Intermittent starting issues.

[Kyle.whitbeck]

JDM 1990 300ZX TT 5 Speed, completely stock.
Car either starts or it doesn't, kind of a crap shoot.
Occasionally when idling rpms drop to around 500 and the car will shake real bad.
Sometimes when I try to drive it it feels almost as if something is clogged
I've "listened" to the injectors, and they are all firing, I have not checked resistance yet.
Car currently has original PTU in it, so I've ordered the new style and adaptor harness.
Any other ideas? When the car runs without these issues it pulls strong and idles fine, I don't get it.

[evildky]

Random starting issue isn't much to go on. Is this possibly a temperature related issue? The CTS and O2 sensors when they fail cause a rich condition that can cause hard or non starts in warm weather or warm restarts.

PTU issues usually cause one or 2 cylinders to miss.

One of the first things you should do is check the ecu for codes! Next, if you suspect a misfire, is to identify which cylinder(s) are at fault. This is actually very simple, with the car idling unplug each COP one at a time, if that cylinder sputters when disconnected it works, reconnect it and move along. When you disconnect a cop and the engine idle does not change you have identified a problem cylinder. Once you have identified a faulty cylinder you must determine if it is lacking fuel, spark, or compression, we generally start by ohming the injectors then by swapping cop and spark plugs with a known good cylinder and retesting. If the injector checks out and the problem does not move with the component swap then you can retest with the cop and spark plug lying on the manifold and the injector unplugged, to visibly look for spark, if still no spark with known good components you likely have a bad ptu or wiring harness. If you have spark then you are either fouling the plug from a bad injector or bad injector o ring ro you have a physical issue with a head gasket, valve seat or piston ring.

[Kyle.whitbeck]

My apologies, I forgot to mention that I did check for codes, when I first purchased the vehichle, I was getting a code 13, cleaned some of the corrosion and plugged it back in, code has since gone away.
I will start unplugging the COP's tonight and go from there.
Could it be an on and off again electrical issue? Like I said, sometimes it runs just fine, other times like complete dog crap

[evildky]

sometimes runs good and sometimes bad, might want to look at the cas, they sometimes fail intermittently and generally get worse before dying completely.

[Kyle.whitbeck]

So starting unplugging Coilpacks, no difference with 1/2 pulled, 3,4,5,6 all made the engine die out, swapped 1/2 with 3 and for, got no difference, 1 and 2 still dead, recently replaced ptu, just a bad harness maybe? Or is that a CaS symptom also?

[Kyle.whitbeck]

Anyone?

[evildky]

So you identified the problem being in cylinders 1 and 2, which for clarification is the front cylinder on each side of the engine. You swapped the cop's with known good cylinders and the problem did not move, did you also move the spark plugs? If so, ohm the injectors on those cylinders and verify the readings by ohming known good cylinders.

[Kyle.whitbeck]

I did not swap plugs also, I don't think it's an injector issue as I'm not even getting spark at the coilpack on 1 and 2, even when swapped with known good coilpack, does my injector have anything to do with power to the coilpack? I don't think so but I've been wrong before lol

[Kyle.whitbeck]

Also no spark verified by me not getting electrocuted regardless of coilpack in 1/2 lol, and more technically by inline spark checker not blinking in 1/2 and getting blink in 3/4

[nissanfreak12]

Which PTU do you have Series 1(silver fins) or series 2(all black)?

[Kyle.whitbeck]

I just switched to the series two as more of a precautionary measure because it came with the series 1 ptu

[nissanfreak12]

Make sure you have continuity between the ECU and the specific cylinders/PTU. This will eliminate the wire harness. Check both injector wire and coil pack wire. It could be as simple as a wire/s are broken causing the separation. If all else checks out, it may be worth sending the ECU to specialty z, concept Z and have them check to make sure one of the drivers is not out.

[Kyle.whitbeck]

Alright so that's on the edge of my knowledge, anyone have any insight to help me accomplish that last test?

[nissanfreak12]

The wiring? or the ECU?

For the wiring;

Under the passenger foot panel is the ECU, remove the wood cover under the carpet and on the middle/left side is the ECU. Unbolt it from the chassis and remove the plug which all will require a 10mm socket. Once removed compare to the chart below and located each wire to the corresponding injector/coil. Use an Ohm meter to see if there is continuity between the harness. You may have to make a separate wire to connect because the ohm meter may not reach from one end to the other. You can also do this from the PTU for the coil packs. Still test from ECU as well.

Dont over think it, its as easy to test as it seems, just seems like a difficult test. I thought the same thing till someone helped me, I basically had a duh moment.

https://www.google.com/search?q=1990+30 ... X8H9MjM%3A

For the ECU;

This you will have to send in to get tested. I know concept z performance does this testing and pretty sure specialty Z does as well. Avoid sending it to Ash, you may not see it for a while and Z1 does it, but sometimes they are backed up and take a while to test. Call them first and talk to them.

Last note, make sure the connectors are clean. If there is any corrosion at all it will hinder testing as well as it actually starting/working.

[nissanfreak12]

I did not swap plugs also, I don't think it's an injector issue as I'm not even getting spark at the coilpack on 1 and 2, even when swapped with known good coilpack, does my injector have anything to do with power to the coilpack? I don't think so but I've been wrong before lol

No, they are their own circuit, but your injector has everything to do if its a dead cylinder. Are the injectors working? When you pull the plug out is it wet? Swap plugs, you can test all day for free, except your time of course, but replacing parts will get expensive fast.

One more thing to add, make sure all the grounds are connected. Mainly the ones at the rear of the plenum, these have been known to fry PTU's if disconnected.

[nissanfreak12]

This is also a great read on the CAS. Basically the CAS send s a signal back to the ECU to tell when to fire on that specific cylinder.

https://z32.wikispaces.com/Ignition+Timing

[Kyle.whitbeck]

Also side note, before I started posting in here, I poked around with a multi-meter, I'm getting ~12v on the middle wire to all Coilpacks if I remember correctly, I'm not sure what the 3 wires that run to each one is for

[evildky]

The good news here is that you have identified a spark issue on #1 and 2, at least you aren't just chasing our tail and throwing parts at the car.

On the COP, one wire is 12v+, one is ground and the other is a 5v square wave that fires the coil pack. You can test each channel going into and out of the ptu using an oscilloscope or a logic probe. The ptu is just a 6 channel transistor, all the inputs should be the same and all the outputs should be the same. the additional 2 wires on the ptu is again 12v+ and ground.

[Kyle.whitbeck]

Is there a spot on the forum where it's broken up geographically? Maybe I can find some local help to help me poke around from anyone who's been doing this a while? I'm in southern NY just outside of NYC