disepyon Posted March 18, 2012 Share Posted March 18, 2012 My problem is that my fuel tank will not fill up full when i put gas in it at the gas station. My fuel gauge is working perfectly so its not that. It always reads a little bit more than half way. Its like the station pump shuts off half way as if its reading a full tank. I just dont understand. I know the station pumps sense the air coming out of the fuel tank because the fuel being put into the tank displaces the air. Do i have to like shove the fuel handle down into the filler hose or something? Thanks, Brent Quote Link to comment Share on other sites More sharing options...
Cannonball89 Posted March 18, 2012 Share Posted March 18, 2012 It might be the vent hose on the top of the tank is clogged. If that's the case, the air can't escape once the fuel level rises above where the filler neck goes into the tank, and the gas will come up the filler neck and shut off the pump before the tank is full. Quote Link to comment Share on other sites More sharing options...
Tony D Posted March 18, 2012 Share Posted March 18, 2012 From empty on your gauge, what does the pump say you take as a fillup? My 260 won't take more than 12 gallons usually. Generally 11 unless I run to fumes. The gauges drift... And as stated, the tank side fills below centreline. If the vent lines are all plugged an air pocket can form depriving you if quite a bit of volume. Generally leaks off the top of the tank are the problem, though. Quote Link to comment Share on other sites More sharing options...
Lazeum Posted March 18, 2012 Share Posted March 18, 2012 I agree with statements above about clogged vent line. A friend of mine was having the same issue, I did a drawing at that time to show him the result. I believe it is self-explanatory Quote Link to comment Share on other sites More sharing options...
Vintage-TechZ Posted March 18, 2012 Share Posted March 18, 2012 My problem is that my fuel tank will not fill up full when i put gas in it at the gas station. My fuel gauge is working perfectly so its not that. It always reads a little bit more than half way. Its like the station pump shuts off half way as if its reading a full tank. I just dont understand. I know the station pumps sense the air coming out of the fuel tank because the fuel being put into the tank displaces the air. Do i have to like shove the fuel handle down into the filler hose or something? Thanks, Brent Brent.....couple of questions here. 1)-How long have you owned this Z ? DO you know its full history in the way of body damage repairs ? 2)- Are you trying to re-fuel with the gas nozzle at full clip/max delivery/fully compressed handle ? 3)-What is the most gallons you've dispensed in the past with this Z ? I ask #1 in case an explore of the fill neck and tank vent lines might need to be done. I ask #2 in case your car cannot accept full delivery, rather it might do better at 1/2 clip or less and then fuel fully. I ask #3 as a baseline study if we're getting anywhere . Cheers, Vinny Quote Link to comment Share on other sites More sharing options...
RebekahsZ Posted March 18, 2012 Share Posted March 18, 2012 (edited) If you enjoy driving your car, just fill 1/2 way fast, then fill the second 1/2 tank slowly, paying attention not to overflow. If you like working on your car, drop the tank, replace the lines with expensive OEM lines (that will crack a year from now anyway), spend the next 2 weeks of spring driving weather cussing, and when you have totally restored your tank, you may still have the same problem. Having worked on my tank a lot-I would just fill the second half slowly. This is a nearly universal Z-car problem - call it character. Have you done your taxes this year, try to get a fuel efficiency tax credit! Edited March 18, 2012 by RebekahsZ Quote Link to comment Share on other sites More sharing options...
Vintage-TechZ Posted March 18, 2012 Share Posted March 18, 2012 If you enjoy driving your car, just fill 1/2 way fast, then fill the second 1/2 tank slowly, paying attention not to overflow. If you like working on your car, drop the tank, replace the lines with expensive OEM lines (that will crack a year from now anyway), spend the next 2 weeks of spring driving weather cussing, and when you have totally restored your tank, you may still have the same problem. Having worked on my tank a lot-I would just fill the second half slowly. This is a nearly universal Z-car problem - call it character. Have you done your taxes this year, try to get a fuel efficiency tax credit! It could be that the fill neck abrupt angle change is preventing even the initial fill to need to be done more slowly ? Some cars just have to fill on the slow clip due to this . Often a nozzle has a liquid sensing device that is vacuum generated and will shut the nozzle flow off when liquid backs up. In this case, liquid may be backing up due to the fill neck configuration....maybe not. Is the nozzle clicking off before a fill ? Or is it just not allowing your tank to fill up at all, no matter how many times you pull the trigger ? Quote Link to comment Share on other sites More sharing options...
