Just had my 104,000 mile '92 dynoed today. Bone stock except for a somewhat dirty air filter and a Dinan chip that was installed by a previous owner. Results look to be similar to others that i have seen except the air/fuel seems to be a bit lean at lower rpm. Any way to correct this?
Dyno results - Air/fuel ratio ?
- Thread starter Doug
- Start date
14.7 to 1 is considered perfect to meet emissions standards so you are real close to that. It does have to run lean especially in the 3000-5000 RPM range you use in normal driving. I really don't see any thing that needs to be changed or can be changed with the stock ECU.
Well, I would think that by 5k or certainly 6k under full load it would be in open-loop mode and running closer to 13:1, but it doesn't approach that until over 7k. That may or may not be “normal” but it certainly doesn’t look optimum. It might be tempting to swap in a stock ECU and see how that looks. When did you last change the fuel filter? Perhaps it is lean until the pump resistor is switched out and the pump has enough juice to supply demand.
Hey Doug,
Thanks for taking the time to post your results. It has been awhile since I have had a chance to see results along with the a/f plots. The NSX, I'll have to say, is really strange in the range of 4800-5800 rpm. I see this consistently in FI charts that I have analyzed and tuned and here it is again showing up in stock form. Frankly, it really doesn't surprise me as I knew this odd section must exist in the baseline if it was so consistently present in the FI charts.
There is a lean spot in this range and you can see that it has a rather dramtic effect on the HP/Torque curves. (See them both tick down when this lean spot occurs and then recover when you get into some better a/f's right about 5800 rpm.)
There is nothing really to worry about with a NA engine. You may want to run some fuel injector cleaner and/or remove them and have them sent out for cleaning/balancing. If you decide to do the later, it would be really interesting to see the "after" results - namely to see if it had any effect.
Anyway, congrats on having/maintaining a car that show up so strongly on the dyno after a mere 100K miles.
Thanks for taking the time to post your results. It has been awhile since I have had a chance to see results along with the a/f plots. The NSX, I'll have to say, is really strange in the range of 4800-5800 rpm. I see this consistently in FI charts that I have analyzed and tuned and here it is again showing up in stock form. Frankly, it really doesn't surprise me as I knew this odd section must exist in the baseline if it was so consistently present in the FI charts.
There is a lean spot in this range and you can see that it has a rather dramtic effect on the HP/Torque curves. (See them both tick down when this lean spot occurs and then recover when you get into some better a/f's right about 5800 rpm.)
There is nothing really to worry about with a NA engine. You may want to run some fuel injector cleaner and/or remove them and have them sent out for cleaning/balancing. If you decide to do the later, it would be really interesting to see the "after" results - namely to see if it had any effect.
Anyway, congrats on having/maintaining a car that show up so strongly on the dyno after a mere 100K miles.
Remember, the car does have a Dinan chip. It was installed in 1998 when there was @60k miles. I guess if there was a problem, it would have shown up in the last 40k miles and 5 years.
Do you have any data at hp/ft.lbs/rpm of stock cars? Curious if the Dinan chip did as claimed in the literature. Not too concerned about peak hp at 7200, but more with down low ft.lbs and mid range stuff.
3500rpm 114.4hp 171.7 ft.lbs
4500rpm 156.3hp 182.4ft.lbs
5500rpm 185.2hp 176.8 ft.lbs
6500rpm 227.8hp 184.1 ft.lbs
Peak is 233hp @7300 and 185ft.lbs @6400
Do you have any data at hp/ft.lbs/rpm of stock cars? Curious if the Dinan chip did as claimed in the literature. Not too concerned about peak hp at 7200, but more with down low ft.lbs and mid range stuff.
3500rpm 114.4hp 171.7 ft.lbs
4500rpm 156.3hp 182.4ft.lbs
5500rpm 185.2hp 176.8 ft.lbs
6500rpm 227.8hp 184.1 ft.lbs
Peak is 233hp @7300 and 185ft.lbs @6400
The range between 4800 and 5800-6000 is the magic range when things happens. If you are able to adjust the ECU you can probably make it better.
4800 RPM is when the CVCS (or IAB) butterfly is opened by the ECU. This will change the induction efficiency and so the ECU will have to adjust its fuel map to match.
5800-6000RPM is when VTEC high lift cams lobes are switched in and this has an even more dramatic effect as the cylinders are filled with even more air and therefore require another adjustment from the ECU.
There is a point when the fuel pump resistor is switched out, running the fuel pump at full speed like sjs mentioned but I haven't determined at which RPM and/or load it's switched by the stock ECU. The pump speed has a dramtic effect as it increases fuel pressure quite a bit. Fuel metering requires adjustment a good 2-3% at idle with the resistor on and off.
Eddy
4800 RPM is when the CVCS (or IAB) butterfly is opened by the ECU. This will change the induction efficiency and so the ECU will have to adjust its fuel map to match.
5800-6000RPM is when VTEC high lift cams lobes are switched in and this has an even more dramatic effect as the cylinders are filled with even more air and therefore require another adjustment from the ECU.
There is a point when the fuel pump resistor is switched out, running the fuel pump at full speed like sjs mentioned but I haven't determined at which RPM and/or load it's switched by the stock ECU. The pump speed has a dramtic effect as it increases fuel pressure quite a bit. Fuel metering requires adjustment a good 2-3% at idle with the resistor on and off.
Eddy
Eddie,
I don't think that the fuel pump 6v - 12v jump will effect fuel pressure at all. In both scenarios, the same factory FPR is in the loop and will serve to stabilize fuel pressure. However, there will be a greater availability of fuel volume - should the injectors need more behind them to "keep up".
I wish I could be positive about the above but my last two Autometer $200 electronic fuel gauges have been defective.
I don't think that the fuel pump 6v - 12v jump will effect fuel pressure at all. In both scenarios, the same factory FPR is in the loop and will serve to stabilize fuel pressure. However, there will be a greater availability of fuel volume - should the injectors need more behind them to "keep up".
I wish I could be positive about the above but my last two Autometer $200 electronic fuel gauges have been defective.
I can't tell you exactly how the fuel pressure changes until I put a gauge on it or datalog it but when the pump is running through the resistor the logical conclusion is that it does lower the pressure as my Motec requires a few more percent more fuel injector duration to keep the engine running with the resistor.
The only thing I can deduce is that when running through the resistor, if the engine isn't running, the pump (w/resistor) will bring the fuel pressure up to the FPR's setting (i.e. 50psi @ 100kPa/no vaccum) but as soon as the engine starts, the pressure will probably drop due to the injectors opening but because the fuel pump is not provided with enough current (or juice per sjs) due to the resistor, it won't maintain the same pressure as when the resistor is switched out or when the engine isn't running. Then when the ECU decides it needs the extra pressure @ higher load/rpm (so it doens't have to open the injector for so long), it switches out the resistor and the pump will ramp up the pressure until the FPR starts bleeding it off (i.e 45psi @ 35kPa/idle).
Eddy
The only thing I can deduce is that when running through the resistor, if the engine isn't running, the pump (w/resistor) will bring the fuel pressure up to the FPR's setting (i.e. 50psi @ 100kPa/no vaccum) but as soon as the engine starts, the pressure will probably drop due to the injectors opening but because the fuel pump is not provided with enough current (or juice per sjs) due to the resistor, it won't maintain the same pressure as when the resistor is switched out or when the engine isn't running. Then when the ECU decides it needs the extra pressure @ higher load/rpm (so it doens't have to open the injector for so long), it switches out the resistor and the pump will ramp up the pressure until the FPR starts bleeding it off (i.e 45psi @ 35kPa/idle).
Eddy
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