I posted previously about too rich on restart. Purge valve open was suggested. XALYTY said: "2004 XJ8slave relay r9 powers a bunch of stuff and then the valve is pulsed to ground directly by the ecm. if the low side driver is shorted it’ll light a hot test light all the time with the key on" That is exactly what I am finding! Have power at the purge valve, and test light shows ground side has continuity to ground ALL THE TIME!

Ohmmeter on the purge valve showed it was shorted, measured 0.3 ohm. (from being held open continuously?) Replaced the purge valve with a used unit, no change to my original hard re-start issue. Now I pulled that replacement purge valve and find it too is shorted. But curiously, F14 fuse never blew.

Question is: what is controlling the ground side of the purge valve? If there was 40 amps going thru the shorted purge valve, why did F14 not blow?

 

Switched ground is via pin 92 on ECM plug.
Check if you have a short to ground on the purge valve and then disconnect the ECM plug to see if the short disappears.
If so, then you likely have a shorted FET or Transistor in the ECM causing the purge valve to be continuously driven (causing overheating of the valve coil and eventual shorting of the coil windings).
Confirmation is to check if pin 92 on ECM shorted to ground pins on ECM when disconnected to rule out a short somewhere in the loom.

If you conclude the ECM has a fault then you can likely send it to get it repaired relatively easily.

 

Thank you for that.
I do have constant continuity to ground at the purge valve connector, and the purge valve tests to be internally shorted. A mystery to me is why that does not cause an overcurrent? F14 never did blow. Is there something on the ground side, on the ECM side, that limits current?

 

If the ECM has a failed FET it doesn't necessarily mean it is a dead short, it could be leaky (lower resistance is still enough to drive coil and cause it to overheat and short windings).
If the failed FET still has a resistance of over 1.0 ohm, then it is possible the fuse will not have enough current going through it to fail if the coil is measuring 0.3 ohms and you also have some incumbent resistance in the loom wiring/connectors as well.

 

OK. Thank you.