disepyon Posted March 18, 2012 Author Share Posted March 18, 2012 (edited) Brent.....couple of questions here. 1)-How long have you owned this Z ? DO you know its full history in the way of body damage repairs ? 2)- Are you trying to re-fuel with the gas nozzle at full clip/max delivery/fully compressed handle ? 3)-What is the most gallons you've dispensed in the past with this Z ? I ask #1 in case an explore of the fill neck and tank vent lines might need to be done. I ask #2 in case your car cannot accept full delivery, rather it might do better at 1/2 clip or less and then fuel fully. I ask #3 as a baseline study if we're getting anywhere . Cheers, Vinny Ived owned the z since october 2011. Only body history i know of is that its been repainted in the past, but i didnt see any signs of any bodyfiller which means to me that there was no place on the car that was hit hard. Frame rails are straight but bent upward because someone in the past jacked up in wrong places. The only real main damage is on the rear bumper on the driver side but its no that bad. When i refill my tank no matter what car im putting gas in, i always have it on slowest clip/speed. here is a history of the gas data for my z (yeah i know im a bit of a nerd, i like to keep track, kind of a habit being a biology major in college). 10/29/2011 Z gas 9.821 gallons at $3.379 super 11/12/2011 Z gas 12.66 gallons at $3.379 super 11/25/2011 Z gas 6.142 gallons at $3.259 Super 2/29/2012 Z gas 11.291 gallons at $3.579 super im actually missing a few data logs for the z gas. In december i pulled the motor to clean it up and change all the gaskets, why there is no report for that month. there was actually one time the gauge read full, not sure which gas day it was but might had been the 11/12. Thanks for all the help fellow z members, ill pull the tank and look at the hoses since the tank is nearly empty now. Edited March 18, 2012 by disepyon Quote Link to comment Share on other sites More sharing options...
disepyon Posted March 18, 2012 Author Share Posted March 18, 2012 From empty on your gauge, what does the pump say you take as a fillup? My 260 won't take more than 12 gallons usually. Generally 11 unless I run to fumes. The gauges drift... And as stated, the tank side fills below centreline. If the vent lines are all plugged an air pocket can form depriving you if quite a bit of volume. Generally leaks off the top of the tank are the problem, though. About average i would say the gas pump reads about 10 gallons more or less. It could be that the fill neck abrupt angle change is preventing even the initial fill to need to be done more slowly ? Some cars just have to fill on the slow clip due to this . Often a nozzle has a liquid sensing device that is vacuum generated and will shut the nozzle flow off when liquid backs up. In this case, liquid may be backing up due to the fill neck configuration....maybe not. Is the nozzle clicking off before a fill ? Or is it just not allowing your tank to fill up at all, no matter how many times you pull the trigger ? Just not allowing the tank not to fill up im assuming. It doesnt click off before i fill or shortly after. Ive never pulled the trigger again after it shuts off it self, but ill try that next time and see if it keeps shutting off. Quote Link to comment Share on other sites More sharing options...
Vintage-TechZ Posted March 18, 2012 Share Posted March 18, 2012 About average i would say the gas pump reads about 10 gallons more or less. Just not allowing the tank not to fill up im assuming. It doesnt click off before i fill or shortly after. Ive never pulled the trigger again after it shuts off it self, but ill try that next time and see if it keeps shutting off. Oh, ok...that is key note to have. Your keeping track certainly doesen't make you nerd-like. Its in fact a smart thing to note. Dummy lights are made for folks who don't even think to do that,lol. In some cases.....adding the cooler fuel slowly at first and then going abit faster after a few gallons can help. Maybe even try full clip speeds to see what happens ? On another note...can you smell fumes-(from gas) after your driving down the road following a fill-up ? Quote Link to comment Share on other sites More sharing options...
NewZed Posted March 18, 2012 Share Posted March 18, 2012 here is a history of the gas data for my z (yeah i know im a bit of a nerd, i like to keep track, kind of a habit being a biology major in college). 10/29/2011 Z gas 9.821 gallons at $3.379 super 11/12/2011 Z gas 12.66 gallons at $3.379 super 11/25/2011 Z gas 6.142 gallons at $3.259 Super 2/29/2012 Z gas 11.291 gallons at $3.579 super 11 - 12 gallons is typical for a fill on my 76 if I let the gauge get down close to E. The capacity is only 17 1/8 gallons. The fuel pickup starts sucking air on hard left turns when the gauge reads ~1/4 full so I get about 12 gallons on every fill, filling up with ~4- 5 gallons still in the tank. The needle tops out above F after a fill. The needle also drops fairly normally to 1/2, sits there for a long time, then drops rapidly. Needle position doesn't really tell much about how much gas is left in the tank. Why do you say that the gauge works perfectly? You could check how much you really have after a fill by siphoning and draining the tank dry if you wanted to know for sure. Quote Link to comment Share on other sites More sharing options...
Tony D Posted March 20, 2012 Share Posted March 20, 2012 There was a gentleman who wanted to argue the capacity of the 260Z and I ran my tank dry and filled it, and repeated. For all the vaunted 16 gallon capacity, 11-13 gallons is ALL you will ever get in there depending on how far up the neck you go, and how low you let it get while driving. If you can see fuel in the filler neck bottom, chances are you are "FULL" and if you fill like I do to get 11-12 each time (I go with 1-2 gallons in the tank usually...hell I fill based on mileage more than gas gauge from experience...) and get the level to within 2" of the top of the neck, you KNOW you should be reading 'F' on the gauge. If you're not, your gauge is drifted. Welcome to the club. Quote Link to comment Share on other sites More sharing options...
