Misfiring

[Phyxius]

I've ran a search and have not been able to find a case quite like this one, so here goes:

 

I have a 280zxt with a freshly rebuilt motor and a new turbo. Sometimes when I first crank it, it's missing on one...sometimes two cylinders. If I make it boost, it stutters for a few seconds and then seems to clear up with a large cloud of greyish-black smoke. It smells really rich most of the time. My thought was that maybe I have a leaking injector or two, or maybe some valve seals are bad.

 

It doesnt always miss on startup, just after it's sat a while. Rain seems to make it worse, but this could be just me.

 

The car never really idles where it is supposed to. Sometimes after a hard run, the RPMs will go from 500-1200 several times before smoothing out in the range of 8-1000. I believe these motors are supposed to idle at about 650rpm.

 

It also likes to buck when going from no throttle to some throttle. My guess here is something to do with deceleration enrichment?

 

 

 

I don't know if this is related, but since it has gotten cold here, the temp gauge rarely goes into the 'normal' range. It operated fine during the warmer months.

 

Any ideas?

[datsunlover]

Well if it happens more in the wet, I'd say check/replace the plug wires, and check the distributor cap/rotor. Could be moisture gettng in there and causing it to miss.. You may have some leaking injectors as well.. and once the engine warms up, it getts better, but they will stil be leaking a bit... could be causing your wandering idle/bucking issues. I'd check the whole ignition system first though.

 

As for the temp guage.. there might be a problem with the thermostat(stickong open), or it's just opening too soon. (get a higher temp thermostat) Hope this helps.

[Guest bastaad525]

Though your symptoms aren't spot on with the 'usual symptoms' for 'corroded connector syndrome' I will say it anyways: Get a can of electrical contact cleaner, take 10 minutes and disconnect all of the connectors on your wiring harness, ECU, AFM, injectors, sensors, and spray them all clean, on the connector and on the sensors etc. themselves. Let everything dry and reconnect everything and see if that helps the problem.

 

 

You'd be surprised how many times this has solved ALL KINDS of funky running, stumbling, bucking, and misfiring problems, for many of us here.

[Phyxius]

I've done this several times before, but not lately....I'll try it again. I've recently changed the cap, plug wires, and plugs, so that shouldnt be a problem. And i replaced the thermostat last april.

[mjfawke]

Just my thoughts....

 

First off - if the EFI thinks the engine is cold it will add extra fuel, so fix the thermostat. Go genuine - stainless steel lasts longer. Check the engine temp sensor to ensure the connector is not in any way corroded, as this will show up as 'cold' engine.

 

The missing cylinders on startup - you might have leaky injector/s which will bleed into the cylinder when the motor is stopped. Disconnect the coil/computer, pull the plugs and crank it over to see what comes out.

 

The bucking when going onto power is more likely the opposite of what you have suggested - under decelleration, the injectors are cut off until revs drop to about 1500rpm (?). Perhaps your idle/enrichment switch on the throttle body is incorrectly adjusted?

 

The high idle is most likely to be an air leak somewhere, unless you have set the idle speed stop higher.