2.3L ('83-'97) Evap system basics and inspection?

[Chapap]

This probably applies to every engine Ford made for two decades, but there’s no option for that except general discussion…. So I put it here.

What needs to be checked on this system? There’s a solenoid on the tank, a vac line from the tank to the evap box under the hood, and a vac line from the box to the throttle body. Is that about it? What are the *vent?* caps on the evap box? Can a faulty evap system trigger codes other than evap related codes: rich or lean condition?

More specifically, I have an intermittent rich condition code (my new MAF may be faulty according to KOEO test, waiting on replacement). I do have a leak in the filler neck… fuel spills out right after pump shuts off. That can’t be good for the evap system… but no evap codes.

 

[RonD]

In 1994 the EVAP system is pretty basic

Hose from the top of the gas tank to charcoal canister in engine bay

Basic diagram of charcoal canister: http://www.gmcmhphotos.com/photos/data/6792/Carbon_Canister_Diagram.gif
The Caps are the Fresh Air Vents

The Purge hose in earlier EVAP systems just ran to a Ported Vacuum source, with EFI that would be on the air cleaner side of throttle plate, so on throttle body but not inside the intake manifold
Ported vacuum is lower vacuum than intake side, and also opposite of "regular vacuum" its low at idle and higher when throttle is opened

There can also be a Purge Valve, 12volt solenoid "air valve", that computer can use to apply regular vacuum to canister
1995 and up always had a Purge valve and a Vent valve, and a Pressure sensor on the hose from tank or at the top of the gas tank, so computer could monitor EVAP systems negative pressure level in the gas tank

In very warm weather, gasoline vapor level is much higher, or if gas tank was overfilled a few times, putting liquid gasoline in the EVAPs hose at gas tank, there could be more vapor being sucked into engine causing computer to lower the open time for injectors and setting Rich code
But that would be a long shot in my opinion

Lean and Rich codes are about the computer's calculated open time for fuel injectors, not about the engine actually running Lean or running Rich
Computer knows its running, in this case, a 2.3 Liter engine, so it already knows EXACTLY how much air is coming in at any RPM or throttle position

Computer knows gasoline air/fuel ratio is 14.7/1, this is a WEIGHT ratio
Air WEIGHT changes alot, so it has MAF sensor and Air Temp sensor to get the weight of the incoming air
There is NO fuel pressure sensor, but 1994 computer is set to use 35psi as the baseline, and computer is programmed for the SIZE/FLOW of the fuel injectors, say 14 POUNDS an hour(weight ratio)
So it calculates how long to open each injector to get the correct WEIGHT of gasoline added to that measured weight of the air, 14.7/1

If O2 sensor shows too much Oxygen in exhaust, called lean, computer opens injectors a bit longer
If O2 sensor shows too little Oxygen in exhaust, called rich, computer reduces open time for injectors
All done in 1, maybe 2, seconds, so very fast corrections
This is called Closed Loop operation

If computer is having to correct it's calculated open time for injectors by more than 20% in either direction, it will set a lean(longer open time) code or rich(shorter open time) code to let driver know there is a problem with the system

More likely issues for rich code would be failing FPR(fuel pressure regulator), check its vacuum hose for gasoline, and if possible check fuel pressure, expected running pressure is 35PSI
The fuel pump is capable of 80+ PSI, if FPR sticks closed then pressure will go higher than 45psi and that would cause Rich codes
An obviously if FPR was leaking and gasoline was being sucked in via the FPRs vacuum line that would set Rich codes

Failing MAF sensor usually causes lean code, but certainly could cause rich code as well

Air Temp sensor(IAT) can also cause lean or rich codes

 

[Chapap]

RA has an in line purge solenoid and the canister just has two ports on it (in/out). I guess if I do have a purge valve, it’s between the tank and canister, cause it’s definitely not between the canister and the engine. I’ll have to track it down. Maybe I’ll block off the evap port on the intake and see what happens. by looking at that diagram, it seems like the evap system would introduce more air than fuel vapor and cause a rich condition if blocked… unless it’s just saturated with gas.

Original FPR looked fine with no leaks, but I changed it anyway when I did injectors. I was going to change IAT, but RA sent me one with the delicate looking sensor part shoved down into the housing. Waiting for replacement. IAT, MAF, fuel press, and evap system are the only remaining things I can think of that can be wrong.

 

[sgtsandman]

Either Eric the Car Guy/ETCG1 or South Main Auto channel just did a video on troubleshooting shooting the system (I can’t remember which) about a month ago. You might want to check them out and see if they give you any ideas on what to check and how to check it.

It wasn’t on a Ranger but the systems on different makes are pretty similar. It might be worth your time.

 

[Chapap]

Either Eric the Car Guy/ETCG1 or South Main Auto channel just did a video on troubleshooting shooting the system (I can’t remember which) about a month ago. You might want to check them out and see if they give you any ideas on what to check and how to check it.

It wasn’t on a Ranger but the systems on different makes are pretty similar. It might be worth your time.

I’ll check that out. I just plugged the line going to the intake and the light came on even more frequently with the same codes stored over my half hr drive. Evap isn’t related to running rich apparently.