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Discussion Starter · #1 ·
1994 Sidekick, 1.8L, 8V, 5-spd, 2-dr, 300K mi.

Ok so I'm back with a new odd prob. Any time I drive my Kick it pulls a vacuum in the gas tank. At times it's been a considerable amount. It does it to some degree every time out. I purchased a new gas cap thinking that was the simple solution. Nope. I pulled the vent line that runs from the filler neck to the tank. I checked the line and both barbs where the hose attaches. All clear and in order. Also the hose does not appear to be collapsing under vacuum. I'm stuck. Anyone run into this before or have any insight? All help is greatly appreciated. The tank has some odd looking, white plastic "box" on top of the tank that I'm uncertain of its function. I wonder if it's involved in in-tank pressure regulation so please fill me in there too. I'm obviously not understanding how this tank "breathes."

Thanks as always
 

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Under normal use, the system is designed to have SOME vacuum. It is an emissions thing. It also has a vent system to recapture fuel vapor. This is the carbon can in the engine bay and one of the vacuum solenoid on the engine. There are check valves, fuel separators and stuff above the fuel tank.

If your tank is getting too much vacuum... as in collapsing the tank, there is a problem.

I haven't actually REALLY looked at THIS system... need to go to work now. If no one else has better advice by the time I get home, I'll look at the system. I have a stack of manuals. ;)

In the mean time: How much vacuum are we talking about? Is the car running ok with out fuel starvation?
 

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Discussion Starter · #3 ·
Mike,
It's difficult to explain the amount of vacuum but it's considerable at times. As in air will rush in for a second or more at its worst when removing the fuel cap. I can't say that it has been able to collapse the tank to any degree but I've never encountered so much vacuum on any other vehicle. As to performance, under acceleration I can feel a hesitation above 2000 rpm that varies in intensity at times. The vacuum in the tank seems to follow the hesitation severity. Just FYI I've changed the (very filthy) fuel filter which eased the hesitation but didn't cure it. I realize that issue could be any number of other things and I'm not chasing that bug right now. I also realize there is a lot of emissions equipment on board and would chunk all of it if I knew I wouldn't throw the computer into a mental episode. But long story short, it's an inordinate amount of vacuum at times. Others it's less but it's always present. The amount it varies also makes me think red flag.
 

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Are you sure that the air is rushing in, rather than out? Normally what you here is pressure coming out, rather than air going in. What kind of gas cap did you get - presumably one for an EVAP system with a vacuum breaker on it?
Info on EVAP system here:
EVAP Evaporative Emission Control System
 

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I was hoping that someone who had actually worked on THIS system would provide advice. The page Bex linked has good general information.

I have worked on older fuel tank vent systems and I read the (small) sections on the fuel tank in both the Sidekick and Tracker manuals. Seems the fuel cap only vents (in) when under a LOT of vacuum. It sounds like it is just a safety feature and not involved in the normal operation.

From my reading, the item most responsible for controlling the pressure (both positive and negative) in the tank is the Tank Pressure Control (TPC) valve on top of the fuel tank. (I have heard of this valve called a "two way check valve." ) It is in the line between the Fuel vapor separator and the line to the carbon canister up by the engine.

Neither manual has a theory of operation for this but from systems I have worked on in the past I'll but out how I THINK it works: Fuel creates vapors (it evaporates) almost all the time. besides being a major source of pollution, it is rather wasteful. So the fuel system is sealed. But as fuel evaporates, it creates pressure. To reduce this pressure before it becomes a safety hazard, it is vented though a carbon can. The activated charcoal in the can traps the vapors but allows "air" vent. This is fine until you run the car and use the fuel. The fuel doesn't evaporate enough vapor to replace the fuel being used, so you end up with a vacuum in the tank rather than pressure. The normal operating relief on this system seem to be from the carbon canister. The fill cap has a safety relief to keep the tank from collapsing.

So any blockage in the line from the vapor separator through the TPC and up to the carbon can, can give the symptoms you describe, plus over pressure of a full fuel tank on a hot day.

