No communication on Crown Vic

[jkcummins]

2000 Crown Vic 5.0l will die at random times, when vehicle dies there is no communication with the scan tool. Have to cycle key in order to have communication with scan tool and for the vehicle to start. thinking possible computer but wanted another tech's opinion.

any help is appreciated.
Thanks, Jake

[sbreland73]

Hi Jake,

Are you sure this has the 5.0L? Looking at Alldata, it only shows the 4.6L. The last year for the 5.0L in the crown Vic was 1991. Have seen Fords with this relay going bad, giving the same symptoms. HTH.

[jkcummins]

Yes it is a 4.6, sorry for the confusion. Ive swaped relays with a known good relay and still died, I have swaped ECM's with a known good ECM and vehicle still dies at random times and will have no communication with the scan tool.

[roadracer587]

Do you have no communications with just the PCM or do you lose communications with all systems. You should have multiple communication lines on the 2000 crown vic. I believe the air bag and abs might be on a different network.

[jkcummins]

I have communication with all other modules but no comm. with the pcm when the vehicle dies. I have to cycle the key and it will start right up and have comm. Getting no codes when the car dies so there for i have no freeze frame data to go off of. any help is very appreciated at this time.


Thanks,
Jake

[sbreland73]

Verify all Power/Grounds to PCM, with testlights, if all hold good, chunk a PCM at it.

[jkcummins]

Ran all new grounds for the PCM and power is present. Already replaced PCM with known good PCM. Also replaced Crank Sensor.... still no change.

[Orevin]

Verify all Power/Grounds to PCM, with testlights, if all hold good, chunk a PCM at it.

If it where that easy...

A shorted Vref can take down a PCM for instance. New PCM won't fix that.

[orlando]

did you get any code from the other modules , and when it does not start before you turn the key off check and see whats missing , spark , injection pulse , fuel pressure , etc .

[jkcummins]

Vehicle has spark when it dies, fuel pressure is good but no injector pulse.

[orlando]

Vehicle has spark when it dies, fuel pressure is good but no injector pulse.

If the injectors got power i would look at the anti-theft system or an after market alarm. Is this a former police car?

[roadracer587]

Check to see if the PCM is being spiked by an output state solenoid. You could be experiencing a PCM reset. If you have the vehicle quit and lose comm. I understand that all you have to do is cycle the key and comm. comes back. I would unplug all the unnecessary output solenoids and see if it still happens. I have heard that a defective coil can spike the computer and cause a similar condition.

[jkcummins]

Yes this is a former police vehicle

[jkcummins]

When the vehicle first came in, it also had codes for shift solenoids and the transmission slips pretty bad under WOT and thats when the vehicle seems to die the most.

[jkcummins]

Injectors have power, no ground when vehicle dies.