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Zed running like a dog


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#1 Mick280zx

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Posted 01 June 2009 - 04:07 PM

Hey guys I hope some of you may be able to help me with my zedx

My 280zx (stocko everything) hasn't been driven that much and hasn't been registered for the last 5 or so years. It runs but runs pretty rough. It stumbles, hesitates and pops and backfires on acceleration, particularly at low speed after having turned corners for example. It accelerates hard at high speeds in the upper rev range and seems to have enough power, but down low is a dog.

I've replaced the fuel filter, spark plugs, checked the resistance of the injectors and high tension leads and looked at the dizzy cap. The fuel pump was replaced not so long ago according to the previous owner. I've run injector cleaner through it as well. It has valvetrain noise even though a mechanic mate I took it to 'checked the valve clearances'.

Just wondering if you guys had any theories from past experiences. I have the factory service manual and I'm slowly accumulating all the tools but I need the advice of other zed freaks to point me in the right direction. Cheers.

#2 Zedman240®

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Posted 01 June 2009 - 06:38 PM

Just wondering does it blow a lot of black smoke? I've heard the cold start injector tend to stick open and make them run like crap. Its located near the throttle body. Give that a check..

#3 Zedback

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Posted 01 June 2009 - 06:53 PM

There is a whole series of checks to run listed in the FSM which are tedious but necessary to step through.  They cover all the sensors and wiring, some are performed directly on the component, many from the ECU plug, you just need an ohm meter. 

There is also a mesh filter on the pickup inside the tank which can get gummed up resulting in poor fuel flow. 


#4 Zeddophile

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Posted 01 June 2009 - 08:15 PM

My guess is someone has fiddled with the adjustment on the airflow metre at some stage, but follow Zedbacks suggestion first, as it ensures that everything else in the system is working fine.

A quick check for the tweaked AFM would be (assuming it idles rough as well as not pulling from low down): Pull the intake tube off the front of the airflow metre, and try closing, then opening the flap a little and see if the idle smoothes out. If you can't close the flap that way, carefully take the black plastic cover off the metre and gently push the needle a little to one side or the other, and listen for the idle to smooth out.  To me it sounds like its running rich, which allows it to go hard up high in the revs, but it will chug and carry on down low.

#5 RBZ 260

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Posted 01 June 2009 - 08:47 PM

if its been sitting for a while ill prob guess what zedback said about gunking of the mesh filter.

also if the fuel is old could make it run crap.

other than that sticky or half cloged injectors could also make it run crap. instead of atomising nicely it could just be spitting and dripping.

possibly sticking injectors due to sitting for long time that what i be doing.

a cheap alternative to try and restore them is to stick them in the ultrasonic cleaner for few minutes hopefully cleaning the crap out. idealy would be good to clean when its off and than turn it on while open to clean the inside. ie hooking it up to 12V supply.better even have it pulsing.


i did a set of falcon ones it was spitting and splutering on efi. dual fuel car. anyway new seal kit from repcoo and few minutes with ulstrasonic the injectors were like new.

so just a tip.

#6 Zedback

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Posted 01 June 2009 - 09:11 PM

Has replacing the filter been a waste of time if I haven't cleaned out the tank yet?

None of it is a waste of time because if you're not doing it now you'll be doing it later anyway!  ;D

I'm with Zeddophile in thinking it's running too rich.  I would start with checking out the coolant temp and air temp sensors, and cleaning the contacts as well as possible.  How old/crappy is the air filter?

Best of luck!

#7 Zedback

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Posted 02 June 2009 - 08:47 PM

Sensors might be ok, just the connections that are shot.

Check the condition of the spark plugs, black and sooty -> running rich.  You might not see the black smoke unless it is REALY bad.  Other's with more experience might chime in here...

For me, Nissan have been pretty good for parts and US eBay for anything else.

#8 Zedback

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Posted 02 June 2009 - 09:15 PM

I've seen new connectors and tails on US eBay but I would imagine an auto electrical parts specialist would have them as well, just haven't gone looking. 
Have walked into nissan parts and had no trouble getting speedo gear for gearbox and clutch throwout bearing.  Can't remember what else, but would only have been mechanical bits.

