8 replies to this topic

[Finchy]

First time Spec Miata owner, picked up car last week and took her out for a shakedown at the weekend.

 

Quickly discovered fuel leaking from the fuel pressure regulator (Aeromotive), end shakedown 

 

Fuel pressure while leaking was showing about 55 psi.

 

Replaced diaphragm but now getting 45 psi. 

Tried replacing the entire regulator, still 45 psi.

Checked with a second pressure gauge also 45 psi.

Adjustment screw is all the way in, pressure drops to 30psi if I back out the screw.

 

Air fuel meter (Innovate) showing 7.4 at 5,000 rpm.

Crimping hose into pressure regulator jumps to 48psi.

Crimping return hose out of pressure regulator has no effect on pressure.

Turn engine off, pressure immediately drops to about 4psi then gradually drops to 0.

 

Other things I can think of

- battery was dead when I got to the track so I had to use jumper cables multiple times.

- left car at the track Friday night, temp was in the 20s.

 

Fuel pressure seemed fine last week so I'm not convinced it's the fuel pump....

Desperately trying to get to Road Atlanta this weekend but I'm all out of ideas. 

Should I replace pump, wave my voodoo stick and hope that works ? 

Any other ideas ?

 

Thanks in advance.

Jason Finch

[Todd Lamb]

Something is wrong with your innovate. Bad sensor or wiring.

The gauges on the regulators are really junky. We just replaced one that read 45, and the new one reads a more believable 58.

[Steve Scheifler]

For sure the Innovate reading is wrong. An engine won't even run at 7.4, and it's the wrong direction (hugely rich) for a low fuel pressure situation.

Your max of 48psi with the line pinched pretty much proves the pump is not delivering, but that may be due to low voltage or current. Do you have 13/14+ volts at idle? Blip the throttle then hold the revs up a bit to be sure the alternator kicks in. If voltage stays down at 12 or less then that's a good place to start.

[Finchy]

New battery, 14+ volts at idle.

 

I tried a second quality gauge so fairly sure the psi is correct.

 

 

 

 

 

 

[Ron Alan]

Had a car at the opener last weekend basically have no FP at the regulator. Would not run. Disconnected fuel out let at top of pump and stuck a piece of hose on nipple and jumped pump...plenty of fuel! Replaced fuel filter and reconnected everything...still no pressure at regulator. Took out filter and blew air in lines toward its location. Reconnected...Fuel and pressure at regulator! Car ran. No idea where and what the blockage was but didn't care!

[Steve Scheifler]

Interesting one Ron.

If that fails, it may be time to swap the pump and cross your fingers. But without a functioning A/F meter you don't really know if it needs more pressure. 42 psi may be fine if it can hold that under full engine load, but without a dyno or the ability to watch (or record) the gauge while you drive it you may need to read spark plugs the old fashioned way.

[Ron Alan]

Had a car at the opener last weekend basically have no FP at the regulator. Would not run. Disconnected fuel out let at top of pump and stuck a piece of hose on nipple and jumped pump...plenty of fuel! Replaced fuel filter and reconnected everything...still no pressure at regulator. Took out filter and blew air in lines toward its location. Reconnected...Fuel and pressure at regulator! Car ran. No idea where and what the blockage was but didn't care!

With Steve on making sure pump is getting voltage. Just lost a motor when alternator went out and voltage got down to 11.3.(don't have a idiot light and driver didn't mention charge light was on)no FP and leaned out motor

[Finchy]

Thanks for the input guys, especially this late.

 

Kind of relieved that the A/F meter is wonky, that's new technology for me so I just assumed it worked and I knew 7.4 was definitely not right, even though it was not right in the wrong direction - doh!

 

With the A/F out of the equation I was wondering the same thing, maybe the engine isn't about to blow up.  

I'll blow the lines, check voltage at pump and inspect plugs, maybe take a fuel pump with me just in case.

 

 

 

 

 

 

 

 

 

[SaulSpeedwell]

What Steve and Todd said.  When the sensor is wrong, everything is wrong - and when sensors go wrong, it is usually much worse than when the mechanical/electromechanical system they are monitoring is wrong.  Never trust ONE sensor.  If two sensors agree, you can generally trust THAT.

 

A GOOD dyno operator with their own well-maintained wideband 02 is one of your best friends in this class, and the car hobby in general.  For a few hundred dollars - maybe less - you will get a decade of experience with 100s of cars, a couple HP of tuning gains, and 1000s of $$$ of advice on what NOT to do and what ISN'T the problem. Huge bang per buck, in my opinion.