How to ADD in evap?

[travisn]

I'm doing a swap in an old car and I'm starting to think about fuel plumbing. I have a fuel cell and was just going to vent to atmosphere but now I'm thinking I should hook up a canister and purge valve. I only have an engine with harness, is it as simple as getting and wiring in the evap canister purge, evap canister vent, and fuel tank pressure sensor? Is there anything else I need to be aware of? What is typically done to remove those that I need to be sure not to do?

[Jon S.]

Firstly, good for you. We install EVAP systems and catalytic converters on every LSx conversion that leaves the shop - whether it is a 1930's Ford or a 1970's Chev. This affords peace of mind to the owners - they can drive them anywhere without a second thought, and can also sell / register them anywhere without issues.

The specific answer to your question depends on what controller you are using (PCM / ECM).

The 1999+ LSx EVAP systems had two primary subsystems, as you pointed out. An EVAP Purge Solenoid (mounted on the intake manifold) and an EVAP Vent Solenoid / Fuel Tank Pressure Sensor mounted in (or adjacent to) the fuel tank.

In an older conversion, like a vehicle that was originally equipped with a Fuel Vapor Storage Canister (Charcoal Canister) between the fuel tank and the engine, you only need the EVAP Purge Solenoid from the LSx system.

The Charcoal Canister would have been originally connected to a ported vacuum source at the base of the carburetor. Plumb this rubber line to the EVAP Purge Solenoid, adjust the tune / DTCs as necessary, and you are good to go.

[travisn]

Thanks for the reply. When I said older I really meant older, 1965 to be exact, haha. There isn't anything from the original car that can be used. The engine is a 98 but I am converting to a 0411 PCM.

I am going to try to source the solenoid and pressure sensor from the guy I got the motor from, otherwise will head to the junk yard and get the parts from a 99-00 gm vehicle.

So long as I hook up those 3 parts to the PCM and relevant fuel tank and intake ports then it will work as intended?

[mbray01]

you also have to have a fuel tank pressure sensor, and the fuel level sensor has to be correctly programmed into the pcm. The system will only draw vapors when between 1/4 and 3/4 tank.

[Jon S.]

Different controllers may use different EVAP diagnostics. With the P01, the requirement for the fuel level to be between 15% and 85%, is the range in which the Fuel Tank Pressure diagnostics will be active (actively looking for a leak in the system).

I don't believe the actions taken (when any EVAP related DTC is set) is to disable any part of the EVAP system. The rational seems to be to get at least some of the fuel vapor into the engine.

In a retrofit application (like this 1965 model) you can make the EVAP system as simple, or as complex, as you like. The goal is to reduce the amount of fuel vapor vented into the atmosphere.

[travisn]

you also have to have a fuel tank pressure sensor, and the fuel level sensor has to be correctly programmed into the pcm. The system will only draw vapors when between 1/4 and 3/4 tank.

Good to know. The fuel cell I am using came with a 0-90 ohm sending unit.

[travisn]

In a retrofit application (like this 1965 model) you can make the EVAP system as simple, or as complex, as you like.

What parameters are tunable? I do plan on (eventually) using all 3 pieces.

[mbray01]

The purge solenoid will not operate if the ecm reads an empty or a full condition, this is done to prevent raw fuel being drawn in after a fuel fill
therefore if the level sensor is not hooked up and properly programmed it will not purge, unless you specifically wire it to turn on. The ecm will not do it. If the level sensor is not hooked up it will read either full, or empty based on the ecm calibration

[Jon S.]

That does not seem to always be true. A broken fuel gauge does not always disable the EVAP system.

GMPP calibrations that were OBD-II compliant, had the EVAP Purge Solenoid (and DTC) active, while the EVAP Vent Solenoid, Fuel Tank Pressure, and Fuel Level were not active.

[Russ K]

The vent valve & fuel tank pressure sensor are just for the pcm to detect if there is a leak in the system (bad fuel cap or purge line etc).

On a retrofit application, you just need the purge valve hooked up to the canister & set the vent valve, pressure sensor & small & large
leak codes set to no error reported.

Russ Kemp

[SteelGreenStallion]

I just did a LM7 5.3 swap in a 01 Mustang and after reading this thread I'm not sure what to think. I simply plugged the tube to the purge solenoid on the motor into the stock Mustang canister. Will this work and purge the canister? Or does it have to have tank pressure and level inputs to the PCM to tell the solenoid valve when to open? The stock Mustang tank doesn't have these.

[Jay@HAP]

you also have to have a fuel tank pressure sensor, and the fuel level sensor has to be correctly programmed into the pcm. The system will only draw vapors when between 1/4 and 3/4 tank.

Does the fuel level sender go directly to the PCM or go through a BCM first?

[travisn]

I'm pretty sure the PCM has an input for fuel level, haven't looked into it in a while though.

[YJUnlimited]

Reviving this old thread. Can anyone confirm if the purge solenoid can be used without the vent/pressure solenoid/sensor? Thanks!