warrenHLS3083301 Posted August 6, 2009 Share Posted August 6, 2009 I recently bought a 81zxt that had been sitting for about seven years, it would start but it would back fire and run poorly, so I did the usual and changed the oil, spark plugs, fuel filter, drained and inspected the gas tank, new fuel. so now it runs like a champ until you put it in drive, then it revs to about 2000 rpm bogs down and backfires until you let off the throttle, the longer you drive it the worse it gets, this leads me to believe that it is the alternator but when i tested it (in neutral) it stays at 12 volts at idle and goes up to 13.5 when you rev it. Could it be the fpr? When i unplug the vacuum line on the fpr it still revs fine in neutral. any help or suggestion would be much appreciated. I got to get this thing running, summer is almost over. Quote Link to comment Share on other sites More sharing options...
warrenHLS3083301 Posted August 7, 2009 Author Share Posted August 7, 2009 bump? Quote Link to comment Share on other sites More sharing options...
randy 77zt Posted August 8, 2009 Share Posted August 8, 2009 youcan tee in a fuel pressure gauge before the fpr and test it.its standard bosch specs-around 32 psi idle-it will climb with boost.if it sat for seven years it probably has plugged injectors-the gas back in those days did not have all the injector cleaner it has now.car will never make full power with clean injectors.while you are it solder on new injector plugs.i have the original oem nissan book for that somewhere.i finally gave up and went to megasquirt. Quote Link to comment Share on other sites More sharing options...
e_racer1999 Posted August 8, 2009 Share Posted August 8, 2009 Did you check the timing> Quote Link to comment Share on other sites More sharing options...
warrenHLS3083301 Posted August 8, 2009 Author Share Posted August 8, 2009 (edited) ok, so I hocked up a fuel pressure gauge after the fuel filter and the pressure is about 28 at idle and it maxes out at 38( this is in neutral), when i unplug the fpr the pressure goes up to 40, when the engine bogs down and stars backfiring the pressure droppes down to 20, just for kicks i swapped a na fpr and no difference. Now my QUESTION is, could i be getting low fuel pressure from a bad fuel pump (stock fuel pump and it makes a lot of noise, even at idle), or could the pump be putting out low pressure because of a low output alternator( 12 volts at idle and goes up to 13.5 when i rev the engine), also the battery light on my gauge cluster is on ( probably a bad ground or a lose wire). I suppose that the return fuel line could be plugged but would that only cause a problem when the engine is under load? and would'nt i have higher fuel pressure?. I have a spare alt but for now i think the signs are pointing to the fuel pump. So what is the best fuel pump to buy? I would like something quiet, durable and able to support my goal of around 250 hp, maybe I should just get a cheap used one just for trouble shooting. I will try to make a video and put it on you tube probably by sat night, if I can figure out how. I don't think it is the timing because the engine will rev to 6000, the turbo will start to spool at 3000 and it sounds great, in neutral, but as soon as you try to drive it it begins to bog down and backfire, and like is said the longer you drive it the worse it gets, mabe the fuel pump is getting hot and I'm loosing pressure. I always thought that when fuel pumps went bad that they quit all together. Edited August 8, 2009 by warrenHLS3083301 spell Quote Link to comment Share on other sites More sharing options...
warrenHLS3083301 Posted August 10, 2009 Author Share Posted August 10, 2009 well today I swapped a spare alternator that I had sitting around, the voltage at idle went up from 12 to 14 so it definitely needed changing but the main problem persists, the fuel pump is still making a lot of noise (even at idle) and the power drops off at 3000 rpm and then it starts backfiring, so I had it sitting in the driveway idling for about 10 minutes when the fuel pump quit all together, I guess I know what I will be replacing next. Quote Link to comment Share on other sites More sharing options...
sweetleaf Posted August 10, 2009 Share Posted August 10, 2009 If the Fuel pressure is dropping down to 20 or so. I would say you either still have some crap in the lines or tank. Or it could be your fuel pump going out. Quote Link to comment Share on other sites More sharing options...
