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evap system school me


2drxploder

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im having some issues with my 99 ranger thats 5.0 swapped. a friend and local mechanic suggested i might have an evap sytem problem. im using stock 4cyl tank, and vapor soleniod and valve. i am throwing a code it says evap system gross leak/no flow. seams to get "vapor locked" when filling with go-juice. i know very little to nothing about this system. should i have swapped the evap system from donor expo? any and all info is appreciated
 


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Dirtman

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Gas pump shutting off when filling could be a canister vent solenoid stuck closed, clogged vent line, or clogged/contaminated canister.

The leak code could literally be almost anything. Bad gas cap, rusted filler neck, hole in the purge line, bad purge solenoid, cracked gas tank.

The evap system is basically "universal" meaning it doesn’t function any differently between 2 different engines or even two different vehicles so the issue is unlikely a result of the engine swap unless you didn’t reconnect something properly.

I would start by replacing the gas cap since they are cheap and are often the cause of a gross leak code, and then take the vent valve and vapor canister off and check/clean them.
 

2drxploder

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i also replaced stock fuel lines to engine and added a return, -8an feed and -6an return. it was returnless style tank i drilled a -6an bulkhead fitting into the top of stock sending unit for a return line, as well as walbro 255 pump.
additionally i guessed at vacuum needed for evap solenoid in engine bay. forgot to get pictures of this area, by process of elimination i thinks its right. someone have some info/pic on this? thanks dirtman, ill get a cap n start there. what does gross leak code mean? like where is it indicating a leak from?
tank not cracked, filler neck looked pretty good actually
 

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What do you mean by "seems to get vapor locked"?

Is it hard to start after fueling, or is it kicking the pump off before it's full?

The evap system has a single sensor to determine pressure, vacuum, and purge flow. It can't tell the difference between a leak so large that it can't pull a vacuum and one of the valves being stuck allowing no flow through the system, because it determines said flow by trying to change the pressure. When it can't make the pressure change it know something is wrong but it can't tell what.
 

Dirtman

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i also replaced stock fuel lines to engine and added a return, -8an feed and -6an return. it was returnless style tank i drilled a -6an bulkhead fitting into the top of stock sending unit for a return line, as well as walbro 255 pump.
additionally i guessed at vacuum needed for evap solenoid in engine bay. forgot to get pictures of this area, by process of elimination i thinks its right. someone have some info/pic on this? thanks dirtman, ill get a cap n start there. what does gross leak code mean? like where is it indicating a leak from?
tank not cracked, filler neck looked pretty good actually
The gas tank has a vent, air needs to be pushed out when fuel goes in and air needs to be sucked in when fuel is being used so it's not a "sealed" system. Basic physics there lol.

To prevent fuel vapors from simply escaping into the air, the tank's vent is connected to a charcoal canister. The charcoal collects the harmful vapors while allowing clean air to pass through. On the end of the canister vent is a solenoid valve that can open and close. It is normally open to allow air flow into the tank.

However, the charcoal can only hold so much vapor before it becomes ineffective. It needs to be purged once in a while to clean it. This is done by the computer first closing off the tank via the evap vent solenoid on the charcoal canister. Then the computer opens the evap purge solenoid which uses engine vacuum to suck all the vapor out of the charcoal canister to be burnt by the engine. At this point the system is sealed and the entire gas tank is under a vacuum. A leak code indicates that the system is not being put under vacuum, there is a pressure sensor on the tank that monitors this. It can't tell where the leak is and like I said it can literally be ANY part of the fuel tank, lines, gas cap, filler neck or solenoids.

After this process finishes the purge valve is closed and the vent valve is opened returning the tank to normal atmospheric pressure and allowing air to freely flow in and out of the vent.

If the vent gets clogged or stuck air can't get out of the tank when you try to fill up at the gas station which will usually result in the gas pump nozzle constantly shutting off before the tank is actually full.