A few checks you can do would be to drive it until you have the hesitation you describe. Then stop and loosen the cap and see it the hesitation goes away. If it does you DO have a vacuum problem.

Next you can try the same procedure but disconnect the line from the tank at the carbon can... to check for a clogged can. It that doesn't work, look for pinched lines and the like. I hope you find something before dropping the fuel tank. I'm trying to think of a way to check the TPC without removing the tank... I am not sure on the exact location of this valve.... the diagrams are on top the tank on the left side. maybe this can be reached...

Good luck.
 

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Discussion Starter · #6 ·
Bex,
I hadn't considered air rushing out as a possibility. I'm inclined to maintain air is rushing in, but I'm going to check that out. Good advice, thanks. Also, the link you included is a good one. As I was reading it I was following my mental image of the fuel system on my Kick. It helped me start understanding some of the components and their functions which is what I need. Thanks there as well.

Mike,
What you're saying falls in line with Bex's link. That's helpful to me in that I can start piecing the theory and functions together. On top of my tank there is a small, translucent white plastic "box" that has a fuel line attached to it. That line then goes forward but I've yet to follow it in its entirety as I had no idea as to its purpose. I'm guessing it is part of the vapor system going to the charcoal canister. Thanks for all your thought on this.

Long story short this tank vent system is far more complicated than I realized. It isn't impossible but it's not exactly straightforward. Why am I not surprised. Tomorrow I'll start looking at the things you guys have turned me onto.

Also, if anyone has a good vacuum diagram I could use it. All of my under hood hoses are in bad shape. I have most all the coolant lines replaced now and plan to start on vacuum. Plus there's a good chance my tank venting problem will cross paths with the vacuum lines.
 

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I think that the box on top of the tank is what they call the 'vapor liquid separator'. The two way check valve is in the fuel line - a small round piece that connects two fuel pipes on the top of the fuel tank. Basically, from what I understand, the liquid fuel comes out of the tank and then 'splices' where the vapor goes to the separator, while the fuel itself goes to the fuel filter. The check valve is further down from the separator, and that part of the system goes to the evap canister. You will have 3 pipes coming away from the tank - one for fuel to the filter, one for vapor to the canister, and the return fuel line. There shouldn't be fuel in the canister part of the system, if it is working correctly.
 

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I've had my fuel tank and lines apart a few times last year, repairing the pump hanger/line assembly, and putting in a new tank since the old one was getting pretty rusty.

Yes there is some mystery to it and here's how mine is at least. The pressure and return lines come through the pump mounting plate. Completely separate from the vapor line which just comes from the top of the tank. Then to the fuel/vapor separator which should always be totally dry unless fuel splashes up for whatever reason. Then being a larger volume than a piece of hose, it gives the fuel a place to fall out of the stream while the vapor continues on its way.

Then it goes to the check valve, which I wasn't exactly sure about. From general descriptions I could find, it's supposed to go let the vapors to the canister, but disallow a possible backfire from making its way to the tank. Mine was installed backwards from this, but from the other PO hackjobs I wasn't sure. Blowing through it to test, the orange stripe molded into the plastic goes on the direction of the flow, like a diode. So when I put in the new tank I installed it for the vapors to flow out but disallow a backfire.

It acts the same. Either way I never had any tank vacuum problems or never hear hissing when I remove the cap. But one thing that is different from the old tank is that I can put in between 1.5 and 2 gallons more before it clicks off. And with about 10k miles with the old setup, and about 10k miles with the new tank, I can tell that it's not the float position, but it's just extra volume at the top being filled. Before at 8 gallons it would be on E. Now it's almost 10 gallons, which makes more sense for an 11 gallon tank. When I removed it the old one on E, there sure wasn't 3 gallons left in the bottom.

