# 1986 Nissan 300zx hard start.



## Treacy (Jul 3, 2013)

I recently bought a 1986 Nissan 300zx for $500. I am 20 years old and this is my first car. The car sat for 12 years, but is in pretty good condition. It is non-turbo and has an automatic trans. There are many things that need to be fixed on it. My main problem is it takes me 13 seconds to start it in the morning. Even after it starts, if I press the gas right away it dies. Once it's running, I have no problems. The "pick up" is horrible too. 0-60 is 13 seconds. I put in new spark plugs (properly gapped), new spark plug wires, new distributor cap, and distributor rotor. The fuel filter is new, but everything else is original. Also the fuel temperature sensor is broken off. Does anyone have any solutions for me?


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## rogoman (Dec 16, 2004)

One of the first things you need to do is replace the timing belt that drives the cams, if you don't know when it was replaced. The replacement interval is every 60,000 mi.

The hard starting and slow acceleration may be due to low fuel pressure or improper ignition timing. There may also be a major intake system vacuum leak.


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## Treacy (Jul 3, 2013)

Thank you rogoman for the quick reply. I don't think the timing belt has ever been replace so I'll change it. 

As for the hard start, how do I go about individually diagnosing these problems, the intake system vacuum leak, ignition timing, low fuel pressure? Also if I have any of these problems what do I need to repair or replace?


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## smj999smj (Jan 1, 2006)

The air regulator mounted on the right side of the intake plenum controls the cold start fast idle. Along with checking "the basics," that might be a good thing to check.


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## Treacy (Jul 3, 2013)

Thanks smj999smj for you reply. How do I go about checking the air regulator? I am still new to cars and could be called an apprentice mechanic. I have a "Haynes" book for my car but it doesn't seem to have a whole lot on the air regulator. Do you have any other suggestions or solutions to help me with my problem?


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## rogoman (Dec 16, 2004)

Treacy said:


> As for the hard start, how do I go about individually diagnosing these problems, the intake system vacuum leak, ignition timing, low fuel pressure?


To check the intake system for a vacuum leak, attach a vacuum gauge to a full vacuum source. With the motor fully warmed up, the reading at idle should be 18 - 20 InHg. At 3,000 RPM, it should be around 21 InHg.

If readings are under 18 InHg, check the intake manifold nuts to make sure they are tight. Also check the intake plenum bellows at the throttle valve and at the MAF for cracks or loose clamps.

To check the ignition timing, first disconnect the idle-up solenoid valve harness connector. The ignition timing should be set to 20 degrees BTDC.

To test the fuel pressure, Tee-in a tempoarary fuel pressure gauge at the output side of the fuel filter. The readings at idle should approximately be as follows:
- with vacuum hose connected to the fuel pressure regulator: 28 psi
- with vacuum hose disconnected from the fuel pressure regulator: 37 psi


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## smj999smj (Jan 1, 2006)

Air regulator is basically an electric motor that controls and air port. Remove it with the engine cold and look inside and you should see a metal door closing off the port. Apply 12v power and ground to the appropriate terminals and the motor inside should run and open the door, thus opening the port. If the rubber elbow hose on it is original, it is probably hard as a rock and brittle, so you may wind up getting a new one.


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## Treacy (Jul 3, 2013)

Thank you rogoman and smj999smj! I'll get to work on your suggestions and give you guys an update when I am finished.


