Fixed! excessive pressure in fuel tank
10-21-2002, 04:01 PM
#1
Melting Slicks
Thread Starter
Fixed! excessive pressure in fuel tank
I saw this thread a few weeks back about guys having the same problem: too much pressure in the fuel tank when the cap is removed. The discussion indicated that the problem is often a clogged purge line running to the charcoal canister. Sure enough, mine was plugged solid. The solution, according to some forum members is to blow out the line with compressed air. However, no amount of compressed air could remove the blockage on mine. Here's what I did:
Disconnect the purge line at the engine compartment where the rubber hose from the canister meets the metal tubing. Also disconnect the purge line at the tank. Jack up the rear of the car. Under the car in front of the driver side rear wheel you will see the metal purge line running alongside your rear brake line. There is a short piece of rubber tubing which connects the metal line which runs under the passenger compartment and into the forward engine compartment to the metal line going to the fuel tank. Disconnect this hose. Blow air through each of the metal lines to find out which is blocked. On my car it was the long one running under the passenger compartment. Shoot some WD-40 into the metal tubing using the red plastic tip extension. Next, find a roll of baling wire. Insert the end of the baling wire into the blocked tube. Keep inserting the baling wire. You can push it in about 1/2" at a time using a pair of pliers. Since the wire doen't have any room to deform and coil up inside the tube, it will keep going even as it snakes through the tube. I was able to insert about 4 feet of wire into the line before it stopped. I then removed the wire and pushed it through from the engine compartment side using the same technique. I was able to break through the crud in the line and then blow it out with compressed air. I then shot some more WD-40 into the line and blew it through to help prevent the line from clogging again. Problem solved!
:cheers:
Disconnect the purge line at the engine compartment where the rubber hose from the canister meets the metal tubing. Also disconnect the purge line at the tank. Jack up the rear of the car. Under the car in front of the driver side rear wheel you will see the metal purge line running alongside your rear brake line. There is a short piece of rubber tubing which connects the metal line which runs under the passenger compartment and into the forward engine compartment to the metal line going to the fuel tank. Disconnect this hose. Blow air through each of the metal lines to find out which is blocked. On my car it was the long one running under the passenger compartment. Shoot some WD-40 into the metal tubing using the red plastic tip extension. Next, find a roll of baling wire. Insert the end of the baling wire into the blocked tube. Keep inserting the baling wire. You can push it in about 1/2" at a time using a pair of pliers. Since the wire doen't have any room to deform and coil up inside the tube, it will keep going even as it snakes through the tube. I was able to insert about 4 feet of wire into the line before it stopped. I then removed the wire and pushed it through from the engine compartment side using the same technique. I was able to break through the crud in the line and then blow it out with compressed air. I then shot some more WD-40 into the line and blew it through to help prevent the line from clogging again. Problem solved!
:cheers:
10-21-2002, 04:18 PM
#3
Advanced
Re: Fixed! excessive pressure in fuel tank (vetracer)
My only question on this is what is considered excessive pressure? I certainly have a great amount of pressure on my 85 coupe on a hot day when the tank is below half full but ordinarily I do not notice an excessive amount of pressure when unscrewing the gas cap. Is there any standard for this or should I just be checking the line to the purge canister?
10-21-2002, 04:32 PM
#5
Melting Slicks
Thread Starter
Re: Fixed! excessive pressure in fuel tank (captainjack)
I definitely knew something wasn't right on mine. If I wasn't holding onto the cap when I unscrewed it, it would blow right off the filler neck and out of my hand!
10-21-2002, 06:10 PM
#7
Race Director
Re: Fixed! excessive pressure in fuel tank (Bluevette85)
Great tip there.
I posted this fix a while back,I think over a year ago or so...its very important for us owners to make sure the lines arent blocked/rusted internally.Mine was so bad the gas was boiling and the tank was so hot I thought it was going to explode.The avpors had no place to go.
I left the bad steel line in place under the car,bought a new steel line the same size and ran it along side of the old one and zip tied them together and put new rubber hoses on them where needed and a new cannister since my was failing anyways.
There is no more extreme pressure problems anymore and it works great.I wanted a fast fix and the line is so small in diameter wasnt a problem to run a new one along side of it to avoid the hassles of removing the old one or something.
Btw this steel line is on the drivers side inner rocker area with the brake lines and runs from the engine bay to the back of the drivers door on the 86.
