Is the ECU in the 4th Gen's the type of ECU that will adjust injector pulse with to compensate for an change in fuel pressure?

Example, If I were to add a adjustable fuel pressure regulator and adjust the pressure and change the A/F ratio to gain more power, will the ECU eventually retune its self to compensate for the change in fuel pressure and adjust injector pulse width to compensate for the change in pressure to get back to the normal A/F ratios programed in it from the factory.

Thanks!

 

I won't pretend to know the answer to your question (although I did understand it)!

Your best bet would be to call Jim Wolf Tech @ 619/442-0680.
If you get the right person, they'll be able to tell you.

 

Nope. The Fuel pump will push "X" amount of pressure to the injectors. Regardless of pressure, pulse-width (amount of time injector is open) will only push the parameters designed into fuelmap you have on your ECU (or reprogrammed ECU).

Will additional (or new high flow) fuel pump gain hp? No, it never does. Its insurance to keep pressure on when car is under load. The limits of injector pulse-width are limited to ECU fuelmap programming. An add-on regulator (like Stillen's) is a waste of money. Limits are programmed into the ECU. The stock fuel pump is good for ~250hp (at the crank).



[Edited by Don in Texas on 09-04-2000 at 10:39 PM]

 

Trying to clarify what you said Don,

The ECU WILL NOT decrease the injector pulse width to compensate for an overly rich A/F ratio caused by a high WOT fuel pressure?

Reason being, I did upgrade my fuel pump for my NOS to a very powerfull pump, 255lph Walbro. It holds pressure on the NOS just fine. But I now show that the fuel pressure is high, ~52psi, under normal WOT operation. My EGT's are low about 740cel, I was told by SGP Racing that 780-800cel is optimum for our motor, so I think I'm running rich. I need to get my A/F ratio gauge hooked back up!

I am trying to figure out if I need to get an adjustable fuel pressure regulator to get the fuel pressure back into spec.(~43psi @WOT), or if the ECU will over time re-learn and adjust the A/F map by adjusting the injector pulse width based on the rich O2 readings caused by the high fuel pressure ?

Thanks Don, u da man!

[QUOTE]Originally posted by Don in Texas
[I]Nope. The Fuel pump will push "X" amount of pressure to the injectors. Regardless of pressure, pulse-width (amount of time injector is open) will only push the parameters designed into fuelmap you have on your ECU (or reprogrammed ECU).

Will additional (or new high flow) fuel pump gain hp? No, it never does. Its insurance to keep pressure on when car is under load. The limits of injector pulse-width are limited to ECU fuelmap programming. An add-on regulator (like Stillen's) is a waste of money. Limits are programmed into the ECU. The stock fuel pump is good for ~250hp (at the crank).

[Edited by MardiGrasMax on 09-04-2000 at 11:37 PM]

 

The ECU won't read rich because of the fuel pressure. Rich/Lean is learned from the MAF/O2 readings. Fuel pressure is fine. If it was TOO high, you'd have found leaking injector o-rings, or fouled plugs (blue smoke).

The pump you have is fine. At WOT stock fuel pressure isn't that high (its around 42psi). Given the extra flow, you're fine. A/F meter won't tell you anything the fuel pressure gauge won't tell you. Readings are not at the pump. Lowering pressure won't make a rich reading go away. (I doubt you're running rich at all, even w/o NOS)

 

I think your question is, "Will the ECU tune out the higher fuel flows due to your higher fuel pressure?" The answer depends on the driving conditions.

Below ~40% throttle the ECU is in closed-loop mode, and will lower the fuel injector pulse widths to compensate for your higher pressures. Now in open loop mode, I'm not positive if there's any correction, but the factory service manual says NOTHING about self-correction in high-throttle conditions, so I don't think the ECU can compensate for your higher fuel pressures when above 40% throttle. Your low exhaust temperatures seem to indicate that you're pretty rich, which indicates to me that the ECU does indeed operate that way.

FYI I got this 40% by using the S-AFC throttle% display and the ECU self-diagnostic mode to indicate closed-loop mode. Past ~40%, the ECU showed the O2 sensor reading to be stationary. Below ~40%, the O2 sensor reading fluctuated from high to low, indicating closed-loop mode.

You cannot lower your fuel pressure as long as the stock regulator is still there. Any downstream pressure regulator or pressure "modifiers" can only increase fuel pressure at the rails. I believe the only way to lower the pressure would be to remove the stock regulator and install an adjustable one. I'm not sure if there are any regulators that can fit the stock mounting location. You may need a regulator-off fitting like this one from JUN-USA:
http://www.junusa.com/parts/engineau...ff_fitting.htm

Of course, you can also use the Super AFC to lean out the flows at 40%+ throttle. There's no point in adjusting anything below 40% since the ECU will tune it right out to get back to stochiometric.

[QUOTE]Originally posted by MardiGrasMax
[I]Trying to clarify what you said Don,

The ECU WILL NOT decrease the injector pulse width to compensate for an overly rich A/F ratio caused by a high WOT fuel pressure?

Reason being, I did upgrade my fuel pump for my NOS to a very powerfull pump, 255lph Walbro. It holds pressure on the NOS just fine. But I now show that the fuel pressure is high, ~52psi, under normal WOT operation. My EGT's are low about 740cel, I was told by SGP Racing that 780-800cel is optimum for our motor, so I think I'm running rich. I need to get my A/F ratio gauge hooked back up!

I am trying to figure out if I need to get an adjustable fuel pressure regulator to get the fuel pressure back into spec.(~43psi @WOT), or if the ECU will over time re-learn and adjust the A/F map by adjusting the injector pulse width based on the rich O2 readings caused by the high fuel pressure ?

Thanks Don, u da man!

 

I was wondering if or who made that adapter for the fuel rail.

Yep Keven my EGT's show rich and you guys have confirmed what I thought about the ECU.

I am still waiting for my replacment S-AFC to come in. Its been over a month...

Did you ever get that trick with the AFC's spare MAF voltage reading to work with the O2 sensor voltage wire?

 

and I would REALLY hate to splice into yet another wire on the ECU only to find it doesn't work...I think I'll eventually do it, but only when I have the time and energy to dedicate to doing it.

 

Perhaps, you could of courese disconnect the ECU and the battery. Then trace the wires with a digital volt meter. You could compare the wires on the other O2 sensors to see wich are for heat and ground, should be the same on the front 3 O2 sensors and the wire for the voltage reading to the ecu should be different for the 3 O2's. then verify it with the DVM.

Since I'm cheep, can you please perhaps E-mail, US mail, or fax me a copy of the ECU wiring diagram in the shop manual? Dam I am cheep!