Fuel Pressure Leakdown
 

Been reading some threads about flooding and fuel pressure and leaky injectors so I decided to see how long it takes my FP to leak down. I have a sard FPR and generic gauge hooked up to it. After I shut the car off it goes from around 32 up to 35 or 36. And then sometimes it will leak down to 5psi after only 15 mins. Sometimes it takes 30 mins. Do you think this could possibly be leaky injectors? Or is it normal? Its been flooding lately and hard to start, but its very intermitent. Also the fuel pump is rewired and I thought this might be the reason I get a high reading during idle(35ish psi). And I have adjusted it with the vacuum off before and fuel pump on and car off to 41psi. Any info or questions are appreciated. Thanks

Chris

******. After I shut the car off it goes from around 32 up to 35 or 36.*****

I think that is normal. Fuel pressure at idle according to the fsm is 28 psi at idle. Your 32 is close enough for me.

The pressure goes up when you shut the engine off, because the vacuum on the fpr vacuum line is now removed. At atmosheric pressure the pressure should be approx 37 psi, so that's what is happening. Loss of vacuum plus higher fuel pressure b/t the pump and the fpr. I've seen the same thing happen when the key is put to OFF. The pressure rises a couple of psi at the rail because the vacuum has been removed and there is still pressure b/t the pump and the rail, and that pressrue is higher than what you were seeing with the engine running.

The thirty minutes or so for leak down seems normal. Less than five minuites makes you wonder if it is the fuel injectors or the fuel pump. Only way to tell would be to tie the injectors to the fuel rail, apply pressure to the rail then remove it and look for dripping. In my mind it would take more than a few drops a minute. It'd almost have to be flowing for the pressure to dr0p down that fast (less than five minutes).

Pressure around idle is 35ish, and its a rewired walbro. I understand about the pressure buildup after shutoff but it leaking down within about 15 or 20 mins is what I was concerned about. I will do the leakdown test soon. Anyone else think thats too fast?

Chris

I'm looking at the series five FSM, Fuel section and it says that after five minutes the pressue should still be More than 18psi after the key is turned to off.

It also has a checkout of the fuel pump by itself for leak down pressue after a given amount of time.

Page F2-46 of the online series five FSM.

Thanks, I'll take a look at it. Although I'm not sure if it would apply seeing as how the car is an s4 with s4 rails, s5 injectors, and aftermarket pump and regulator. Damn I need a standalone.

Chris