#9 Zeddophile

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Posted 14 June 2009 - 12:07 PM

I've tried banging it (lightly) pulling on it, levering it and talking to it but it isn't coming out. Short of heat ( :o) or some miracle chemical gasket killer I've got no option but to remove the whole tank so I can get a better angle on my old screwdriver to pry the bugger off! While I'm at it I'm going to replenish all the hoses etc.


There's your problem, you see - you were talking to it, not swearing and threatening it with physical violence!  Seriously through (never looked under a 280zx), can you get a razor blade in between the tank and the sender and cut through the gasket goo?  Even if you can only do it on one side, it should loosen it up enough to be able to lever it off.... 

Although some gasket sealants are pretty strong, genuine Land Rover sump sealant sticks so well you have to hammer steel wedges in between the sump and block all the way round, and bend the sump to get the bloody thing off.  Then you get to spend an hour panel beating it back into shape  ::)  I think my Rangie sump is leaking at the back too, and guess what I used to put it on....

#10 Mick280zx

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Posted 20 June 2009 - 07:30 AM

Unfortunately there's no room to get under the sucker with a razor or anything else without taking the tank off. I think I'm just going to leave the darn thing alone before I end up with a full-on rebuild on my hands! It's starting to get to the point of diminishing returns this darn car.  :-[

#11 pauly_adams

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Posted 03 July 2009 - 06:17 PM

ok i bit the bullet yesterday and bought micks 280zx i have norrowed it down to fuel. all sensors are working but fuel pressure is low, the presure is not even as high as my 260z fuel pump. when i got the car it drove 120km with no problem like mick explained to me it was burbly down low untill you hit 3000 rpm or put your foot into it then it drove like a dream no lack of power or anything  but when i got home it started playing up and had no power and when you hit the accelerator it just died i thought i may have ran out of fuel due to a dodgy fuel gauge so i went to the fuel station and got more fuel put it in and still the same thing. so this afternoon i put some fuel in the air cleaner and sure enough started strait away ran fine no lack of power down low or anthing, well till the fuel in the filter ran out. so heres my question could this be the sighn of the fuel pump breaking down or is it more likely the strainer in the tank is blocked.


cheers pauly


#12 Zeddophile

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Posted 03 July 2009 - 07:31 PM

Few things to check for low fuel pressure:

Is the fuel pressure regulator stuck open?  Take the return hose off and run the fuel pump, if you have low pressure and the fuel is pouring out of the reg, its stuck open (i'm assuming you have a fuel pressure gauge?)

If ok, can you borrow a fuel pump off a mate with a VL commodore?  Should fit straight in, and see if it runs alright with that.

The last one, which is pretty likely due to the fact that it ran pretty well to start with and progressively got worse is indeed the strainer - picks up the crap from the bottom of the tank, and slowly clogs itself up.  Usually when this happens, over a period of hours the crud all drops off the strainer, and then when you restart it, car will run fine until the suction of the pump drags it all back up into the strainer again.  Probably quickest and easiest way to try this theory is when its running crap, turn off and remove the fuel cap.  Then remove the feed hose from the fuel pump (at pump) and blast compressed air through it back into the tank to clear the strainer.  Reconnect the hose, and see if it runs ok.  If it does, enjoy getting that fuel tank out for a look see.

I haven't mentioned fuel filter as Mick said he's replaced that, however this could provide useful info.  If you can pull the filter off without letting ALL the fuel out of it (especially at the inlet end, make sure it doesn't come out there at all, not so much an issue if you lose it from the other end, but some fuel needs to stay in it), try this test: Get a clean glass jar (or similar), and tip the contents of the filter into it from the INLET end.  Blow on the outlet end as well, to force the fuel out quickly.  What this does is cause the fuel to drag the contents of the filter back out into the jar, and if you end up with a jar full of fuel with brown crap floating around in it, you know you've got crap in the tank (the finer pieces of which is making its way through the strainer and fuel pump).

