TxTechZ Posted February 5, 2009 Share Posted February 5, 2009 Here is my situation. I recently purchased a 77 280z that had been sitting for a few years. I have read and search on this site and solved numerous problems on the car, but here we are with a problem that has got me stumped. I have replaced/repaired the following that pertains to the fuel system: Injectors Injector connectors fuel filter removed fuel rail and cleaned and replaced all flex lines new fuel pump with new flex lines from tank all the old gas drained out and replaced (full) fuel lines blown out from fuel pump to fuel filter Here is the problem I am having. If the car sits overnight I can start the car and have around 34psi of fuel pressure. This continues for 3-5 minutes when the fuel pressure starts to drop until the car dies, of course. So, I am thinking there is possibly something broke loose in the tank and has partially clogged the fuel pump. I pulled the fuel pump and it was clear on the intake side?? Next, I placed a clear fuel filter inline just after it leaves the tank so I could see if any debris was coming from the tank, none so far. Here is the interesting part. Once I get enough fuel to prime the pump, and pressurize the lines to 34psi and start the car I can see that there is air coming from the tank into the fuel filter. This large amount of air causes the pump to cavitate and loose pressure. I have tried to lightly pressurize the gas tank to evacuate the air from the fuel line (since it has to go over the frame rail) but when I watch the see thru filter I see large amounts of air going into the filter instead of fuel being pushed thru the lines. How is this possible? Is the fuel pickup line possibly jacked up inside the tank? I have blown compressed air back thru the pickup line into the tank and it does appear to have blockage as gas spewed out of the gas cap. Should there be fuel coming out a pretty descent rate once the air is evacutated from the line going over the frame rail? Any help or suggestions would be greatly appreciated! If I pull the tank will I be able to see the pickup line going into the tank? As far as I can tell the car has not had any damage to the rear, to suppect that tank has been modified. Sorry for the numerous questions... I do own the Haynes manual and Clymer manuals, and read the EFI Bilble numerous times (awesome info there). This site has answered many questions without having to post my own, thanks. Quote Link to comment Share on other sites More sharing options...
FlatBlack Posted February 5, 2009 Share Posted February 5, 2009 How are you pressurizing the tank? I believe it is supposed to be vented, not pressurized. From the FSM: http://www.atlanticz.ca/zclub/techtips/explodedviews/280z/77fsm/fuel%20tank.gif Quote Link to comment Share on other sites More sharing options...
TxTechZ Posted February 5, 2009 Author Share Posted February 5, 2009 How are you pressurizing the tank? I believe it is supposed to be vented, not pressurized. From the FSM: http://www.atlanticz.ca/zclub/techtips/explodedviews/280z/77fsm/fuel%20tank.gif What I did was disconnect the fuel line from the inlet of the pump and place it in a fuel can then I placed a rag over the fuel inlet (gas cap) and pumped air from my compressor. I can visibly see air bubbling in the see thru fuel filter I installed after the fuel tank outlet for the fuel pump. I just messed with it some more and can visibly see air coming from the tank outlet into the seethru filter. With the tank full there should not be any air making its way to the tank outlet/pickup if it is on the bottom of the tank, correct? I guess my next move is to remove the tank and see what is up with the pickup line inside the tank. The way it is acting leads me to believe that it is somewhere near the top of the fuel level, since it is getting a mixture of fuel and air.... Quote Link to comment Share on other sites More sharing options...
woldson Posted February 6, 2009 Share Posted February 6, 2009 Sounds to me like you have some kind of crack or break or loose connection on suction side. This of couse would allow air to be sucked up as well as fuel. How full is the tank? Quote Link to comment Share on other sites More sharing options...
TxTechZ Posted February 6, 2009 Author Share Posted February 6, 2009 Tank is completely full, to the point where you can see fuel in the filler neck. There are no leaks what so ever. I will be pulling the tank to take a look inside, and find out what the heck is going on. Quote Link to comment Share on other sites More sharing options...
dirtbiker245 Posted February 6, 2009 Share Posted February 6, 2009 im actually experiencing almost the same problem right now! Ive got a 70 240 with a 280 turbo motor in it. The pump keeps somehow getting air. Then I hear it cavitating and then the pump dies on me... :-/ Ive been through two pumps before I realized this is what was going on. after seeing one person suggest it could be a crack in the line that under pressure is letting air in, im gonna just go get a completely new tank to pump line. Good luck with correcting your problem... i'll keep you updated on mine too and let you know if I get it fixed. Dont worry, you arent the only person to ever experience this! Quote Link to comment Share on other sites More sharing options...