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## Treacy (Jul 3, 2013)

Hi guys, 

So I just replaced the fuel injectors today. It's something I have been wanting to do for a while. I was also hoping that it might be part of the problem why my car is hard to start. So after I replaced the injectors and installed everything I started my car. Well my problems have gotten worse. I have an extremely bad idle that cannot be corrected by checking the timing. If I push on the gas pedal the car does throttle up, but roughly and then the rpms start to drop to 7,6, and 5. At 5 the car sound so bad I just shut it off. One of these time I did try giving it a little gas, but then it died. All the spark plug wires are seated correctly and all the electrical plugs are all plugged in tight. Nothing looks out of the ordinary. Could this be my problem from earlier that just got worse from me "messing" with my car so much. I did try starting the car without the air regulator electrical plug actually plugged in and it started up just the same. While the engine was running, I plugged the electrical plug back into the air regulator. This extremely bad idle be related to anything other then the fuel injectors I put in? Possibly a bad MAF or air regulator? 
I am new to cars. Literally I learned everything I a doing from working on this car. Unfortunately for me there isn't a whole lot on z31s and not a whole lot of people own or work on them. For a novice mechanic it is extremelt difficult to work on this car. So I ask that you guys have some patients with me. I need all the help I can get.


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## smj999smj (Jan 1, 2006)

I would get a "noid light" for Bosch-style fuel injectors to test each injector harness and make sure it's firing, assuming you already checked to make sure the ignition wires were crossed up when you had it apart. (Maybe first you should double check your firing order?) IIRC, Z31's fired all six injectors at start-up and then fired each bank of injectors separately. In other words, cylinders 1-3-5 fire all at once and 2-4-6 fires all at once. Originally, each injector had a separate ground wire to the ECM. When Nissan came out with it's voluntary fuel injection campaign on the 300ZX years ago, the kit cam with an injector subharness that ran each bank of fuel injectors off of the two wires going to the center injector on that bank. These subharnesses were identified by a piece of yellow or gray tape wrapped around the harness; you'll have to check and see if this was performed on your vehicle or not, or you could have a Nissan dealer check your VIN to see if the campaign was performed on your vehicle. In the two-wire configuration, if one of those two wires became open or shorted, it would cause the entire bank of cylinder to not fire the injectors, causing the engine to run very poorly. The noid light can verify this if this is the case.


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## rogoman (Dec 16, 2004)

If the ignition wiring is correct and a 'noid light' test on each injector show they are all firing, then you'll have to isolate the cylinder(s) that may be dead. You can do this by pulling a spark wire from a plug one at a time while the engine is idling. Once you find the dead cylinder(s), you 'll have to determine if there is an ignition or a fuel problem. If the dead cylinder has a good ignition spark, then the injector may be dead.


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## smj999smj (Jan 1, 2006)

Then there's always the possibility of a mechanical issue, ie jumped timing.


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## Treacy (Jul 3, 2013)

Gentlemen,

I am happy to say I found the source to this recent bad idle problem. One of the spark plugs became unseated and one spark plug cracked. After tightening the one and replacing the other, everything runs fine. Tomorrow morning when I start the car, I will see if the new injectors fix the hard start problem, even if only a little. Quick question, all of my spark plugs are Champions. Not by choice either. The plug that cracked, I replaced with a NGK spark plug. Will having different brand plugs like that, effect performance or any general workings of the car. Also I've heard that if the battery is "unplugged" from the car that a security thing occurs in the car and the radio won't work. Is this true?


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## smj999smj (Jan 1, 2006)

Nissans come from the factory with NGK spark plugs, like most Asian makes, and it is best to stick with NGK. Certain plugs, especially Bosch platinums, don't perform well in Nissan engines. In general, aftermarket parts on the whole often don't fare well in Nissans. When it comes to ignition parts, stick with NGK spark plugs, NGK or genuine Nissan spark plug wires and genuine Nissan distributor caps and rotors. For the correct NGK plugs for your vehicle, go to NGK Spark Plugs USA and use the part locator.


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## Treacy (Jul 3, 2013)

Follow up,

Since the fuel injector change, my 300zx starts up like a dream. It's a feeling I've never had before and it's great! 

As for the spark plugs, I will definitely change those over to NGK when my next spark plug tune-up rolls around. 

