# My 1990 300zx won't start. PLEASE HELP.



## 90z32 (Jan 28, 2012)

Ok, so here is my issue. I have a 1990 300zx n/a. Automatic trans. It just stopped working the other day. I checked all my fluids. All good. New Battery and terminals. Cleaned all grounds. I checked fuel supply and that is good. I checked for spark at each coil individually. All good. I checked the ecu codes and it turned up code 21 (ignition signal) and code 34 (detonation sensor circuit). I Changed the PTU and the camshaft position sensor. Still no start. Any help would be great. Thank you.


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## smj999smj (Jan 1, 2006)

Are the injectors firing? Have you tried spraying some carb cleaner into the throttle bodies to see if it will start on that? Are the spark plugs fouled? Compression checked?


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## 90z32 (Jan 28, 2012)

*re: fuel injectors and spraying carb cleaner in the throatle bodies.*

I just did that yesterday. The injectors are firing. The fuel pump is running and all that. But no fire. I opened up the line between the fuel filter and the objectors rail and it had enough pressure to spray a steady stream of fuel about fifteen feet so I think its the fuel pressure regulators. I'm replacing them today and we will see. :newbie:


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## smj999smj (Jan 1, 2006)

Could be...but I would just install a fuel pressure gauge and test them before going through the trouble and expense of replacing them.


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## 90z32 (Jan 28, 2012)

*re: fuel pressure gauge.*

I don't have a fuel pressure gauge but i have tried 3 different fuel pumps and I replaced the pressure regulators today. If I spray ether into the intake it fires right up. without ether it won't fire at all. I just replaced the Crank Angle Sensor and the Power Transistor Unit. The car sat un-started and un-moved for 4 months. I put a new battery, terminals and battery cables and it hasn't started since.


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## smj999smj (Jan 1, 2006)

If you spray ether (carb cleaner works just as well and it's a lot less volatile) into the engine and it fires, that tells you it's a fuel delivery issue and it allows you to rule out ignition and engine mechanical issues. You need to see what the fuel pressure is, so find a parts store that has a loaner program, find someone that has one that will let you borrow it or purchase one. A good one for your vehicle would be the Actron CP7838 - Professional Fuel Pressure Tester Kit. It cost about $40 and you can get it from Sears that sell automotive tools, Amazon.com, and Summit Racing, to name a few. BTW, have you pulled any of the spark plugs lately just to check and make sure they're not gas fouled? Also note that the fuel pump system in your Z is not like other Nissan models of the same year. Rather than have the fuel pump use a body ground, the ground on your fuel pump is "duty-cycled" using a fuel pump control unit, located at the left, rear wheel well. If you need the diagnostic flowchart and wiring diagram for the fuel pump system, send me an e-mail at [email protected] and put "RE: 300ZX Fuel pump diagnostics" in the subject line.


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## jdg (Aug 27, 2009)

smj999smj said:


> Rather than have the fuel pump use a body ground, the ground on your fuel pump is "duty-cycled" using a fuel pump control unit, located at the left, rear wheel well.


Just curious here...
Is this one of those vehicles that "duty-cycles" the fuel pump to maintain X amount of pressure in the rails...that is rather than using an FPR (either engine or tank mounted type...)?


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## 90z32 (Jan 28, 2012)

*RE: fuel pressure.*

I was just wondering, for sake of ruling out the obvious. On my 1990 300zx n/a. If the fuel pump control unit is bad, can the fuel pump still be running, just not at the right pressure??? I am familiar with the 80's models but not these new 300zx's. I have a friend coming by with a pressure gauge this week. Also, what is the pressure supposed to be at?


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## mickyz90 (Feb 27, 2015)

Hey guys iv had this 1990 300 zx for about a month, I did a valve cover gasket job and she was idling fine for 15-20 min and someone just pushed the wire harness and it shut down and will crank but won't start. I did pull a cylinder out and got no spark from it. Check Engine Light Is Giving code 21 (ignition signal circuit) how do I go about fixing this? And sorry new to this as well not sure how to word asking


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## smj999smj (Jan 1, 2006)

My suggestion would be to download or purchase a genuine Nissan service manual for a 1990 300ZX and follow the diagnostic steps given for your trouble code. Hopefully you have a multi-meter and experience using it because it sounds by your desciption that you "may" have an open or shorted wire, or a bad harness connection. The service manual gives step-by-step directions on how to isolate the problem to the exact cause.


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## mickyz90 (Feb 27, 2015)

That's exactly what I did and I got to the power transistor. It didn't pass so I'm replacing that and hoping it fixes the problem. Thinking the touching of the wire harnesse was just coincidence. Thank you very much


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