General 560cc 1g base fuel pressure.

[looseboost]

I have a quick question concerning fuel pressure, I have a 255 rewired, aeromotive afpr, and 560cc injectors, this is on a 1g where the stock fuel pressure is 37-38psi where it is currently set, Im wondering if I should set the fuel pressure to 43psi where the injectors are tested? Or should I leave it where it is set?, I'm just attempting to get the proper amount of flow without complicating tuning.

 

[lil corb]

If you have a 1g leave it to where it should be 37-39. If you are using ECMLINK, it'll ask what CC are the injectors, that compensates for the amount of fuel the ecu sends to injectors.

 

[looseboost]

No link yet tuning with safc2 and wideband.

 

[talontd92tsi]

NO Link, set it @37.5 psi

 

[looseboost]

Thanks guys.

 

[Mello]

Gee I guess I'm the oddball. Set the pressure as specified by the injectors. 1g's injectors are flow rated lower & why their set lower. Fuel pressure is set by injector design & best atomization pressure across the injector nozzle, which is constant from the fuel pressure regulator.

 

[curt-s]

The ECU, by default, is set to open and hold the injector open a specific amount of time based on the stock 450cc injectors set at the base fuel pressure for a 1g. It knows what they flow at that rate for a specific unit of time. If you change the pressure to the "universally tested at" rate of 43.5 or so, you're changing the flow rate and will have to compensate extra in the SAFC, possibly overrunning it because you cannot change the parameters enough to dial in the extra air. You're modifying not only flow rate but pressure; two variables you'd have to compensate for.

On the other hand, keeping the pressure the same and just tuning based on the increased flow rate for the higher flowing 560cc injectors will make your job that much easier.

Even ECMlink calculates the flow rate of your injectors when you compensate for larger sets this way. You can specify a new base fuel pressure, but it will convert to whatever the stock is for the platform you're running on.

 

[steve]

1g's injectors are flow rated lower & why their set lower.

The 1G injectors are all rated at the standard 3bar (43.5psi) pressure. They are used at various other pressure in a DSM for reasons we can speculate at but only the original engineers know for sure. The ECU is programmed with that effective flow rate and the injector response times vs voltage for that use case. In a 1G manual car the effective flow rate is about 411cc/sec vs the rating 450cc/sec due to the difference in base fuel pressure.

 

[talontd92tsi]

The ECU, by default, is set to open and hold the injector open a specific amount of time based on the stock 450cc injectors set at the base fuel pressure for a 1g. It knows what they flow at that rate for a specific unit of time. If you change the pressure to the "universally tested at" rate of 43.5 or so, you're changing the flow rate and will have to compensate extra in the SAFC, possibly overrunning it because you cannot change the parameters enough to dial in the extra air. You're modifying not only flow rate but pressure; two variables you'd have to compensate for.

On the other hand, keeping the pressure the same and just tuning based on the increased flow rate for the higher flowing 560cc injectors will make your job that much easier.

Even ECMlink calculates the flow rate of your injectors when you compensate for larger sets this way. You can specify a new base fuel pressure, but it will convert to whatever the stock is for the platform you're running on.

I ran into a similar problem when I first put my old 91 on the road. The previous owner had put a NT fuel pressure regulator which has 47psi base pressure (give or take). I had to pull 10-11% out across the board on the SAFC (way back in the day ) to get the car to actually run and not pour raw fuel out the tailpipe.

You are 100% correct that the ECU can't compensate for the extra fuel pressure.

 

[1990TSIAWDTALON]

Throw a 2G maf on that thing.

 

[GRAVEDIGGER]

Throw a 2G maf on that thing.

That's right! A 2g maf will put you just about where you need to be with those injectors. That's what I'd do too.

 

[curt-s]

I ran into a similar problem when I first put my old 91 on the road. The previous owner had put a NT fuel pressure regulator which has 47psi base pressure (give or take). I had to pull 10-11% out across the board on the SAFC (way back in the day ) to get the car to actually run and not pour raw fuel out the tailpipe.

You are 100% correct that the ECU can't compensate for the extra fuel pressure.

Well, it will try when it sees the O2 feedback It will pull fuel by a massive amount to try and compensate, but still run like shit. Not to mention the time it takes in order to reach that learning point it will be dumping fuel in and washing everything out. It would make for a pretty interesting exhaust colour, though.

2G MAF, pretty popular swap to compensate for that size of injector, lots have done it. It won't run as well as it would with a tuning solution, but the plug harness adapter is a DIY item, and it will at least get you off to a running start. It's also a much more accurate sensor in the whole shot. You should actually do pretty good with that.

What I've found with them is your filter + filter adapter make a HUGE difference in airflow readings, however. At idle with a 2G MAF and a 2G ECU I've had to drop my Hz by around 8% and then increase above 150Hz. I've got the crappy adapter without the smooth lead-in, though, and a sub-5" filter to boot, so I have no doubts about it screwing with the airflow. Anyway, different conversation and I'm good to leave work now.

 

[talontd92tsi]

Well, it will try when it sees the O2 feedback It will pull fuel by a massive amount to try and compensate, but still run like shit. Not to mention the time it takes in order to reach that learning point it will be dumping fuel in and washing everything out. It would make for a pretty interesting exhaust colour, though.

2G MAF, pretty popular swap to compensate for that size of injector, lots have done it. It won't run as well as it would with a tuning solution, but the plug harness adapter is a DIY item, and it will at least get you off to a running start. It's also a much more accurate sensor in the whole shot. You should actually do pretty good with that.

What I've found with them is your filter + filter adapter make a HUGE difference in airflow readings, however. At idle with a 2G MAF and a 2G ECU I've had to drop my Hz by around 8% and then increase above 150Hz. I've got the crappy adapter without the smooth lead-in, though, and a sub-5" filter to boot, so I have no doubts about it screwing with the airflow. Anyway, different conversation and I'm good to leave work now.

You're correct, it will TRY, it just can't go far enough .

It filled my entire carport with a crazy soot fog in about 10 seconds.

Once I figured out the problem, and got the idle sorted, it would register DEEP in the 9's on the wideband (pretty sure it started breaking up like crazy somewhere around 9.3:1 . Pulled out some fuel and got her into the high 10's low 11's. Lots more power.