NewZed Posted March 20, 2012 Share Posted March 20, 2012 Thanks for taking away the feeling of security I used to have, riding around on E, knowing that there was still 4-5 gallons in the tank. Quote Link to comment Share on other sites More sharing options...
RebekahsZ Posted December 3, 2012 Share Posted December 3, 2012 Old topic but I still need help and at least this shows I did some searching. I recently drove my LS2/240z across 4 states and had a really aggrevating time with the fuel gauge. It was all over the place, varying like crazy. Sometimes it would say 1/4 tank, then by the time I found a station it was back up to 1/2. I can't ever seem to make the gauge say FULL. Sometimes it would say it was empty, so I'd go to get gas and I could only put a buck's worth of gas in it (at today's prices, that's about a drop). I always fill to the top of the neck about 4 inches below the cap. Next time, it would let me fill 5 bucks, then 3, then 9. The trip was great, except for the constant fear of running out of gas. I thought that I had a venting problem, but I worked today on checking it out. Went to station and filled fuel from a reading of E to 3/4, it was 4.4 gallons. To check to see if it is truly full, I used a siphon T-d into one of the vent hoses with a clamp on all the other vent hoses. I can siphon gas by hooking a siphon pump to the vent hose (which is at the very top of the tank), and the fuel only drops in the fill tube at the rate at which I'm siphoning. I then removed the siphon and hooked my mouth to the siphon hose and when I suck on the hose, the level in the fill tube drops and when I blow on the siphon hose, the level in the fill tube rises and when I stop blowing and let the tube vent, the fuel level in the fill tube drops back down and I can hear gurgling in the vent line. So: I think right now my tank is 100% full and venting properly. Damn gauge is reading 1/2 tank. I replaced my fuel sender with a brand new stock sender recently and my next step is to check the ohms on it from another thread I found. Tony D, you talk about gauge drift. What is that and can I fix it? If the sender has proper resistence, I guess the gauge is next (I hate getting under the dash!!!!!!!!!!!) Quote Link to comment Share on other sites More sharing options...
zohanisback Posted December 3, 2012 Share Posted December 3, 2012 I would check ohms at gauge if you can get to the wiring without much trouble. Check it full and then once you know it should be between 1/4 and 1/2 tank. If the ohms are within spec, you are probably looking at a new gauge. Could be a faulty sender out of the box though, too. It does happen. Either way, I don't know anything about fixing gauge drift or recalibration. If the problem happened before you replaced the sender, too, then probably not the sender, but if it got worse after replacing the sender, it could be the sender or corroded wires. Check connections on both ends, too. Corrosion increases resistance, so it can play into the measurement as well. Here are some posts that might help: http://www.classiczcars.com/forums/thread2308.html http://www.zcar.com/forum/10-70-83-tech-discussion-forum/47992-fuel-guage-calibration.html Quote Link to comment Share on other sites More sharing options...
RebekahsZ Posted December 3, 2012 Share Posted December 3, 2012 Thank you so much! I will use these links and a couple I found to check it this week and report back. Really appreciate it. Quote Link to comment Share on other sites More sharing options...
zohanisback Posted December 3, 2012 Share Posted December 3, 2012 No worries, good luck! Thinking back on it now, my gauge read 2/3 when it was full, but accurate when it was low, so I just left it, lol! Quote Link to comment Share on other sites More sharing options...
Tony D Posted December 7, 2012 Share Posted December 7, 2012 Harness gets resistance as it gets older... The response you get from the sender is MORE than 0-XXohms, it's wound closer together at one point to give more resistance for 1mm float drop than at other places (see the drawing earlier to see why)... So as resistance builds you may never get to "empty" once you are below 1/2 tank, or vice versa. If the sender wires are corroded and the wiper doesn't contact well, it will jump all over as well. Resistance anywhere can cause back feeds in the sensor loop. I had some crossed wires from the PO on my 73... For quite a ahile my gauge read ore toy...until I stepped on the brakes! Then itvslooooowly went to "Full"! Quote Link to comment Share on other sites More sharing options...
RebekahsZ Posted December 8, 2012 Share Posted December 8, 2012 This is on the list for tomorrow. Will post results from the suggestions. Quote Link to comment Share on other sites More sharing options...
Xnke Posted December 8, 2012 Share Posted December 8, 2012 My tank, including the bottom two inches of an L24 oil pan sump welded to the bottom, will hold 15 gallons if I drain the tank out and then put the plug back in. If I fill up when the gauge reads just to the bottom of the empty mark, then the pump will show 12.5 or 13 gallons; the very first time I put a full tank of gas in, the car was coming back to the house from paint on a rollback and the tank was completely dry. I had my buddy unload the car at the gas station, and he helped me roll it to the pump, we put the tank drain plug back in and the tank took 15.1 gallons. Best part is that even getting not great milage, it STILL lasts two weeks of driving to work, as opposed to my old van that I filled up the 24 gallon tank every week! Quote Link to comment Share on other sites More sharing options...
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