Problem starting while engine is hot

[jp_miata]

I have a 2000 miata that often will not start when the engine is hot. This does not happen every time, but is quite frequent.

The engine turns over strong, but just sounds like it is not getting gas. On the no-gas suspiscion I gave it a shot of ether (while it was in it's "not starting" state) and it ran for a second or two (long enough to burn all the ether). That really leads me to believe that it is getting spark, but not gas (or possibly air?).

Can anyone out there give me any advice???

Thanks!!!

jason

 

[MiaTurbo]

Fuel pressure regulator leaking down? How long until it starts again?

 

[jp_miata]

Hey Thanks for the response. The down time seems to vary...anywhere from 5 minutes to almost an hour. I have not determined if it actually has to cool or if it is just luck and it decides it wants to crank.

Tell me more about this regulator.

Also, it appears that Haynes does not make a manual for a post 1997 miata. Does anyone know of a manual?

Thanks
Jason

 

[MiaTurbo]

the fact that you need to spray to start it points to a fuel issue. Several posibilities: fuel pump, regulator, injectors, or any of the wiring in between.

 

[MiaTurbo]

to answer your question, the fuel pressure regulator is the little can looking thing on your fuel rail. I has a vacuume sensing diaphram in it. At high vacuume times, like idle and cruise, the diaphram is open to allow fuel to return to the tank since the engine needs little fuel. But when you stomp on the loud pedal, the vacuume drops, the diaphram closes, and more go-juice it injected thru the injectors.

 

[jp_miata]

Interesting! I am going to check for voltage at the pump first. I am going to run a temporary jumper so I can perform a voltage check WHILE the problem is occuring...that will define the problem as being before, at, or after the pump.

I believe there is a test point for pump voltage at the test plug. Does anyone know which pin would be the fuel pump?

Thanks!

 

[MiaTurbo]

That sux that there is no Haynes manual for the NB. I really would like to help, but it's hard to do so over the net. I'm afraid that I may send you on a wild goose chase since I can't put my hands on the car in person...

 

[jp_miata]

I think I can wing it with the pre-97 manual...I picked it up last night.

 

[jp_miata]

Voltage good

OK, today I was able to duplicate the problem and confirm battery voltage AT the fuel pump. Any advice? I am going to attempt to now confirm good fuel pressure during the problem. Any Tips?

Thanks!
Jason

 

[TheMAN]

the NB uses a returnless fuel system, therefore the FPR is by the fuel pump
all the FPR looking things you see under the hood are pulsation dampers... but if those go bad, it could cause fuel pressure issues too

 

[jp_miata]

What am I seeing that looks like a fuel return line?

JP

 

[jp_miata]

I didn't know it had bee so long since I started this thread.

I solved the problem. It was the camshaft sensor.

I took it to the Mazda dealer and paid for an analysis. They found problems with both the camshaft position sensor (referred to by some parts retailers as an upper cranksaft position sensor) and the crankshaft sensor (lower). Since the crankshaft sensor (lower) was on backorder I only replaced the camshaft sensor...problem solved!!!! The crank sensor is finally in, so I am going to go ahead and replace it since the computer showed problems there, too.

Thanks for all the advice and time y'all gave me!!!!!

Jason

 

[Mazdaspeedgirl]

Glad you solved the problem. I think the info in this thread can help us all if we find the same issues occurring with our NBs.

 

[jp_miata]

Helping others is why I posted my fix. I hope it helps. The upper sensor is a 2 minute fix, but the lower is a tricky little booger. The lower has to be spaced from the crank output pulley...too close will damage the sensor...too far away will not allow it to detect the little lobes on the pulley.