:)
[Modified by Bill's86Coupe, 4:12 PM 10/21/2002]
I posted this fix a while back,I think over a year ago or so...its very important for us owners to make sure the lines arent blocked/rusted internally.Mine was so bad the gas was boiling and the tank was so hot I thought it was going to explode.The avpors had no place to go.
I left the bad steel line in place under the car,bought a new steel line the same size and ran it along side of the old one and zip tied them together and put new rubber hoses on them where needed and a new cannister since my was failing anyways.
There is no more extreme pressure problems anymore and it works great.I wanted a fast fix and the line is so small in diameter wasnt a problem to run a new one along side of it to avoid the hassles of removing the old one or something.
Btw this steel line is on the drivers side inner rocker area with the brake lines and runs from the engine bay to the back of the drivers door on the 86.
:)
[Modified by Bill's86Coupe, 4:12 PM 10/21/2002]
10-28-2002, 04:01 PM
#8
Le Mans Master
Re: Fixed! excessive pressure in fuel tank (Bill's86Coupe)
Did any of you guys with excessive tank pressure, have a crappy idle? (and it would even stall on you sometimes) ? Thanks!
10-28-2002, 04:24 PM
#9
Intermediate
Member Since: Aug 2002
Location: tyngsboro mass
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Re: Fixed! excessive pressure in fuel tank (TIMSPEED)
ok stupid question time!!!!! mine has had pressure for over 3 years that i have owned it! thought it was normal! are you all saying its suposed to have zero pressure when you unscrew the gascap?
10-28-2002, 06:18 PM
#10
Melting Slicks
Thread Starter
Re: Fixed! excessive pressure in fuel tank (mtlwiz)
I haven't noticed any pressure in the tank anymore and I have filled up about four times since my original post. It is cooler outside, though, maybe that has something to do with it.
10-28-2002, 06:54 PM
#11
Safety Car
Re: Fixed! excessive pressure in fuel tank (vetracer)
FYI...I don't know about the 85's but on the 92 there is a valve between the gas tank and canister. When the gas tank pressure reaches 7/10 of a pound, the valve opens and purges the vapors (and pressure) to the canister. When the pressure dips below the 7/10 pound in the tank, the valve closes to the canister. Sometimes that valve will go bad causing excessive tank pressure.
08-05-2016, 08:58 AM
#12
2nd Gear
Member Since: Aug 2016
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What year
Just curious what year you are working on. I have a 92 that is having the same issue and I have checked the line from the canister to the engine compartment and it is not blocked. I have replaced the valve between the the tank and the canister and the purge solenoid mounted on the intake. I'm a little lost about the metal line you spoke of that runs on the driver's side, the only I have is a hard plastic that runs under the passenger side. Mine is getting pretty bad, on a hot day if I park the car for a few minutes and restart the motor floods out and dies unless I remember to release the pressure in the tank first. Any help would be greatly appreciated.
08-05-2016, 09:22 AM
#13
Team Owner
Stupid question but even if it pressurizes, isn't the cap designed to release the pressure past a point? So what if it builds up? What happens? Also, what if we just vented to atmosphere? Any harm? I can't see any harm. Anyone?
08-05-2016, 10:22 AM
#14
Drifting
Very interesting, thanks for sharing. I'm going to take a look at the FSM and pinpoint the lines. Mine has had alot of pressure for about 10 years now....
08-05-2016, 12:20 PM
#15
Team Owner
It hasn't tripped any codes yet, has it? IIRC some of them would if the cap was off but not sure about higher pressure. Any bad effects?
08-05-2016, 03:19 PM
#16
Drifting
08-05-2016, 04:42 PM
#17
Team Owner
In my fantasies, girls want what I have down there and guys are envious and worried that I'll spoil the women for them. Man can dreamSeriously, I really don't know if there is an issue since the worst it can do is make it easier for the pump to pressurize the system. Even then, the FPR will bleed off the excess pressure or so my thinking goes. I suppose if it ever got too pressurized, it could damage something but I doubt it.
What about venting to atmosphere? Everybody but the greenie weenies are going to be happy.
My thought is this. IF it costs me money and/or time to fix it, there had better be something wrong with it as opposed to "I think someone is looking my way.". Let me tell you about the parable of the old man, the boy and the donkey.
