1990 NA 300zx intermittent spark in no. 2 cylinder

[gotens21]

as the posting states I am having problems with my z. Is this a misfire? No check engine light is on, so what is it?

[nghtrain88]

have you pulled the plug? is it at all fouled?

[gotens21]

yes I pulled the plug and pack and swapped them into the no. 1 cylinder but the intermittent stayed in the no. 2 cydinder, the plug was slightly black but thats it btw it is a NKG plug.

[nghtrain88]

have you checked the injector for operation and resistance? I had a bad injector that was causing my car to miss and hesistate too

[gotens21]

well the injector in that cylinder is new, but will that really mess with the spark?

[freakonaleash1187]

Could be your coil pack. Swap you coil packs and see if the misfire follows the coil pack.

[gotens21]

yeah I did that and no change in the 2nd cylinder.

[evildky]

you just replaced the injector in that cylinder and are getting intermitant failure? how are the coil pack and injector connectors? and the black plug would imply rich condition, either weak or failing spark or oversized injector, are you sure you got the right size injector?

[gotens21]

yeah its the right injector I don't know what it could be...

[nghtrain88]

a black plug doesnt necessarily imply richness does it? richness is just a higher fuel to air ratio, the black plug could be an oil leak or a bad piston ring or something.. the fouled/ semi-fouled plug is probably why it is not sparking the way it should

did the plug smell like oil?

[Zwicked]

Pull the PTU (and CAS) plugs and check for corrosion on the terminals. Doesn't take much to keep the signal from getting through

[gotens21]

no the plug did not smell like oil, i did a compression check and all cylinders were over 180 psi. I will check the ptu to see if there is a bad connection.

[Zwicked]

If you have the newer PTU (black one) there are 3 plugs (1 one PTU, 2 sub-harness). The CAS plug should also be checked as well as injector plugs.A dead give-away is if any of the rubber boots are cracked

[gotens21]

Ok I used connector cleaner on the PTU and the CAS and now I have no spark. >.<

[Zwicked]

If you have no spark at all, either the connector is not seated properly, a bent connector pin that isn't in the female part, or the PTU is dead.

A couple questions:

1. Do you have the old silver PTU or the updated black one?2. Was there a lot of visual corrosion on the connectors? Usually it's greenish in color. Spray cleaner alone won't do it. You need to take a very narrow screwdriver or pick and scrape it all off so it;s back to copper, and then use some cleaner. Dielectric grease is a good idea to put on when you are finished so moisture can't get in.

I suspect that it's one of the connectors isn't on correctly. The CAS one is very easy to get on crooked and/or not seated all the way.

[gotens21]

I acutally have 2 PTU's and both are the black one. The connectors were a greenish color and how do I tell if the PTU is bad? neither of mine make a difference.

[Zwicked]

http://www.300zx.co.uk/cgi-bin/manual.cgi

Section Engine Fuel & Emissions Control page 179

If the terminals are green, make sure you scrape all of it off all pins on all connectors, then use some good contact cleaner. That green stuff keeps it from making a connection and it won't run, or run right. If some show it, good chances they all might.

Check: PTU, CAS, MAF, Coolant Temp, Injectors, FICD, Aux Air Valve, Fuel Temp,
Modified by Zwicked at 9:28 AM 7/18/2007

[gotens21]

You nailed it Zwik. the PTU I have is the black one so it has the adaptor harness on it and all those connections were green, so I started to clean the plugs but the connection plug part all the way to the actual wire was all green and crappy. so I said screw it and gor out my trusty soldering gun and cut out the extra plugs and soldered the wires together so it is now a straight shot and it works GREAT! THX A MILL!

[gotens21]

on another note the car didn't start because the ground for the ING. Relay was oxidized so i cleaned that up and thats good too.

[Zwicked]

Pull the plugs on the CAS and PTU. If the terminals are corroded that's likely your issue.