My last performance issue is: when my car comes to a stop it idles low down to 6-5 rpm and can stall. If I it the gas it tends to ward the stalling off. I believe I found the problem to that though. I just check my idle speed last night and when I went to unplug the idle up solenoid, I found the clip is broken. So the plug was partially unplugged. I wired it closed and then cleaned the throttle body. Hopefully tomorrow after I've cleaned the MAF, I will have no more problems with my 300zx.

I've give you guys a heads up and let you know how everything goes.

Thank you guys so much for all your help! Give yourselves a pat on the back, because your making my first car become my dream car.


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## GiseleLentine (Jul 25, 2013)

Well first thing you really did buy a very old model..i mean that car is 12 years old..what do you expect from it..i think you should definitely shell out some money and get it overhauled. Because once this problem is fixed i am pretty much sure that an another one is very likely to pop up..so it is better to get it repaired.


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## Treacy (Jul 3, 2013)

I would love to over haul it, but I'm on a "barely-making-it" college student budget. If it's farely cheap to do and something I think I can handle, I do it. I did pretty much over haul a few of the major systems in the car.

Ignition system: New spark plugs, new spark plug wires, new distributor cap, and new distributor rotor.

Fuel system: New fuel filter, new FPR, and new fuel injectors.

The air system and maybe my fuel pump are the things I'm a little concerned about. I have a slight heisitation issue when it comes to acceleration and idle problem that only occurs when I'm at a stop light, stop sign, etc.

I do have a new cone filter and I plan on cleaning the MAF. 

All that said I absolutely love my z31. I'm surprise that not a whole lot of people have interest in them. 

By the way: do any of you guys know where to find replacement hose that come out from the upper intake pipe? Mine work, but are definitely on their way out the door.


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## smj999smj (Jan 1, 2006)

"Well first thing you really did buy a very old model..i mean that car is 12 years old.."

Well, being an '86 model, it's actually 27 years old!

If you are talking about the rubber air ducts, you can still get them from Nissan. Refer to the parts diagram link:

http://www.nissanpartszone.com/Page...7&isBigPicture=true#ctl00_cphView_pnlPartList


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## GiseleLentine (Jul 25, 2013)

Sorry my bad..i misunderstood sitting of car as its lifetime. And Treacy, i might have something for you..why don't you visit autoanything.com..i did buy a set of tires from them..they were not of the best quality but they did come at a relatively cheaper price..so my suggestion would be to purchase from them for now so that you can get along with your ride for time being and when you gather up enough money, you can just switch to better quality parts..also i'd suggest you to visit a flea market once a while..they really have great prices on used spare parts..you might get lucky out there.


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## Treacy (Jul 3, 2013)

Thank you smj999smj for the link. It was very helpful. Thanks for the advice GiseleLentine. They have flea markets all the time in the town near my college. I'll have to stop by and check them out more often. 

Update:

I cleaned my MAF yesterday. It was pretty clean by the looks of it. The problems with stalling while stopped and heisitated acceration have not go away. I'm starting to think my fuel pump will go at anytime. It's the only part of the fuel system that hasn't been replaced. What are your thoughts on this issue? Should I replace the fuel pump?


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## smj999smj (Jan 1, 2006)

There's a plate in the trunk over the fuel pump. Remove it and inspect the top of the sending unit as these were known to corrode and rust over the years. If that looks good, get a fuel pressure test gauge (many auto parts stores have them in their tool loaner programs) and test the fuel pressure and see if it's within specs. If the fuel pressure is within specs, I don't see any reason to replace it.


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## Treacy (Jul 3, 2013)

Sounds like a plan smj999smj. I'll have a look at the sending unit as soon as I can. In the case that the sending unit is bad, are they farely easy to find? I've never heard of an auto tool loaner program. Does PepBoys or Advanced Auto Parts have a tool loaner program?


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## smj999smj (Jan 1, 2006)

I know the Advance Auto Parts near me does. Give them a call. Most of the parts for your car are still available from Nissan. In most cases, you are better off sticking with genuine Nissan parts, depending on what it is. The unfortunate thing is the most of the Nissan parts for vehicles that were made in Japan tend to be a lot more expensive that those made in the US. For example, a strut for an Altima might be $90 compared to a Japan-produced Maxima or Z-car, which might be $300+. On the plus side, the 300ZX is a popular car so even though your car is almost 30-years-old, you can still get parts for it!

