Fuel Pressure Mods, Perf. Gains, Dead Opossum
07-18-2002, 01:59 PM
#1
Three Wheelin'
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Fuel Pressure Mods, Perf. Gains, Dead Opossum
I finally received my adjuatable pressure regulator and gauge for the 928TT. I got the unit from 928 Specialists. It is a very nice machined unit that fit perfectly in the location of the stock unit.
I strted out with the stock fuel pressure blowing through the 914 1.7 liter injectors that were installed on my car by Callaway. The result was a fat mixture everwhere. 0.9 to 1 volt (O2 Sensor) across the range in open loop. So I knew I had some room to move down with the pressure. This was at 37 psig.
I went down to 35 psig, not much change, but the car did feel as though it had better throttle response, especially when going into the positive side of manifold pressure. The voltage readings came down somewhat...but I was still not happy.
I then went down to 30 psig and noticed a big improvement. The voltages came down to the 0.78-0.96 range, so while I am still fat, I have some extra fuel to help with charge cooling. The throttle response is greatly improved, and the car gets onto the boost side much earlier than it used to. I can now get boost at 2200 RPM in 5th gear.
I measured the peak acceleration with the G-tech and I am now getting a peak of just over 0.5 gs on full throttle with the modifications. I used to get about 0.45 peak. It was warm here last night, so I am waiting for a 50 degree day to see how it really runs. That will be a while.
The best part is now I am not so smelly rich on the low end. It is actually lean at idle, since I still have to run the car in open loop (it surges in closed loop). I hope this doesn't cause problems, because I like the way the car runs now.
I think the only other option for me would be to go back to the stock injectors and run the pressure up.
For anybody running positive manifold pressure, this regulator is money well spent. I am very happy with the unit.
The only bad news, was the fact that an Opossum lost its life in the tuning process!
I strted out with the stock fuel pressure blowing through the 914 1.7 liter injectors that were installed on my car by Callaway. The result was a fat mixture everwhere. 0.9 to 1 volt (O2 Sensor) across the range in open loop. So I knew I had some room to move down with the pressure. This was at 37 psig.
I went down to 35 psig, not much change, but the car did feel as though it had better throttle response, especially when going into the positive side of manifold pressure. The voltage readings came down somewhat...but I was still not happy.
I then went down to 30 psig and noticed a big improvement. The voltages came down to the 0.78-0.96 range, so while I am still fat, I have some extra fuel to help with charge cooling. The throttle response is greatly improved, and the car gets onto the boost side much earlier than it used to. I can now get boost at 2200 RPM in 5th gear.
I measured the peak acceleration with the G-tech and I am now getting a peak of just over 0.5 gs on full throttle with the modifications. I used to get about 0.45 peak. It was warm here last night, so I am waiting for a 50 degree day to see how it really runs. That will be a while.
The best part is now I am not so smelly rich on the low end. It is actually lean at idle, since I still have to run the car in open loop (it surges in closed loop). I hope this doesn't cause problems, because I like the way the car runs now.
I think the only other option for me would be to go back to the stock injectors and run the pressure up.
For anybody running positive manifold pressure, this regulator is money well spent. I am very happy with the unit.
The only bad news, was the fact that an Opossum lost its life in the tuning process!
07-18-2002, 04:28 PM
#3
Three Wheelin'
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Yes, open loop means the O2 sensor is "out of the loop", or simply unplugged In my case, the computer is making radical corrections (beacuse of the 914 injectors), thus the reason for the surging. The sensor is automatically taken out of the loop under WOT. It won't hurt to run your car there, but ideally is should be connected.
07-18-2002, 09:24 PM
#4
We had a choice?
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Bad news? That should have been good news. Fresh meat for Dinner! Possum stew, ahhh, the memories...
Anthony Tate
79/928 Silver Metallic <img src="graemlins/burnout.gif" border="0" alt="[burnout]" />
Anthony Tate
79/928 Silver Metallic <img src="graemlins/burnout.gif" border="0" alt="[burnout]" />
07-19-2002, 05:43 PM
#5
Racer
John K2, I was looking at the wire diagrams today and ran across something you may want to try.
First, with a jumper wire connect ( Bridge) the White and Brown wire from the LH control harness (that is what your O2 sensor was hooked to). This tells the LH your car doen't have an O2 sensor instead of it thinking it there, but bad (open/zero volts).
Second, call one of the BIG 3 and Ask them about the coded plug that plugs into the EZK. I would think that if you got one for a 928 without Catalyzer would help you out as well.
JM.02/HTH
Max
First, with a jumper wire connect ( Bridge) the White and Brown wire from the LH control harness (that is what your O2 sensor was hooked to). This tells the LH your car doen't have an O2 sensor instead of it thinking it there, but bad (open/zero volts).
Second, call one of the BIG 3 and Ask them about the coded plug that plugs into the EZK. I would think that if you got one for a 928 without Catalyzer would help you out as well.
JM.02/HTH
Max