Fuel Pump - Hissing Sound 1998 Boxster

[AK986]

Hi Guys, 

 

I'm stuck with the P1124 and P1126 codes. I did a smoke test multiple times and found no vacuum leak. However, I noticed the fuel pump making a hissing sound. Is this normal? 

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[JFP in PA]

P1124 and 1126 indicate that the intake mixture is so lean the DME cannot compensate.  The hissing sound you hear is a vacuum leak, probably in the EVAP systen that is causing the lean condition, or the fuel system pressure bleeding off at the pump doing the same thing.  Time to test fuel pressure and delivery rates, if they are good, you are back to a vacuum leak.

[AK986]

Always to the rescue 🙂, thank you JFP. 

 

I ordered a new MAF sensor. The current one is reading 11.75 KGH at idle, which is lower than the normal range, I believe. I replaced the vent value last weekend, and I did not hear any noise. This is directly from under the battery. I couldn't move the battery to see it properly because of the short cables. Once I removed the battery, I checked all the connections, and they seemed fine.  That's definitely not a normal sound, right? I order the fuel pressure gauge to test the pressure. 

[JFP in PA]

It should not be hissing.

[AK986]

I took the battery out and inspected all the connections and wires on the fuel pump. I found one wire that was barely holding on, which was for the vent sensor. It's hard to inspect without the battery on and the car running. I tried taking the battery out and connecting the wire with jumper cables, but the car wouldn't start. The terminal wires are so short, lol. 

 

Any idea what that hissing could be? 

Edited September 20 by AK986

[JFP in PA]

I would correct the vent senor wire and put it back together and see if the noise is gone.

[AK986]

Hissing is still there lol.. Sadly. 

[JFP in PA]

Have done the fuel system tests yet?

[AK986]

I'm going to do that today. I ordered the fuel pressure test kit, which arrived yesterday evening. If the pressure is low, then it's probably the fuel pump. The car has been parked for ten years. 

[JFP in PA]

What I would be looking for is the fuel pressure at idle, and after sitting for a bit, recheck the sitting pressure, plus the delivery rate. Fuel pressure and delivery rates are tested by connecting an appropriate gauge to the port (items #6-7 in the diagram) on the fuel rail. Engine off pressure 3.8 +/- 0.2 bar; engine idling 3.3 +/- 0.2 bar. A second critical fuel system test for these cars is delivery, or how much fuel volume is the pump putting out. In 30 seconds, your pump should deliver at least 850 cc of fuel.