My '90 Sovereign w/ 39K miles has a check engine light, with the VCM indicating Fuel Fail 89 which I understand to be a purge valve or related failure. I had read that one should be able to hear the purge valve click (open? closed?) when turning the ignition on. Had my wife turn the key while I listened but couldn't hear anything over the car's other various clicks and buzzes in the ignition mode. Replaced the purge valve and just to be safe, the short reducer hose it connected to as it had been wrapped in black tape by the previous owner. A thorough inspection of the other hoses associated with the charcoal canister showed them all intact and going where they should though I noticed that the one going to the bottom side of the intake manifold had been replaced. Hmmm... Someone else has been messing around in here but everything matches the parts diagram. However, with one hose wrapped in tape and another replaced, it was obvious I wasn't the first person to look at something in this area which is a red flag that I'm not the first to encounter an issue.

After disconnecting the battery for an extended period (while doing some other work), I started the car and the check engine / Fuel Fail 89 immediately appeared. This led me to believe that there is an electrical issue that the computer detected as it occurred before even starting the car. Tried the "listen for the click" again but heard nothing. Having already checked a fuse that I believe is associated with the purge valve, I next wondered if the valve wasn't receiving voltage. Hooked up the voltmeter, turned the ignition on, checked the meter and it registered 12 volts (more or less). Turned off the ignition and removed the key and the meter still registered 12 volts! Huh??? Voltage always on? I didn't start the car to see what happens but at this point, I'm hoping someone can explain the purge valve operation to me. When should it be powered? When should it not? When does the computer tell the valve to direct vapors to the intake? Is there always voltage to the valve, even when the car is off? And if there is voltage to the valve, why can't I hear the valve click when I unplug the wire?

All opinions, views, and explanations appreciated.

 

Hi Tony,

It helps to remember that the XJ40 was intentionally designed with many of its circuits switched on the ground side instead of the power side. This apparently led to a significant weight savings in copper wire and other electrical components.

The carbon canister purge valve receives constant battery/alternator B+ power on the Brown wire with Black tracer stripe. To open the valve, the Engine Control Module (ECM) connects the Purple/Green wire to ground. However, this connection to ground is pulsed rapidly by a square wave signal (Pulse Width Modulation or PWM), which controls the opening and closing of the purge valve in a fashion similar to the operation of the fuel injectors. By pulsing the valve open and closed, the ECM is able to control the flow of fuel vapors from the carbon canister into the engine intake manifold.

On our '93, I was often able to resolve FF89 for a year or two at a time by cleaning the ground point on the left inner wheel arch. On your '90, there is also a yellow connector under the air filter housing that can develop an intermittent connection.

See the DTC 89 purge valve diagnostics in this manual:

Jaguar AJ6 Engine Management System / OBDI Diagnostic Guide

Cheers,

Don

 

Thanks for the response Don. I had cleaned the yellow connector along with many others in the engine bay. Will have to take a closer look at the grounds. And thanks for the reminder about the diagnostic guide which I had completely forgotten to review. I'm a paper kinda guy and having never printed the guide, it never dawned on me to look it up online.

 

+1 on the paper thing. I have all this stuff saved in my computer, but it's almost never where I think to look.