Slight misfire, and hoping someone can clear some things up on my car *updated*

[KnightoftheRound]

Hey all, I have some problems with my 82 280ZX that are bothering me that I would like to clear up, things that I can't figure out. Car is a 82 with 81 L28ET, 83 Dizzy with Z31 ECCS.

 

Replaced all 6 injectors with ones from Dr. Injector, new OEM plugs gapped to .038. Car has slight misfire at idle and through RPM range, very noticeable if you hold it at various RPMs. It is not cylinder specific, pulling injector connectors on every cylinder does not alter the idle that much. Spark is a good white spark, Z31 Ignitor, Z31 coil, Taylor plug wires, new cap and rotor. Also would like to add, that bringing down the out of the box gap to .038 reduced the misfire quite a bit.

 

Have not checked fuel pressure yet. Pulling vacuum line off FPR does not do anything positive to idle, if anything it sounds like it gets a little worse. Timing is set to about 20btdc. I have no air leaks nor fuel leaks, FPR is new as well as filter.

 

Computer shows codes for Crank Angle Sensor, Fuel Temp Sensor, AC, Neutral Switch, and Start Signal, and detonation sensor.

 

CAS and disk is one from a known well running but sitting 85T, with no damage or dirt on disc, have not ruled it out as a possible malfunctioning unit yet.

Haven't checked on throttle switch yet but I can't imagine it would affect idle smoothness or anything above 2k rpm.

Tried 5 different Z31 MAFs I have in my garage, all tested OK to FSM procedure, no change in running with any except one of them, this one was the only one with the adjuster screw exposed.

 

Now, I know if the CAS was malfunctioning I would definitely see a change in operation...if you have the key on and rotate the distributor you can hear the injectors fire, but considering the problem was damned near gone with that ONE MAF, it makes me wonder if the MAF needs adjustment.

 

I have NEVER been able to get the little lights to flash for the 02 sensor operation, I have held the RPMS at a steady 2-2.2k rpms for 2 minutes up to 4 minutes straight and never gotten them to start blinking. Multimeter test at the ECU prong for 02 while running shows voltage from 02, 02 sensor is also a brand new Nissan unit.

 

CHTS is new as well, and also tests within spec. All grounds are clean and free of corrosion, battery ground cable is new.

 

Not sure what to look for here...another weird thing is that the Z31 ECCS swap always calls from bypassing the dropping resistors with ECUS pre-88. My car would NOT run WITHOUT the dropping resistors after warm up, with my ECU being a Nissan remanned unit from an 85T car.

 

Really at a loss, not sure what to look for here this time, or what to rule out. I have searched and read other similar issues of idle misfires, but I don't recall seeing any on a Z31 ecu.

 

Any thoughts?

 

EDIT:Checked harness continuity between ECU and CAS, MAF, o2 sensor, det sensor, and verified TPS function, TPS code is gone. Rechecked timing. Interesting to note that I do not see any timing advance upon rev up, or timing retard on rev up with det sensor disconnected. Still unable to get ECU to shoot 02 sensor blinks. Car has obvious stutter under load, and miss under no load at around 2.8-3k rpm.

Edited March 22, 2010 by KnightoftheRound

[Ineptitude01]

This probably sounds stupid, but how clean are the pins on the ECU? Mine were slightly corroded, and it was causing a lot of bad problems. Dying randomly, bad idle, backfiring, popping, inability to rev over 2000, etc etc.

 

The pins LOOKED great, but I was able to scrape at them and discover some corrosion. I didn't fix it until last night, when I ditched the regular contact cleaner and got some Caig DeOxit Gold. After a few sprays, all my problems went away.

[S130Z]

You stated bringing your gap down to .038 lessened your missfires. I gap my plugs on my turbo motor at .028. Close your gap a bit more and see if it helps out.

[KnightoftheRound]

Thanks for some responses guys.

 

Haven't gotten to it yet due to rain, but I am also going to double-check all my ignition splices. (after all, its a L28ET Swap, Z31 ECU swap, AND Z31 coil/transistor swap, all of which require some splices)

 

So far:

 

I put the one MAF on the car that slightly quieted the miss down. I still can't adjust it as I cannot get the lights indicating 02 response on the ECU to blink. Voltage from 02 (Checked at ECU connector while running) on my multimeter does not bounce around like I think it would, BUT if you lean it out by creating a vacuum leak, voltage drops, although, if you pull the hose on the FPR, voltage doesn't increase (Running richer), which I find strange. Otherwise it hands around .5v.

 

Timing was actually at 17ish BTDC, adjusted to 20. Computer still does NOT alter timing back and forth depending on conditions.

 

Computer still shoots CAS and Det. Sensor codes. (This actually bothers me more than the misfire, considering the car pulls great and has NO issues pegging the speedo)

 

Will look at those ECU pins, although I did the plug/unplug a bunch of times trick, but Ill double check. I might head up to the local Z junk yard and swap a couple ECUS for giggles.

 

Like I said, if you wiggle the ECU connectors, the car will run WORSE, OR sometimes almost die. It never actually gets better than its current state though. Perhaps I should grab some Z31 ECU connectors and splice them in sometime as well.

 

Let me hear what you guys have to say, Ill check up on these things as soon as I can.

[Ineptitude01]

Will look at those ECU pins, although I did the plug/unplug a bunch of times trick, but Ill double check. I might head up to the local Z junk yard and swap a couple ECUS for giggles.

 

Like I said, if you wiggle the ECU connectors, the car will run WORSE, OR sometimes almost die. It never actually gets better than its current state though. Perhaps I should grab some Z31 ECU connectors and splice them in sometime as well.

 

These are the exact symptoms I was experiencing. I was afraid to touch my ECU connectors, and I've been driving with the trim off there, so I could wiggle them if it died. That eventually stopped really helping, and felt hackish, so I moved on to electronics cleaner, battery cleaner, contact cleaner, etc. It all made it a little bit better, but in the end, it was about as bad, and if I poked the connectors the wrong way... death.

 

I sprayed this DeOxit stuff on, and plugged the cables back in immediately. (Then I took them back out and shook the excess fluid out of them ). After that, I had an 800rpm idle, no backfiring on deceleration, no popping, and it felt smooth as glass. More importantly, nothing I can now do to the connectors short of unplugging them completely will change the running operation of the car. Not even the tone. I can't even make it hiccup.

 

I forget which member on here suggested it. I suspect it was Roger, but I can't remember. Good call, though.

[KnightoftheRound]

Used Caig Deoxit D5 on injector, ECU, and all sensor connectors. Ran a LOT smoother, no more dying when wiggling connectors. Replaced plugs with brand new NISSAN branded NGK plugs package pregapped to .038, runs like a dream.

 

Thanks for the tip Ineptitude!

 

Sensor codes remain, but that is an issue and topic for another day. Case closed for now.

[chasm8]

this sounds like my problem.i have a 82 280zxt 2+2,it idles at 800 rpm then after about 30min when at normal temp,it starts idling weird.It idle between 800rpm and 200rpms.Ichecked for vac leaks,fuel pressure,and compression test is good.could cleanig the ecu help?