After thinking about this, I remember the fuel pump and fuel sender are separate in this vehicle; there should be an access plate for each, if I'm not mistaken, so the sender doesn't come into play for the fuel pump operation. It's been awhile since I've had to work on one!


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## smj999smj (Jan 1, 2006)

Yeah, now my memory is restored! Check the part diagram link below. The unit for the gauge is part code 25060. Part 17020Y is the fuel pump and part 17010Y is the fuel pump assy., which comes with the fuel pump. Check the top of 17010Y for the corrosion. If you do need a pump, get the assy. as it's only another $30 more than the pump alone.

http://www.nissanpartszone.com/Page...2&isBigPicture=true#ctl00_cphView_pnlPartList


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## Treacy (Jul 3, 2013)

Update:

I replaced the air regulator and I'm not seeing any real difference in my cold start. Not as bad a cold start before though.

I ended up buying a fuel pressure tester and it comes with the "T" fitting so I don't have to go and buy one separately. I'm going to test my fuel pressure asap, but I am curious the outlet on this "T" fitting looks kind of like a car tire in that it looks like it would hold to fuel back even when the pressure gauge isn't attached. Would it be wise to cap the "T" fitting and leave it on the fuel line?


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## Treacy (Jul 3, 2013)

Hi Guys,

I checked the fuel pressure this afternoon. It was 28 psi with the vacuum connected and 38 psi disconnected. 

My next move is to check the vacuum. I check around the engine compartment with carb cleaner trying to find a leak, but I wasn't able to cause the engine to stubble with the carb cleaner. I sprayed around the intake collector and all the vacuum connections. 

I plan on replacing all of my vacuum lines in the next couple weeks. They are all bad looking, cracked, old, or extremely easy to take off with little to no effort. 

I'll keep you updated.


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## Treacy (Jul 3, 2013)

I just performed the vacuum test on my z. I "T" it into the vacuum line that comes out of the front of manifold. The line near the fpr line. It fluctuated ever so slightly between 22-18 in Hg. Mostly is sat at 20 in Hg. I guess that means there is no vacuum leak?


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## rogoman (Dec 16, 2004)

18-22 in hg is good vacuum which means no vacuum leak. Fuel pressure looks good too.

On a cold engine, a good air regulator will idle the engine at around 1200 rpm.

You might want to check the idle-up solenoid for the idling problem.


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## Treacy (Jul 3, 2013)

Good to hear on the other things. 

Do the idle-up solenoids tend to malfunction or is it a matter of adjusting it?


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## rogoman (Dec 16, 2004)

The idle-up solenoid itself has no adjustment. It's part of the AAC valve. There are only two adjustments on the assembly; one is the base idle speed, which is to the right, and the other one is for the FICD. The FICD is a secondary solenoid. When it opens, it allows a specified amount of additional air to enter. It's purpose is to raise the idle immediately when turning on the A/C compressor, or when the power steering pump is under heavy load (turning the steering wheel while idling, for example). The additional idle speed is to help the engine compensate for the added load of these accessories, rather than simply stalling out.


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## Treacy (Jul 3, 2013)

Ok. I'll have a look at it and see what I come across. I'll consult the Haynes book and see if they have some trouble shooting tips for the AAC. 

Thanks for the reply rogoman. I'll keep you posted on the results.


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## Treacy (Jul 3, 2013)

Update:

This is long over due. but here goes. I finally found the culprit to my idle issues. I changed the spark plugs, which were 5 Champions & 1 NGK to 6 NGK V-power, and now my Z runs like a dream. There is still a very minimal idle change here and there, but no where near as bad as before. It's no longer a problem now. I still have a hard starting problem when the engine is cold though.


