car fuel problems, need advice.

[Banging 6 in a row]

So my car idles really low, almost to the point of stalling out. its an 83 280zx non turbo with a manual 5 speed. I took it to the shop and they told me i needed a new MAF, fuel pressure regulator, and coolant temp sensor. they put in the MAF and i decided to do the rest of the work myself. I put the new (from a parts car) regulator on today and it still looks like its a diesel, with a bunch of black smoke and an idle around 500 rpms. A fuel system pressure test told me that there was actually around 32 psi instead of the normal 35 to 37. I clamped the return line until i was able to increase the pressure to well over the 37 psi mark (almost up to 50) and there was no change in the idle. Im out of ideas, and am left with only assumptions. im thinking maybe the cold start injector or maybe (but unlikley) it actually is the coolant temp sensor thats telling the computer to run lean?

any ideas or suggestions would be helpful, except telling me to buy a new car.

[evildky]

first thing I'd do is find out if you are in fact running on 6 cylinderds, with ti idling, unplug the injectors one at a time, if there is no change you know that cylinder is not firing for whatever reason, with an idle that low I suspect you're only "banging 4 or 5 in a row"

and when measuring your fuel pressure was this with the vac lone removed and plugged? at idle the vac line lowers your fuel pressure

check for a missing sylinder and let us know we'll walk you through it

[Banging 6 in a row]

haha alright man thanks, ill do that tonight.

[Banging 6 in a row]

I am pretty positive that all my cylinders are fireing. I know what its like to drive it on only 5 of them and when i can actually get it started and get the rpms up it feels normal. I unplugged all the injectors one at a time and the idle dipped even lower (it was almost un noticable) but when i gave it throtle on only 5 injectors the engine immediatly died. I also took out the cold start plug and found that its coverd in schmootz. It looked like the side of the motor with the leaking gaskets and 20 years of dirt. that was somewhat alarming finding out that thats what the inside of my intake manifold looks like. I was gonna take the intake apart and look at the throttle body, but im too tired and frustrated so im just gonna take it to my dealership in the morning and pay the $40 an hour employee price. But im still curious to see what you think, so let me know.

[evildky]

if you unplugged one cylinder and it made no difference at idle it's a misfire in that cylinder, you could havea miss at idle that clears up at higher rpm, if all your cylinders are firing, I'd verify timing and make sure the llugs and wires are up to task, generally if you can handle form the cap to each plug while running and not get shocked your cap and wires are good, plugs well taht obvious, pull them out, check the gap, and look for signs of rich or lean on each one

[Pharaohabq]

But when you do pull spark plugs while the engine is running, you'll want to use only one hand and try to insulate your body from the car since if you have a bad plug wire, the spark can get you, and at that voltage/amperage it could be deadly, if not very painful. so please be careful, and wear rubber gloves if you have them.

Phar

[reggiegsd]

An easy way to see if a cylinder is firing is to drip a drop of water on the exhaust header at each exhaust outlet. If one does not evaporate as vigorously as the others then that cylinder isn't firing.

To check injectors, use a mechanics stethoscope (they are cheap, get one) and listen to each injector. The good ones will "click" the bad one will do nothing.

[evildky]

I didn't suggest pulling the plug wires, I suggested pulling injector plugs and then crunning your hand over each wire to see if ti shocks you, not the most fun thing to do but effective, if they are good they won't shock you, better plan, buy a new cap and wires just to eb safe and spare yourself the shock

[Banging 6 in a row]

the cap is fairly new, i did new plug wires a week ago and double checked to make sure theyre in the right sequence. Stethoscope? a screwdriver works just as good and all injectors are firing. i pulled the spark plugs last night too and they were pretty fouled. black like charcoal. the back three were a little worse than the front three. the front three injectors were just replaced and i did the back ones alittle less than a year ago, so im pretty sure all the injectors are good.

[Banging 6 in a row]

o and i turned the idle speed screw up this morning before i drove it to the shop and once it warmed up i was able to let off the pedal without it stalling.

[evildky]

you said you replaced the chts, how are the wires and connector? how is the O2 sensor and and it's wire and connector?

[Banging 6 in a row]

chts? and my chilton manual is with the car in the shop, but im pretty sure theres no o2 sensor. MAF or ilde air speed

[evildky]

CHTS= Cylinder Head Temp Sensor, you said you replaced the temp sensor, so I assumed you meant the CHTS and not the Temp sender or the thermoswitch all of which are located in the lower thermostat housing on the P79 head but the CHTS is the only one that will effect the way the car runs

[Banging 6 in a row]

the shop told me that my coolant temp sensor was bad and is the cause of the rough ilde. it was really cool for arizona today too, so i got to drive the car home. the high today was 75 but it was around 90 when i started having problems. When i went to instal my new coolant temp sensor it was too small for the hole. so im assuming that Nissan gave me the wrong kind of sensor or im just retarded and i pulled out the wrong one. CTS is right under the thermostat housing and to the cars right of the distributor cap right?

[Banging 6 in a row]

yea they definetly gave me a chts, which could still be the problem, but im going to measure the resistance in the old one compared to the new one before i replace a part that dosnt need it. Does anyone know how much resistance should be in the CTS at certain temperatures?

[evildky]

from my megasquirt settings:-4f=28681 ohms86f-2238 ohms210f=177 ohms

[Banging 6 in a row]

The old CHTS is ok so im gonna try and take the new one back. and i had the CTS up to 200f and i couldnt get a reading below 2000 ohms. Bad?

[evildky]

yeah sounds like it's bad

[Banging 6 in a row]

and what about my exaust gas sensor? i was skimming my chilton manual and found a section that said it should be replaced every 30,000 miles? ive never heard of that before but i thought that i could replace it while im in a sensor pulling frenzy

[evildky]

the O2 sensor? they say they are to be replaced every 80k as best I know