I had similar situations with a couple of the GMs where the check valve stuck and putting gas in the car was hell, had to trickle it in and took forever or it would kick off the pump, but it often helped to leave the nozzle partway out when filling. If you have this problem then it's a clogged EVAP system but it doesn't sound like you do, unless you can't fill your tank fully either.

I found a diagram that shows a 2nd possibility for the Trackick system, which shows a check valve with 2 outputs instead of 1, and a device connected to that. I am assuming that is a pressure sensor for OBD2 vehicles.

Yes like Bex said I'd confirm the type of cap you got, because that's where the vacuum relief is supposed to happen and with the cutting out, it sounds like a possibility. The EVAP lines are supposed to be more of a pressure relief. I'd really try to confirm which way it's happening.
 

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Then it goes to the check valve, which I wasn't exactly sure about. From general descriptions I could find, it's supposed to go let the vapors to the canister, but disallow a possible backfire from making its way to the tank. Mine was installed backwards from this, but from the other PO hackjobs I wasn't sure. Blowing through it to test, the orange stripe molded into the plastic goes on the direction of the flow, like a diode.
I believe that blowing back toward the tank, through this valve, can render it useless. It is meant to only allow the vapor to go one way so you shouldn't blow on it from the opposite direction.

Before at 8 gallons it would be on E. Now it's almost 10 gallons, which makes more sense for an 11 gallon tank. When I removed it the old one on E, there sure wasn't 3 gallons left in the bottom.
'E' is kind of relative, and may not be tremendously accurate, as it depends on the gauge, the float, etc., rather than what is actually in your tank. I find that my gauge can sit on E for a surprisingly long period of time, and yet I have never had the tank low enough where I needed 10 gallons. Apparently the Suzuki 'idea' was that, when the needle hits the red E mark, there are 3 gallons of gas left - but of course, if your needle has been sitting on E for a number of miles, your gauge isn't accurate, etc., this may not be the case.
By the way, with an EVAP system, you should never 'top off' your tank.....
 

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Discussion Starter · #10 ·
TLC,
I'm going to have to read your post a few times to fully get the idea, but I think I follow what you're saying. I haven't had time to chase the fuel lines yet today but it's on my to-do list. I will say that the cap that was on my Kick & the new one I purchased both appear to be made to seal tightly at the neck. The both also have what appears to be spring load valves in them. That's what sent me down the bad cap path initially. The old cap appears thoroughly used so I thought easy fix. Nope. Also, I have no trouble filling the tank. At 1/4 on the gauge I can easily put in 7-8 gals which is appropriate with the tank's volume. Out of frustration I've considered removing the cap gasket and letting it go. Of course I know that's not wise and I don't like "fixing" things unless it's done properly. I guess I'll keep chasing this bug. Oh and thanks, TLC, for the info.
 

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Yes I only blew on the valve with my lips, just to check which way it actually functioned. Didn't hook it to a compressor or anything. So good to know my theory is correct about it being installed so the vapors only flow away from the tank.

I only top off the tank to the first click of the pump, while slowing the pump to a reasonable flow of about 0.1 gallons per second when I know I'm down to the last gallon or so. I always do this with any vehicle. Because I like to accurately keep track of my MPG. My trips are usually to the same place, same stations, same pumps, and with at least 10k experience with it both ways I have a very good idea how much is in there based on the gauge and other factors. (With a small tank and regularly doing mental math to decide if you will make it to a cheaper gas station many miles away with some to spare, you have to be good at it. I just got back from a 700 mile weekend to transport my daughter and have been doing it 22+ times a year for 11 years, plus 52 miles a day for work.) Both old and new tanks have been extremely consistent over their 10k miles. When I changed the tank I ran it to the same point that it had always taken 8 gallons to fill, which is just to E, not driving around for awhile on E. And there was around a gallon left after tipping it all the different ways to get the gas from the baffles. Certainly wasn't 3 gallons left. Averaging everything I'd say it's about a 1.75 gallon difference old to new. I only got 10 gallons in it once when I knew I was pushing it, but at the same point of pushing it with the old setup it was just over 8 gallons. And I don't like to run it way low often.

