280zx coughs and sputters

[rollypolly_zx]

so when I first got the car last year in may it ran rich but fine. after some minor things (replacing all the vacuum lines, adjusting timing, ect. just basic maintenance and getting the car back up to par) it ran, a little rich, but really good, smooth and reliably. but starting about 2 months ago it had some minor issues with coughing or running super rich on and off for a little bit. after a while it started to cough and sputter really bad, it dumped fuel and sometimes wouldn't even idle let alone give any power and struggled to climb rpm while still coughing and running like it wasn't firing on a cylinder or two. it did this on and off and i eventually narrowed it down to injectors. i replaced all of the injectors with re-built ones and replaced the fuel rail with a billet one and an aftermarket pressure regulator. after this it ran insanely well and smooth but after a few days it started doing the coughing and misfire thing again. after alot of tracking and checking i havent gotten far. it does it worse when its cold but itle do it when warm too, its completely random as well, itle run perfect for a day or two then the next itle almost be impossible to let run without smoking the garage out, and its been getting worse and worse. the only thing i can think is old/bad connectors for the injectors or other parts, bad headgasket (but it wouldn't be this random and on and off) or a bad sensor. the biggest thing is itle run smooth and perfect then randomly do it, be it 30 min later, the next day, or even when im driving sometimes. mechanically the engine is sound with alot of care put into making sure everything is replaced and up to par. the major aftermarket done so far is a strait pipe (done by previous owner) a cold air intake, and some minor stuff. the billet fuel rail, regulator, and injectors arent to blame because it did this before and if anything its helped. any advice or help would be greatly appreciated as im stumped and have never seen this before. also to clarify by coughing i mean really rough, almost like a misfire. shaky, hesitates heavily, almost no power, dumps smoke and fuel out the exhaust and sometimes cant even idle when it warms up and droppes the idle. and this happens throughout all the rpm and regardless of temp.

edit: I forgot to mention that the distributer, which is not old having been replaced very recently before that car was sold to me, had some unusual carbom build up. ive checked it a month or so ago and it was perfectly clean but it now has carbon on the contact patches. after cleaning these it made no difference.
On top of tat the coil is leaking oil on the connector but after cleaning it all off it made no difference (new one is on the way) however i dont think this is the cause but i could be wrong.

 

[TimFZ]

Have you checked your fuel pressure before the fuel rail? I assume you have checked filters etc to make sure no debris is coming through to the filters or pump.

Also, are you using ethanol free 99 octane from Esso or at least E5 from shell etc? E10 will potentially make it run weak as its oxygen rich and moves ideal stochiometric ratio from 14.7 to 1 to closer to 14 to 1 so needs resetting for this.

Other than that, is your return line free flowing or blocking? Can't think off hand of anything else to try.

 

[Huw]

Nothing to do with the above. Most likely it’s a bad temperature sensor or connection to the temperature sensor. As the car has the same symptoms both hot or cold the ECU is not seeing the correct operating temperature and so enriching the mix. If it’s was happening only when cold it would be the thermotime unit that controls the cold start injector for extra fuel on start up. (Choke in old money). Start with checking the temp sensor connector, then the sensor itself. There are three temp sensor units, on the thermostat housing. One with the single connector is for the temp gauge, the bigger unit is the thermotime unit, the last one is the temp sensor in question.

Let me know how you get on.

 

[Huw]

Worth looking at this if you haven’t got it already.

 

[Ped]

Think Huw is right. Check the connections onto the engine sensors. They usually go crispy and may well be missing their retaining clips.

I had poor running issue too and this fixed it, so this may help:
https://zclub.net/community/index.php?threads/engine-running-rich-suspect-connections.24078/

PS: Just a thought, it could possibly be a problem with the fuel pump. The next time it happens, try and tap the fuel pump with a length of wood. If it suddenly runs better you will have the answer.

 

[rollypolly_zx]

Have you checked your fuel pressure before the fuel rail? I assume you have checked filters etc to make sure no debris is coming through to the filters or pump.

Also, are you using ethanol free 99 octane from Esso or at least E5 from shell etc? E10 will potentially make it run weak as its oxygen rich and moves ideal stochiometric ratio from 14.7 to 1 to closer to 14 to 1 so needs resetting for this.

Other than that, is your return line free flowing or blocking? Can't think off hand of anything else to try.

The fuel pressure in the rail holds steady and I have replaced the fuel filter, cleaned the mesh in the pump, and the lines are clean. I'll be replacing the fuel pump soon as it's wining on startup but fuel delivery isn't the issue as far as I can tell. As for gas I use just standard and haven't had issues relating to the fuel although I could try 99 and see. It's just so random I don't think the fuel would cause it. I also tried the fuel pump trick just to see and nothing happened.

