Fuel Pressure Test. Is something wrong?

[DJ23GSX]

I've been battling high idc's so today i checked my fp to see if it was raising 1:1. My first test at 42psi bfp i applied 20psi to the afpr and as expected fp raised to 62psi. I upped the boost soure to 25psi and got 66psi fp but no matter how much more boost pressure i added to the afpr it would not raise fp over 66psi. I also tried 45psi bfp and added 25psi to the afpr and got the same 66psi fp. Its a brand new aeromotive afpr. I am also running a rewired walbro 255. Shouldn't the walbro be able to push that much fp under that much boost? I pinched off the return line for a moment and even then i only saw 68-70psi fp. Last summer i replaced the seal on the pump where it meets the sending unit.

I've been battling high idc's (90%) on 650's 2g maf fmic and a s16g at 20psi on 93 octane and was hoping this was the culprit but after seeing the afpr raise the fp accurately up to around 23psi i don't think this is the problem.


I'm looking for any ideas on what might be going on or somethings to look into.

Thanks

 

[dcjackson22]

are your plugs white? if so you have the same problem i have.

 

[steve]

I've been battling high idc's so today i checked my fp to see if it was raising 1:1. My first test at 42psi bfp i applied 20psi to the afpr and as expected fp raised to 62psi. I upped the boost soure to 25psi and got 66psi fp but no matter how much more boost pressure i added to the afpr it would not raise fp over 66psi. I also tried 45psi bfp and added 25psi to the afpr and got the same 66psi fp. Its a brand new aeromotive afpr. I am also running a rewired walbro 255. Shouldn't the walbro be able to push that much fp under that much boost? I pinched off the return line for a moment and even then i only saw 68-70psi fp. Last summer i replaced the seal on the pump where it meets the sending unit.

I've been battling high idc's (90%) on 650's 2g maf fmic and a s16g at 20psi on 93 octane and was hoping this was the culprit but after seeing the afpr raise the fp accurately up to around 23psi i don't think this is the problem.


I'm looking for any ideas on what might be going on or somethings to look into.

Thanks

A couple of things to keep in mind.

At WOT the car is in open loop so the ECU has no idea if your running rich or lean. The injector pulse width and the IDC derived from the IPW are solely based on measured airflow, the ECU's injector global, and any enrichments the ECU thinks it needs to add.

Adjusting the base fuel pressure will have no effect on the IDC, unless you also make changes in the tune to maintain the same AFR.

Fuel pumps have a pressure relief valve. It limits the pressure at the pump and once it opens the flow rate drops off quickly. Every restriction between the pump and the fuel rail causes a pressure drop so while you might be seeing 66 psi at the regulator you could be seeing 75+ psi at the pump depending on the losses in the hoses, fittings, filter, etc. It the seal to the pickup pipe isn't good you'll also be limited to the max pressure before it leaks so badly the pump can't pump build any more pressure.

 

[DJ23GSX]

A couple of things to keep in mind.

At WOT the car is in open loop so the ECU has no idea if your running rich or lean. The injector pulse width and the IDC derived from the IPW are solely based on measured airflow, the ECU's injector global, and any enrichments the ECU thinks it needs to add.

Adjusting the base fuel pressure will have no effect on the IDC, unless you also make changes in the tune to maintain the same AFR.

Fuel pumps have a pressure relief valve. It limits the pressure at the pump and once it opens the flow rate drops off quickly. Every restriction between the pump and the fuel rail causes a pressure drop so while you might be seeing 66 psi at the regulator you could be seeing 75+ psi at the pump depending on the losses in the hoses, fittings, filter, etc. It the seal to the pickup pipe isn't good you'll also be limited to the max pressure before it leaks so badly the pump can't pump build any more pressure.

Thanks i was waiting for your input. You've helped me out with some good info in the past.


I figured out it was the fp gauge that wasn't reading correctly. I put my old one back in and without any changes to the regulator my bfp went from 42psi up to 50psi. Once i set my bfp back down to 42psi i hooked up a boost source and the regulator indeed raised fp 1:1 all the way up to 35psi. Now that the bfp is back down to a true 42psi and not running at 50psi i am sure i will have to richen up the safc a bit pushing my idc's even higher. My plugs are more greyish than white i'd say. I've been searching threads for a few weeks and only a few people are having to dump as much fuel as i am with the similar mods. Most are well into the negative % hi safc settings and i am closing in on +10% hi safc settings at 20psi on a s16g 2g maf 650s fmic rewired walbro 255 aeromotive afpr. I don't believe its rich knock either because it does come down when i add fuel.