Help Please

I have to admit to being confused by some of your replies. It's not clear to me the reported units of measure (volts or Ohms) and HOW the measurement was taken (IE from which point to which point). Remember that you are taking the readings and know what you are doing. I'm not there to see it and can only rely on what you put into the thread. Asking me to guess risks going on a wild goose chase.

For a ground wire pathway, 0.8 Ohms is still seems on the high side. If this is too high or not depends upon the size of the load. On the other hand a voltage drop ground test 0.8 volt is EXCESSIVELY high (0.250 volt limit).

But given that you appear to not be able to pick up any injector return lines at the PCM and suspect a wiring problem, I would look at the large C104 connector in the engine bay. Take it apart. Clean both sides with electric contact cleaner. Dry with compressed air. Put a small amount of di-electric grease in each of the female pin holes. Don't put too much as hydrolocking could occur.

As for the signal return lines the usual way to perform this test is to disconnect the device on both ends and then measure the resistance between the return wire and a known good ground. This should be a very high (open) Ohm reading. Next use a scrap piece of wire to extend one VOM lead measure the resistance through the signal return wire. This should be low. This is where having a set of wring diagrams comes in handy to find the wire colors and connector pin outs.

Another good piece of information to have is the voltage measurement between the injector RETURN side and a known good ground with the motor cranking. We should see 12 volts when the injector is open and low voltage when the injector is commanded closed. I would like to compare these readings between a working and non working injector. As a reminder the wire on the supply side should be a solid and constant 12 volts.

It also seems silly to me to ignore the clicking CCRM. It would be handy to know which relay inside the CCRM is clicking. With the CCRM clicking try reading the voltage between the following wires and a known good ground. What we want to know is if the voltage is coming/going with the clicks.

• cooling fan low speed - pin #1 R/O
• cooling fan high speed - pin #6 O/LB
• fuel pump - pin #5 DG/Y
• PCM power - pin #24 R
• AC clutch - pin #23 BK/Y

In the interest of being complete, how did you re-program anti-theft (PATS) after the PCM swap? Did ANY symptoms change after swapping the PCM?

To confirm that you have inspected:

• the grounds around the radiator core support and they are clean and tight.
• The black wire with white stripe that goes around the battery to a single pin connector. CONFIRM that it is clean and tight.
• The motor grounding strap from the left hand motor mount to the frame rail. This strap is normally visible near the oil filter.
• That you have perform the alternator voltage drop test on the positive and negative lines and it is less than 0.250 volts with the key on.

I think we may have a disconnect here. It seems to me that you are measuring the ground resistance AWAY from battery negative (or said in another way this is a ground loop). This isn't really giving any useful information. Once the connector near the battery is split taking any measurements away from the battery will also read the resistance of the device at the far end (ground loop). That's likely why you are seeing resistance values so high.

The resistance measurements need to be taken from the device TOWARDS battery negative.

For proof reconnect everything and then go to the ground at the air breather. Now take the resistance measurement with one lead on the battery negative and the other lead on the ground being tested. Pay close attention to any ground reading more than 1 Ohm unless the circuit is known to be a high amp circuit.

Jim5208 said:

Have 0.3 ohms at pin 15 B/W at connecter of ccrm. That's with one lead on battery -

Click to expand...

A fractional Ohm for a pilot duty circuit is fine. Likely we can rule out a bad CCRM ground as the "cause" of the CCRM clicking.

But there are other "possible" causes. What about the rest of the tests requested?

Back in post #25 I asked for some voltage measurements at the CCRM. The CCRM is a relay that controls power to many of the car's systems. It would be EXPECTED to not have power down stream of the CCRM IF the CCRM's relays are not latching (the clicking!).

Based upon the information in this thread IMO it's a waste of time to perform additional trouble shooting until it has been CONFIRMED that the CCRM is working correctly.

So that we are on the same game page, you have taken resistance measurements on all of the fuel injectors and they are close to each other. Right?

Based upon your last post the CCRM relays that are "clicking" are for the cooling fan. The Mustang uses a "fail safe" circuit for the cooling fan. That is the CCRM needs a signal from the PCM to stop the cooling fan. IF this signal is missing, then then cooling fan runs.

What I'm looking to rule out is IF the PCM is coming and going. And each time that it does the CCRM cooling fan relay clicks.

What are some things that could cause the PCM (more than one) to come/go? Well since we have confirmed a SOLID 12 volts at the CCRM pin #24 (PCM power feed), that leaves:

• bad PCM ground
• loose connection at the PCM
• Excessive power draw causing the PCM to kick out on a thermal
• going to assume that the PCM is good since this same symptom has occurred on more than one PCM.

There are several ways to attack this. I can't help myself as I'm a big believer in basics. So let's first CONFIRM all of the grounds at the PCM are capable of carrying a full current load. Since this is a high power circuit the voltage drop method is the best to use. With the VOM in the voltage mode and the black lead on battery negative, measure the key on voltage by back probing (use a very small thin wire or a sewing T-pin):

• the Black wires with the white stripe (G104) PCM Pins 24, 51, 76, 77,103
• the all black wires (G201) PCM pins 25
• PCM (G201), pin #33 (PK/O)

We are expecting each voltage drop reading to be less than 250 mV (that's 0.250 volts). I'm also interested to find out IF the voltage drop reading changes as the CCRM relay clicks.

Next since we can change the symptom by unplugging injectors let's rule out the Excessive power draw theory. Let's disconnect:

• All 4 O2 sensors.
• MAF
• both coil packs.
• IAC
• DPFE
• Cooling fan
• all (8) injectors.
• EVAP purge flow sensor
• IF automatic the large electrical connector on the transmission DTR shifter control.

Does the CCRM click now?

IF not, then we need to plug back in the sensors one at a time to see if the symptom changes. This will tell us which sensor is the offending sensor.