Fix: SN

Nov 23, 2023

A few days in stop and go traffic with the AC on with our 1995 Mustang GT "Project Rewind" sent us unwittingly into one of the most common problems owners of the SN-95 Mustang experience. A strong gasoline odour began coming through the air vents while sitting at stop lights and idling.

At speed it would go away, but when we’d stop again it was strong enough to give you a headache and make eyes burn. We immediately pulled over and popped the hood, searching for fuel leaks but found none. After a careful trip back to the garage we inspected more intensely with the engine idling

Looking for leaks and narrowing down the location of the smell, we confirmed it to be coming strongly from the passenger side of the engine compartment. We shut the car down and Googled "1995 Mustang gas smell’ which gave us pages of forum threads describing the very same issue.

This era of Mustang is particular to this issue due the evaporative emissions control system (EECS) which has a rubber hose and inline canister purge valve (CANP) located directly over the top of the passenger side exhaust header (Photo 3) . This routing exposes it to extreme heat which causes both rotting of the hose but also failure of the valve – either of which will cause a strong odour from escaping gasoline vapours.

The EECS system hose and purge valve are routed directly over the heat of exhaust header, making them prone to failure.

The purpose of the EECS system is to route expanding gasoline vapours from the top of the fuel tank to the engine intake tract as a way to prevent the vapours from escaping to the environment. The vapour line goes into a charcoal storage and scrubbing canister located in the passenger side fender well, then routes into the engine bay.

The inline CANP (Photo 1) controlled by the computer regulates the flow of vapours into the intake manifold. The valve which is located at the rear passenger side of the engine is closed when the engine is off. The computer will open it at start up to allow expanding tank vapours to purge into the intake tract.

Over time, the extreme heat sources turn the hose to a crusty cracking mess. The heat also can cause the CANP to fail. Either condition will cause vapour smell, and even a rough idle if the hose is leaking vacuum.

Upon inspection of our own car, we found the EECS hose was indeed rotted and crumbling. It was so bad that it literally came apart in our hands as we began to remove it. It was clear this line was the likely source of our gasoline vapour smell. As you can see in the photos the cracks were visible, but went all the way to the core of the hose. Later testing also showed our CANP was defective and had to be replaced.

Our EECS hose was rotted through from end to end in addition to a failed purge valve.

Because both the hoses and the CANP needed replacement, we planned out the project. The hose fix is inexpensive, but there is a good bit of labor involved replace it right. Five feet of heavy duty vacuum line at our local parts store was only $3.50. Replacing the entire length of hose however requires a day's work, as both termination points are hidden away behind and under components that must be removed to get the them.

The CANP is an item that runs $65-85 new depending on where you purchase it. You can test the old one a number of ways. We tested it by removing the canister side hose after the car was at operating temperature. If it is open, your idle should start to falter and you should have vacuum at the valve inlet. This test is not conclusive as the computer does not have the valve open at all times.

Our manual had a second test method which involved using a multimeter on it to measure its resistance. The manual stated it should have 30-90 Ohms resistance. Ours had 8 Ohms. Strike 2. The third test method is to apply a 12 volt current to the valve when off the car and see if it opens. We didn't perform this test, but it is likely the easiest one to do. Ours failed the first two and that was enough for us.

For the record, the reason a failed CANP can cause vapour smell even if the hoses are good is because it prevents the charcoal canister from emptying. Pressure build-up over time can saturate the canister and eventually the odour begins to come from the atmospheric vent. The canister is vented to the lower front wheel well just under the ABS unit and air intake. On our car much of the strongest gas odour was coming from this location.

Removal of the upper intake manifold is necessary to replace the entire EECS hose.

To get started on the fix, the first thing needed is to carefully disconnect the electrical connection to the CANP. We noted the flow direction in which it was installed before cutting its lines loose.

The starting point for the replacement line is the EVAP charcoal canister inside the passenger side fender well (Photo 5). Getting to it requires the removal of the left front wheel and the inner fender liner. It takes about an hour to jack up the car, remove the wheel and get into the spot where the canister is located. We replaced the hose starting at the canister, and snaked it through the side wall to the engine compartment.

The other end of the hose connects well under the middle of the upper intake manifold a spot that is impossible to see or reach by hand (Photo 4). Replacing this section of the hose requires removal of the upper intake manifold to gain access. If the hose had been in good condition at this spot we might have spliced the replacement hose, but unfortunately it was cracked and rotted all the way under the intake.

Removing he upper intake is a significant job that requires disconnecting several vacuum lines, electrical connections, EGR valve and throttle linkages. We will forgo the detail on this part of the job as it is an article unto itself. The rub is that its removal and replacement required a new set of gaskets, which cost about $15.00. Also if you must take this step, budget up to 2 hours depending on your skill level.

The charcoal canister is located in the passenger side fender well, requiring removal of wheel and splash shield for access.

Getting the intake off allowed us replace the EECS hose that was rotten and inspect the PCV hoses for similar rot. They were in good condition, but we added hose clamps to their hidden connections to save us future leaks that would warrant the intake manifold's removal again. We also cleaned and inspected the fuel rails for signs of leakage since the gas odour was the whole reason we were here.

After reinstalling the upper intake we cut the excess length of the new EECS the hoses to join at the purge valve, ensuring we had reinstalled it in the same direction as it had been removed. We then taped the hose to the white plastic attachment clip with electrical tape as it had been from the factory (Photo 7).

Upon firing the car up we let it idle for about 10 minutes and warm up, constantly on the sniff for gasoline vapours. Not smelling anything we then took it for a test drive with the AC on to replicate the circumstances in which the smells originally came up.

In stop and go driving the smell was gone. We allowed the engine to get to a good temperature just to be sure. After returning we again let the engine idle and gave it the sniff test, the smell was gone.

One bonus that came from this repair was a smoother idle. Because this line is a part of the vacuum circuit, its cracked state had been giving us a vacuum leak. Our idle had been suffering from a slight and intermittent shake which is now entirely gone.

Repair Parts:

5 feet – 5/16" vacuum hoseUpper Intake Gasket SetCanister Purge Valve

Repair Time: 3-4 hoursRepair Difficulty 1-10: 6