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tooright 11-29-2011 03:00 PM

fuel pressure regulator????
2000 Wrangler, 4.0 .... plugs,wires,intake, throttle body all good (NO ENGINE LIGHT). Hard starting; go from "start" (failed attempt) to "on" then back to start, fires right up. Once a week or so, stalls at idle and shuts down .... cold or hot. Starts right back up.
Fuel pressure at manifold: key "on" .... immediate 47-48 psi then falling off after one second to 30 psi, bleeding down to 24-20 psi. Engine running .... 47-48 psi steady. Shut down engine, immediate bleed off in pressure to 25-30 psi then slowly bleed down to 18-20 psi.
Dealership sells only pump with regulator. Advanced auto sells seperate or together pump and regulator.
Feels like a fuel pressure regulator to me ..... advice as how to narrow it down????

my98tj 11-29-2011 03:28 PM

i think you have narrowed it down to the pressure regulator. sells them for around $60.

sfhusser 11-30-2011 07:18 AM

When you shut down the engine, it is normal to bleed off pressure. Any type of fluid pressure system will automatically start bleeding down when the pump is stopped, so that is not a big deal. What is interesting is when you are bleeding down from start up. I don't know what the normal PSI should be after start up, but my understanding of fluid dynamics, is that you will get a sudden burst in pressure at start up, and will slowly bleed down to a stable pressure. For a fuel injection system, I would think that anything from 30 to 60 PSI depending on the type of FI system you are using is not that far off from normal.
The interesting part is that the pressure will bleed off before you start the engine. The fuel pressure should stay high (47-48) when key is on, start up should be around the same, and then drop off. That is interesting that you are dropping at the "priming" point. I don't know if I would say that is a regulator problem rather more a pump problem. It seems that as the pressure builds it is pushing back against the pump causing the pump to slow down, almost like a backflow problem.
Just my two cents.

tooright 11-30-2011 12:57 PM

Normal PSI should be 47-48 +/- 2 psi ..... There is no bleed down on pressure with the engine running; just when the ignition is put to "on" position (no attempt to start) does the pressure rapidly rise to 47 psi then drop off suddenly (1 second) to 25 psi or so.
Mechanic at dealership said pump will run for 3 seconds then shut down if no rpm detected. He also stated that once the pressure is up, there should be no bleed-down.
Disturbing as to why there is engine stalls every few days ..... unknown what fuel pressure is at time of stall as I am sitting at idle at a stop light 9/10 times.
Should not the pump be suppling pressure with engine running reguardless of regulator status???

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