Hi all,

I've got a low fuel pressure problem that started after replacing my engine with a brand new crate engine. I used to run a surge tank with the factory system feeding it but have now reverted back to just using the factory system, connecting the lines as they were from factory.

I've searched and done heaps of diagnosis but have got myself stumped on what to check next. These are the things i've checked so far:

replaced fuel pump relay
checked voltage to pump at idle (8.4v)
changed fuel pumps
checked the fuel cradle for any split hoses
bypassed the factory pump housing filter in case it caused any restriction
made sure the pump to filter housing oring is seated properly and even tried double oring along with factory white plastic collar
disconnected both feed and return lines from tank to engine and blew through them to make sure it wasnt blocked
looked at all the lines whilst car was idling to check for any leaks

I fitted an adjustable FPR to the car so i can see what the fuel pressure is and am able to adjust it so that it is on 3 bar without vacuum line attached. The problem i have is that i am also able to adjust fuel pressure all the way down to 5 psi, which is not normal right? Our cars have always suffered from high pressure problems and from what i have read, unless there is a problem, getting it under 25psi is impossible with the factory system in place.

Any help is greatly appreciated! Thanks in advance.

 

The cars don't really have an issue keeping pressure down with the stock pump as it has variable voltage as you've noted in your checks. The factory FPR should get you 43-ish psi. Having really low pressure with the regulator wide-open at 84v doesn't seem worrying at all. Seeing under 25psi with the stock regulator would indicate a problem. Does your aftermarket FPR have a 1:1 rising rate like the factory? If not, that might cause tuning issues. As long as you're getting the 3 bars at setup like you stated, and you're more than likely just fine.

Most of the high pressure issues are with a hardwired, high-volume pump replacing the factory setup with the factory pump housing being a return restriction.

 

sorry i should have added that it's not a stock pump but a DW300c and my adjustable FPR is 1:1 rising rate.

I guess my issue is noticing that i can adjust the fuel pressure down to nearly zero as i really didnt think this was possible with all the inbuilt restrictions our cars suffer from, and indicated that there must be a problem with fuel supply. Also, my tuner told me that the map from the shop that did the engine swap is adding a heap of fuel, so much so, that i really need to get this fixed before he can tune my car.

next step for me is to fit a fuel pressure gauge and see what the pressure is using the factory fpr and see if it's running lower than 40-odd psi

thanks for your help!