#13 pauly_adams

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Posted 03 July 2009 - 09:31 PM

my brother came up with an idea that should be able to tell me which one is the problem. he said get a glass jar etc fill with petrol and get the inlet from the pump and put it into the jar if its not the pump there should be a blast of fuel again and if it is the pump it will do the same thing as it is now. also does anyone else know what voltage the pump should hae as i metered it and there was only 11v which seems ok but i thought it should be 12v.


cheers pauly

#14 Zeddophile

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Posted 03 July 2009 - 10:58 PM

The problem with that test is that the jar will run out very quickly, and you do NOT want to run an EFI pump with no fuel in it.  The remaining vapour can be set off by the arcing of the brushes inside the pump, and it can go off like a shrapnel grenade.  Remember with an EFI system, a majority of the fuel being pumped is not actually injected into the engine, but returns to the fuel tank.  I'd suggest if you are doing this, put the return from the fuel rail back into the container as well, and use a litre or more container.  If you can't feed the return back into the container, use a jerrycan with 5 or so litres in it.  A bosch 070 (generic replacement pump which will have the same specs as yours, used for alfas/commodores/anything with an L-jetronic that uses that style of pump) will flow 2.25 litres per minute at 3 bar.  If you are using a half litre jar, you get less than 15 seconds testing - and that includes fuel pumped while cranking.

And 11 volts should be fine for running the pump.  Its capable of running probably twice the pressure of an L28 fuel reg, so its not stressed at all to put out the 2.5 bar required.  If you were running a really high fuel system pressure, yes you'd probably need the voltage to be higher to keep consistent pressure, but in this case I'd be surprised if its the problem.

#15 Scoota G

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Posted 03 July 2009 - 11:05 PM

Have you done a psi / compression check on all cylinders?

#16 pauly_adams

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Posted 04 July 2009 - 01:41 PM

compression seems fine on all cylenders its just the pump has no flow to it. the presure looks like its getting up there but as soon as the car cranks all over so today im going to clean out the filter in the tank.

cheers pauly

#17 kalium

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Posted 04 July 2009 - 08:04 PM

My guess is someone has fiddled with the adjustment on the airflow metre at some stage, but follow Zedbacks suggestion first, as it ensures that everything else in the system is working fine.


You adjust the Lean/Rich mix on the AFM by the screw yes? I think mine is out (mainly because I was playing with it without knowing what I was doing...). Is there a sure fire way to get this back to where it should be? It chugs and backfires downlow but then pulls up top.

Cheers

#18 Mick280zx

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Posted 04 July 2009 - 08:08 PM

Be interested to know how you went getting that bloody fuel sender out Pauly

#19 Mick280zx

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Posted 04 July 2009 - 08:15 PM



I haven't mentioned fuel filter as Mick said he's replaced that, however this could provide useful info.  If you can pull the filter off without letting ALL the fuel out of it (especially at the inlet end, make sure it doesn't come out there at all, not so much an issue if you lose it from the other end, but some fuel needs to stay in it), try this test: Get a clean glass jar (or similar), and tip the contents of the filter into it from the INLET end.  Blow on the outlet end as well, to force the fuel out quickly.  What this does is cause the fuel to drag the contents of the filter back out into the jar, and if you end up with a jar full of fuel with brown crap floating around in it, you know you've got crap in the tank (the finer pieces of which is making its way through the strainer and fuel pump).


I did this procedure with the old filter (which funnily enough was still a JECS filter  :o) and yes it contained brownish fluid but not much in the way of particles.  I dismissed the colour of the fuel due to the fact I'd added lots of injector cleaner... which itself was dark red!

#20 pauly_adams

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Posted 04 July 2009 - 08:23 PM

ok got the fuel sender out and like mick said it was a real nightmare had to use a prybar a ball pien hammer and a old sealt belt i will wright up how i removed it later. now for the good part, i checked the screen filter and it was quite clean i did still clean it though also found out why the fuel gauge wasnt working the fuel float had had a hole so i done a patch job and works for now but will be needing a new one. now im down to the fuel pump or some other issue eg eletrical problem (ecu or something ). i will be getting a fuel pump hopefuly tomorrow or monday although i was wondering if any of the members would know what else could cause the fuel pump to have pressure on start up and then loose presure i have cleaned the fuel lines also and put some decent conectors on the fuel pump.

any input will be appreciated so keep the posts coming.

cheers pauly





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