A MAN and his son were once going with their Donkey to market. As they were walking along by its side a countryman passed them and said: “You fools, what is a Donkey for but to ride upon?” 1
So the Man put the Boy on the Donkey and they went on their way. But soon they passed a group of men, one of whom said: “See that lazy youngster, he lets his father walk while he rides.” 2
So the Man ordered his Boy to get off, and got on himself. But they hadn’t gone far when they passed two women, one of whom said to the other: “Shame on that lazy lout to let his poor little son trudge along.” 3
Well, the Man didn’t know what to do, but at last he took his Boy up before him on the Donkey. By this time they had come to the town, and the passers-by began to jeer and point at them. The Man stopped and asked what they were scoffing at. The men said: “Aren’t you ashamed of yourself for overloading that poor Donkey of yours—you and your hulking son?” 4
The Man and Boy got off and tried to think what to do. They thought and they thought, till at last they cut down a pole, tied the Donkey’s feet to it, and raised the pole and the Donkey to their shoulders. They went along amid the laughter of all who met them till they came to Market Bridge, when the Donkey, getting one of his feet loose, kicked out and caused the Boy to drop his end of the pole. In the struggle the Donkey fell over the bridge, and his fore-feet being tied together he was drowned. 5
“That will teach you,” said an old man who had followed them:
“PLEASE ALL, AND YOU WILL PLEASE NONE.”
So the Man put the Boy on the Donkey and they went on their way. But soon they passed a group of men, one of whom said: “See that lazy youngster, he lets his father walk while he rides.” 2
So the Man ordered his Boy to get off, and got on himself. But they hadn’t gone far when they passed two women, one of whom said to the other: “Shame on that lazy lout to let his poor little son trudge along.” 3
Well, the Man didn’t know what to do, but at last he took his Boy up before him on the Donkey. By this time they had come to the town, and the passers-by began to jeer and point at them. The Man stopped and asked what they were scoffing at. The men said: “Aren’t you ashamed of yourself for overloading that poor Donkey of yours—you and your hulking son?” 4
The Man and Boy got off and tried to think what to do. They thought and they thought, till at last they cut down a pole, tied the Donkey’s feet to it, and raised the pole and the Donkey to their shoulders. They went along amid the laughter of all who met them till they came to Market Bridge, when the Donkey, getting one of his feet loose, kicked out and caused the Boy to drop his end of the pole. In the struggle the Donkey fell over the bridge, and his fore-feet being tied together he was drowned. 5
“That will teach you,” said an old man who had followed them:
“PLEASE ALL, AND YOU WILL PLEASE NONE.”
08-05-2016, 11:04 PM
#18
Race Director
There was a change in the canister location that affects the routing of the vapor lines. In early C4s the vapor canister is under the driver's side headlight and the vapor line runs along the frame on the driver's side. In later years (I don't know when it started) the canister is next to the fuel tank on the passenger side and the vapor line runs along the frame on the passenger side.
08-06-2016, 08:12 AM
#19
Team Owner
Yes. There is a pressure release valve in the cap. Normally it never activates because the vapors are released into the canister.
There was a change in the canister location that affects the routing of the vapor lines. In early C4s the vapor canister is under the driver's side headlight and the vapor line runs along the frame on the driver's side. In later years (I don't know when it started) the canister is next to the fuel tank on the passenger side and the vapor line runs along the frame on the passenger side.
There was a change in the canister location that affects the routing of the vapor lines. In early C4s the vapor canister is under the driver's side headlight and the vapor line runs along the frame on the driver's side. In later years (I don't know when it started) the canister is next to the fuel tank on the passenger side and the vapor line runs along the frame on the passenger side.
08-07-2016, 10:01 AM
#20
Tank pressure
I posted a few weeks ago about high pressure in my tank on my 86. I took the vent line off the tank, little 4 inch piece of hose in front of left rear wheel (on frame rail) and hose to purge valve. Had compressed air flowing thru all lines.Purge valve was clogged with rust,Cleaned it 1st time around. But changed it after still getting huge pressure...Swapped fuel cap off wife's 90. No more pressure. Tried cleaning old cap with brake cleaner...No luck. Ordered new fuel cap...Just my thoughts...Ziggy The 86 had so much pressure, it stretched the right side fuel tank strap. gas was HOT. Scared the s** t out of me
Last edited by Ziggy*; 08-07-2016 at 10:17 AM. Reason: Addition