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connecting fuel pressure & return lines backwards - what may be damaged?

themangeraaad

NAXJA Forum User
Location
Halifax, MA
This question isn't regarding a Jeep but figure the question may be somewhat generic and I might find some advice here...

If the fuel pressure/return lines were reversed and an engine was turned over for a bit, what (if anything) could have been damaged?

Backstory:
Over the past week we had to swap out the engine in my friend's Miata. Got everything finished up last night but the engine wouldn't turn over smoothly. I checked some stuff and figured out that one of the guys had reversed the fuel pressure & return lines when re-connecting them after installing the new engine. Got that straightened out and now the engine turns over smooth but doesn't fire up.

Here's what I know:
  • Engine has spark
  • Doesn't seem to be getting fuel to the cylinders
  • Has fuel at the rail, however we don't have any way to check the fuel pressure

My friend said that many people on miata forums have reported that an engine (or other part) dying could take an old fuel pump with it. Well needless to say his fuel pump is quite old so he is swapping in a new pump tonight (along with the fuel filter) hoping that is his problem. Figure the pump was old anyway so might as well get a new one installed.

The plan:
  • Install new fuel pump/filter
  • If pump doesn't fix the problem - swap injectors from parts engine
  • If injectors don't fix the problem - swap Crank Angle Sensor from parts engine

Any advice on other parts to check would be appreciated though I know it's a completely different vehicle so help may be limited...

FWIW: We double checked all connections last night and everything checked out OK so we don't think that's the problem.

Thanks
-Scott
 
I don't think anything would be damaged. The only thing might be the fuel pressure regulator but you can test that real easy by measuring the pressure at the Schrader Valve. While I have a guage, my first test is always to use a screwdriver and depressing the Schrader Valve insert. You should get a good healthy squirt of fuel.

See if you can borrow/rent a NOID light set. That will allow you to see if the pulses are making their way from the ECU to the injectors.
 
Thanks. The Miata fuel rail doesn't have a schrader valve, that was the first thing I looked for. And will definitely look into a NOID light if the fixes we try tonight don't work. :thumbup:
 
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