Help! Hard Starting, Rough Idle, White Smoke, and Gas Smell

[Nate_the_IV]

Hello, gents and ladies. I have recently created this account as there is a problem I just cannot solve about my 1996 Nissan 300ZX and I hope to get some direction to what the problem may be.

My car:
1996 Nissan 300ZX
Naturally Aspirated 3.0 L V6 DOHC
Manual Transmission
No mods or swaps (that I know of), all original with 52K miles

Here is a synopsis of what is going on:
-Hard starts
-Initial rough and erratic idle
-Strong smell of Gasoline
-White Smoke expells from the exhaust (even at 72+ degrees farenheit)
-After about 20 seconds, it slowly corrects(?) itself and when driving it drives perfectly fine.

Here is what I have done:
-Changed fuel pump
-Changed fuel filter
-Changed fuel pump relay
-Changed air filter

I started having this problem a little over a month ago. Initially, I thought it was a fuel delivery problem. When I bought the vehicle, it was running fine but I also did not hear the "bad fuel pump whine" until after I stopped and left a shopping mall after I picked up the vehicle. I did not think much of it as I had no idea what it was as I drove back home 300 miles with no other problems from the car.

3 hours later after I let it sit, I decided to go for another joy ride. Alas, Lo and behold it did not start. It would crank, but absolutely no start. I cleaned the throttle body and replaced the air filter. It started, but after a very long crank. I then turned my attention to the fuel pump as I began investigating the sound and I replaced it about 2 weeks ago. But before that, I also took the vehicle to my local Nissan dealership where they said the codes were suggesting a bad fuel pump relay and so I got it replaced. The dealership was of no aid from then on as the technician reported on his joy ride that the car had no other "obvious or noticeable problems". It did not fix the hard starting issue, but it did start. I then proceeded to the install of both fuel pump and fuel filter, the car started right up without hesitation. I, of course, basked in the moment of having succesfully found the problem. I turned the ignition off after about three minutes of letting the car idle and later came back about 15 minutes later to start it up only for the same crap to happen again, hard start. It cranks but it takes about 3, 3 second turns for it to stutter and slowly rise up the RPM to 1500 where it stays. If I turn off the car at that time and turn the key to ignition again, it starts right up as any car would. Goes to 2300 RPM, then to 1500 RPM, and finally at idle 1000-900 RPM. Another weird thing I noticed was that after I turn the car on and try to turn it off about two seconds later, the engine does not shut off, even with the key out of the ignition. Also, the smoke from the exhaust and smell of gasoline did not occur until after I changed the fuel pump.

I know it is a long read, but I am trying to give all the details as to give you guys a better idea of what is going on. Anything can help. I really appreciate it! If you need me to go more in depth into something let me know! Ask questions if needed!

[rgregoryb]

Google " premierz 300zx hesitation" it covers just about everything step by step.

[Nate_the_IV]

Thanks, rgregoryb! I have started reading through it and I am starting to form a couple of ideas of what may be the cause. I will post updates on the vehicle after I replace the spark plugs (of course with NGK R PFR5B-11)and PCV valve (all of which I had ordered before the first post).

[elecfus]

white smoke = water.
water is quenching the combustion.
fuel is unburnt
unburnt fuel and steam comes out the exhaust.
blown head gasket or a water line leaking somewhere into the intake.
have you topped up the coolant at all?

get a consult cable and start checking all your sensors and calibrating them. throttle position sensor needs to be calibrated to idle properly. often it's adjusted to idle high to hide other problems with the car. what error codes do you have?

[Nate_the_IV]

I have not thought about that. I doubt the previous had done so. I will fill it with coolant and get back to yiu on that.
As for any codes, when I took it into Nissan the only error code was for the fuel pump relay. As of now, I will probably need to recheck for any.
Update: After the installation of the spark plugs, the car started up fine. I let it cool down for about an hour only for it to have a hard start again. So I will definitely start turning to sensors now.

[Nate_the_IV]

Another thing I noticed was that when removing the negative terminal for a long period of time and reconnecting it, the car starts right up without any problems. Could it be that one of the sensors "resets"? I am starting to think the problem lies within the electronics. I am going to do some investigation and give you guys an update.

[budget300zx]

Does your fan come on with the key switch?

have you checked your fuel pressure? try cycling the key a few times before starting it and see if that helps.

[Nate_the_IV]

Just checked if the fan comes on with someone checking both the timing belt and fan, and they checked out good. I will try to get a fuel pressure gauge after work tomorrow and let you know the psi. I know fuel is getting there (took out line to fuel filter and turned key to see if gas spurted out and it did. Also checked if fuel rail is also receiving fuel and it does), just not sure if the pressure is good. I will try to Ohm the fuel injectors sometime this week as well, but I have some doubt it is that as the car runs fine when driving with no hesitation. Only problem is when starting.

