rough accerlating
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tjwolfie568
- Posts: 3
- Joined: Fri Mar 16, 2007 2:00 pm
- Car: 1984 nissan 720 pickup
- Contact:
rough accerlating
it idles ok but when you push down it sputters and tries to die i have read this forum it is a 84 720 with i think a z20. I haven't been able to find a tag on the motor it just had a tune up, new plugs (all8) cap n rotor wires new fuel filter. I am wondering if it could be the fuel pump failing I know my carb is not in good shape I just bought the truck a few weeks ago and was running pretty good I regapped the plugs and went on a test drive ran great till i got home it started to act like it was starving for gas they had the gap wrong from the place i bought it . It does or did blow alot of carbon out, it idles just fine. I was told it could be a vacuum leak (checked couldn't find one ) but when I remove one of the air tubes that go to the air cleaner (air input to carb and/or from manifold ) it wont stay running any ideas and anyplace to get a stock carb I have one more emissions test and according to state law i have to have all emissions working soI can not put on a weber carb like iI want to do for at least a year i cant find any numbers on carb but i think it is a Hitachi. Thanks in advance sorry if this is to long i am a newb here
Re: rough accerlating (tjwolfie568)
Welcome to NICO! There are so few 720 owners out there and it's too bad because it really is a good truck. If you have 8 spark plugs then the engine is the NAPZ Series engine but it could be either the 2.0 or 2.4L
(EASY ITEMS)1) If you have any spark plug wires in the wrong order this will also cause your problem. It will idle fine, because the second bank of spark plugs spark can mask the problem. Just for fun when I had my 720, I tried running the engine on the each bank separately. The engine actually ran....but no very well. I do recall when I did my plugs and wires for the first time that I got 2 wires reversed and I had the coils reversed too. When that happened the engine would revv up to 2000rpm and that was it.
2) This may sound silly but have you changed both fuel filters? My 1985 720 4x4 had one at the tank and another under the hood. There is also a permanent granular copper filter located where the main fuel line connects to the carb (A little Carb Claner can be used to clean this item). Dirty filters will let your engine idle but prevent the fuel pump from pulling enough volume to run the engine past 1500-2000 rpm.
3) The NAPZ will always run terrible if there are small vacuum leaks and will sometimes shut down when you open more than one vacuum line. That's normal. ( This may not be your issue )
More difficult items:1) The other thing that can happen is the accelerator pump, a small rubber diaphragm that spits a little extra fuel into the carb when you hit the accelerator pedal, can become brittle and develop tears or holes.
2) If you suspect a fuel pump you can do a flow test to find out if it is functioning right. (You need to disconnect both coil wires and tape them over so the engine can't start and so there are no sparks to ignite fuel vapours. Pull the fuel line from the carb and let it flow into a clean glass bottle or jar with some measured increments on it. You turn the engine over 5-10 times and check to see how much fuel is in the jar at the end. The mechanical fuel pump should give a certain amount of fuel each time it pumps. ( I think it should spit 1/2 ounce each time but it's been 10 years since I read about this so I am not 100% sure on the volume amount.)
Keep us posted as I would like to know what you discover.
(EASY ITEMS)1) If you have any spark plug wires in the wrong order this will also cause your problem. It will idle fine, because the second bank of spark plugs spark can mask the problem. Just for fun when I had my 720, I tried running the engine on the each bank separately. The engine actually ran....but no very well. I do recall when I did my plugs and wires for the first time that I got 2 wires reversed and I had the coils reversed too. When that happened the engine would revv up to 2000rpm and that was it.
2) This may sound silly but have you changed both fuel filters? My 1985 720 4x4 had one at the tank and another under the hood. There is also a permanent granular copper filter located where the main fuel line connects to the carb (A little Carb Claner can be used to clean this item). Dirty filters will let your engine idle but prevent the fuel pump from pulling enough volume to run the engine past 1500-2000 rpm.
3) The NAPZ will always run terrible if there are small vacuum leaks and will sometimes shut down when you open more than one vacuum line. That's normal. ( This may not be your issue )
More difficult items:1) The other thing that can happen is the accelerator pump, a small rubber diaphragm that spits a little extra fuel into the carb when you hit the accelerator pedal, can become brittle and develop tears or holes.
2) If you suspect a fuel pump you can do a flow test to find out if it is functioning right. (You need to disconnect both coil wires and tape them over so the engine can't start and so there are no sparks to ignite fuel vapours. Pull the fuel line from the carb and let it flow into a clean glass bottle or jar with some measured increments on it. You turn the engine over 5-10 times and check to see how much fuel is in the jar at the end. The mechanical fuel pump should give a certain amount of fuel each time it pumps. ( I think it should spit 1/2 ounce each time but it's been 10 years since I read about this so I am not 100% sure on the volume amount.)
Keep us posted as I would like to know what you discover.
Re: rough accerlating (Big-Bird)
I also googled Datsun 720 Fuel systems and found this post about bad idle.
100% PIRATED POST!!
I suspect that the carb is gummed up. You may need to clean the carb and check any adjustments that can be made to the carb. Of course, you could just convert to a Weber DGV carb and gain so much over the stock Hitachi carb. There are also sidedraft Weber carb manifolds of the Nissan L4.