TxTechZ Posted February 6, 2009 Author Share Posted February 6, 2009 Dirtbiker, I will explore that idea.....there is only 1/2" not covered in fuel hose but that is an idea worth exploring prior to dropping the tank. I'll let you know. Quote Link to comment Share on other sites More sharing options...
TxTechZ Posted February 6, 2009 Author Share Posted February 6, 2009 I just pulled the fuel sender out to inspect the pickup lines. I cant see the end of the pickup line but it is running uphill inside the tank??? The return line is running downhill towards the bottom of the tank. After further inspection it looks like the pickup line has been repaired possibly from the different looking welds on the outside fitting. I will drop the tank and get a better look at the situation and maybe this will help someone else out. Quote Link to comment Share on other sites More sharing options...
TxTechZ Posted February 7, 2009 Author Share Posted February 7, 2009 Update....dropped the tank and it was full of rust and debris! I think it was deep enough(1/4" to 1/2") to cover the inlets on the bottom of the intake cylindrical baffle(what ever its official name is ??) That possibly could cause the cylinder to drain down low enough, regardless of the tanks fuel level, for the fuel to create a vortex effect and cause the intake to suck in air, thus cavitation and loss of fuel pressure. Secondly, the fuel outlet line was partially blocked by something.... I was able to clear the line with compressed air and high pressure water after numerous attempts. The fuel line now flows 10x's better and obviously is unrestricted. After getting it boiled out on Monday, we will see is it solves the air in the fuel line issue. I think it will, but time will tell. Quote Link to comment Share on other sites More sharing options...
woldson Posted February 7, 2009 Share Posted February 7, 2009 Can you somehow pressure check those welds before it gose back in? Ya know, since it's out and such... Give her a bj. Quote Link to comment Share on other sites More sharing options...
TxTechZ Posted February 7, 2009 Author Share Posted February 7, 2009 I'll make sure they pressure test/leak test and possibly flow test the outlet tube when its at the shop. Quote Link to comment Share on other sites More sharing options...
jgautosport Posted February 8, 2009 Share Posted February 8, 2009 I've never had a starvation problem but now that I've read this you got me thinking. My see thru filter in between my tank and pump does not have a Steady flow. It looks like air is just juggling through. My fuel pressures are off but I just thought it was my gauge on my rail. Im interested to see what you find with this. I did the same thing though. Blew out my lines added a walbro and changed my filters, added a adjustablee FPR and I still dont get a steady flow when I look at the see thru filter. Quote Link to comment Share on other sites More sharing options...
TxTechZ Posted February 19, 2009 Author Share Posted February 19, 2009 Got the tank back and installed. It works like a champ, the fuel starvation problem is gone! We are now on the road. I did have to clean it out with concrete etcher to get the last of the rust out. That was real easy to do, I highly recommend doing that part yourself. Put on the rubber gloves and mask and get to shakin'!!! Quote Link to comment Share on other sites More sharing options...
woldson Posted February 20, 2009 Share Posted February 20, 2009 Did they find a problem? Congrats by the waY! Quote Link to comment Share on other sites More sharing options...
TxTechZ Posted February 22, 2009 Author Share Posted February 22, 2009 I was able to remove the blockage prior to having it boiled out. It was not easy, something you want to do with the tank dropped(combination of compressed air and high pressure water). The shop I took it to did not find any problems with the tank after cleaning it. They said they pressure tested it and flow checked the lines?!? I think the sending line had been clogged due to the pump suction and it just took time to dislodging what ever was in there. I would recommend removing all of the rubber padding from the tank prior to having it cleaned. I really didn't consider all of the rubber pads coming off, but I did loose one. Just FYI. Quote Link to comment Share on other sites More sharing options...
woldson Posted February 22, 2009 Share Posted February 22, 2009 Great, thanks:) Quote Link to comment Share on other sites More sharing options...
bmarchuk Posted March 5, 2009 Share Posted March 5, 2009 Does your clear filter still have air inside it? Mine has and I thought it was normal, since the in and out hoses are smaller than the filter diameter.. Unlesss it was filled prior to installation of course. Quote Link to comment Share on other sites More sharing options...
TxTechZ Posted March 6, 2009 Author Share Posted March 6, 2009 I will check on that. I am on duty now, but I will let you know tonight. Quote Link to comment Share on other sites More sharing options...
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