Well like the title says I am having a problem with my spark plugs fouling out. I have had to change them once a week, every week since I owned the car. Its a 1990 300ZX TT. I always run 93 octane or better gas, synthetic oil, and NGK plugs. I had my TPS adjusted cause it was running almost 8 volts at idle now its 4.1 volts. Thought that they were getting gas fouled but it is still doing it so now I not so sure. Can anyone help? Thanks

check the clolor of the plugs.. in the Haynes Z manual its got a page at the back with idfferent spark plug colors and what they mean.. give that try..

also the type of NGK plug can have a difference. Hot ones, cold ones..
I run the standard 240Z plug which is number BP6ES. I have also run these plugs in almost every car you can think of eg. Chrysler 6. toyota. Chev..
they have a really wide heat range.

Maybe your spark is really weak??

Right! Heat range is always a factor.

The standard NGK plug for my L24 240 was BP6ES. Said so, right in the manual and in the owner's book. But my individual car always ran better on NGK BP 5 ES plugs, so that's what I have fed it since about 1973. Using that heatrange my plugs stayed pretty and clean until they burned up from mileage. No idea why it preferred that plug.

You might only need a hotter plug. But like Pete said, you should use a chart to "read" your sparkies and determine what's happening to them. If you're pushing oil past the rings or sucking it down the valves, it won't matter what heat range you use.

I also spoke with one guy who claimed his Turbo was spitting oil into the intake, altho I never pictured how that would happen. Is there any black or blue smoke out the tail? (Black = rich mixture; Blue = burning oil. Either will foul plugs).

Frank T
MbrshpDir

There are a number of areas to look at. Because of the numerous vacuum lines it is a must to do a boost/vac test to check for cracked or broken hoses. Also perform a ECU code check to see about sensor codes. check base timing.

What kind of maintainance records do you have for your Z? PCV valves ever been changed?

Check TPS ohm reading should be between .44 and .46

you can also schedule to stop by on a Sat or Sun morn. and I could take a look, hook it up to the ConZult computer. I am located in Danbury, CT

Rich

Ok so this it what I have learned so far. First regardless of what it says on the outside of the box from NGK, the spark plugs do need to be gapped. The NGK plugs come gapped from 0.32 to 0.35. Not close enough when the vehicle calls for 0.44. The TPS is set at 0.45 volts so that is right on. I tested the coils and the number 5 cylinder showing way too much resistance. Rich from RDZ was kind enough to supply me a new coil. Thanks Rich. I installed the coil and it still woundn't fire on that cylinder. I changed it to a different cylinder and it fired properly. Unlike that one that was there before that regardless of the cylinder it was located on would not fire. The coil is definately good now, the plug fires in other cylinders and I check the wiring to the coil and voltwise it measures the same as all the other coils. It could be the injector but I have a heavy smell of gas in the exhaust when the injector is plugged in and when I dissconnect it the smell goes away leading me to believe that the injector works. Could be a grounding issue with the plug? If anyone has had this happen please let me know. Thanks

Check compression, I don't like where we are headed. if compression is good. then check injector ohm reading, should read around 12.5.

One lone defective plug wire?

Try swapping wires with a known-good cylinder and zee if there's a difference......

If that doesn't work, take it to RDZ and throw money on it. (You've probably got one of those new-fangled distributorless ignition systems, huh? I'm WAYYYY out of my league here )

Frank

I just discussed this matter with someone who has FAR more experience than I have with Turbo cars.

He said if the boost is high enough, the rings can fail to maintain a good seat and let compression get by them into the crankcase (typical blow-by, except that it's caused by an overly-enthusiastic Turbo, even when the rings are normally good).

That blown-by compression can whip up a pretty good oil vapor cloud in the crankcase, which then gets pushed thru the Crankcase Ventilation system (PCV) and get sucked into your chambers FOULING YOUR PLUGS.

He said a quick check for that is to disconnect one end of your PCV hose and watch it for oil being spit out. Hold a white cloth in front of it and see if you get black oil drops spitting on it or see puffs of smoke or vapor. You might run the car awhile with the hose disconnected, then check to see if your clean plugs are staying clean, or even turn your boost down if possible and see if clean plugs still foul.

Sounds believable to me. It's still 'backyard mechanix', and RDZ would have the Magic Meters to tell you exactly what's causing this.

Great news fellow Z owners my baby is alive again!!!! I trace down the wiring and found a partially broken wire on one of the connections for the Ignition control module. The person that had the car before re-located the ICM and extened the wiring. I was able to cut and splice the wire back together and now the car is run perfect again. Wow its been two weeks and I forgot how much power the car has. Thanks for everyones help in this matter and for helping me brainstorm. If you guys hadn't offered suggestions I would have never found the root cause. I guess that when a car gets to be 20 years old the wiring should probally be check form time to time. I appreciate all the time that you guys sacrificed to take care of me. Thanks again. And thanks again RDZ for the Ignition coil. Mine was definately smoked. I tried reconnectiong it last night and it still wouldn't fire, even after I fixed the broken wire I would still be at square one.

Sooooo, the stretched wire caused the Ignition Control Module to produce a weakened Zap to the plugs, causing them all to foul?

Wow. Each time I learn about the possible problems with "computer Zs", I become more thankful for my dirt-simple 240!

Frank

Sounds like a lot of folks out there know these babies! One thing we always look for on these cars with higher miles are the connectors for the coils. They invariably get old and brittle from age and heat and begin to make poor contact. The connectors are available from Kent-Moore through Nissan dealers. I already got six set aside. RDM