Trouble shooting EVAP controls

Looking for help trouble shooting the EVAP emissions controls on my 1998 4.0 litre supercharged V8. This is a UK spec car with the single canister system. The issue is a smell of raw fuel under the car and drawn into the cabin with windows/roof open.

I replaced the purge valve LNC1515AA (form a salvage dealer) and the Rochester valve a little while ago but no improvement. I am now trying to get to the bottom of this once and for all.

I have just visually checked the hoses and lines and all appear correct. With engine off there is no flow through the charcoal canister; at idle there is flow, so I assume the Rochester valve is OK. This makes me suspect the purge valve. The wiring connections are purple and white. I get fluctuating voltage readings by back probing both with the engine running but don’t know the correct voltage values so am only guessing the readings mean that the signal to the PV is OK. There are no codes stored which again suggests to me that the electrics are within tolerance.

I took one of these apart recently to try and figure out how it works (see pics). As I figure it out, inlet vacuum acting on the diaphragm is insufficient in itself to open the purge lines but the added pull from the electromagnet is sufficient.

Any tips on trouble shooting/repair would be much appreciated.


Maybe the canister needs replacement or airing.
It’s a Ford part.

Could be, but they are NLA as new items and the old one looks like it must be cut open to replace the activated charcoal. How do you “air” it without cutting it open?


You could blow thru them.
and leave them out in the sun light

When the car is left standing there is a build up of fuel vapour pressure in the tank (hiss on opening fuel cap). On start up the pressure is relieved (presumably because the Rochester valve opens) and this vapour is emitted from the canister vent hose to atmosphere (causing the fuel smell).

I have just clamped off the vent hose and re-started the engine but the tank pressure is now not relieved. If the Purge Valve was working I would have thought that pressure would have been relieved (direct to the inlet manifold). That suggests it is the PV which is faulty?


Have just removed the clamp and re-started the engine. Held a piece of tissue paper against the open end of the vent pipe and can detect no flow into the canister. I have no idea on what timescale the PV cycles but the voltage readings I got from back probing the PV connector suggests every few seconds/a minute or so and that would have been time enough to detect flow into the canister.


I didn’t think the electric valve would open until.

The engine was warm,
You were driving on part throttle.

Well that’s how it is on some cars

I thought I would post a conclusion in case anyone else might find it helpful.

The canister was absolutely saturated with fuel vapour. Over a day and a half I blew through it using a low pressure air line and left it out in the sun in between. The vapours reduced but were still there. So I cut it open at the “fat” end along the assembly joint using a sharp knife and spread the charcoal out thinly in the sun to air. It was only a short step from there to renewing the charcoal pellets with fresh from an on line supplier. You will need about 1.5 litres or 780 grammes at 3mm pellet size. Reassembled and sealed with RTV silicone along the cut line. The original charcoal pellet size is 2mm; I couldn’t find an exact match so bought the nearest available - 3mm. This may have changed the absorptive capacity a little but hopefully not enough to matter.

Test run OK. Hopefully a permanent cure for the fuel smell.


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Thanks for the feedback.
Good to hear.

I thought it was just a honeycoomb, maybe that is just at the end ?

What looks like the end of a honeycomb is a perforated retaining plate. Behind that is a filter pod and behind that the carbon pellets.

This is the amount of carbon inside (with grateful thanks to my wife for the loan of her kitchen equipment)!


Thank you so much for the pictures.

I also have a gold tray like that.