my replacement PCM or CCRM are the correct one or I'm still missing an appropriate signal to trigger the relays. Once I had the PCM running, I hot wired the fuel pump, still no go. Guessing this means the PCM isn't triggering the injectors. More to this puzzle...

 

[jbserra]

I had convinced myself that the old CCRM was dead and that the NAPA CCRM was possibly the wrong one. Bought a used "tested" exact Ford model replacement and no joy. Pretty sure the CCRM is not coming up still. Will re-check all voltages to figure out why it's not turning on...

 

[jbserra]

Ok, if the most recent diagram I pulled is correct and it's actually the internals for my CCRM, pin 13 should be switched hot. I reviewed my measured voltages and had nothing on pin 13, but had no idea if it was supposed to. Hoping this lead pans out...

 

[jbserra]

PIN 13! WOOHOO PIN13!!!

Car started and proceeded to smoke the coolant level sensor. So, now I have two things to work through:

1) Figure out where the PIN13 input wire smoked because it's not connected somewhere. Could also run a new wire.
2) Figure out the short in the coolant sensor wiring or it could just be the sensor itself. Right now, unplugging it takes care of the issue.

Hopefully, this helps someone who has a similar computer no boot up in the future.

 

[jbserra]

What's funny is the PIN 13 wire, red with green stripe, is also one of the three wires on the coolant sensor. I checked connectivity between the two and they were the same wire. Also funny, is under the dash by the ignition, the switched power is a slightly thicker red with green stripe. I ran a jumper from the ignition wire to the coolant sensor wire (with the sensor still unplugged) and I'm back in business.

I'm wondering if red/green is switched power for a couple of things in the engine bay.

I'll trace the wire further when I pull off the intake next time, but it is possible that it was just the coolant sensor that started the dominoes. If I can find a replacement coolant sensor, I might try it as well, but I'm not sure why I would do that since the overflow is almost always empty (triggering the dash light), yet there is never low coolant in the radiator/system.

Again, just trying to add all the info here in case someone can use it. Thanks!

 

[kevinspann]

Nice work. My car recently died as well, but I smelled nothing burnt. I've got another PCM coming that should hopefully fix it. This gives me something else to look at though, thanks.

 

[rubydist]

yours would not be the first mtx coolant sensor that shorted and caused a problem. not real common, but has happened on occasion before.

 

[jbserra]

Nice work. My car recently died as well, but I smelled nothing burnt. I've got another PCM coming that should hopefully fix it. This gives me something else to look at though, thanks.

No computer codes? Not coming up at all? Is the CCRM PIN24 12v when you have the car on but not started? This feeds power back to the PCM.

yours would not be the first mtx coolant sensor that shorted and caused a problem. not real common, but has happened on occasion before.

How about an ATX coolant sensor? The car was originally an ATX and has the overflow bottle behind the battery versus off the radiator support.

 

[rubydist]

I have never seen the atx coolant sensor get shorted out, but I have seen it so built up with crud that the sensor did not work properly. It is possible with the design of it, that there is enough iron in the crud buildup that it is shorting.