On the other hand if the vent never closes or there is a hole anywhere in the system, when the computer tries to purge the canister you get a leak code since the tank is not properly sealed.
 
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P0455 Evaporative Emission Control System Leak Detected (gross leak)

Means filling the tank should be easy, lol

So your issue with filling the tank is most likely a filler tube issue in a 1999 Ranger
1999 Should look like this: https://images-na.ssl-images-amazon.com/images/I/61-+DIRejkL._AC_SY355_.jpg

So there is a larger pipe for filling, and a smaller Vent pipe to let the air out while filling
There are rubber hoses at the end of each so it can connect to the tank
If the air can't get out while gas is going in, then the pressure in the tank builds up and causes pump to click off

So my guess is that there is a problem with the filler, could be on filler pipe or vent pipe


Gross EVAP leak could be related if one on the rubber hoses has kinked and split, so leaking air
EVAP system uses engine vacuum to create slight negative pressure in the gas tank
So when you start the engine and start to drive the computer applies vacuum to the gas tank
Then stops vacuum and watches a pressure gauge to see if vacuum is holding, if it is not holding at all then "gross" leak
No gas cap would be a gross leak, lol
EVAP codes can't cause running issues, just not that kind of a system

Vapor lock can't happen on fuel injection systems because they run fuel pressure of 20 to 70psi, in a 1999 its 60psi
You could still have symptoms like a vapor lock, but wouldn't be fuel related, just heat related
With a 5.0l under the hood you could be building up too much heat in engine bay as outside temps warm up
This can effect connections and even coil packs as heat builds up

If you have an electric cooling fan you may need to have it running more to keep up engine bay air circulation to cool upper engine bay
You could just try running without the hood to see if "vapor lock" symptom goes away
 
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2drxploder

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Lots of helpful info. I'll get diving into it. My vapor lock i was referring to was tank filling issue, not heating heating fuel in engine bay.
 

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If you get a short hose and damp towel you can often find a gas tank air leak
A helper is best, with good lungs, lol
Take off gas cap
Put end of hose in tank, use damp/wet towel/rag wrapped around hose to seal the opening
Blow into the hose
Tank should hold pressure, it won't in this case because of P0455
But you can hear the air escaping, find out where that is, if its on filler/vent hoses that could solve both issues

Also check engine bay, EVAP hose to tank is there

DO NOT use an air compressor for this!!!!
Human lungs can generate about 2psi of pressure, so can't "blow off" EVAP hoses
No air compressor can be turned down that low, so it would BLOW OFF hoses
 

Dirtman

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If you get a short hose and damp towel you can often find a gas tank air leak
A helper is best, with good lungs, lol
Take off gas cap
Put end of hose in tank, use damp/wet towel/rag wrapped around hose to seal the opening
Blow into the hose
Tank should hold pressure, it won't in this case because of P0455
But you can hear the air escaping, find out where that is, if its on filler/vent hoses that could solve both issues

Also check engine bay, EVAP hose to tank is there

DO NOT use an air compressor for this!!!!
Human lungs can generate about 2psi of pressure, so can't "blow off" EVAP hoses
No air compressor can be turned down that low, so it would BLOW OFF hoses
You would have to also plug the vent solenoid line for this though
 

RonD

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No, not really, it would leak air through charcoal canister but should be pretty quiet

But good heads up for hearing a leak by the EVAP canister
 

Dirtman

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Another good reason to own a smoke machine. :icon_rofl:
 

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Its called a Vape :)
 

Dirtman

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Its called a Vape :)
I've seen/done the cigar trick but never thought about a vape gizmo! Those things make insane amounts of smoke! My buddy vapes and he can fog up a room in 2 puffs. :icon_rofl:

I may go buy one and keep it in the truck for roadside smoke tests. :icon_rofl:
 

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2drxploder

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I attempted a homemade smoke machine it failed, too much air
 


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