I've just noticed something with my MAP readings that I did not see before.

At ilde I am in the 60s with a 107 LSA cam. This has been normal.

Now, when I raise the RPM to about 3250 the MAP readings dive to the 30s and the fuel pressure drops to 32-33 psi (It is set to 37 with idle vacuum and 43 w/o). I've never noticed this before.

Is this correct MAP behavior? The fuel pressure should increase with higher MAP values. Why is the fuel pressure being pulled down with the low MAP pressures? It's almost as though the intake is getting pressurized by a stuck intake valve.

Also, how far should the MAP readings fluctuate when recording 10 records/sec. Mine are all over the place,

 

The fuel pressure regulator is vacuum referenced. Low MAP = high vacuum. High vacuum = lower fuel rail pressure. If you get 37psi with 60kPa, you would logically get 4.4psi less at 30kPa.

 

Injuneer,

My MAP readings are pulsing up and down as recorded by DataMaster at WOT and all other times.

Ex: 94.9, 92.3, 93.4, 96.2, 91.9, 96.0, 90.8, 94.9

The rpm is also pulsing:

ex: 5875, 5800, 5975, 5850, 6025, 6000, 6025, 6125, 6150, 6125, 6325

Is this a loose ground, partially broken wire, etc?

What power source/ground is connected to both circuits?

 

A misfire would cause the RPM to drop and the MAP to burp, simultaneously.

 

So, typically, a mis-fire would cause a false lean reading on the wideband O2 (and stock narrow-band O2) because of the unburnt oxygen.

If the wide-band O2 was reading 12.6 (which is in the left header), you would be inclined to think you were OK on AFR.

So you would look to the right side for the mis-fire and lean O2 reading.

At WOT the BLMs lock on 128 so the stock 02s are not affecting the AFR (yes / no ?). The right side stock O2 sensor readings are 20 to 30 points higher than the left. And they get further apart as the RPMs increase. (20 points higher at 5000 rpm [924 to 946] and are 30 points higher at 6300 rpm [962 to 995].

The Map readings fluctuate more as the rpm is increased.

Am I right to deduce that the higher O2 mv readings are leaner due to the higher volts given off by the sensor.

Should I be looking to the right side?

 

At WOT, you are in open loop mode so the O2 sensors are not part of the control loop. But, their voltage (what you're calling "points") should then read near 1. Higher means richer, and above .950V is typical at WOT.

 

Then the left side is slightly leaner. But the AFR is 12.6:1 on the left.

Doesn't appear to be a mis-fire then, because the AFR is not false lean.

If it's not an ignition miss, any thoughts on the MAP and RPM pulsing?

 

I have seen it before. Lower MAP values, especially at WOT, can point to inefficient combustion.

With regard to tuning, one thing that can affect this is timing. Insufficient advance can cause power to fall off, which is evidenced by a slight vacuum. The other variable is airflow. Check your air filter, try cleaning it. Intake restrictions could do it too. And lastly, fuel could play a role--not enough or too much would cause power to fall off.

From what I've read, and from experience, this kind of behavior (partial vacuum at WOT) can be a sign that there is more power to be had; sometimes with tuning.

 

Yes.

Depends.

If your high load long term fuel trims (BLM's) were adding fuel in closed loop, the PCM will use Cell 15 BLM's to fuel at WOT (PE mode). They will not be 128. If the high load BLM's were cutting fuel in closed loop, the PCM will use either Cell 15 or Cell 18 for fueling, but will lock the BLM's at 128.

The main problem with using the stock narrow-band sensors is that they are not accurate at anything other than 14.7:1. When you go WOT, the graph of volts vs A/F ratio flattens out, and it takes a very large change in A/F ratio to make a change in the output volts. BUT.... at those A/F ratios, the narrow-band sensors become very sensitive to operating temperature, and a small change in operating temperature affects the output volts more than a large change in A/F ratio. Hence, the fact one side is 20 or 30mV higher than the other may indicate a difference in A/F ratio, or it may indicate a difference in operating temperature.

From my experience, a stock tune at WOT will produce narrow-band O2 volts in the 925mV range. But the stock tune is excessively rich, so you sometimes see better power with the
volts at 900mV or below. 962 and 995mV are generally indicative of a VERY rich condition. You need to use your wideband on both sides to see how they compare.

Look at your Cell 15 BLM's. If they are significantly above 128, they are affecting your PE mode operation, and causing it to run rich.