What AFPR Set Pressure for 19lb Injectors?

[Overlord475]

Purchased an 88 325 (2.7L seta) a while back with the following modes:

Mark D Chip (91oct)
19lb Injectors
AFPR (with gauge)
IE Shorty Headers
Free Flow exhaust

Wondering what pressure the AFPR should be set to for this set up? The car is running a bit rich.

What is the calculation to determine this? This would be helpful as I will be doing the 2.7i swap within the next 2 months

[mpowerful]

What exactly are the injectors? Are they rated at 19lbs at 3bar? 3 bar = 43psi. 2.5 bar = 36.3psi. At 2.5bar a 19lb injector will flow 17.34lb/hr. Anyway what is the chip tuned for? 14.5? If so I would set it to flow at or near that. 1.75 = 25.4psi which will put your 19lb injectors at 14.5lb/hr.

[shadowracer]

Is the reg. the type you adjust and it maintains a specific pressure or is it a rising rate?

I ask because I'm using a rising rate reg. that I found being set according to install instructions caused my car to run so rich that it looked like I had a diesel engine running poorly by how black the back of my car was.

I got the car on a dyno and lowered the fuel pressure down to 24lbs. at idle, which then under load would rise up to 40-42lbs.

[jlevie]

Is the chip specifically for 19lb injectors? If so you'd want ~25psi at idle and 36-37psi at at WOT.

[digger]

what are the SETA stock injectors rated at?

[Overlord475]

What exactly are the injectors? Are they rated at 19lbs at 3bar? 3 bar = 43psi. 2.5 bar = 36.3psi. At 2.5bar a 19lb injector will flow 17.34lb/hr. Anyway what is the chip tuned for? 14.5? If so I would set it to flow at or near that. 1.75 = 25.4psi which will put your 19lb injectors at 14.5lb/hr.

To my understanding they are 19lb mustang injectors

This is the AFPR Kit (w/ integrated pressure gauge):

http://www.vacmotorsports.com/catalo...tyle-bosch.htm

As for the Mark D chip, I am unsure of how many bars the injectors are tuned for.
I was told that the chip was for 19lb injectors and 91oct gas.

Again all of the above was installed by the PO.

EDIT:

After adjusting the FPR down to ~26psi (it wouldn't go any lower) the car had a very hard time idling, when rev'd the fuel pressure actually dropped to around 22psi.
When adjusting the FPR up to 34psi the car idled well again, and when rev'd the fuel pressure increased to around 42psi.

[mpowerful]

Is the chip specifically for 19lb injectors? If so you'd want ~25psi at idle and 36-37psi at at WOT.

The m20 stock uses a rising rate (vacuum regulated) fpr. So basically it maintains 3 bar. At idle you should have around 9psi or vacuum at the injector so the fuel pressure should be around 32-35 ish for 3 bar regulator. If the markD chip is tuned for stock 3 bar regulator with 19lb/hr injectors then you would want to set your idle pressure around 32-35 psi. This should rise under full load to 42-43 (3 bar) when the mainfold pressure is nearly 0. Any lower than that and it would be to low.

*** Is my math wrong? : (

[digger]

i dont like AFPR if there is an O2 sensor in the system. the ECU is trying to hit a fixed target anyway and it is pretty good at it (within reason of course). does the SETA have an O2 sensor?

im not familiar with the ETA or SETA systems but on the B25 the 19lb just drop right in and idle fine and fuel close enough to be driveable and refined. if the ECU has to correct too much it can cause extreme ends of the tune to be out a bit so its far from the best solution

[Overlord475]

i dont like AFPR if there is an O2 sensor in the system. the ECU is trying to hit a fixed target anyway and it is pretty good at it (within reason of course). does the SETA have an O2 sensor?

im not familiar with the ETA or SETA systems but on the B25 the 19lb just drop right in and idle fine and fuel close enough to be driveable and refined. if the ECU has to correct too much it can cause extreme ends of the tune to be out a bit so its far from the best solution

Yes, the SETA has an O2 sensor and is Motronic 1.3.

I have a brand new OE 3.0 bar FPR. Thoughts of putting this in place of the AFPR?

[jlevie]

When adjusting the FPR up to 34psi the car idled well again, and when rev'd the fuel pressure increased to around 42psi.

That would be about right and very close to what a 3.0bar FPR would do.

[jlevie]

i dont like AFPR if there is an O2 sensor in the system. the ECU is trying to hit a fixed target anyway and it is pretty good at it (within reason of course). does the SETA have an O2 sensor?

If you understand how the DME works AFR data is useful. You disconnect the DME (or battery) to clear learned adaptions, make a dyno run, and adjust aiming for 14:1. Rinse & repeat as necessary.

[digger]

If you understand how the DME works AFR data is useful. You disconnect the DME (or battery) to clear learned adaptions, make a dyno run, and adjust aiming for 14:1. Rinse & repeat as necessary.

i used an AFPR at one point and it was a waste of money, you end up with a half assed tune for not much cheaper than a proper one. the O2 sensor and adaptions means it works ok for a while only as the pressure adjustment is global adjustment only so unless you want to keep resetting the ECU it changes soon enough....i ended up a custom dyno chip done without the O2 sensor so you can have non WOT mixtures something other than 14.7:1.

i think there is something else wrong, the engine should idle 14.7:1 in closed loop regardless if you set it to 3b or 2.5b or 3.5b i know because i tried it years ago.

[mpowerful]

Motronic goes to open loop at wot so you can run an o2 and it will tune ratios other than 14:7 at wot. It wont at part throttle because motronic runs closed loop at all other times except cold start.

[nando]

you would be better off just sticking to stock injectors, or getting a tune, than running too-big injectors at a low fuel pressure.

I wouldn't run an M20 at less than 3 bar if I could help it..

[digger]

Motronic goes to open loop at wot so you can run an o2 and it will tune ratios other than 14:7 at wot. It wont at part throttle because motronic runs closed loop at all other times except cold start.

yeah so 99% of the time you should have the correct mixture without the need for a $300 AFPR ...as nando says run the right injector for the chip at hand and use the factory fuel pressure and you are good to go.... the chip should say what it is on the label. get the bosch p/n of the injector and verify the injector flow rating. if it matches up then there is a problem somewhere else most likely