94 Taurus CCRM Nightmare--Rod to the rescue?

[ram2442]

I have been battling with a 1994 Taurus Wagon with 3.8L for the last month...and the car is winning. Started having trouble starting in the mornings, soon required fluid to start after sitting more than 2 hours. Check engine light started coming on during warm up but no codes are present or stored. Started running rough and really rich during warm up with no acceleration. Check engine now remains on most of the time. Engine runs rough and rich. I have:

Replaced battery
Replaced MAF Sensor
Replaced Air Charge Sensor
Replaced Throttle Position Sensor
Replaced Coolant Temp Sensor

Checked all grounds and verified fuel line pressure.

That's when I started messing with CCRM and PCM. I have found something that I can't account for: One leg of the relay circuit that controls the PCM has only about 5-6 volts in the key on position when backprobing at the CCRM. The wiring diagram states that it controls the "PCM Power Relay Enable" (Pin 13). What should the voltage be, and does this indicate that the CCRM is bad?

[shorod]

If the check engine light is on most of the time now, what codes are displayed? If the check engine light is on but there are no codes, I would suspect the PCM. Ford PCMs have been pretty reliable though, but that doesn't mean they can't have issues.

Pin 13 controls the PCM relay coil. It gets power from the ignition switch when the key is in the run or start position. If you were measuring the voltage with the key in the off or ACC position, 5-6 volts may not be all that unusal. In Run and Start, it should have battery voltage.

What was the fuel pressure when you measured it? Also, you mention that you changed the coolant temperature sensor, but if I remember correctly, your car has one sensor for the PCM and guage and one for the cooling fan on the radiator. Which one did you change? I'm on business travel currently and cannot check my service manual.

I think the '94 also has heated oxygen sensors. You may want to check them as well. If the sensor heaters are not working properly, they could lead to improper air/fuel mixture.

Check for carbon build-up on the back of the throttle plate and remove the Idle Air Control (IAC) servo and inspect it for carbon build up.

Good luck!

-Rod

[ram2442]

Went ahead and pulled the PCM, and it was in bad shape. Burnt odor and residue on the circuit board. Ordered a new one. Will see if that does the trick.

[austin_mod]

I've been having the same issues with my '92 f-350, poor starting, no codes, runs rich when you start it with a little fluid, did replacing the PCM sort things out for you? My truck was running fine on friday and no go on monday... please shoot me a reply if replacing your computer sorted things out. Thanks

[shorod]

Since ram2442 has only posted in this thread, and hasn't posted for 2 years, I'm not sure they'll respond here. It would be great if they do, but I wouldn't count on it.

When you say "...runs rich when you start it with a little fluid..." what fluid are you talking about? Are you saying it will only start if you give it a little starting fluid?

Have you checked the fuel pressure at the fuel rail, assuming your F-350 is a gasoline engine and not diesel.

Were there any environmental changes between Friday and Monday, such as a 20 degree drop in temperature, that may give clues as to the issue?

-Rod

[Goody28]

Hey All,
I have a '94 Taurus GL Wagon. The A/C quit working a while back, I shot the wires back to the CCRM. I opened it up and found 4 relays and what appears to be a voltage inverter (mounted to a heat sink) that had melted down. I'm trying to replace this part and fix the CCRM myself. Does anyone know of a source to find these parts? If I can find the voltage, etc... I can find a replacement. The wiring diagrams don't show voltages or actual functions. Thanks in advance!

[shorod]

That TO-220 part is a transistor, not a voltage regulator if I remember correctly. The part has a house part number on it though, so there isn't a direct cross reference to a standard part. If I remember correctly, the part is an NPN bipolar junction transistor, and I swapped it out for a 10-amp part with the same pinout for my test unit. Unfortunately (or fortunately) I haven't had a need for a test CCRM so I don't know if I properly picked a part for it. I was still in high school at the time and my knowledge of electronics was less than it is now, so I don't have a lot of faith in my skills at the time or my recall of the work either.

-Rod

[Goody28]

Thanks Rod, you're right, it is a TO220 form factor. I can't read the part number, most of it is melted away and is in 3 pieces. I did get the first 4 of the PN-5102 and a couple on the 2d row-H3. I also found the manufacturer, Harris Semiconductor. That company has since been broken up and sold. I found a part on the NTE site, NTE2317 that looks like a possible replacement, it is a TO218. Is that compatible? What do you think?

[shorod]

Well, what about the NTE2317 makes you think it is compatible? If you're just going by my recall of the specs, that's not a safe bet. The information on the second row is probably just the lot/date code information and not of benefit when attempting to cross reference.

On the one I replaced, I had the full part number, I was not able to find a cross reference in the ECG catalog (which was the same as NTE for all practical purposes).

I'll check my work room and see if I by chance still have the repaired CCRM and see if I can determine quickly if I made an appropriate choice.

-Rod

[shorod]

Apparently I do not still have it, or I forgot what I did with it. I suspect that I threw it out during my last move since I no longer had my '93 SHO and didn't expect I'd ever have a use for it.

-Rod

[Goody28]

Hi Again, Sorry for taking so long to post, things are very bus. I had looked at the NTE 2317, the specs looked pretty good along with the description:

The NTE2317 is a multiepitaxial bipolar NPN transistor in a monolithic Darlington configuration mounted in a TO218 type package designed for use in automotive ignition applications and inverter circuits for motor controls. Controlled performances in the linear region make this device particularly
suitable for car ignitions where current limiting is achieved desaturing the darlington

However, it looks like the voltage is too high. Do you know of a source that lists the item specs? The NTE site doesn't allow you to compare item specs...

Thanks Again!

[shorod]

The TO-218 package is larger than a TO-220. It won't be a drop in, and I think you could find something that's a better fit. I took a look at the block diagram for the CCRM and am guessing that the inverter is the one for the fan control. I suspect that the PCM provides a ground to the inverter to power the fan, which would imply that the TO-220 part is probably a PNP transistor. Since the transistor only activates a relay coil, it won't need to handle more than an amp or two of current from Collector to Emitter. Since the duty cycle could be pretty long, you'd want to derate the part and the heat sink is a good idea.

The old paper NTE and ECG catalogs had a selection guide section that would aid in finding a part that may meet the needs. Many of the discrete semiconductor websites still have a similar selection guide. You may be able to get far enough using Digi-Key's website too.

However, to pick something you'll also need to know what the pinout is. Unless you can reverse engineer the circuit well enough, you'll probably almost need to find one from a salvage yard that is still working and use a Super Cricket or diode tester to determine the appropriate pinout. The Super Cricket would also help you determine parameters. Of course, if you get a working one from the salvage yard, why cut it open to reverse engineer it rather than just install and be done with it. Maybe you can get two, one to fix the car and one to reverse engineer.

Boy, I wish I had saved my old "rebuilt" test one....

-Rod

[borninabarn]

Its Just a throw away car.I have an original owner car that has 70k.And I gave $300.Just another ford.No wonder they are searching for air?In truth I think all t

[shorod]

Originally Posted by borninabarn

Its Just a throw away car.I have an original owner car that has 70k.And I gave $300.Just another ford.No wonder they are searching for air?In truth I think all t

Hunh?

[g1smith]

The CCRM failed in my '95 Mustang GT.
After creating a basic schmatic, I determined it was a PNP transistor in a TO220 case. I replaced it with a TIP32, 4AMP transistor. It worked for a few months. I'm not certain if the freon has leaked out or if the transistor has burn to a crisp again.
TIP32 NTE292 PNP 4 AMP Cont Audio Temp 150C
TIP42 NTE197 PNP 7 AMP Cont 10 Peak 40W