Anyway, as suggested above by dimefury the gas could be bad and you should drain out all the old gas. I think there should be a drain plug in the bottom of the gas tank, but you can also use a small electric fuel pump and come vinal hose. Stick the hose down the gas filler and connect the pump to 12v. That is how I do it.
OK, after you drain out the gas, put in something like BG 44K or 2 or 3 bottles of any fuel system cleaner and then put some good gas (you do not need anything above regular low octane gas, premium would be a waste in the standard low compression L20B engine).NOW, run the car at idle (or in your case just keep it alive) for about 30 min or a little longer. Then stop the truck and leave it for about 18-24 hours. After that, see if it is any better. Even if it is not, drive it around for the day and it may start doing better.
No mater if it is better or not, you should take it to high RPM on the highway and do a "Ferrari tune-up" for a few miles. Don't redline it, but keep the RPMs high. This will help to blow out carbon that has built up in the engine.
Once you have done all of this, and if it is still not right, you may need to rebuild/replace the carb.
100% PIRATED POST!!
I suspect that the carb is gummed up. You may need to clean the carb and check any adjustments that can be made to the carb. Of course, you could just convert to a Weber DGV carb and gain so much over the stock Hitachi carb. There are also sidedraft Weber carb manifolds of the Nissan L4.
Anyway, as suggested above by dimefury the gas could be bad and you should drain out all the old gas. I think there should be a drain plug in the bottom of the gas tank, but you can also use a small electric fuel pump and come vinal hose. Stick the hose down the gas filler and connect the pump to 12v. That is how I do it.
OK, after you drain out the gas, put in something like BG 44K or 2 or 3 bottles of any fuel system cleaner and then put some good gas (you do not need anything above regular low octane gas, premium would be a waste in the standard low compression L20B engine).NOW, run the car at idle (or in your case just keep it alive) for about 30 min or a little longer. Then stop the truck and leave it for about 18-24 hours. After that, see if it is any better. Even if it is not, drive it around for the day and it may start doing better.
No mater if it is better or not, you should take it to high RPM on the highway and do a "Ferrari tune-up" for a few miles. Don't redline it, but keep the RPMs high. This will help to blow out carbon that has built up in the engine.
Once you have done all of this, and if it is still not right, you may need to rebuild/replace the carb.
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tjwolfie568
- Posts: 3
- Joined: Fri Mar 16, 2007 2:00 pm
- Car: 1984 nissan 720 pickup
- Contact:
Re: rough accerlating (tjwolfie568)
well i found out i have a few vacuum lines plugged up so i wd 40 them and next pay day i am going to replace all vacuum lines also noticed there is a few parts missing on the carb or maybe suppose to be like that i do have the z20 found the engine tag i regapped the plugs checked the coils i did 2 test drives today first one it surged like a roller coaster not as bad though i was able to drive it the second one backfired once and seemed to blow something out and drove nice a little hesitation then seemd to clear it self out not sure what i did but suspect it has to do with the vacuum lines i have one filter by the pump and the carb has one filter cant get that one off to clean 2 lines was gummed up it seems ok now took almost a week to work on the thing i love this lil truck i post a pic soon on what it looks like after some additions i added to it when it tried to stall the first post i made it sounded like it was gasping u could hear air being sucked very loudly so i may have a gummed up carb it has been sitting along time before i got it i keep posted on what i have done and problems i run into on another post topic thanks for the help i want a weber but i am afraid it wont pass the last emissions test it has left but after i get done it pretty much going to be all new or rebuilt on the top end ,carb, egr ,ect also i am going to a junkyard to get a carb to rebuild i never done before so i going to learn now lol so if i screw up wont be a big deal i got to learn some how thanks again big bird alot of good advice i keep posted on whats what with this little 720
Re: rough accerlating (tjwolfie568)
That last post needs some punctuation. It's almost impossible to read.
But I'm glad that you made some headway to fix your problems.
Good on ya mate!
But I'm glad that you made some headway to fix your problems.
Good on ya mate!
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tjwolfie568
- Posts: 3
- Joined: Fri Mar 16, 2007 2:00 pm
- Car: 1984 nissan 720 pickup
- Contact:
Re: rough accerlating (tjwolfie568)
sorry about that i have a bad habit of bad writing lol well it ran great for awhile then started doing it again but not as bad . i noticed though at the fuel pump and the filter it looked like was blowing bubbles (in the filter) i am pretty sure i nailed it down to either the bad carb or weak fuel pump, is there any fuel pumps that are compatible the only one i seemed to find is one that looks nothing like what i have in there and is way costly around $125. could i put a generic one in it? i did that with one of my old cars awhile back and no problems with it . or is there a relay that goes to it that might be bad ? by the way i just love these smiley's lol
Re: rough accerlating (tjwolfie568)
Fuel pumps are mechanical and need to fit on the engine in order to function.
Your fuel pump runs off an eccentric cam on the cam shaft. ( thats why it's attached to the side of the head.
You might be able to locate a fuel pump from another Nissan/Datsun with the same engine, but as far as I know the pumps were not used on other manufactured vehicles.
Your fuel pump runs off an eccentric cam on the cam shaft. ( thats why it's attached to the side of the head.
You might be able to locate a fuel pump from another Nissan/Datsun with the same engine, but as far as I know the pumps were not used on other manufactured vehicles.