 

[Huw]

Temperature sensor is the best culprit mate or poor connector to it. Rich running like your describing has nothing to do with pump or fuel pressure it’s an input fault to the ECU. It’s normally a temperature sensor or the at AFM fault ( or connection) but an AFM fault is unlikely from your symptoms as you’ve described them.

P.S. Pump is supposed to whine slightly on start up, it’s pressurising the system before the key is in the ignition position.

p.p.s Ditch the recon injectors at some point and get some proper ones. Recons have a poor track record for reliability and are false economy most of the time. They are a consumable item so why the hell they get reconned is beyond me.

 

[rollypolly_zx]

Temperature sensor is the best culprit mate or poor connector to it. Rich running like your describing has nothing to do with pump or fuel pressure it’s an input fault to the ECU. It’s normally a temperature sensor or the at AFM fault ( or connection) but an AFM fault is unlikely from your symptoms as you’ve described them.

P.S. Pump is supposed to whine slightly on start up, it’s pressurising the system before the key is in the ignition position.

p.p.s Ditch the recon injectors at some point and get some proper ones. Recons have a poor track record for reliability and are false economy most of the time. They are a consumable item so why the hell they get reconned is beyond me.

Yeah, I plan on upgrading injectors sometime thus summer, these are just to hold me over until then. After alot of looking and testing I didn't find anything wrong with any connectors or the thermostat. But about an hour ago I was admittedly frustrated and decided it was a good idea to punch the afm and magically the car ran good for a little . After a Lil investigation it seems the one connector I didn't check which was the one on the afm was dirty/lose so it was just shifting and causing a bad connection. I've checked the afm and it was good before but I never thought to check the connector or function while it was running rough. So as for now I think I have my answer to the issue and do plan on fixing it tomorrow morning and hopefully that's the primary cause I'll post an update on if that was the full issue or not.

 

[SteveG]

Following this, learning about 280zx issues. Scuse ignorance what is AFM?

Today I was happy to fix a cutting out issue. Bad connection on the distributor control module

 

[rollypolly_zx]

Following this, learning about 280zx issues. Scuse ignorance what is AFM?

Today I was happy to fix a cutting out issue. Bad connection on the distributor control module

The alot of people call it the afm but it's actual name is the maf (mass airflow sensor) it's the metal kinda box with a black cover on it that sits between your intake and intake manifold. It monitors the airflow and sends that to the ecu which adjusts the air fuel mixture accordingly. If it has a bad connection to the ecu then the ecu could get confused because it's getting either broken or no data on how much air is going in so it just dumpes yo much or not enough fuel to compensate

 

[jonbills]

The alot of people call it the afm but it's actual name is the maf (mass airflow sensor) it's the metal kinda box with a black cover on it that sits between your intake and intake manifold. It monitors the airflow and sends that to the ecu which adjusts the air fuel mixture accordingly. If it has a bad connection to the ecu then the ecu could get confused because it's getting either broken or no data on how much air is going in so it just dumpes yo much or not enough fuel to compensate

It was called an AFM by Nissan in the 80s. Although the terms are sort of used interchangeably, back when they were called AFMs, they were a mechanical flapper device and when the MAF term came in, it was commonly a heated wire device. I'm sure there isn't a strict separation between the two terms like that, but it is definitely correct to call this one an AFM.

 

[Huw]

It was called an AFM by Nissan in the 80s. Although the terms are sort of used interchangeably, back when they were called AFMs, they were a mechanical flapper device and when the MAF term came in, it was commonly a heated wire device. I'm sure there isn't a strict separation between the two terms like that, but it is definitely correct to call this one an AFM.

Spot on Jon. The AFM on the ZX measures air flow and air temperature. The ECU is pure analogue beastie so all inputs from the AFM are voltage levels from the thermistor and potentiometer on the air flap. So as you can imagine any bad or dirty connectors will add resistance to the circuit and the ECU will see the wrong voltage and the mix will go all to hell. All good fun when chasing running issues. It is worth changing all the connectors as Ped mentioned earlier so you know the connectors are good. Connectors are readily available.

 

[chris frizzell]

my 280z has all these problems every it laid up ,like everyone says the key area to look at is the temp send the thermotine and the conection to the cold starter clean them up .also i have a billet fuel fail with a aftermarket FPR and it should run about 38 to 42 psi good luck .

 

[SteveG]

The alot of people call it the afm but it's actual name is the maf (mass airflow sensor) it's the metal kinda box with a black cover on it that sits between your intake and intake manifold. It monitors the airflow and sends that to the ecu which adjusts the air fuel mixture accordingly. If it has a bad connection to the ecu then the ecu could get confused because it's getting either broken or no data on how much air is going in so it just dumpes yo much or not enough fuel to compensate

Cheers, Thank you