[elecfus]

you mean the engine runs like crap and its losing coolant when its cold? common head seal problem. when it heats up, the metal expands to seal the gaps. you're probably in for a head resurfacing and gasket replacement. I've seen people crank a car for 5 minutes on a string of batteries to get it to start and warm up to try to sell it as a working engine.

check your coolant pressure when the engine is cold. you can use an old bicycle tyre and any air pump with a gauge and just hold it onto the radiator tightly, pump it up and see if the pressure drops. or pay a mechanic to test it/get a proper tool.

check your spark plugs after cranking it a few times before it starts to see if any particular one is dirtier than another.

the ECU loads the base fuel and timing maps when it is reset. it has this table stored in an EPROM memory chip. once it loads them it starts to adjust them to give a better air/fuel ratio. it will also set the car in limp mode if any of the sensors arnt calibrated properly or are malfunctioning. in limp mode and with bad sensors it can retard the timing as much as 30 degrees while starting. if one of your sensors is bad enough to cause bad readings but also just not quite bad enough to set off a MIL or store a code then it can cause problems. sometimes o2 sensors partly fail giving bad readings. or maybe the smoke is just soot baking off the inside of the exhaust and the 02 sensors cant get a good reading because the engine is running rich. from memory I think you can run the car in a failsafe mode with o2 sensors disconnected. it will run like s*** and use a tank of gas in 100km but it will run.

a fuelling problem will give you black smoke. unless you somehow got water into the fuel system when you changed the pump.

i'd be betting on it being your heads.

[elecfus]

another thing is, if it's over fuelling on start, you can crank the engine a few times, stop, go wide open throttle with the gas pedal, crank it for a few seconds, then try to crank it again. when you crank an EFI car at WOT it cuts the gas. i think its a safety feature to stop a binding throttle body from letting you start the car on a redline but its also how you clear a flooded engine.

[Nate_the_IV]

Just did a coolant flush (as I found some sludge) and cleaned it out. No more white smoke.

But, on to another problem I failed to mention. I realized that my ZX was running pretty rich as I am only getting about 16.8~17.24 mpg (this is based on three fill ups and by dividing the amount of miles driven by the gallons of gas. It was driven till near empty which I know is bad but I had a feeling that I was getting way less mpgs than normal). I may need to go ahead and do a compression test just to be sure that it is not low compression as that could mean getting an engine rebuilt. Other factors that I realized I may be running rich was the bad idling and blackened spark plugs. I may just end up taking the ZX to a mechanic to check it through...

[Nate_the_IV]

another thing is, if it's over fuelling on start, you can crank the engine a few times, stop, go wide open throttle with the gas pedal, crank it for a few seconds, then try to crank it again. when you crank an EFI car at WOT it cuts the gas. i think its a safety feature to stop a binding throttle body from letting you start the car on a redline but its also how you clear a flooded engine.

Thanks elecfus! I did the WOT and it did just that and shut off, so I assume I did that correctly...

[elecfus]

did you check the codes? just bridge two pins on the consult port to get the codes to flash if you dont have a consult cable. but really, get a consult cable.
it will run in limp mode if a sensor is buggered. same goes for setting the throttle body sensor. the ignition module wont throw an error code. is it the 1st gen or 2nd gen type?
the gen1 modules just die. hot pieces of crap with a giant heatsink. gen2 also dies but less often. anyway if you're getting a weak or no spark it will also run like crap.
1
2

[budget300zx]

Just checked if the fan comes on with someone checking both the timing belt and fan, and they checked out good. I will try to get a fuel pressure gauge after work tomorrow and let you know the psi. I know fuel is getting there (took out line to fuel filter and turned key to see if gas spurted out and it did. Also checked if fuel rail is also receiving fuel and it does), just not sure if the pressure is good. I will try to Ohm the fuel injectors sometime this week as well, but I have some doubt it is that as the car runs fine when driving with no hesitation. Only problem is when starting.

If your electric fan is coming on with the key it may be direct wired to an ignition power source. This can back feed power and delay turn off. My stock fan was wired this way but has since been altered, no more delayed turn off.

[Nate_the_IV]

One month later after the topic was started and I finally fixed the hard start issue. It turned out the car was not starting well due to a FPR that was sending fuel to the faulty damper which in turn would send a little bit of fuel into the vacuum lines. Thus, I suspect that the fuel was "choking"/"drowning" the faulty damper that would other wise control the pulses of the fuel injectors. (I feel like this is incorrect ?)
I do apologize for not having shared my findings sooner, but work and homework have been hectic lately. But, here are some things I learned:
1. The car would actually start faster if I disconnected the vacuum line going to the damper as fuel would not choke the line.
2. The only reason why my car would start faster after working on it or leaving the battery disconnected was due to I somehow always leaving a fuel line open which would allow the fuel to evaporate and thus eliminating the potentiality of a hard start as I have now found out.
3. FPR was actually making the car run too rich (I measured a constant 55 psi on fuel pressure), which resulted in the smell of gasoline.
4. Rough idle was due to the injectors not pulsating correctly as the damper was not working well.
5. As a newbie, things get confusing,
After replacing both the FPR and damper with OEM ones from Z1, the car is running great.
So, all in all I do appreciate all of the help. Thanks guys!

[rgregoryb]

Good to hear, and thanks for coming back with the solution!