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## Treacy (Jul 3, 2013)

Changed the ignition coil and O2 sensor. No change with the O2 sensor. Slightly shorter hard start time with the iginition coil and stronger faster engine starts once the engine is warm.


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## BeyondBiscuits2 (Jan 18, 2006)

I had the same issue with my Z before I rebuilt my engine. No matter what I did, it took forever to start on a cold morning, and would run terribly until it warmed up. I replaced everything from the distributor to the coolant temperature sensor, but with no avail. I ended up consulting a Nissan mechanic, who told me it was a common problem with the VG30E. Apparently, it happens to higher mileage VGs, and is caused by carbon. I ended up rebuilding my engine, and when I did, I had the cylinder heads professionally cleaned as well as the intake plenum and runners. Between that and new head gaskets (I did not touch the piston rings, by the way), she fires up like a champ every cold morning now.

Long story short, you might consider running a carbon cleaner through your engine, something like Seafoam or a rival product.


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## Treacy (Jul 3, 2013)

Yeah I've just about tried everything myself. One of my last attempts to fix this problem is to replace my timing belt, which is due anyway. I followed your advice though and I bought two cans of Seafoam today. I put one in the fuel tank and the second one I'm probably going to put in the oil and crankcase.


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## Treacy (Jul 3, 2013)

Update:

I changed my timing belt, water pump, tensioner pulley, and tensioner spring, camshaft seal. The tensioner pulley was disintegrating and I had a leaking camshaft seal. The tensioner pulley fell apart in my hands. My idle is smooth and my performance has gottne better. Not to mention I'm not leaking oil any more. 

Still doing the sea foam treatment.


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## Treacy (Jul 3, 2013)

I replaced the throttle postion sensor a few days ago and it still hard starts. I'm still trying to track down the hard starting problem.


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## Treacy (Jul 3, 2013)

I replaced all of my vacuum lines yesterday with high performance blue silicone vacuum lines. Not only does my z start up normally, but my engine compartment looks amazing.  Those old, cracked, black vacuum lines really do make an engine look horrible. If only I had changed the vacuum lines sooner, I would have not have spent so much money on other fixes. It is what it is.


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## RenaAlvidrez (Nov 25, 2013)

why to think of what have not been happened as now the time you are done with it instead leaving it to fix in the future any time .. so enjoy it !


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## Treacy (Jul 3, 2013)

So I am not out of the woods yet. The hard start problem is there but nothing like it was before. I have pretty much isolated the problem to the fuel pump. I believe (I am almost 90% sure) that I have a weak/sludgy/lazy/slow fuel pump or the check valve in it is bad. My z only hard starts when the fuel wasn't previously under pressure. Since it only hard starts in the morning on the first start, the pump has to be the culprit. 

I'll keep you updated.


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## xwmstormx (May 9, 2014)

Interesting little conversation.

My Z has the same hard start issues. Tracked it down to either the Fuel Temp Sensor or the Fuel Pump. One from the ECU and by verifying the issues using a DVM. I did break the FTS during testing so replacing that with the Fuel Pressure Regulator.

The Fuel Temp sensor (which you said is broke) monitors the fuel temp which tells the ECU to either richen up or lean out the fuel. That being broken the ECU can't enrichen the fuel on a cold start.


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## Treacy (Jul 3, 2013)

Everything in the fuel system is brand new. New: Fuel Pump, fuel filter, Fuel Pressure regulator, fuel temperature sensor, and fuel injectors. 

Everything in ignition is brand new. New: battery, rotor, distributor cap, spark plug wires, and spark plugs. 

The air system is the only thing not completely replaced. I only replaced the air regulator and vacuum lines. My MAF is clean and worked last time I checked. My PCV works. My EGR valve is the rustiest part under my hood at the moment and my air duct pipes really need to be replaced. 

If you guys have any ideas, I would be grateful. My next thing to replace is the EGR valve. Unless blocking it off is a better idea.


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