Jump to content

Photo

Need help with a 1997 Miata

- - - - -

  • Please log in to reply
4 replies to this topic

#1
SlowPoke

SlowPoke

    Junior Member

  • Members
  • Pip
  • 6 posts
  • Location:Bristol
  • Region:East TN
  • Car Year:1997
  • Car Number:7

I am running a 1997 Miata with headers and a free flow intake in ITA. It consistently requires over 60 psi fuel pressure to keep the mixture in the proper range (approx. 12.6 at full throttle at 6000 rpm). I am having trouble keeping a fuel pump in the car for much more than a weekend. The car might run ok on Sat. but then on Sun. the fuel pressure starts to fall off and the A/F shows the engine is leaning out. I have been through three fuel pumps in four weekends of racing. I change the fuel filter with the pump but the filter removed is free flowing. I have the fuel pump wired on an after market switch rather than the factory circuit. Any ideas why this car requires such high fuel pressure and why the fuel pumps don't last any time at all in this car? Any assistance is appreciated.



#2
callumhay

callumhay

    Member

  • Members
  • PipPipPip
  • 163 posts
  • Location:tampa
  • Region:fl
  • Car Year:1999
  • Car Number:35
I've got a couple of thoughts..maybe you have done them already but if not maybe they will help.

If the pump is failing, then either it's electrical or mechanical. ..I can't think of anything else but maybe there is. Electrical seems most likely..have you replaced your aftermarket switch? It could be shorting especially if it has another 12 v input for a light. How about the ground? Is it in good bare metal and solid connection?. Is there a fuse in the circuit? If not, put one in and see if it blows before the pump. If you wired the pump on to an existing circuit in the car, maybe there is a problem with one of the components in that circuit, if that component is not being used, it could be shorting and you not know it . Presumably it's fine to run the pump independent of the ignition switch ..but I think there are others on the site who can better answer that. What was the reason for deleting the factory supply to the pump?

In terms of mechanical, is it possible that something could be plugging the flow from the pump to the injectors (including the injectors) . It is probably unlikely but if work has been done on the fuel lines and something fell in ( meaning a piece of the plastic quick connect) or a hose is kinked that could give you a problem with flow to the injectors and maybe burn the pump out. I think this is probably unlikely but mention it in case you have been working on the lines. Again there may be others on here who could chime in on whether this is BS! Since fuel pressure is measured in the return, I think it's possible that obstruction before the injectors would not be measurable without tapping in to the fuel line at the inlet pipe to the injectors.

Hope this helps, if you figure it out , post the cause.

Cal

#3
Ron Alan

Ron Alan

    Veteran Member

  • Members
  • PipPipPipPipPip
  • 3,732 posts
  • Location:Northern CA
  • Car Year:1995

Considering my 95 SM unrestricted at 44psi(with FPR)is running fat and safe dont quite understand why 60 psi isnt cutting it??

 

Do you have 60 psi at the near fuel rail under load?

 

I think the fuel pump just runs constant... but pretty sure if the voltage drops it acts like a rheostat and spins slower causing a decrease in pressure? Voltage issue?


Ron

RAmotorsports

 

Donor - Made PayPal donation Bona fide - A bonafide Spec Miata driver

#4
Martinracing98

Martinracing98

    Member

  • Members
  • PipPipPip
  • 143 posts
Electric motors will run at same power even if voltage drops. This means they will draw more current. So low voltage will cause them to run hot. I would check voltage at pump. Maybe wire is to small, or bad connection.

#5
Jeff Wasilko

Jeff Wasilko

    Member

  • Members
  • PipPipPip
  • 271 posts
  • Location:Boston, MA
  • Region:NER
  • Car Year:1995
  • Car Number:08

FYI My ITA Miata runs at around 40-41PSI peak.






0 user(s) are reading this topic

0 members, 0 guests, 0 anonymous users