KasbeKZ

major problems with my new (to me) N/A 1990 300zx. the oil pressure guage has been useless. i know this because it changes very quickly and stays on zero for sometimes very long amounts of time. been driving like this for almost 1500 miles. i'm about to change it. but today i started it to leave work and as i pulled out, it seemed to be missing. it continuted to miss very consistently all the way home. the engine has a rattle... maybe something thats been there though. in conclusion, power starved, wierd smells, running very rough, and sounding pretty... rough, but not smoking and still shows plenty of oil pressure when the guage is working. please help! does it sound like oil deperivation or actually a spark miss? and what do i do? i did get new plugs and pressure sending unit. they'll be in tomarow. and thanks to everyone that has helped me so far. this forum is awesome.

Ratfink

Well, oil deprivation is usually noticeable through other things like really high temps and engines grenading. Rough running along with your gauge not working can be nothing but a coincidence. So don't get too scared just yet. You say rattle.
Is it a rattle that caries with engine RPM?
Is it a loud knock?
A tapping sound?
Or does it rattle like a ball in a spray paint can?
If it's running rough and it's the ladder, than my guess is fuel/spark/timing.
You need 4 things to occur on a 4 stroke gasoline engine for it to run correct.
Fuel/Air ratio, Compression, Timing, Spark.
Have all those four things working correct and you have a beautiful running engine. Yeah, there are a lot of other systems on a vehicle, but people make them more complicated than they have to be.
Start at the system that you think is failing, common problems with that system, then work your way to the least likely problem. Get a starting point, and nothing is impossible to figure out. Just break it down into small jobs.
One thing that is hard is figuring out other peoples sounds and rough running conditions over the internet with out a lot of background and other info.

You are not smoking. This makes me guess that your compression is good. Skip that for now.
Smells.. What kind of smell. Describe it. That can tell a lot. From oil, to gas, to coolant. Even a gassing battery. Specific parts burning, etc.
If you can be specific to the location of the sound, and what it sounds like this will help too.
You can use a stethoscope, or just a hard rad that you can touch to your ear and various engine parts to determine where it is coming from.

You can do things like figure out which specific cylinder is not firing too. Use the old redneck spit method. (Spray bottle if you want)
Put water/spit on each part of the exhaust manifold for all cylinders after it just gets hot. Don't run it forever. Just a minute or so. That way when the water touches the manifold or header, it will sizzle on the live cylinders and not on the bad. Could be a spark plug wire. Who knows.

Anyway, I could go on for hours here, but I don't think people want to read it all at once. Let's start working the possibilities and narrow it down some.

hoov100

check codes, disconnect the coil pack plugs one by one to find the cylinder thats missing, check plug, if good check the coil pack if the coil pack is good, check your wiring, probably just time for a new set of plugs..

i would personally just get and autometer or VDO oil pressure gauge instead of going with the disapointing stock one..

KasbeKZ

thankyou SO much ratfink! that is very good news to hear. its not that loud of a knock. actually i havn't heard it yet. that was my dad listening closely. but i'll get back on that tomarow. now that i htink of it, i think the smell was unburnt fuel. i also hope that lol. thanks hoov too. i don't really have any idea how to check codes. where could i look this up? and very importantly to anybody, what do i set the plug gap at?

hoov100

http://www.ttzd.com/tech/diagnostictech.html
http://twinturbo.net/ttnettech/tech.aspx

dont set plug gaps if you using the recommended plugs..

Ratfink

Don't set plug gaps if you are using recomended plugs???

I always check my plug gaps. Not always reset them. But, always check them. Too many butter-fingers out there dropping packs of spark plugs to be trusted.

hoov100

platinum tip plugs should already be set when you get them..

NismoPick

Yes... you SHOULD check the gap even if they are new. They can be banged around in their box... maybe someone removed them, one got dropped...

Whatever the case, ALWAYS check spark plug gap before install. It takes 30 seconds and is well worth it.

hoov100

i never said dont check, i said dont set..

KasbeKZ

well thanks. would it be stupid to persist and ask if anyone knows the manufacturers suggested gap setting? i cant find it anywhere

NismoPick

And if it's out of spec... you don't set it?

hoov100

IF it is out of gap you should be very careful.

KasbeKZ

points gap?...

KasbeKZ

plug gap. sorry. not a distributer

Ratfink

Yeah, use the tool for it, don't just shove something between the tip and push it open. You bend from the back part where it turns 90°. Anyway. I didn't want to start an argument here. Sorry if that was the result.

b300z

i believe stock is around .045"

KasbeKZ

well thanks for all the help. i did all those things only to find that i was getting perfect fuel and spark in each cylender. my question now is: what do i do about my bad head? i don't know if it can be rebuilt because it looks like the cam cap is all worn out. this is where the rattle was coming from.

Goofyz

I guess i don't understand....you don't set the gap on the plugs for a z32. The car does it itself. Any new plug should be close enough so the computer can adjust to work with the other plugs. That's part of the charm of individual ignition coils... But if you feel like checking the gaps and using a timing light for tuning, i suggest you get a Ford or Chevy.

Ratfink

My Z uses a timing light, and I set the gaps. Does that make it a Ford? haha

No, just older.

So there is no gap to pre set the plugs at even with individual coils??? That still does not sound right. There should still be a tolerance. A range. Because you can have gap to close to create a good combustion, and you can still have one wide enough that it does not want to spark strong. If you disagree, come on over and let me play with you spark plugs. lol

Yeah, it makes up for a lot of error, but call me crazy if I would set them anyway. Crazy is fine. Lazy is not.

Ask someone trying to get the best ET's they can at th track, and ask them if they don't check the gap. I would guess that they do. Regaurdless of the ignition system.

The cap is worn? Or just the bearings? If the cap itself is bad, you should be able to get oversized bearings and have it machined.

entropy31

you do need proper gap on a z32. sparkplug manufacturers claim gaps are pre-set, but they can be knocked out of tolerance on the way from the plant to your garage. it is always best to check them for proper gap. no car can physically adjust the gap on a sparkplug, not even the z32. it can compensate for incorrect gap to a degree, but performance suffers.

Matt K

Let me get this right, no oil pressure indicated & you feel free to drive it around? I'd replace the oil pressure sender (they go bad frequently on Z32's) or hook up a real, mechanical gauge before I'd even start it...

hoov100

as long as the low oil pressure light doesnt come on its all good.

Comorat2x2

Wow....I just....good god....

KasbeKZ

maybe i described the oil pressure incorrectly. the guage would jump suddenly form a good oil pressure to 0, and back suddenly. after all this happened, i replaced the sending unit and the reading was higher and more consistant. i think i found the problem to be REALLY f-ed up valves caused by rich running. i have 2 new heads on order. oil deprivation no longer seems likely.

P.S. this job has been pretty confusing. a new kind of car for me and a new kind of work.

KasbeKZ

and the oil pressure light never did come on. i didn't even know there was one. but on that note, might there be a low oil pressure cut off? i figure that if a generator has one then a 300zx might.