Anyway Porkins yes it sounds like your tank fills like mine does so I'd say there's probably no EVAP blockage. Was it an actual cap listed for a Sidekick, or just a new cap that happened to fit?
 

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Discussion Starter · #12 ·
TLC,
Cap I got was per my local NAPA based on my particular vehicle. So I'd say it's correct. The local NAPA is a good one. But, interestingly enough, yesterday I began chasing the lines only to realize it's a maze of both hard & rubber lines on top of my tank. There's no real way to i.d. much w/o pulling the tank. Frustrated, I went to the charcoal canister and its 2 lines on top are labeled "to tank" & "purge." I used my mouth & pulled a vacuum on to tank line. I felt a slight resistance then got gas vapors. For fun (not really), I did the same on the purge. Gas vapors again. So I then went & drove the wheels off of it for several miles but before I left I cracked the cap (got a very slight vacuum) then made sure it was tight. Got home & checked again. No vacuum in tank. That was the 1st time since I've owned it to not get vacuum in the tank. I'm not ready to declare it cured but I might now be on the right track. I need to drive it more and check again.
 

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Discussion Starter · #13 ·
Oh & I should point out I'd have never thought to pull air through the lines at the canister had you guys not helped me understand the system. Thank you all.
 

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... I used my mouth & pulled a vacuum on to tank line. I felt a slight resistance then got gas vapors. ...
Considering all the chemicals that are in gasoline, this is not something that I would recommend. In fact it is something that I would discourage as it is very unsafe. :eek:

I had an Uncle who damaged his lungs with a trick something like this... notice the use of the word "HAD."

With your mouth and lungs on fuel lines, Blow... maybe. Suck.... NEVER.

That said... like I first said... blockage in a line.
 

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Discussion Starter · #15 ·
Mike,
I'm very much aware of the "it's a bad idea" angle. I didn't want to do it but I also didn't want to drop the tank. I'm glad I didn't choose that same day to take up smoking. I would not recommend my method by any means so kids, do as I say, not as I do. But I did fill my lungs with air first only pulling vapor into my mouth. To paraphrase one of my fellow Arkansans, "I didn't inhale."
 

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Hi Porkins, sounds like you are on your way to figuring this out. But I thought I would add my experience with the EVAP system too.
On my car, I nearly always get a Vacuum rush of air when I take the gas cap off. The more empty the tank is, the larger the "whoosh". Also, the warmer ambient air temp, the large the whoosh.

Last year when I stopped hearing that whoosh consistently, I figured it was just odd temps. But when I went to our local emissions station to prepare for license plate renewal, they failed me due to lack of vacuum in the tank.

To help me troubleshoot where my system vacuum leak might be, and what test I had to prepare to pass, I researched the testing station's methods: First they find the Charcoal cannister and determine the line going back to the tank. They pinch off or remove and cap that line. Then they remove the fuel filler cap from your vehicle and replace it with their cap that is attached via a small hose to a machine that very carefully creates a tiny vacuum in your tank. It is a rather complicated device that uses columns of water to gently create about 2 inches of vacuum. The testing machine then stops building vacuum and seals itself and waits approx a minute to see if your system will hold the vacuum for that time period.

Interesting side note, while doing this research I found that more pollution comes from bad Evap Control Systems than out of the exhaust.

Anyway, I used one of those one man brake bleeder devices to test the testers. I took the hose going from cannister back to tank and connected it to bleeder device and pumped the handle. Sure enough I could not hold a vacuum. Most shops that say they can cure emissions failure, also have what is commonly referred to as a smoke machine. They will pump smoke into your tank and then look at all lines for the escaping smoke.

I did not have the luxury of a smoke machine, so I went against common advice and pressurized my evap line at the cannister going back to the tank. HOWEVER, I used a tiny less than 2 psi amount of pressure. I believe the advice to NOT pressurize the evap system if valid, but I felt if I stayed below what the testing stations pull in vacuum I would be okay.