warrenHLS3083301 Posted August 11, 2009 Author Share Posted August 11, 2009 most likely it is the pump, it is 28 years old. It could also be the strainer on the end of the fuel sending unit, I did clean it before i put it back in, but I think I will take it out all together and see if it makes a difference. When I crimp the return line the fuel pressure jumps to 80 psi ,so why would it drop so much when the engine is under load? it must be a blockage in the fuel line somewhere, if it is what can I use to flush the line? a fuel line enima so to speak, turpentine, acetone, kerosene, or do I just put my lips together and blow? Quote Link to comment Share on other sites More sharing options...
randy 77zt Posted August 12, 2009 Share Posted August 12, 2009 there is a strainer in the tank.you can check this buy connectin a piece of fuel line to the pump and dropping it in a gallon can of gas.run fuel pressure test again-if it stays at spec you need to work on the gas tank.you can have it boiled out and coated inside.basically your fuel pump might be pulling vacuem on the supply side Quote Link to comment Share on other sites More sharing options...
naviathan Posted August 13, 2009 Share Posted August 13, 2009 Try the test with the fuel cap removed. That will eliminate any vacuum problems with the tank causing the issue. If the issue goes away look at the vapor canister and related lines all the way to the tank. When you remove gas from the tank with the pump, you need to displace that fuel with air in the tank. If the vapor lines are clogged you create a vacuum and the pump can't pull fuel. These pumps don't draw much, they're intended for gravity feed almost like a pressure booster for your plumbing. Quote Link to comment Share on other sites More sharing options...
warrenHLS3083301 Posted August 26, 2009 Author Share Posted August 26, 2009 well, time for an update. I took the fuel sending unit out of the tank and the filter/strainer looks clean, but I decided to take it out of the equation, and when I removed it I found a blockage of black amber like varnish, could this have been the problem? I proceeded to flush out the pick up tube with acetone and when I was satisfied it was clean I put everything back together, now time for a midnight test drive. It runs a lot better than before, it used to sputter and backfire at 2500-3000 rpm and now at 4000 rpm, so thinking there must be another blockage in the fuel lines I took it to a local shop and had them flush out the fuel lines, and it runs a little smoother but still not getting full power. !@#$ I want my 150$ back. The longer I drive the worse it gets maybe the fuel pump is heating up and is not supplying the fuel needed, is there a fuel pump relay that could be bad? has anyone had this kind of fuel pump problem before? Quote Link to comment Share on other sites More sharing options...
warrenHLS3083301 Posted August 28, 2009 Author Share Posted August 28, 2009 success, I found the problem. took the fuel pump out today and decided to take it apart to see if it was worn out, the metal collar looked good, everything inside looked clean and new, not bad for a 28 year old pump, then I looked through the inlet hole only to find a screen/filter almost completely plugged with rust and gunk, after removing the filter and reinstalling the pump the car runs great. Quote Link to comment Share on other sites More sharing options...
woldson Posted August 29, 2009 Share Posted August 29, 2009 Ummm, why did you just not clean the filter? Your pump may not look so good in the future. Quote Link to comment Share on other sites More sharing options...
warrenHLS3083301 Posted August 29, 2009 Author Share Posted August 29, 2009 Ummm, why did you just not clean the filter? Your pump may not look so good in the future. the filter was too hard to remove in one piece, and I don't think it is necessary as there is a filter in the tank and one in the engine bay, and besides I want to upgrade to an aeromotive in the future. When I say it was too hard to remove I mean that after working night shift and being awake for more than 24hrs I poked a hole in the filter with a screwdriver, oups Quote Link to comment Share on other sites More sharing options...
woldson Posted August 30, 2009 Share Posted August 30, 2009 Teehee, got it;) Quote Link to comment Share on other sites More sharing options...
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