With under 2 PSI on that line, I started squirting soapy water on all the lines from cannister to tank, watching for bubbles. Didnt find any there. Then I went to the tank and from the wheel well leaning in, I squirted the Fuel Vapor Separator. Sure enough, that is where the leak was. The seam of that little plastic tank had developed a tiny leak. I repaired the leak with a plastic welder. Rechecked how much vacuum I could hold with the brake bleeder and this time I had to stop myself at 2 PSI. Before I could not even go that high.

Took it back for retesting at the Emissions Station and all was well. I have been hearing the whoosh at the gas station ever since then. And breathe a sigh of relief when i do.

I had no drivability issues throughout this whole ordeal. Engine ran great and didn't care if its evap system had a vacuum or not. But the local DMV cared a lot. grin.

I realize this is sort of the opposite of your issue, but I hope some of this info might help you troubleshoot, or even help you decide you may not have an issue.

randy
 

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Discussion Starter · #17 ·
Randy,
I appreciate you chiming in. However, it leaves me a tad confused. From the comments of others the consensus seems to be little to no vacuum at the tank. I do follow what you're saying & why. I can now see why a slight vacuum was designed into the system. The problem I have, at least in part, is determining a baseline for what's "normal." As you say, determining if I have a prob at all. My Kick had no trouble pulling a vacuum in the tank. In fact it did it seemingly too well which is what started me down this path. But I'm new to this vehicle and am learning the ropes. Quite frankly, I find my Zuk to be just a tad odd compared to my previous vehicles. Regardless I can tell you that I'm no longer pulling a vacuum at the tank, or at least so far. Sadly, I'm not sure if I did right or wrong now but my performance is somewhat improved so I'm going to run with it. I'm fortunate to live in a state that doesn't inspect vehicles for licensure purposes so if I screwed up it's not a huge deal. I do appreciate your input and explanation of the system. I'm always interested educating myself especially considering most all the probs I've encountered so far on my Zuk have been more complex than they appear. I'll get it ironed out eventually though.
 

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Good to hear Porkins, sounds like you're getting it figured out. Sounds like maybe you didn't have a vacuum problem but a pressure buildup problem from a sticking check valve. Hard to say about the stumbling though, but hope you get familiar enough with it all to figure it all out.

BTW, my 2nd and 6th grade teacher (same woman, tiny school) said things to us like "oh don't you just love going to a gas station and smelling the gas" and "oh don't you just love standing behind the school bus and smelling the exhaust". She was serious too, she loved it. This was in the 80s, these days it would have probably gotten her canned. My daughter and I joke about it, but the teacher happens to still be doing just fine.
 

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From the comments of others the consensus seems to be little to no vacuum at the tank.
Have you ever determined whether what you are hearing is pressure coming out, rather than your thought of vacuum flowing in to the tank? As the system is pressurized, you will have pressure being released when you open the gas cap, unless there is a leak in the system.

Edit: As stated in above posts, the amount of pressure will vary, depending on the temperature, the amount of gas in the tank, etc.
 

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Discussion Starter · #20 ·
I never felt any air rushing out so I locked in on it being a vacuum. There were several instances where the rushing air was considerable. It was enough that I would think I might have felt it. But with that said, maybe it was exhaling. I immediately thought vacuum and gave it no other consideration. I'm still inclined to think that but I wouldn't bet on it now. Either way, the slight hesitation I had seems eased. As I said previously the hesitation under acceleration seemed to ebb and flow according to the amount of vacuum (or pressure) I had in the tank. As for having it figured...I dunno. It's running a little better so I'll take dumb luck as a solution if I have too.

TLC, I'm with you on the way school has changed. Sounds like you and I are from the same era. I had a bus driver when I was a kid that would stomp the brakes on the bus HARD if we were being too noisy or rowdy. The old brake check would bounce our heads off the seats in front of us. It got our attn for sure. I'm not sure that method would fly these days but it makes me laugh still.
 
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